Rhodium complexes of 1,3-di-tert-butylcyclopentadiene

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Title:
Rhodium complexes of 1,3-di-tert-butylcyclopentadiene synthesis, structure and properties
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xiii, 153 leaves : ill. ; 29 cm.
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English
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Lee, Hun Ju, 1955-
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Subjects / Keywords:
Organometallic compounds   ( lcsh )
Rhodium   ( lcsh )
Organic compounds -- Synthesis   ( lcsh )
Complex compounds   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
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bibliography   ( marcgt )
non-fiction   ( marcgt )

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Thesis:
Thesis (Ph. D.)--University of Florida, 1993.
Bibliography:
Includes bibliographical references (leaves 147-152).
Statement of Responsibility:
by Hun Ju Lee.
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Typescript.
General Note:
Vita.

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University of Florida
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All applicable rights reserved by the source institution and holding location.
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Full Text









RHODIUM COMPLEXES OF 1, 3-DI-TERT-BUTYLCYCLOPENTADIENE:
SYNTHESIS, STRUCTURE AND PROPERTIES














BY


HUN JU LEE


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY



UNIVERSITY OF FLORIDA


1993































TO MY MOTHER, WHO PASSED AWAY WITHOUT SEEING MY SUCCESS.













TABLE OF CONTENTS

ACKNOWLEDGMENTS .................................

LIST OF TABLES ..................................

LIST OF FIGURES .................................

ABSTRACT ........................................

CHAPTERS

1. INTRODUCTION ...............................


2. PREPARATION OF DI-TERT-BUTYLCYCLOPENTADIENE

Introduction ..............................

Synthesis of tert-Butylcyclopentadiene ....

Synthesis of Di-tert-Butylcyclopentadiene .


............ ii

............ vi

.......... viii

............ xi



..... ...... 1


(Cp**H)


3. CHEMISTRY OF 1,3-DI-TERT-BUTYLCYCLOPENTADIENYLRHODIUM
DICHLORIDE DIMER [Cp**RhCl2]2


Introduction ........................................

Preparation .........................................

X-ray Crystallography ...............................


4. REACTIONS OF [Cp**RhCl2]2

Introduction ........................................

Reaction with PPh3. ...................................

Reaction with P(CH3)3 ................................

Reaction with CH3COOAg ...............................

Reaction with AgNO3. ..................................


iii


. 12

. 14

. 17


..31

..32

.. 36

..36

..39






5. STRUCTURE AND SPECTRA OF Cp**Rh(PPh3)C12

Introduction .......................................... 41

Structure and Spectra ................................. 43

X-ray Crystallography ................................. 47


6. SYNTHESIS OF Cp**Rh(COD)(COD= cycloocta-1,5-diene)

Introduction .......................................... 61

Preparation... ........................................ 64

NMR Spectroscopy........................................ 65


7. CHEMISTRY OF Cp**Rh(PINACOLATE)

Introduction .......................................... 69

Preparation ........................................... 72

NMR Spectroscopy ...................................... 73

X-ray Crystallography. ................................. 77



8. REDUCTIVE-ELIMINATION AND OXIDATIVE-ADDITION CHEMISTRY
OF Cp**Rh(PINACOLATE)

Introduction .......................................... 89

Photolysis of Cp**Rh(pinacolate) with CH3I ............ 90

Reaction of Cp**Rh(pinacolate) with CH3I ..............91

Photolysis of Cp**Rh(pinacolate) with CHC13 ............ 95

Reaction of Cp**Rh(pinacolate) with CHC13 ............ 98

Photolysis of Cp**Rh(pinacolate) with 12 ............... 99

Reaction of Cp**Rh(pinacolate) with 12 ................100

Reaction of Cp**Rh(pinacolate) with PhSO2C1 ...........101

Reaction of Cp**Rh(pinacolate) with DPPE ..............103






9. APPLICATION OF A STABLE Cp**Rh(I)(PPh3)

Introduction .................................. ....... 105

Preparation of Cp**Rh(I)(PPh3) .......................106

Oxidative-Addition of CHC13 to Cp**Rh(I)(PPh3) ......109

Oxidative-Addition of 12 to Cp**Rh(I)(PPh3) ......110

10. DIMERIZATION ........................................ 112

11. EXPERIMENTAL .................................. ....... 130

REFERENCES ........................................... ...... 147

BIOGRAPHICAL SKETCH ........................................ 153








LIST OF TABLES


TABLE PAGE

2-1 1H NMR spectral data for tert-butylcyclopentadiene
in CDC3 ............................................... 9

2-2 1H NMR spectral data for di-tert-butylcyclopentadiene
in CDC13 ............................................. 10

3-1 13C NMR spectral data for the compound 3-2 .......... 15

3-2 Crystallographic data of the compound 3-2 ........... 18

3-3 Fractional coordinates and equivalent isotropic thermal
parameters for the non-H atoms of the compound 3-2 .. 24

3-4 Bond lengths and angles for the non-H atoms of the
compound 3-2 ........................................ 26

4-1 NMR spectral data for the compound 4-2 in CDCI3 ..... 34

5-1 1H NMR spectral data for the compound 5-1 in C6D6.... 42

5-2 1H NMR spectral data for the compound 4-3 ........... 44

5-3 13C NMR spectral data for the compound 4-3 .......... 46

5-4 Crystallographic data for the compound 5-2 .......... 48

5-5 Fractional coordinates and equivalent isotropic thermal
parameters for the non-H atoms of the compound 4-3 .. 52

5-6 Bond lengths and angles for the non-H atoms of the
compound 4-3 ........................................ 54

5-7 Anisotropic thermal parameters for the non-H atoms of
the compound 4-3 .................................... 56

5-8 Fractional coordinates and isotropic thermal parameters
for the H atoms of the compound 4-3 ................. 57






5-9 Bond lengths and angles for the non-H atoms of the
compound 4-3 ................................. ....... 58

6-1 NMR spectral data for the compound 6-5 in CDC13. .... 66

6-2 NMR spectral data for the compound 6-6 in CDC13. ..... 68

7-1 1H NMR spectral data for the compound 7-1. .......... 74

7-2 13C NMR spectral data for the compound 7-1. ......... 74

7-3 Crystallographic data for the compound 7-1. ......... 79

7-4 Fractional coordinates and equivalent isotropic thermal
parameters for the non-H atoms of the compound 7-1 .. 85

7-5 Bond lengths and angles for the non-H atoms of the
compound 7-1 ........................................ 86

7-6 Anisotropic thermal parameters for the non-H atoms of
the compound 7-1 .................................... 87

7-7 Comparison of substituent deviations from a ring
plane. ............................................... 88

10-1 Crystallographic data for the compound 10-10 ....... 121


10-2 Fractional coordinates and isotropic thermal parameters
for the H atoms of the compound 10-10 .............. 126

10-3 Bond lengths and angles for the non-H atoms of the
compound 10-10. ..................................... 127

10-4 Fractional coordinates and isotropic thermal parameters
for the non-H atoms of the compound 10-10 .......... 128


vii








LIST OF FIGURES


FIGURE

Fig.2-1.

Fig.2-2.

Fig.3-2.

Fig.3-3.

Fig.3-4.

Fig.3-5.

Fig.4-1.

Fig.4-2.

Fig.4-3.

Fig.4-4.

Fig.4-5.

Fig.4-6.

Fig.4-7.

Fig.4-8.

Fig.4-9.

Fig.4-10.

Fig.5-1.

Fig.5-2.


PAGE


Synthesis of mono-butylcyclopentadiene ...

Synthesis of di-tert-butylcyclopentadiene


..... 810

..... 10


1H NMR spectrum of 3-2 in CDC13 ...............


13C NMR spectrum of 3-2 in CDC13 ..

Molecular structure of isomer A of

Molecular structure of isomer B of

Synthesis of Cp**Rh(PMe3)Cl2(4-2) .

1H NMR spectrum of 4-2 in CDC13 ...

13C NMR spectrum of 4-2 in CDC13 ..

Synthesis of Cp**Rh(PPh3)Cl2(4-3) .

Synthesis of Cp**Rh(AcO)2(4-4) ....

1H NMR spectrum of 4-4 in CDC13 ...

13C NMR spectrum of 4-4 in CDC13 ..

Synthesis of Cp**Rh(N03)2(4-5) ....

1H NMR spectrum of 4-5 in CDC13 ...

13C NMR spectrum of 4-5 in CDCL3 ..

IH NMR spectrum of 4-3 in CDC13 ...

13C NMR spectrum of 4-3 in CDC13 ..


Fig.5-3. Molecular structure of 4-3 ............


........ 50


viii


............

13 2 .........

13 2 ........






Fig.5-4.


Fig. 5-5.


Fig. 6-1.

Fig. 6-2.

Fig. 6-3.

Fig. 6-4.

Fig. 6-5.

Fig. 6-6.

Fig. 6-7.

Fig. 7-1.

Fig.7-2.

Fig.7-3.

Fig.7-4.

Fig.7-5.

Fig.7-6.

Fig.7-7.

Fig.7-8.

Fig.7-9.

Fig.7-10.

Fig.7-11.

Fig.7-12.


The crystallographically determined ring carbon
internuclear bond distances in 4-3 ............ 51

Deviation of a tert-butyl group from the ring
plane ......................................... 52

The synthesis of [Rh(COD)Cl]2 (6-2) ........... 61

The synthesis of [Rh(15-C5H5) (COD)] (6-3) ....... 63

The synthesis of Cp*Rh(COD)(6-4) .............. 66

The synthesis of Cp**Rh(COD)(6-5) ............. 66

1H NMR spectrum of 6-5 in CDC13 ............... 67

13C NMR spectrum of 6-5 in CDC13 .............. 67

The structure of 6-6 for NMR assignments ...... 68

Reductive-elimination of Rh(III)complex ....... 70

The photolysis of Cp**Rh(pinacolate) (7-1) ..... 72

The synthesis of Cp**Rh(pinacolate)(7-1) ...... 72

Numbering of (7-1) ............................ 74

1H NMR spectrum of 7-1 in CDC13 ............... 75

1H NMR spectrum of 7-1 in C6D6 ................ 75

13C NMR spectrum of 7-1 in CDCl3 .............. 76

13C NMR spectrum of 7-1 in C6D6 ............... 76

Thermal ellipsoids drawing for 7-1 ............ 81

Drawing for conformation isomer 7-1a .......... 82

Drawing for conformation isomer 7-lb .......... 82

Selected bond lengths and angles for Cp** ligand
of 7-1 ........................................ 84

ix







Fig.7-13.


Fig.7-14.

Fig.8-1.

Fig.8-2.

Fig.8-3.

Fig.8-4.

Fig.8-5.

Fig.8-6.

Fig.8-7.

Fig.8-8.

Fig.8-9.

Fig.8-10.

Fig.9-1.

Fig.9-2.

Fig.9-3.

Fig.10-1.


Fig.10-2.

Fig.10-3.


Fig.10-4.

Fig.10-5.

Fig.10-6.


Selected bond lengths and angles for pinacolate
ligand of 7-1.................................. 85


Deviation of substituent from a ring plane ...

Photolysis of Pt(glycolate) complex ..........

Oxidative-addition of acetone to Cp**Rh(I) ...

Photolysis of 7-1 with CH3I ..................

Reaction of Cp**Rh(pinacolate) with CH3I .....

Photolysis of Cp**Rh(pinacolate) with CHC13 ..

Reaction of Cp**Rh(pinacolate) with CHC13 ....

Photolysis of Cp**Rh(pinacolate) with 12 .....

Reaction of Cp**Rh(pinacolate) with 12 .......

Reaction of Cp**Rh(pinacolate) with Ph(S02)Cl.

Trapping of 8-4 with DPPE ....................

Synthesis of Cp**Rh(I)PPh3 ...................

Oxidative-addition of CHC13 to 9-1 ...........

Oxidative-addition of 12 to 9-2 ..............

The photolysis of (7-1) for the synthesis of
nonbridged dimer(10-8) .......................

The generation of dimer of Cp**Rh(I) .........

The photolysis of (7-1) for the synthesis of
the dimer(10-8 and 10-10) ....................

1H NMR spectrum of 10-8 in C6D6 ..............

1H NMR spectrum of 10-10 in C6D6 .............

Molecular structure of 10-10 .................

x


. 88

. 91

. 92

. 95

. 96

. 97

* 99

100

101

102

104

107

109

111


115

116


117

119

119

124











Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

RHODIUM COMPLEXES OF 1,3-DI-TERT-BUTYLCYCLOPENTADIENE:
SYNTHESIS, STRUCTURE AND PROPERTIES


By

Hun Ju Lee

May, 1993




Chairman: Dr. John F. Helling
Major Department: Chemistry

The complex 1,3-di-tert-butylcyclopentadienylrhodium

dichloride [Cp**RhCl2]2(3-2) was prepared for the first time.

Its structure was characterized by standard identification

methods (1H NMR, 13C NMR, mass spectroscopy, etc). The evidence

of dimeric form was given by x-ray crystallography. The x-ray

data of this complex are discussed in terms of Rh-Rh

separation, distance of Rh-Cl(bridging) and Rh-Cl(terminal),

and deviation of the tert-butyl groups from the ring plane.

This complex(3-2) was used to synthesize several mononuclear

compounds including Cp**Rh(PMe3)Cl2(4-2), Cp**Rh(PPh3)Cl2

(4-3), Cp**Rh(AcO)2(4-4) and Cp**Rh(N03)2(4-5).

The structure of 4-3 was of interest due to the coupling

of ring protons with phosphorus of PPh3. 1H NMR and 13C NMR

were discussed in terms of the couplings. The variable





temperature 1H NMR spectra gives the proof of the rigidity of

4-3. The x-ray crystallography was discussed to examine the

rigidity of that structure and compare the deviation of the

tert-butyl groups from the ring plane with those of 3-2.

The glycolate complex Cp**Rh(pinacolate)(7-1) could be

synthesized from 3-2 in good yield. The 1H NMR and 13C NMR and

FAB mass spectrum were examined to characterize it and the x-

ray crystallography was discussed in terms of deviation of

the tert-butyl groups from the ring plane. The successful

preparation of 7-1 provided a chance to study reductive-

elimination and oxidative-addition chemistry. The photolysis

of 7-1 caused the cleavage of the Rh-0 bonds, which generated

a reactive 14-electron intermediate Cp**Rh(I)(8-4) via

reductive-elimination. The intermediate(8-4) undergoes

reaction with Mel, CHC13, 12, PhSO2Cl and DPPE to give the

products; [Cp**RhI2]2(8-7), [Cp**RhCl2]2(1-2),

Cp**Rh(O2SPh)2(8-10) and Cp**Rh(DPPE) (8-11). The intermediate

Cp**Rh(I) (PPh3) (9-1), which is stable under nitrogen, was

isolated and used for further oxidative-addition chemistry.

The mechanism for product formation was proposed in each

reaction.

The irradiation of Cp**Rh(pinacolate)(7-1) in the

absence of other reagents leads to dimerization of

Cp**Rh(I) (8-4) to give a bridged, metal-metal bonded complex,

[Cp**Rh]2(pinacolate)(10-10), and a non-bridged [Cp**Rh]2

(10-8).


xii






The complex 10-8 is the first known rhodium complex

containing a non-bridged, rhodium-rhodium double bond.


xiii











CHAPTER 1
INTRODUCTION


General Overview


The pentamethylcyclopentadienyl ligand(Cp*) has played

an important part in the development of the chemistry of

transition metal complexes.1 Compared to cyclopentadienyl

metal complexes, those containing the Cp* ligand generally

exhibit better stability and higher solubility. Introduction

of tert-butyl substituents into the Cp ring has been of

interest because of the potentially greater stability and

hydrocarbon solubility of such metal complexes compared to

their Cp analogs. Relatively little work2-6 has been done on

metal complexes containing Cp ligands with bulky

substituents. Thus it seemed desirable to synthesize and

study di-tert-butylcyclopentadienyl(Cp**)metal complexes.

Such complexes were expected to offer advantageous solubility

and stability characteristics similar to those of Cp*

complexes and might also offer the possibility of size

selective reaction chemistry because of partial shielding of

the metal atom by the tert-butyl groups.

The synthesis of the Cp* half-sandwich complexes of Rh

and Ir7 (e.g., [Rh(C5Me5)Cl2]2) has been reported and they have

been found to be both thermally stable and quite reactive. The







compound [Rh(C5Me5)Cl2]2 undergoes metathetical replacement of

the chloride ligands to give mononuclear compounds on

treatment with NaX in refluxing methanol. The analogous Cp**

complex, [Cp**RhCl2]2 was chosen as an initial synthetic

target in this work because of its promise for conversion to

other Cp**Rh derivatives of interest.

Reductive-elimination reactions are known to be as

mechanistically diverse as oxidative-addition reactions. The

mechanisms of several reductive-elimination reactions have

been studied in detail.75 Recently it has been reported that

ultraviolet irradiation of transition-metal glycolate

complexes leads to irreversible fragmentation via cleavage of

M-O bonds, with concomitant transfer of two electrons to the

metal center.8 Photolysis of thermally stable platinum(II)

glycolate complexes gave two organic carbonyl compounds and

the reactive (dppe)Pt(O) intermediate.

It was expected that Cp**Rh(glycolate) type compounds

could be synthesized from [Cp**RhCl2]2(1-2.), and that the

photolysis of Cp**Rh(glycolate) would generate the reactive 14

electron intermediate Cp**Rh(I), a species which should

readily react with molecules capable of adding oxidatively.

Such a 14-electron intermediate was regarded as very useful

for examination of the oxidative-addition chemistry of

rhodium(I) under relatively mild conditions. Toward this end a

study was made of the behavior of Cp**Rh(I) in the presence of

several kinds of potential oxidants.




3


This research has focused on the systematic study of the

reductive-elimination of Cp**Rh(pinacolate), the oxidative-

addition chemistry, and dimerization of the reactive Cp**Rh

intermediate and to a lesser extent, related chemistry of

[Cp**RhCl2]2 and some of its other derivatives.













CHAPTER 2
PREPARATION OF DI-TERT-BUTYLCYCLOPENTADIENE(Cp**H)


Introduction


The cyclopentadienyl(Cp) ring has played a major role in

the development of organometallic chemistry since the

discovery of ferrocene in 1951.9 A common feature in the

investigation of organometallic chemistry has been the 15-

coordination of a cyclopentadienyl ring to a metal center.

The Cp ring has turned out to be a rather versatile ligand

and has been observed to coordinate to metal fragments in a

number of different Y10,11 and x-bonding orientations.12-15 The

various bonding modes of the Cp ligand to metal fragments

have been examined in several molecular systems.16

The effect of substituents is illustrated by the penta-

methylcyclopentadienyl ligand(referred to as Cp*), which

forms a series of complexes. Compared to the Cp derivatives,

metal complexes containing the Cp* ligand are more stable. It

has been pointed out17 that, while the T5-C5H5 ligand is

sometimes displaced from Rh under acidic conditions, or in

the presence of H2, the corresponding Cp* ligand remains

attached.




5




Furthermore, the electron donating inductive effect of

five methyl groups appears to help stabilize cationic species

and tends to produce low spin(maximum spin pairing). For

example, Cp*2Mn,9 which is low spin (one unpaired electron),

is stable toward hydrolysis and has a shorter Mn-to-ring

distance(by 0.3 A) than Cp2Mn, which is easily hydrolyzed and

is pyrophoric. High spin transition metal complexes are

typically labile. Magnetic studies of decamethylmanganocene

showed that permethylation of the Cp- ring results in an

exclusively low-spin 2E2g electronic configuration, in

contrast to other manganocenes where high spin 6Aig states are

thermally populated.18 The practical large-scale synthesis for

Cp* complexes has been done.19


Relatively little work on the steric effects of changing

cyclopentadienyl ligand substituents has been reported,2-6

primarily because bulky cyclopentadienes have not been

readily available. However, there have been studies of a few

metal complexes containing the 1,3-di-tert-

butylcyclopentadienyl group (Cp**). Introduction of tert-

butyl substituents into the cyclopentadienyl ring has been of

interest because of the potentially greater stability and

hydrocarbon solubility of the metal complexes compared to Cp

complexes. Cp** complexes of group 15 elements phosphorus,

arsenic and antimony were synthesized and recognized as air

sensitive but thermally stable by Jutzi and Peter.20







Metallocenes of the type Cp**2M (2-1) (group 14 elements

Ge, Sn,and Pb) were also synthesized together with half-

sandwich complexes of the type Cp**M (BF4) (2-2) .21


Recently Okuda22 reported the synthesis of the Cp**

complexes Cp**Fe(CO)2Cl (2-3), Cp2**Co+ (2-4) and Cp2**TiCl2

(2-5).


M= Ge, Sn, Pb


M +





M= Ge, Sn, Pb


2-2


Co


2-4


Ee

CO


--CI
Ti


2-3


2-5









tert-Butyl ring substituents might also be expected to

alter the chemical reactivity of cyclopentadienyl complexes

since they should inhibit attack at neighboring carbons or at

the metal atom to a greater extent than a methyl or hydrogen

substituent. The inductive effect of two tert-butyl groups

should make the coordinated metal atom somewhat more

electron-rich than in a Cp complex but less electron-rich

than in Cp** complex.

A good measure of the steric effect of a substituent is

the ligand cone angle(0). Tolman23 calculated a 0 for

unsubstituted cyclopentadienyl of 1360. The size of the Cp*

ligand, which has a large cone angle, probably adds some

kinetic stability to otherwise reactive metal centers. It

seemed desirable to synthesize and study Cp** metal complexes

because of their probable good stability and solubility

characteristics, the possibility of selective reaction

chemistry, a new synthetic route to Cp**H, the relatively few

previous studies of such compounds, and the expected ease of

analysis by NMR spectroscopy.



Synthesis of tert-Butvlcvclopentadiene24



An ethylmagnesium bromide solution was prepared by

treating ethyl bromide with magnesium in diethyl ether at 0C.

The metallation of cyclopentadiene with ethylmagnesium









bromide in boiling ether provides cyclopentadienylmagnesium

bromide(CpMgBr). Treatment of the ether solution of CpMgBr

with tert-butyl chloride resulted in the formation of mono-

tert-butylcyclopentadiene(2-6) in 60 % yield as shown in

Figure 2-1.




+ CH 3CH 2MgBr fMgBr +







+ +t-Bu C1 C
MgBr
2-6
60%


Fig.2-1. Synthesis of mono-butylcyclopentadiene.



It was characterized by 1H NMR and 13C NMR spectra. The
1H NMR spectrum shows one singlet at 8 1.09 for tert-butyl

protons and four peaks for Cp ring protons at 8 2.87, 8 6.05,

8 6.10 and 8 6.18 as listed in Table 2-1. The spectrum is

identical with that reported in the literature.24








Table 2-1. 1H NMR spectral data for tert-butylcyclopentadiene
in CDCl3



structure ring-H (ppm) tert-butyl (ppm)


H2 : 6.05,d,1H

H3 : 6.10,t,lH H6 : 1.09,s,9H
5
4 s --6
H4 : 6.18,q,lH

2-6 H5 : 2.87,d,2H





Synthesis of di-tert-butvlcvcloDentadiene25a



Di-tert-butylcyclopentadiene can be synthesized in a

manner similar to that used for mono-tert-

butylcyclopentadiene. Treatment of mono-tert-

butylcyclopentadiene with CH3CH2MgBr at 00C led to the

formation of tert-butylcyclopentadienylmagnesium bromide.

Alkylation with tert-butyl chloride produced a mixture of

1,3-di-tert-butylcyclopentadiene(2-8) and 1,4-di-tert-

butylcyclopentadiene(2-7) in a ratio of 70:30 as shown in

Figure 2-2. The 1H NMR spectra of 2-7 and 2-8 are listed in

Table 2-2. The spectrum of 2-8 is identical to that reported

in the literature.25a The spectrum of 2-7 was not described in

Reference 25a.









+ CH3CH2MgBr 0oC


2-6


- I'r


+ t-Bu Cl c o +


2-7


51%
Fig.2-2. Synthesis of di-tert-butylcyclopentadiene.


Table 2-2. 1H NMR spectral data for di-tert-butylcyclo-
pentadiene in CDC13


structure ring-H (ppm) tert-butyl (ppm)


H2,3: 6.02,s,2H

3^-I H l--6lS
3 H6:1.15,s, 18H

H5: 2.93,s,2H


H2: 6.20,s,lH H6:1.16,s,9H




7' H4: 5.78,t,1H H7:1.17,s,9H

H5: 2.90,d,2H


MgBr +







The mixture(2-7 and 2-8) was also characterized by SP/EI mass

spectra, which exhibited an m/e 178 peak, as well as by 1H

NMR(Table 2-2) and 13C NMR spectra(Table 2-3).

Recently it was reported that di-tert-butylcyclo

pentadiene(Cp**H) could be prepared in high yields by phase-

transfer-catalyzed alkylation.26 Since we had difficulties

preparing di-tert-butylcyclopentadiene(Cp**H), using that

process we chose the older synthetic route.24,25a


Table 2-3. 13C NMR spectral data for di-tert-butylcyclo-
pentadiene in CDC13.



structure ring-C (ppm) tert-butyl (ppm)


C1,4:158.10
5

3 C6:29.39

2-7 C2,3:133.83

C5: 121.01



C2: 123.80





7' C4: 123.00

2-8 C5: 119.42 C6:29.70

C1: 156.46 C7:30.95

C3: 159.62













CHAPTER 3
CHEMISTRY OF 1,3-DI-TERT-BUTYLCYCLOPENTADIENYLRHODIUM
DICHLORIDE DIMER [Cp**RhCl2]2



Introduction


Considerable research has centered on metal complexes

which contain the Cp*(C5Me5) ligand since such complexes are

known for good stability as well as easy crystallization in

contrast to some Cp(C5H5) analogs. The synthesis of the

pentamethylcyclopentadienyl(n5-C5Me5) half-sandwich complexes

of Rh and Ir (e.g., [Rh(C5Me5)Cl2]2) has been interesting

because they offer a quite exceptional blend of stability and

reactivity seldom found even among phosphine complexes. This

arises from the strong C5Me5-metal bond (which survives acidic

and basic as well as reducing and oxidizing conditions) on

one hand and from the liability of the ligands on the other,

which allows useful reactions to occur.

The rhodium complexes of Cp are known but their

syntheses are somewhat difficult. However, worst of all, once

the Rh-C5H5 bond has been formed, it turns out to be quite

reactive and easily cleaved by a variety of reagents

(including hydrogen) which do not affect the Rh-C5Me5 bond.

In addition, [CpRhCl2]nl7 is amorphous and insoluble in most

solvents in contrast to [Cp*RhCl2]2.







The first Cp* complex of Rh was prepared in the reaction

of RhCl3"3H20 with hexamethylbicyclo[2.2.0]hexa-2,5-

diene.27,28 After its initial incorrect description as a

complex of this diene, the red crystalline compound obtained

in this reaction was correctly identified as [Cp*RhCl2]2 and

was shown crystallographically to have the structure 3-1.

Notably, the Rh2C12 bridge is planar and not folded, and the

Rh-Rh distance of 3.719 A demonstrates the absence of an

Rh-Rh bond.29 The same compound can be prepared directly from

RhC13"3H20 and pentamethylcyclopentadiene(Cp*H)28 or

1-(l-chloroethyl)pentamethylcyclopentadiene.27 In each case

the crystalline dimer is found to be soluble in organic

solvents.






S1 hzk / Cl
Rh R




3-1



For this work it was desirable that rhodium complexes be

made which would retain the cyclopentadienyl ligand during

the changes in oxidation state and coordination number

expected to occur during the reactions to be studied. The

Cp** ligand was expected to parallel the Cp* ligand in

satisfying this requirement.











Preparation of [Cp**RhCl212


Hydrated rhodium trichloride, RhCl3(H20)n, was heated to

2000C in a stream of dry HCl gas to give anhydrous RhCl3.30

Treatment of a THF solution of RhCl3 with Cp**Li under reflux

gave the air-stable compound 3-2 in very good yield(65%) as

shown in Figure 3-1. Recrystallization with CHCl3/pentane

gave orange crystals which were finally identified by 1H and
13C NMR, mass spectrum, elemental analysis and x-ray

crystallography.


RhCl3o 3H20





2-7 ,2-8






Li


+ HC1


2000C RhC3
------ RhC13


0
0C
+ n-BuLi THF, 4hr
THF, 4hr


+ R hC 13 reflux >,', [ >- < -
3 THF, 8 hr
Rh



3-2


Fig.3-1. Synthesis of [Cp**RhCl2]2(3-2)







The 1H NMR spectrum recorded at room temperature shows

one singlet at 8 1.36 for two tert-butyl groups, one singlet

at 8 5.67 for two Cp ring protons(H4,5) and a singlet at 8

5.37 for a single Cp ring proton(H2) as shown in Table 3-1

The 13C NMR spectrum shows that the resonances of the two

tert-butyl groups are equivalent at 830.88 and the ring

carbons are split by rhodium as shown in Fig.3-3.

It was not possible from 1H and 13C NMR to ascertain

whether or not the structure was dimeric. The final proof of

the presence of the dimer came from x-ray structure

determination.



Rh




3-2


Table 3-1. 13C NMR spectral data for the compound 3-2



solvent ring C (ppm) tert-butyl C (ppm)



CDC13 C2: 81.24, d, JRh-c=7.52 Hz C6: 31.37, s.
C4,5: 82.36, d, JRh-c=9.90 Hz C7: 30.08, s.
C1,3: 108.75, d, JRh-c=3.38 Hz


C6D6 C2: 80.86, d, JRh-c= 11.30 Hz C6: 31.04, s.
C4,5: 82.36, d, JRh-c= 6.12 Hz C7 : 30.20, s
C1,3: 107.72, d, JRh-c= 5.54 Hz






























Fig.3-2. 1H NMR spectrum of 3-2 in CDC13


Fig.3-3. 13C NMR spectrum of 3-2 in CDC13









X-ray Crystallography



An x-ray diffraction study was performed on the complex

(Cp**RhCl)2(9-Cl)2(-2.). Crystallization from methylene chloride

and heptane gave small, red-orange colored crystals suitable for

single crystal x-ray diffraction. Data were collected at room

temperature on a Siemens R3m/V diffractometer equipped with a

graphite monochromator utilizing MoKa radiation (X = 0.71073 A).

Forty reflections with 20.00 5 206 22.0 were used to refine the

cell parameters. Reflections(6459) were collected using the co-scan

method. Four reflections (023, 223, 113, 113) were measured every

ninety six reflections to monitor instrument and crystal stability

(maximum correction on I was < 0.99 %). Absorption corrections

were applied based on measured crystal faces using SHELXTL plus

(Sheldrick)31; absorption coefficient, g = 14.34 cm-l(min. and max.

transmission factors are 0.354 and 0.408, respectively).

The structure was solved by the heavy-atom method in

SHELXTL plus (Scheldrick)31 from which the locations of the

three Rh atoms in the asymmetric unit were obtained. The

asymmetric unit contains one dimer in a general position and

half of another dimer sitting on a center of inversion. The

rest of the non-hydrogen atoms were obtained from a

subsequent difference Fourier map. The structure was refined

in SHELXTL plus using full-matrix least squares. The non-H

atoms were treated anisotropically, whereas the positions of

the hydrogen atoms were calculated in ideal positions and







their isotropic thermal parameters were fixed. Four hundred

thirty three parameters were refined and Y 0 ( IFol IFcI)2

was minimized; o=1/(aIFoj)2, Y( Fo) = 0.5 kI -1/2({[( I )]2 +

(0.02I)2 }1/2 I(intensity)= ( I peak Ibackground )(scan
rate), and 0(I) = (I peak + I background)1/2 (scan rate), k

is the correction due to decay and Lp effects, 0.02 is a

factor used to down weight intense reflections and to account

for instrument instability. The linear absorption

coefficient was calculated from values from the International

Tables for X-ray Crystallography.32 Scattering factors for

non-hydrogen atoms were taken from Cromer and Mann33 with

anomalous-dispersion corrections from Cromer and Liberman,34

while those of hydrogen atoms were from Stewart, Davidson and

Simpson.


Table 3-2. Crystallographic data of 3-2


A. Crystal data (298 OK)
a, A
b, A
c, A
b, deg
V, A3
dcalc, g cm-3(298 K)
Empirical formula
Formula wt, amu
Crystal system
Space group
Z


F(000), electrons


I
22.584(3)
12.175(1)
33.325(6)
94.05(1)
9140(2)
1.531
C26H42Cl4Rh2
702.2
Monoclinic
C 2/c
12
4272








Table 3-2 continued


B. Data collection (298 OK)
Radiation, X (A)
Mode
Scan range


Background


Scan rate, deg. min.-I
20 range, deg.
Range of h k 1



Total reflections measured
Unique reflections
Absorption coeff. [l (Mo-Ka), cm-1


C. Structure refinement
S, Goodness-of-fit
Reflections used, I > 20(I)


No. of variables
R, (OR* (%)
R, (OR* all data (%)
Rint. (%)
Max. shift/esd


MO-Ka, 0.71073
0)-scan
Symmetrically over 1.2 about
Kal,2 maximum
offset 1.0 and -1.0 in 0 from
Kal,2 maximum
3 6
3 45


0 < h
0 < k
-35 < 1
6459
5971
14.34


< 24
< 13
< 35


1.52
4740


433
4.11, 4.71
5.76, 5.10
1.06
0.001







Table 3-2 continued.


min. peak in diff. Four. map (e A-3) -0.46
max. peak in diff. Four. map (e A-3) 0.54


* Relevant expressions are as follows, where in the footnote Fo
and Fc represent, respectively, the observed and calculated
structure-factor amplitudes.
Function minimized was (O(IFoi IFcI)2, where (= (o(F))-2
R = (l iIFoI IFcII) / YIFol
0)R = [)(IFol IFcl)2 / X Fo012]1/2
S = [ (O(IFol IFcl)2 / (m-n)]1/2


The molecule consists of two isomers as shown in Figure

3-4 and 3-5. Each isomer has [Cp**RhCl] units bridged by two
g2-chloride ligands. The molecule has precise (i.e.,

crystallographically required) Ci symmetry. Atoms in the

"other half" of the molecule, which is related to the basic

unit by the transformation (x',y',z') = (-x,-y,-z), are

labeled with a prime.

The rhodium atom may be regarded as in an oxidation

state of +3 (d6 configuration). It achieves the expected

noble gas configuration by the donation of six electrons from
a [1T5-Cp**-] anion and two electrons from each of three

chloride ligands (Clll, ClI, C12) for isomer A. The

coordination geometry of the rhodium(III) atom is that

loosely referred to as a three-legged piano stool.

For isomer A angles between the chloride ligands are

Cll-Rhl-Cl2= 80.670(6), C11-Rhl-Cll = 91.290(7) and C12-Rhl-

Clll = 90.620(7). The terminal chloride ligand is slightly




















C30
1 C29


C10


C121


C24



C33 1


C12


C12


C13


Fig.3-4. Molecular structure of isomer A of 3-2






















C50


C49


)C42


k C131 C5 C52
C51


C53




Fig.3-5. Molecular structure of isomer B of 3-2


closer to the rhodium atom than are the bridging chloride
o o
ligands (Rh-C111 = 2.368 A vs. Rh-Cll = 2.447 A and Rh-Cl2 =
o
2.447 A); the mean difference is, however, only ca.0.079
0
A.


C48







Individual rhodium-carbon bond distances range from Rh-
o o
C(1)=2.215(7) A to Rh-C(4)=2.150(6) A, the average value

being 2.183 A. Although there is substantial liberation

motion of the [Cp**] ligand about its fivefold axis, the bond

lengths within the system are not unreasonable.

Carbon-carbon distances within the carbocyclic ring
0 0
range from C(4)-C(5)=1.386(10) A to C(3)-C(4)=1.461(10) A,

averaging 1.432 A, as compared to the accepted C-C

(n-cyclopentadienyl) distance of approximately 1.43 X.35

C(ring)-tert-butyl bond distances are not so adversely

affected by liberation: They have the same length 1.502 A in

one Cp ring and show a little difference in the other Cp
0 0
ring; C(26)-C(21)=1.505 A, C(23)-C(27)=1.526 A. The average

value is 1.509 A (i.e., indistinguishable from the accepted

C(sp2)-C(sp3) distance of 1.510(5) A.36 The tert-butyl

substituents deviated from the Cp ring plane with the
o
individual displacements being +0.10 A for C(6) and C(7),

+0.16 A for C(26) and C(27), +0.07 A for C(47) and +0.15 A

for C(46). The average deviation is 0.11 A, and the

deviation angle of the tert-butyl group from the ring plane

is 4.80. The geometries of [T5-Cp*RhCl]2(9-Cl)2(3-1) and [pT5-

Cp**RhCl]2(9-Cl)2(3-2) are compared in Table 3-6. They appear

to be similar with the only significant difference being the
0 0
Rh-Cl length(2.45 A vs 2.36 A). The Rh-Rh distance in 3-2 is

also somewhat shorter than for the Cp* analog(3.72 A);
0 0
3.680(6) A for isomer A and 3.664(5) A for isomer B of 3-2.








Table 3-3. Fractional coordinates and equivalent isotropica
thermal parameters (A2) for the non-H atoms of the compound
3-2.

Atom x y z U


Rhl
Rh2
Rh3
C11
C12
C13
Clli
C121
C131
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C21
C22
C23
C24
C25
C26
C27
C28
C29


0.33663 (2)
0.28814(2)
0.44743 (3)
0.27728(9)
0.36756(8)
0.45494(11)
0.41605(10)
0.22173 (8)
0.4011(2)
0.2906(3)
0.3478(3)
0.3532(3)
0.2959(3)
0.2596(3)
0.2669(3)
0.4043(3)
0.2155(5)
0.3157(4)
0.2434(4)
0.4062(5)
0.3958(5)
0.4614(4)
0.2380(3)
0.2907(3)
0.3420(3)
0.3210(4)
0.2595(4)
0.1749(3)
0.4060(3)
0.1709(4)
0.1599(3)


1.30173(4)
1.39272(4)
1.00198(5)
1.23500(14)
1.4361(2)
0.9238(3)
1.1850(2)
1.49683(14)
1.1602(2)
1.2343(6)
1.2757(6)
1.3900(6)
1.4210(6)
1.3293(6)
1.1204(6)
1.4631(7)
1.0959(8)
1.0353(7)
1.1170(7)
1.4731(9)
1.5781(8)
1.4181(10)
1.3609(5)
1.2942(6)
1.3611(6)
1.4724(6)
1.4738(6)
1.3235(6)
1.3212(7)
1.2794(7)
1.2312(7)


0.13564(2)
0.233390(10)
-0.04446(2)
0.18924(5)
0.18886(5)
0.02335(6)
0.15710(6)
0.18809(5)
-0.02039(9)
0.0828(2)
0.0730(2)
0.0817(2)
0.0961(2)
0.0965(2)
0.0750(2)
0.0729(2)
0.0999(3)
0.0813(3)
0.0305(2)
0.0282(3)
0.0895(3)
0.0900(4)
0.2848(2)
0.2867(2)
0.2885(2)
0.2873(2)
0.2857(2)
0.2875(2)
0.2954(2)
0.3310(2)
0.2577(3)


0.0410(2)
0.0362(2)
0.0514(2)
0.0536(8)
0.0473(6)
0.1094(13)
0.0686(8)
0.0488(6)
0.1210(15)
0.046(3)
0.044(3)
0.044(3)
0.048(3)
0.050(3)
0.054(3)
0.058(3)
0.113(5)
0.086(4)
0.078(4)
0.112(6)
0.118(6)
0.143(5)
0.038(2)
0.038(2)
0.042(3)
0.052(3)
0.050(3)
0.048(3)
0.057(3)
0.070(3)
0.070(3)







Table 3-3 continued


Atom x sz U


C30
C31
C32
C33
C41
C42
C43
C44
C45
C46
C47
C48
C49
C50
C51
C52
C53


0.1315(3)
0.4490(4)
0.4179(4)
0.4133(4)
0.4428(3)
0.3858(3)
0.3890(3)
0.4499(3)
0.4815(3)
0.4571(3)
0.3378(3)
0.5189(4)
0.4116(4)
0.4568(4)
0.3583(4)
0.2947(3)
0.3040(3)


1.4188(7)
1.4173(8)
1.2256(8)
1.2807(9)
1.0106(6)
0.9824(6)
0.8822(6)
0.8471(6)
0.9236(6)
1.1038(7)
0.8230(6)
1.1495(9)
1.1939(7)
1.0549(8)
0.7211(7)
0.7868(7)
0.8982(7)


0.2804(3)
0.2897(3)
0.2675(3)
0.3392(2)
-0.1084(2)
-0.0945(2)
-0.0729(2)
-0.0730(2)
-0.0938(2)
-0.1362(2)
-0.0558(2)
-0.1240(3)
-0.1360(3)
-0.1789(2)
-0.0325(3)
-0.0915(2)
-0.0290(2)


AFor anisotropic atoms,


the U value is Ueq, calculated as Ueq


= 1/3 Xiij Uij ai* aj* Aij where Aij is the dot product of
the ith and jth direct space unit cell vectors.


0.074(3)
0.087(4)
0.075(4)
0.086(4)
0.045(3)
0.041(2)
0.043 (2)
0.054(3)
0.055(3)
0.056(3)
0.048(3)
0.100(5)
0.090(4)
0.083(4)
0.077(4)
0.066(3)
0.063(3)








Table 3-4. Bond lengths(A) and angles(o) for the non-H atoms


1-2-3


Cll
Cll
C12

Cl
C2
C3
C4
C5
Cll
Cli
C12
C121
C21
C22
C23
C24
C25
C13
Cl3a
C131
C41
C42
C43
C44
Rhl
Rhl
Rh3
C2
C2
C2
C5
C5
C6
C3
C3
Rhl
C4
C4
C4
C7
C7
Rhl
C5
C5
Rhl
Rhl
Rhl


Rhl
Rhl
Rhl
Rhl
Rhl
Rhl
Rhl
Rhl
Rhl
Rh2
Rh2
Rh2
Rh2
Rh2
Rh2
Rh2
Rh2
Rh2
Rh3
Rh3
Rh3
Rh3
Rh3
Rh3
Rh3
Cll
C12
C13
Cl
Cl
Cl
Cl
Cl
Cl
C2
C2
C2
C3
C3
C3
C3
C3
C3
C4
C4
C4
C5
C5


C12




C3
C4
C5
ClI
C12
C121
C121
C21




Cll
C131
C13





Rh2
Rh2
Rh3 a
C5
C6
Rhl
C6
Rhl
Rhl
Rhl
Cl
Cl
C7
Rhl
C2
Rhl
C2
C2
Rhl
C3
C3
Cl
C4


2.447(2)

2.477(2)
2.360(2)
2.145(7)
2.145(6)
2.150(6)
2.125(7)
2.125(7)
2.421(2)

2.464(2)
2.411(2)
2.154(6)
2.140(6)
2.165(6)
2.129(7)
2.142(7)
2.447(2)
2.440(3)
2.359(3)
2.130(6)
2.110(6)
2.143(7)
2.114(8)



1.444(10)


1.443(10)

1.502(10)
1.424(10)


1.461(10)


1.502(11)


1.386(10)


80.67(6)
91.29(7)
90.62(7)





91.9(2)
81.42(6)
90.27(6)
87.56(6)
104.7(2)





90.41(11)
82.86(9)





98.23 (7)
96.28(7)
97.14(10)
104.7(6)
126.7(6)
70.3(4)
128.3(7)
69.5(4)
129.8(5)
70.8(4)
111.1(6)
70.3(4)
128.4(6)
69.1(4)
104.7(6)
129.8(5)
126.5(6)
70.4(4)
71.0(4)
109.4(6)
70.9(4)
71.0(4)
71.0(4)







Table 3-4 continued


1
C1
C8
C8
C8
C9
C9
C10
C11
Cll
Cll
C12
C12
C13
C22
C22
C22
C25
C25
C26
C23
C23
Rh2
C24
C24
C24
C27
C27
Rh2
C25
C25
Rh2
Rh2
Rh2
C21
C28
C28
C28
C29
C29
C30
C31
C31
C31
C32
C32
C33
C42
C42
C42


2
C5
C6
C6
C6
C6
C6
C6
C7
C7
C7
C7
C7
C7
C21
C21
C21
C21
C21
C21
C22
C22
C22
C23
C23
C23
C23
C23
C23
C24
C24
C24
C25
C25
C25
C26
C26
C26
C26
C26
C26
C27
C27
C27
C27
C27
C27
C41
C41
C41


3
C4
C9
C10
Cl
C10
Cl1
Cl
C12
C13
C3
C13
C3
C3
C25
C26
Rh2
C26
Rh2
Rh2
Rh2
C21
C21
C27
Rh2
C22
Rh2
C22
C22
Rh2
C23
C23
C21
C24
C24
C29
C30
C21
C30
C21
C21
C32
C33
C23
C33
C23
C23
C45
C46
Rh3


1.503(13)


1.517(12)

1.542(10)
1.501(12)


1.522(13)

1.477(13)
1.438(9)


1.458(10)

1.505(10)
1.414(9)


1.436(10)


1.526(10)


1.386(12)





1.554(10)


1.523(11)

1.526(11)
1.540(12)


1.525(12)

1.538(11)
1.441(10)


1-2-3
110.0(7)
111.8(7)
107.4(7)
111.7(7)
108.1(7)
111.1(6)
106.5(6)
107.4(8)
109.1(8)
108.5(7)
109.3(8)
110.9(7)
111.6(7)
105.0(6)
127.7(6)
69.9(4)
126.8(6)
69.7(4)
130.9(4)
71.8(4)
110.5(6)
71.0(3)
127.8(7)
69.1(4)
105.9(6)
130.8(5)
126.0(6)
69.8(3)
71.6(4)
110.0(6)
71.8(4)
70.6(4)
70.6(4)
108.7(6)
109.2(6)
109.1(6)
106.1(5)
110.5(6)
110.6(6)
111.3 (6)
111.4(7)
109.5(6)
109.7(7)
108.8(7)
110.9(6)
106.4(6)
104.6(6)
127.6(6)
69.4(4)







Table 3-4 continued


1 2 3 1-2 1-2-3


C45
C45
C46
C43
C43
Rh3
C44
C44
C44
C47
C47
Rh3
C45
C45
Rh3
Rh3
Rh3
C41
C48
C48
C48
C49
C49
C50
C51
C51
C51
C52
C52
C53


C41
C41
C41
C42
C42
C42
C43
C43
C43
C43
C43
C43
C44
C44
C44
C45
C45
C45
C46
C46
C46
C46
C46
C46
C47
C47
C47
C47
C47
C47


C46
Rh3
Rh3
Rh3
C41
C41
C47
Rh3
C42
Rh3
C42
C42
Rh3
C43
C43
C41
C44
C44
C49
C50
C41
C50
C41
C41
C52
C53
C43
C53
C43
C43


1.437(10)

1.514(11)
1.415(9)


1.440(10)


1.510(10)


1.389(11)





1.532(12)


1.503(12)

1.540(11)
1.518(11)


1.547(10)

1.520(11)


127.5(6)
68.8(4)
130.7(5)
71.8(4)
110.7(6)
70.9(4)
128.1(6)
69.2(4)
105.7(6)
128.4(5)
126.2(6)
69.3(4)
70.0(4)
109.1(6)
71.3(4)
71.4(4)
71.5(4)
110.0(6)
110.1(7)
109.3(7)
109.8(6)
109.2(7)
111.6(7)
106.7(7)
108.3(6)
109.8(6)
111.7(6)
107.9(6)
107.6(6)
111.4(6)







Table 3-5. Anisotropic thermal parametersa for the non-H atoms


Atom U11


Rhl
Rh2
Rh3
Cll
C12
C13
Clll
C121
C131
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
Cll
C12
C13
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C41
C42
C43
C44
C45
C46
C47
C48
C49
C50


0.0515(4)
0.0478(3)
0.0438(4)
0.0911(15)
0.0511(11)
0.086(2)
0.0790(15)
0.0551(11)
0.158(3)
0.055(5)
0.051(5)
0.058(5)
0.055(5)
0.048(5)
0.067(5)
0.057(5)
0.139(10)
0.105(8)
0.092(7)
0.144(10)
0.148(11)
0.066(7)
0.048(4)
0.046(4)
0.048(4)
0.079(6)
0.071(6)
0.052(5)
0.048(5)
0.054(5)
0.052(5)
0.059(5)
0.060(6)
0.057(5)
0.058(6)
0.049(5)
0.032(4)
0.043(4)
0.049(5)
0.047(5)
0.045(4)
0.049(5)
0.088(7)
0.108(8)
0.077(6)


U22

0.0393(4)
0.0300(3)
0.0760(4)
0.0321(15)
0.0521(11)
0.203(2)
0.0759(15)
0.0468(11)
0.090(3)
0.048(5)
0.054(5)
0.046(5)
0.043(5)
0.052(5)
0.055(5)
0.058(5)
0.103(10)
0.044(8)
0.081(7)
0.130(10)
0.077(11)
0.147(7)
0.040(4)
0.038(4)
0.050(4)
0.041(6)
0.044(6)
0.055(5)
0.084(5)
0.095(5)
0.071(5)
0.097(5)
0.126(6)
0.101(5)
0.138(6)
0.048(5)
0.050(4)
0.047(4)
0.055(5)
0.068(5)
0.070(4)
0.050(5)
0.129(7)
0.076(8)
0.128(6)


U33

0.0326(3)
0.0309(3)
0.0342(5)
0.0395(10)
0.0393(11)
0.037(3)
0.0499(14)
0.0435(11)
0.125(2)
0.035(5)
0.026(5)
0.027(4)
0.046(4)
0.049(5)
0.041(5)
0.057(5)
0.102(8)
0.104(5)
0.058(6)
0.061(9)
0.135(8)
0.213(11)
0.028(4)
0.031(4)
0.025(5)
0.034(5)
0.036(5)
0.038(5)
0.037(6)
0.064(7)
0.086(6)
0.066(7)
0.074(9)
0.065(7)
0.061(9)
0.037(4)
0.041(4)
0.036(4)
0.056(5)
0.052(5)
0.052(5)
0.046(5)
0.081(9)
0.088(7)
0.042(8)


U12

0.0120(2)
0.0024(2)
-0.0151(3)
-0.0074(9)
-0.0022(8)
-0.0825(11)
0.0426(10)
0.0097(8)
-0.028(2)
0.005(3)
0.014(3)
0.004(3)
0.024(3)
0.013(4)
-0.011(4)
0.000(4)
-0.065(7)
-0.006(6)
0.003(5)
-0.062(6)
-0.028(8)
-0.030(8)
0.005(3)
0.009(3)
-0.005(3)
-0.009(4)
0.012(4)
0.013(3)
-0.001(3)
0.009(4)
-0.009(4)
0.025(4)
-0.023(5)
0.017(4)
0.010(4)
-0.007(3)
-0.003(3)
-0.002(3)
0.010(4)
0.009(4)
-0.012(4)
-0.010(3)
-0.055(6)
-0.006(6)
-0.008(4)


U13

0.0054(3)
0.0023(2)
0.0020(3)
0.0178(8)
0.0071(8)
-0.015(2)
-0.0023(11)
-0.0046(9)
0.078(2)
0.002(3)
0.004(3)
-0.000(3)
-0.003(4)
0.005(4)
0.006(4)
-0.002(4)
0.051(7)
-0.027(5)
-0.010(5)
0.013(6)
0.055(7)
-0.019(11)
0.007(3)
0.007(3)
-0.004(3)
-0.001(3)
0.005(3)
0.006(4)
-0.001(4)
0.018(5)
0.004(5)
0.010(5)
0.001(6)
-0.005(5)
-0.007(6)
-0.003(4)
-0.003(3)
-0.006(3)
0.008(4)
0.010(4)
-0.000(4)
0.007(4)
-0.010(6)
0.027(6)
-0.007(5)


U23

0.0009(3)
0.0007(3)
-0.0135(3)
-0.0026(10)
0.0002(10)
0.0142(12)
-0.0006(11)
0.0045(10)
-0.063(2)
0.002(4)
0.005(4)
0.007(4)
0.006(4)
0.007(5)
-0.005(4)
0.010(5)
-0.033(8)
0.004(8)
-0.011(5)
0.018(6)
-0.017(10)
0.098(15)
0.001(4)
0.001(4)
0.010(4)
-0.000(4)
-0.010(4)
0.003(4)
0.019(4)
0.017(5)
-0.016(6)
0.006(6)
0.024(6)
0.009(6)
0.043(6)
-0.005(4)
0.001(4)
-0.010(4)
-0.000(5)
-0.016(5)
0.006(5)
-0.000(4)
0.033(7)
0.023(7)
0.006(5)








Table 3-5 continued.


Atom

C51
C52
C53


U11


0.089(7)
0.060(5)
0.054(5)


U22


0.070(7)
0.068(5)
0.085(5)


U33


0.072(6)
0.068(6)
0.050(6)


U12


-0.007(5)
-0.021(4)
-0.014(4)


U113


U23


0.009(5)
-0.008(5)
0.002(5)


0.014(6)
-0.007(5)
-0.004(5)


AThe Uij are the mean-square amplitudes of vibration in A2 from the
general temperature factor expression

exp[-272(h2a*2Ull + k2b*2U22 + 12c*2U33 + 2hka*b*Ul2 + 2hla*c*Ul3
+ 2klb*c*U23)]



Table 3-6.Comparison of selected intramolecular parameters of
[T5-Cp*RhCl]2(9-Cl)2(3-1) and [T5-Cp**RhCl]2(9-Cl)2(3-2)


[T5-Cp*RhCl]2 (-Cl)2


[T5-Cp**RhCl]2(J-Cl)2


O
Rh-Rh, A 3.7191 (6) 3.680(6),3.664(5)
0
Rh-Cl, A 2.4522 (10) 2.360 (2)
(terminal)
o
Rh-Cl, A
(bridging) 2.4649 (11) 2.447 (2)

Rh-Cl-Rh' (o) 98.29 (3) 98.23 (7)













CHAPTER 4
APPLICATION OF [Cp**RhCl2]2


Introduction


The dimeric dichloro(pentamethylcyclopentadienyl)rhodium,

[Rh(C5Me5)Cl2]2(3-1), has attracted attention because of its

potential catalytic activity. Maitlis and co-workers found

that it could be used as a catalyst for hydrogenation of

alkenes and arenes.37'38 It has been pointed out that while

the 15-C5H5 ligand is easily displaced from Rh under acidic

conditions, or in the presence of H2, the corresponding

C5Me5(Cp*) ligand survives such conditions.39 Furthermore, the

electron-donating inductive effect of five methyl groups

appears to help stabilize cationic species, and the steric

bulk of the Cp* ligand probably adds some kinetic stability to

otherwise reactive Rh centers.

The compound 3-1 undergoes metathetical replacement of

the chloride ligands on treatment with NaX in refluxing

methanol(X= Br, I, N3, NCO, SCN).40-42 Reactions of 3-1 with

silver carboxylates produce the neutral carboxylate compounds

Cp*Rh[OC(O)R]2.43 Reduction of 3-1 with NaBH4 in the presence

of base yields the bridging hydride complex(4-1),44 which has

a much shorter Rh-Rh separation(2.906 A) than that in the

parent complex 3-1.










Rh R
H1



4-1



The compound(3-1) also undergoes a variety of reactions in

which the halogen bridge is split by a donor ligand to give

the neutral mononuclear compounds Cp*Rh(L)Cl2 (L= PPh3, dppe,

Py, MeNC) .41,45 The reaction of 3-1 with cyclohexadienes was

also studied.46

Since 3-1 was already known for significant activity, it

was thus of interest to apply the rhodium complex(3-2),which

has bulkier groups than 3-1, to analogous reactions to study

the difference in chemistry. Several compounds were reacted

with 3-2 and the 1H NMR and 13C NMR spectra of the subsequent

products measured.



Reaction of 3-2 with PMe3



Reaction of 3-2 with a little excess of PMe3 in THF at

room temperature for 12 hr led to the formation of an air-

stable, red-yellow solid. Recrystallization from CH2C12 and

pentane gave a product in 62 % yield which was found to be

the mononuclear complex, Cp**Rh(PMe3)Cl2 (4-2) by 1H NMR and

13C NMR.











1 Rh + PMe3 12 hr Rh
2 /\ 3 2,C "1 ,
Cl Cl 2 THF Cl I C1
S- PMe3

3-2 4-2

Fig.4-1. Synthesis of Cp**Rh(PMe3)Cl2 (4-2)



spectroscopy and FAB MS. The 1H NMR and 13C NMR spectra of

4-2 are listed in Table 4-1. As shown in Figure 4-2 the 1H

NMR spectrum of 4-2 exhibits peaks attributable to the tert-

butyl protons, the Cp**ring protons, and the methyl protons

of the coordinated PMe3. In the 1H NMR, one Cp** ring

proton(H2) is found as a doublet(JP-H= 9.75 Hz) at 8 5.56 due

to splitting by phosphorus. The other two ring protons(H4'5)
of the Cp** ring also appear as a doublet at 8 4.59 but have

a very small coupling to phosphorus(JP-H=l.08 Hz). The methyl

protons of PMe3 are found as a doublet at 8 1.75 in the 1H NMR

with a large coupling to phosphorus(Jp-H=12.21 Hz). The 13C

NMR absorptions of the Cp** ring show two sets of resonances,
a resonance assigned to C2 at 6 71.20 (JRh-c=8.41 Hz) and a

resonance assigned to C4,5 at 6 82.80 (JRh-c=20.25 Hz), both

of which are doublets as a result of coupling to rhodium. The

methyl carbons of PMe3 appear as a doublet at 8 17.36 (Jp-c=

34.37 Hz) and are coupled to phosphorus.









P7



Me/P. 8

Me

4-2


Table 4-1. NMR spectral data for the compound 4-2
in CDC13


tert-butyl ring(ppm) PMe3 (ppm)



H7: 1.33, s H2:5.56,d,lH H8:1.75,d,9H
1H NMR Jp-H=9.75 Hz JP-H=12.21 Hz


H4,5:4.59,d,2H
Jp-H=1.08 Hz

13C NMR C7: 29.79,s C2: 71.20, d C8: 17.36,d
C6: 30.66,s JRh-C= 8.41 Hz Jp-c=34.37 Hz

C4,5: 82.80,d
JRh-C= 20.25 Hz

C1,3: 129.21,d
JRh-c= 9.25 Hz













SIa I
-. 1






.. L ... .. ..
" j.** ** j I.*J "I '0,"" ^ P *****


Fig.4-2. 1H NMR spectrum of 4-2 in CDC13


Fig.4-3 13C NMR spectrum of 4-2 in CDC13







Reaction of 3-2 with a little excess of PPh3 in THF at

room temperature for 6 hr led to the formation of an air

stable mononuclear complex Cp**Rh(PPh3)Cl2(4-3) in 89 % yield.

It was characterized by 1H NMR, 13C NMR and FAB MS.

Crystallization from CH2C12 and heptane gave air stable, red

crystals suitable for x-ray crystallography, which supports

the mononuclear structure of 4-3. The 1H NMR and 13C NMR

spectra of 4-3 are similar to those of 4-2. The structure and

spectra will be reviewed in Chapter 5 in detail.





1 Rh + PPh3 6 hr Rh
S/ \ 25
Cl Cl 2 THF CI Cl
\ PPh3

3-2 4-3

Fig.4-4. Synthesis of Cp**Rh(PPh3)Cl2 (4-3)



Reaction of 3-2 with Silver Acetate



Reaction of 3-2 with silver acetate proceeds in THF at

room temperature for 2 hr to afford yellow-orange crystals of

mononuclear product Cp**Rh(OAc)2(4-4) in 86 % yield. It was

characterized by m.p, 1H NMR and 13C NMR spectroscopy. As

shown in Figure 4-6, the 1H NMR spectrum of 4-4 exhibits

peaks attributable to tert-butyl protons, Cp** ring protons,

and CH3 protons of the coordinated acetate(AcO) groups. The 1H

and 13C resonances for the tert-butyl group appear at







positions similar to those found for other Cp** compounds.

Coordination of the acetate group was suggested by a peak at
8 2.02 in the 1H NMR. The 13C NMR spectrum also exhibits two

singlet peaks at 5 38.40 and 8113.27 which may be assigned to

the methyl and carbonyl carbons, respectively. Three peaks

were observed for Cp** ring carbons in the 13C NMR spectrum,
analogous to those of other Cp** complexes: 8 69.43(JRh-C=

8.13 Hz), 873.97(JRh-c= 9.23 Hz), and 8113.20(JRh-C= 9.51 Hz).

Each ring carbon is coupled to rhodium.






Rh + 2 CH OO Ag 2 hr Rh

C Cl 2 THF AcO Ac

4-4
3-2


Fig.4-5. Synthesis of Cp**Rh(OAc)2(4-4)




























Fig.4-6. 1H NMR spectrum of 4-4 in CDC13


Fig.4-7 13C NMR spectrum of 4-4 in CDC13







Reaction of 3-2 with Silver Nitrate



Reaction of 3-2 with silver nitrate proceeds in THF at

room temperature for 1 hr to afford yellow-orange crystals of

mononuclear product Cp**Rh(NO3)2(4-5) in 89 % yield. It was

characterized by m.p, FAB MS, 1H NMR and 13C NMR spectroscopy.
The 1H NMR spectrum of 4-5 exhibits peaks at 81.40, 85.44

(JRh-H= 4.14 Hz) and 8 5.60(JRh-H= 1.05 Hz) attributable to

tert-butyl protons and Cp** ring protons. The 13C resonances

for the tert-butyl group also appear at positions (829.19,

831.27) similar to those found for other Cp** compounds.

Three peaks were observed for Cp** ring carbons in the 13C NMR

spectrum, analogous to those of other Cp** complexes and each
ring carbon is coupled to rhodium: 868.14(JRh-C= 7.32 Hz),

869.81(JRh-c= 8.33 Hz), and 8116.42 (JRh-c= 9.01 Hz).








Rh + 2 AgNO3 25C I RhN

A NN THF (


3-2 4-5


Fig.4-8. Synthesis of Cp**Rh(NO3)2(4-5)





























Fig.4-9. 1H NMR spectrum of jA- in CDC13


Fig.4-10. 13C NMR spectrum of 4-5 in CDC13













CHAPTER 5
STRUCTURE AND SPECTRA OF Cp**Rh(PPh3)Cl2

Introduction


The story of rotational barriers in compounds is a topic

of interest to chemists, as conformational stability is

important in terms of understanding both chemical bonding and

stereospecific reactivity. In general, the barrier to

rotation about the metal-to-ring bond in bis(T15-

cyclopentadienyl)metal complexes is very small. The T5-Cp

ring rotates very fast at the room temperature, typically 10-
11ll47a and in no case has it been stopped in solution. For

ferrocenes, the barrier to rotation is 2-5 kcal/mol.47b An

electron diffraction study of ferrocenes indicates that in

the vapor state the Cp rings rotate freely about the common

orthogonal axis.48 Molecular orbital treatments 49,50 of

ferrocene suggest that no major barrier exists against free

rotation of the Cp rings. Estimated values of the rotational

barrier for other metallocenes and for cyclopentadienyl metal

carbonyls are of the same order of magnitude.

There are two factors which affect the value of the

rotational barrier, the bulkiness of the substituents on the

Cp ring and the volume of the ligands coordinated to the

metal. For example, the activation free energy for rotation







about Cp*2Zr-CH(SiMe3)2 51 is exceptionally high, 13.41.8

kcal/mol due to the bulky ligand.

The first conformationally rigid structures with bulky

ring substituents were three half-sandwich complexes of

cobalt reported by Werner,52 5-1 and two analogs. Their 1H NMR

data proved that they were rotationally rigid even at 1000C.





Co

Me PMe3







Table 5-1. 1H NMR spectral (ppm)data for the compound
5-152 in C6D6.



Ring-H PMe3 t-Butyl



H2: 3.37, 1H, d 1.11, 9H, d 1.28, 18H, s
Jp-H=6.0 Hz Jp-H=6.5 Hz

1.09, 9H, d
Jp-H=6.5 Hz

H4,5: 3.69, 2H, d
JP-H=4.5 Hz


Therefore, in the case of the substituted cyclopentadienyl

complexes C5H5-nRnMLm it should be possible by choice of







sufficiently bulky substituents R and voluminous (especially

not rod-shaped) ligands L to hinder rotation about the metal-

to-ring bond to such an extent that certain conformers can be

frozen. Since Cp**Rh(PPh3)Cl2 has two bulky tert-butyl groups

on the Cp ring and a voluminous PPh3 ligand, it is expected

to exhibit hindered rotation about metal-Cp ring axis.



Structure and SDectra



As shown in Fig.5-1, the 1H NMR spectrum of 4-3

exhibited peaks attributable to the tert-butyl protons, the

Cp ring protons and the phenyl protons of the phosphorus

ligand. The phenyl resonances show typical complex structures

resulting from splitting by phosphorus.53a The Cp ring protons

resonances might be expected to be split by rhodium (103Rh,

100% abundance, spin 1/2) and by phosphorus, but coupling by

rhodium was not observed. Coupling of such ring protons to

rhodium is generally small (ca. 0.4 cps)53b and rarely found.

The 13C NMR spectrum (Fig.5-2) indicates that the carbons of

the Cp ring are split by rhodium as shown in Table 5-3, but

the 1H NMR shows that only one proton out of three of the

Cp** ring is split by phosphorus as shown in Fig.5-1. The

peaks at 8 4.06 and 8 5.54 are in the area ratio of 2:1. Thus

the singlet resonance at 8 4.06 is assigned to H4,H5 and the

doublet resonance of 5 5.54 is assigned to H2 (Table 5-2). The

fact that only the peak at 8 5.54 is split significantly by








phosphorus is interpreted to mean that the structure is

rotationally rigid. Phosphorus exhibits moderate coupling

(Jp-H= 8.31Hz in CDCl3) to the ring proton in a trans

relationship but its coupling to the cis ring protons is

small(Jp-H= 1.44 Hz) in CDC13 and undetectable in C6D6. The 1H

NMR spectrum was unchanged when measured at 600C, indicating

that the rotational barrier is at least 11.2 kcal/mol.






Rh


C I C
PPh3
A4-3



Table 5-2. 1H NMR spectral data(ppm) for the compound 4-3


Solvent tert-Butyl Ring H PPh353a


CDC13 1.23,s,18H H2: 5.54, d 7.37, m, 9H
JP-H =8.31 Hz JP-H = 9.96Hz

H4,5:4.06, d 7.92, m, 6H
Jp-H= 1.44 Hz JP-H =16.80Hz



C6D6 1.18,s,18H H2: 5.42, d, 6.98, d, 9H
JP-H =9.84 Hz JP-H = 6.70Hz

H4,5:4.06, s 8.12, m, 6H
JP-H =17.70Hz





























Fig.5-1. 1H NMR spectrum of a4-3 in CDC13


Fig.5-2. 13C NMR spectrum of A-3 in CDC13







Table 5-3. 13C NMR spectral data(ppm) for the compound 4-3



solvent ring C(a) tert-butyl C(a) PPh3(b)



CDC13 C2: 74.30, d C6: 33.22, s 127.96, d
JRh-c= 8.40 Hz Jp-C= 10.40 Hz
C4: 77.80, d C7: 29.37, s 130.44, d
JRh-c= 4.04 Hz Jp-C= 2.56 Hz

C5: 78.05, d 134.38, d
JRh-c= 4.06 Hz Jp-c= 9.41 Hz

C1'3: 131.89, d
JRh-c= 5.28 Hz


C2: 74.26, d C6: 33.28, s 130.40, d
JRh-C=7.50 Hz Jp-c= 2.48 Hz

C6D6 C4,5:76.90, d C7: 29.47, s 135.04, d
JRh-C=7.51 Hz Jp-c= 9.44 Hz

134.38, d

Jp-c= 9.41 Hz



* assignment(a) is based on 53a(ref), and (b) is based on 53c



The 31P NMR(C6D6) spectrum shows the resonance at 8 54.81

for PPh3. The question of why two tert-butyl substituents

hinder rotation of the Cp ring might be explained in terms of

a "gear mechanism".52 When a Cp** ring is present, it is

impossible on rotation about the metal-ring axis for the

tert-butyl groups to get past the triphenylphosphine ligand

despite rotation about the C-CMe3 bond.







X-ray Crystalloaraphy



An x-ray diffraction study was performed on the complex

Cp**Rh(PPh3)Cl2(5-2). Crystallization from methylene chloride and

heptane gave air stable, red crystals suitable for single crystal

x-ray diffraction. Data were collected at room temperature on a

Siemens R3m/V diffractometer equipped with a graphite
monochromator utilizing MoKa radiation (X= 0.71073 A). Fifty

reflections with 20.00 290 22.00 were used to refine the cell

parameters. 3973 reflections (2 equivalent sets; -10 < h < 10, 0

< k < 15, -11 < 1 < 11) were collected using the w-scan method.

Four reflections (122, 131, 011, 021) were measured every 96

reflections to monitor instrument and crystal stability (maximum

correction on I was < 1.02 %). Absorption corrections were not

applied due to the small crystal size; g = 8.5 cm-1.

The structure was solved by the heavy-atom method in

SHELXTL plus (Scheldrick)31 from which the location of the Rh

atom was obtained. The rest of the nonhydrogen atoms were

obtained from a subsequent difference Fourier map. The

structure was refined in SHELXTL plus using full-matrix

least squares. The non-H atoms were treated anisotropically,

while the positions of the hydrogen atoms were calculated in

ideal positions and their isotropic thermal parameters were
fixed. Three hundred fifteen parameters were refined and 0 (

IFoI IFcI)2 was minimized; w=l/(oaYFoQ)2, G( Fo) = 0.5 kI
-1/2{[(( I )]2 + (0.021)2 }1/2 I(intensity)= ( I peak -

Ibackground )(scan rate ), and o(I) = ( I peak + I







background)1/2 (scan rate), k is the correction due to decay
and Lp effects, 0.02 is a factor used to down weight intense

reflections and to account for instrument instability. The

linear absorption coefficient was calculated from values from

the International Tables for X-ray Crystallography.32

Scattering factors for non-hydrogen atoms were taken from

Cromer and Mann33 with anomalous-dispersion corrections from

Cromer and Liberman,34 while those of hydrogen atoms were from

Stewart, Davidson and Simpson.

Crystallographic data and data collection parameters

are summarized in Table 5-4. A drawing showing the atom-

numbering scheme for 4-3 is presented in Figure 5-4. Table

5-5 lists the nonhydrogen atom fractional coordinates and

equivalent isoptopic thermal parameters.



Table 5-4. Crystallographic data for the compound 4-3


A. Crystal data (298 OK)

a, A 10.008(1)
b, A 13.993(2)
c, A 10.351(1)
b, deg. 97.74(1)
v, A3 1436.4(3)
dcalc, g cm-3(298 K) 1.418
Empirical formula C3lH36PCl2Rh
Formula wt, g 613.38
Crystal system Monoclinic







Table 5-4 continued


Space group
Z
F(000), electrons


B. Data collection (298 OK)
Radiation, X (A)
Mode
Scan range


Background


Scan rate, deg. min.-1
20 range, deg.
Range of h k 1
(2 equivalent sets))


Total reflections measured
Unique reflections
Absorption coeff. l (Mo-Ka), cm-1


C. Structure refinement
S, Goodness-of-fit
Reflections used, I > 2a(I)
No. of variables
R, (OR* (%)
R, (OR* all data (%)
Rint. (%)
Max. shift/esd


Mo-Ka, 0.71073
co-scan
Symmetrically over 1.2 about
Kal,2 maximum
offset 1.0 and -1.0 in Co froN
Kal,2 maximum
3 6
3 45


-10 <
0 <
-11 <
3973
1988
8.5


< 10
< 15
< 11


1.00
1844
315
2.75, 3.06
3.24, 3.21
2.28
0.001


min. peak in diff. four. map (e A-3)
max. peak in diff. four. map (e A-3)


P21
2
632


-0.34
0.28






Table 5-4 continued

Relevant expressions are as follows, where in the footnote Fo
and Fc represent, respectively, the observed and calculated
structure-factor amplitudes.
Function minimized was 0)(IFol IFcl)2, where (o= (s(F))-2
R = (I IFol IFcl I) / JIFol
(OR .= [(0(IFol IFcl)2 /1 Fo12]1/2
S = [oj(IFol IFcI)2 / (m-n)]1/2

C7




CC12

C!
C41
C2 Rh
C5 P





C12 C10


Fig.5-3. Molecular structure of 4-3.









The interatomic distances and bond angles for Cp**Rh(PPh3)C12

are listed in Table 5-6. The molecular configuration (Figure

5-3) consists of a rhodium atom bonded to one Cp** ligand,

two chloride ligands, and one PPh3 ligand. The angles between

the ligands coordinated to Rh are not identical; Cll-Rh-C12 =

87.97(7)0, Cll-Rh-P = 87.86(6)0, C12-Rh-P = 91.74(7)0

Also, one chlorine is slightly closer to the Rh atom
0 0
than is the other; Cll-Rh=2.372(2) A, C12-Rh=2.399(2) A. The

cyclopentadienyl C(ring)-C(ring) bond lengths are the same

within experimental error, approximately 1.43 A.


2 1.428(9)
1.42 ) )
1 3

1.431( .440(10)
5 4
1.424(10)


Fig.5-4. The crystallographically determined ring
carbon internuclear bond distances(A) in 4-3.


Table 5-6 reveals that there is a small deviation from

planarity in the Cp** ring. Evidence for a slight ring

puckering is given by the difference of Rh-C(ring) distances.

Individual rhodium-carbon distances range from Rh-C(4)

2.144 A to Rh-C(3) 2.259 X, the average value being 2.209 X.

It is apparent that the carbons bonded to tert-butyl groups

are somewhat farther from rhodium than the others, Rh-C(3)







0 0
2.259(7) A, Rh-C(1) 2.251(7) A. A second distortion is the

displacement of the tert-butyl groups out of the Cp ring

plane and away from the rhodium atom; C(6) and C(10) of the

tert-butyl groups deviate from the ring plane. The angular

separation(r) from the ring plane(10.30) is larger than that

observed for (Cp**RhCl2)2(4.80) and the distance(d) from the

ring plane (0.29 A)is longer. This might be due to the fact

that the size of the PPh3 ligand crowds the other ligands

sufficiently that the tert-butyl groups are pushed away from

the metal atom.

CH3 CH3

CH
---- d




Rh

Fig.5-5. Deviation of a tert-butyl group from the ring
plane

Table 5-5. Fractional coordinates and equivalent
isotropica thermal parameters (A2) for the non-H atoms
of compound 4-3.

Atom x y z U

Rh 0.19287(4) 0.0 0.13521(4) 0.03132(14)
Cll 0.1084(2) 0.04004(14) 0.3317(2) 0.0575(8)
C12 -0.0158(2) -0.0817(2) 0.0687(2) 0.0562(7)
P 0.2878(2) -0.13563(13) 0.2405(2) 0.0320(5)
C1 0.2133(7) 0.0542(5) -0.0659(6) 0.038(2)
C2 0.1829(7) 0.1326(5) 0.0124(6) 0.039(2)







Table 5-5 continued


Atom x y z U


C3 0.2877(6)
C4 0.3804(6)
C5 0.3353(6)
C6 0.1465(8)
C7 0.1552(12)
C8 -0.0035(8)
C9 0.2240(10)
C10 0.3083(9)
C11 0.3794(10)
C12 0.4022(12)
C13 0.1766(8)
C21 0.4622(6)
C22 0.5684(7)
C23 0.6985(8)
C24 0.7236(8)
C25 0.6187(9)
C26 0.4874(7)
C31 0.2148(7)
C32 0.2949(7)
C33 0.2374(9)
C34 0.1019(9)
C35 0.0183(8)
C36 0.0755(7)
C41 0.2996(7)
C42 0.3747(10)
C43 0.3713(10)
C44 0.2933(9)
C45 0.2225(9)
C46 0.2220(8)

aFor anisotropic atoms,
= 1/3 YiYj Uij ai* aj*


0.1453(5)
0.0674(5)
0.0127(7)
0.0334(6)
-0.0696(7)
0.0631(7)
0.0934(8)
0.2288(6)
0.1994(7)
0.2980(7)
0.2802(6)
-0.1086(5)
-0.1321(6)
-0.0998(7)
-0.0487(7)
-0.0243(5)
-0.0549(6)
-0.1864(5)
-0.2320(6)
-0.2797(6)
-0.2834(6)
-0.2372(6)
-0.1884(5)
-0.2430(5)
-0.3203(7)
-0.4057(6)
-0.4139(7)
-0.3389(7)
-0.2531(6)

the U value


0.1191(7)
0.1115(7)
-0.0020(6)
-0.2025(7)
-0.2422(9)
-0.2217(7)
-0.2904(8)
0.2091(8)
0.3455(8)
0.1445(11)
0.2230(8)
0.3077(7)
0.2415(7)
0.2865(10)
0.3967(11)
0.4645(9)
0.4217(7)
0.3775(6)
0.4780(7)
0.5714(8)
0.5680(8)
0.4726(7)
0.3758(7)
0.1422(7)
0.1923(9)
0.1239(10)
0.0045(10)
-0.0462(8)
0.0215(8)


is Ueq, calculated as Ueq


Aij where Aij is the dot product of


the ith and jth direct space unit cell vectors.


0.038(2)
0.038(2)
0.038(2)
0.048(3)
0.076(5)
0.067(3)
0.072(4)
0.049(3)
0.070(4)
0.079(4)
0.061(3)
0.037(2)
0.048(3)
0.065(3)
0.073(3)
0.066(3)
0.048(3)
0.034(2)
0.047(3)
0.060(3)
0.058(3)
0.051(3)
0.043(2)
0.038(2)
0.061(3)
0.073(4)
0.066(3)
0.068(4)
0.053(3)







Table 5-6. Bond lengths
of compound 4-3

1 2 3


Cll
Cll
C12
C1
C2
C3
C4
C5
C21
C21
C21
C31
C31
C41
C2
C2
C5
C6
C3
C4
C4
C10
C5
C1
C7
C7
C7
C8
C8
C9
Cli
Cll


Rh
Rh
Rh
Rh
Rh
Rh
Rh
Rh
P
P
P
P
P
P
Cl
C1
C1
C1
C2
C3
C3
C3
C4
C5
C6
C6
C6
C6
C6
C6
C10
C10


C12
P
P







C31
C41
Rh
C41
Rh
Rh
C5
C6
C6

C1
C10
C2
C2
C3
C4
C8
C9
Cl
C9
Cl
C1
C12
C13


(A) and angles (0) for the non-H atoms


1-2

2.372(2)

2.399(2)
2.251(7)
2.244(7)
2.259(7)
2.144(7)
2.151(6)
1.829(6)



1.824(7)


1.827(8)
1.421(10)


1.431(9)
1.508(9)
1.428(9)
1.440(10)


1.491(11)
1.424(10)


1.505(13)



1.545(11)


1.524(13)
1.549(12)


1-2-3

87.79(7)
87.78(6)
91.74(7)







104.3(3)
104.6(3)
108.5(2)
100.1(3)
120.1(2)
117.6(2)
106.5(6)
125.6(6)
126.7(6)

110.2(6)
126.2(6)
106.0(6)
127.3(6)
108.5(6)
108.6(7)
108.2(7)
108.2(7)
114.0(7)
109.8(7)
111.7(6)
104.9(6)
109.0(7)
109.6(7)







Table 5-6 continued


1 2


Cll
C12
C12
C13
C22
C22
C26
C23
C24
C25
C26
C21
C32
C32
C36
C33
C34
C35
C36
C31
C42
C42
C46
C43
C44
C45
C46
C41


C10
C10
C10
C10
C21
C21
C21
C22
C23
C24
C25
C26
C31
C31
C31
C32
C33
C34
C35
C36
C41
C41
C41
C42
C43
C44
C45
C46


C3
C13
C3
C3
C26
P
P
C21
C22
C23
C24
C25
C36
P
P
C31
C32
C33
C34
C35
C46
P
P
C41
C42
C43
C44
C45


1-2



1.561(15)

1.526(12)
1.380(10)


1.393(10)
1.398(10)
1.341(14)
1.382(14)
1.396(11)


1.381(9)

1.392(9)
1.364(12)
1.353(13)
1.368(11)
1.397(11)


1.379(12)


1.387(10)
1.387(13)
1.375(13)
1.334(13)
1.391(13)


1-2-3

111.7(7)
109.0(7)
105.0(7)
112.3(6)
119.0(6)
121.4(5)
119.3(5)
120.2(7)
121.0(8)
119.7(8)
120.6(8)
119.4(7)
118.6(7)
120.9(5)
120.2(5)
120.1(7)
121.2(7)
120.9(8)
118.6(7)
120.5(6)
118.0(7)
120.6(6)
121.0(6)
120.7(8)
120.1(8)
119.7(9)
121.3(8)
120.1(7)







Table 5-7. Anisotropic
atoms of compound 4-3.


thermal parameters for the non-H


Atom

Rh
Cll
C12
P
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
Cll
C12
C13
C21
C22
C23
C24
C25
C26
C31
C32
C33
C34
C35
C36
C41


Ull

0.0273(2)
0.0796(14)
0.0327(9)
0.0278(9)
0.044(4)
0.047(4)
0.033(4)
0.028(3)
0.040(3)
0.062(5)
0.116(9)
0.059(5)
0.091(7)
0.047(5)
0.068(6)
0.098(8)
0.079(6)
0.024(3)
0.031(4)
0.032(5)
0.032(5)
0.067(5)
0.047(4)
0.038(4)
0.037(4)
0.062(6)
0.078(6)
0.045(5)
0.029(4)
0.035(4)


U22

0.0357(2)
0.0477(14)
0.0822(9)
0.0330(9)
0.036(4)
0.032(4)
0.040(4)
0.040(3)
0.043(3)
0.056(5)
0.063(9)
0.091(5)
0.078(7)
0.049(5)
0.077(6)
0.061(8)
0.043(6)
0.034(3)
0.062(4)
0.076(5)
0.060(5)
0.043(5)
0.042(4)
0.029(4)
0.059(4)
0.061(6)
0.044(6)
0.065(5)
0.050(4)
0.038(4)


U33

0.0313(3)
0.0522(11)
0.0514(15)
0.0366(10)
0.035(4)
0.036(4)
0.043(4)
0.044(4)
0.035(5)
0.027(6)
0.045(7)
0.047(7)
0.047(7)
0.046(5)
0.061(7)
0.084(7)
0.060(5)
0.051(4)
0.054(5)
0.090(7)
0.120(6)
0.080(7)
0.053(4)
0.036(4)
0.048(5)
0.062(5)
0.058(5)
0.046(6)
0.052(5)
0.042(4)


U12

0.0047(2)
0.0113(10)
-0.0124(8)
0.0029(7)
-0.001(3)
0.000(3)
-0.007(3)
-0.000(3)
0.005(3)
-0.002(3)
0.010(5)
-0.011(4)
-0.012(5)
0.005(4)
-0.004(4)
-0.027(6)
0.019(4)
0.001(3)
0.011(3)
0.012(5)
-0.009(5)
-0.011(5)
-0.004(4)
-0.002(3)
0.006(4)
0.015(4)
-0.016(5)
-0.014(4)
-0.007(3)
0.003(4)


U13

0.0052(3)
0.0348(9)
-0.0021(11)
0.0088(9)
0.011(3)
0.003(3)
0.010(4)
0.005(3)
0.015(4)
0.004(3)
-0.002(5)
-0.010(5)
0.007(5)
-0.007(4)
-0.011(5)
0.036(6)
0.001(4)
-0.001(3)
0.013(4)
0.014(6)
-0.010(6)
-0.022(4)
-0.003(4)
0.012(3)
0.014(4)
0.025(5)
0.032(4)
0.017(5)
0.011(4)
0.012(4)


U23

0.0005(2)
-0.0042(11)
0.0080(11)
0.0014(10)
0.001(4)
0.011(4)
0.006(4)
0.008(4)
0.006(3)
0.007(4)
-0.016(6)
0.007(5)
0.010(5)
-0.007(5)
-0.013(5)
-0.010(8)
0.001(5)
0.005(4)
0.013(5)
0.027(7)
0.020(8)
-0.002(6)
0.008(5)
-0.002(4)
0.016(4)
0.028(5)
0.001(5)
-0.004(6)
-0.005(5)
-0.003(5)







Table 5-7 continued


Atom


C42
C43
C44
C45
C46


Ull U22 U33 U12 U13 U23


0.066(6)
0.081(7)
0.068(6)
0.088(7)
0.063(5)


0.056(6)
0.043(7)
0.043(6)
0.068(7)
0.050(5)


0.061(6)
0.094(5)
0.091(5)
0.051(7)
0.046(5)


0.013(5)
0.020(6)
-0.005(5)
-0.000(5)
0.001(4)


0.006(5)
0.010(5)
0.030(5)
0.023(5)
0.013(4)


-0.005(6)
-0.016(7)
-0.027(7)
-0.021(5)
-0.001(5)


AThe Uij are the mean-square amplitudes of vibration in A2 from the general temperature factor expn

exp[-22(h2a*2Ull 1 + k2b*2U22 +12c*2U33 + 2hka*b*U12 + 2hla*c*U13 + 2klb*c*U23)]



Table 5-8. Fractional coordinates and isotropic
thermal parameters (A2) for the H atoms of compound 4-3.


Atom

H2
H4
H5
H7a
H7b
H7c
H8a
H8b
H8c
H9a
H9b
H9c
Hlla
Hllb
Hllc
H12a


x

0.10335
0.45931
0.37934
0.10694
0.24801
0.1162
-0.01109
-0.05246
-0.04023
0.18659
0.31711
0.21714
0.4622
0.32165
0.39839
0.4198


y

0.17138
0.05454
-0.04276
-0.1087
-0.08902
-0.07679
0.12871
0.02347
0.05545
0.08362
0.07457
0.15972
0.16701
0.15749
0.25542
0.35391


z

-0.00417
0.17259
-0.03084
-0.18793
-0.2325
-0.33163
-0.19676
-0.1686
-031168
-0.37978
-0.27822
-0.26858
0.33648
0.38628
0.39828
0.19789


U

0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08








Table 5-8 continued


Atom

H12b
H12c
H13a
H13b
H13c
H22
H23
H24
H25
H26
H32
H33
H34
H35
H36
H42
H43
H44
H45
H46


0.35865
0.48566
0.19458
0.11576
0.13644
0.55288
0.77108
0.81402
0.63614
0.41533
0.39131
0.2941
0.06383
-0.07772
0.01834
0.42976
0.42371
0.28984
0.17063
0.16791


Table 5-9. Bond lengths
atoms of compound 4-3


1 2


3


(A) and angles (0) of the H


1-2


0.960(7)



0.960(6)


1-2-3


124.9(7)
122.8(5)
124.8(6)
125.7(7)
119.8(5)


0.31638
0.26639
0.33326
0.23673
0.30306
-0.17065
-0.11432
-0.02922
0.01423
-0.03923
-0.23
-0.3114
-0.31891
-0.23823
-0.15612
-0.31512
-0.45924
-0.47326
-0.34423
-0.20063


0.05981
0.13606
0.28153
0.2569
0.13917
0.16416
0.23778
0.42846
0.5417
0.47045
0.48228
0.64057
0.63357
0.4721
0.30758
0.2754
0.15988
-0.04226
-0.13096
-0.0155


0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08






Table 5-9 continued

1 2


H4
H5
H5
H5
H7a
H7a
H7a
H7b
H7b
H7c
H8a
H8a
H8a
H8b
H8b
H8c
H9a
H9a
H9a
H9b
H9b
H9c
Hlla
Hlla
Hlla
Hllb
Hllb
H1llc
H12a
H12a
H12a
H12b
H12b


C4
C5
C5
C5
C7
C7
C7
C7
C7
C7
C8
C8
C8
C8
C8
C8
C9
C9
C9
C9
C9
C9
Cll
Cll
Cll
Cll
Cll
Cll
C12
C12
C12
C12
C12


C3
Rh
C1
C4
H7b
H7c
C6
H7c
C6
C6
H8b
H8c
C6
H8c
C6
C6
H9b
H9c
C6
H9c
C6
C6
Hllb
Hllc
C10
Hllc
C10
C10
H12b
H12c
C10
H12c
C10


1-2



0.960(9)



0.960(11)



0.960(11)


0.960(9)
0.960(10)



0.960(9)


0.960(7)
0.960(8)



0.960(10)


0.960(11)
0.960(10)



0.960(10)


0.960(9)
0.960(10)



0.960(11)


125.8(7)
120.7(6)
125.7(6)
125.7(6)
109.5(9)
109.5(10)
109.5(9)
109.5(10)
109.5(9)
109.4(8)
109.5(8)
109.5(9)
109.4(7)
109.5(8)
109.5(7)
109.5(7)
109.5(9)
109.5(9)
109.5(8)
109.5(9)
109.5(8)
109.5(8)
109.5(9)
109.5(9)
109.5(8)
109.5(9)
109.5(8)
109.5(8)
109.5(10)
109.5(11)
109.5(10)
109.5(11)
109.4(9)







Table 5-9 continued

1 2


H12c
H13a
H13a
H13a
H13b
H13b
H13c
H22
H22
H23
H23
H24
H24
H25
H25
H26
H26
H32
H32
H33
H33
H34
H34
H35
H35
H36
H36
H42
H42
H43
H43
H44


C12
C13
C13
C13
C13
C13
C13
C22
C22
C23
C23
C24
C24
C25
C25
C26
C26
C32
C32
C33
C33
C34
C34
C35
C35
C36
C36
C42
C42
C43
C43
C44


C10
H13b
H13c
C10
H13c
C10
C10
C23
C21
C24
C22
C25
C23
C26
C24
C21
C25
C33
C31
C34
C32
C35
C33
C36
C34
C31
C35
C43
C41
C44
C42
C45


1-2


0.960(11)
0.960(8)



0.960(9)


0.960(8)
0.960(8)

0.960(9)

0.960(8)


0.960(9)


0.960(8)

0.960(7)


0.960(8)


0.960(9)

0.960(8)

0.960(7)


0.960(9)


0.960(9)

0.960(10)


109.5(9)
109.5(9)
109.5(8)
109.5(7)
109.5(8)
109.5(8)
109.5(8)
119.9(8)
120.0(6)
119.4(8)
119.5(9)
120.1(10)
120.1(10)
119.7(9)
119.7(8)
120.3(7)
120.3(7)
119.9(7)
119.9(7)
119.4(9)
119.4(8)
119.5(9)
119.6(8)
120.7(7)
120.7(8)
119.8(7)
119.8(7)
119.6(9)
119.7(9)
119.9(9)
120.0(9)
120.1(9)












CHAPTER 6
SYNTHESIS OF CP**Rh(COD)(COD= CYCLOOCTA-1,5-DIENE)


Introduction

Nonconjugated diene complexes of rhodium can be
synthesized by two routes involving either the reduction of
[RhCl3.3H20] in aqueous solution by the diene or by

displacement of two alkene ligands from the compounds
[{RhCl(alkene)2)2] (alkene= cis-cyclooctene) by the diene.54 It

is known that the former is more convenient, but does not
work well for several dienes; the latter is more versatile.
The reduction of [RhCl3-3H20] in refluxing EtOH in the
presence of 1,5-cyclooctadiene(COD)(6-1) over a period of

hours affords the beautifully crystalline, orange, air stable
derivative [Rh(COD)Cl]2 (6-2) as shown in Figure 6-1.55






RhCl 3 3Hp + Rh

2

Fig. 6-1. The synthesis of [Rh(COD)Cl]2 (6-2)







The same compound can be obtained by the reaction of

1,5-cyclooctadiene with [{RhCl(C2H4)2}2] as can the

perdeuterated analog.56 If the reaction of 1,5-COD with

ethanol and [RhC13-3H20] is studied more carefully, all excess

1,5-COD is isomerized to 1,3-COD and appreciable amounts of

1,4-COD can be detected.57 Isomerization must be rapid, since

the final product(6-2) does not catalyze the isomerization.

Thus, while 1,3-COD is the most thermodynamically favored

isomer of COD in the free state, the 1,5-COD is the favored

isomer when coordinated to Rh(I). The 1H NMR studies of the

relative stabilities and liabilities of a variety of diene

complexes of rhodium indicate the COD complexes are the most

stable, but also the most labile.58 The bridging chloride

ligand in 6-2 can be replaced with a variety of halide and

anions(X) by stirring the chloro-complex with a large excess

of NaX.55,59

The complex [Rh(T5-C5H5)(COD)] (6-3) is one of the

relatively few rhodium complexes to be synthesized in which

only hydrocarbon ligands are bound to the metal. This

compound is most conveniently prepared by the reaction of

cyclopentadienylsodium or cyclopentadienylthallium with

{RhC (COD) 2.54












Cl
LI::k--< *cl*


+ CpNa -


Rh


Fig. 6-2. The synthesis of [Rh(T5-C5H5)(COD)] (6-3)




The pentamethylcyclopentadienyl derivative(6-4) has been
prepared60a by the reaction of [ (T5-C5Me5)RhCl212(1-1) with
6-1 as shown in Figure 6-3. To assist in evaluating the
potential of the Cp** in the study of rhodium chemistry, the
derivatives [Cp**Rh(COD)](6-5 and 6-6) were synthesized and
their properties were compared with those of 6-3 and 6-4.


3-1
Fig.6-2. The synthesis of Cp*Rh(COD)(6-4)


6-4







Synthesis of Cp**Rh(COD)


The reaction of 6-2 with a little excess of Cp**Li under

reflux in THF resulted in a mixture of the tert-

butylcyclopentadienylrhodium(I) complex (t-C4H9C5H4)CpRh (COD)

(6-6) and di-tert-cyclobutylpentadienylrhodium complex

Cp**Rh(COD) (6-5) which were identified by 1H NMR and 13C NMR.

The separation of this mixture was performed through column

chromatography on A1203 using pentane as a eluent and provide

a 72 % yield of 6-5 and a 5 % yield of 6-6, which were

characterized by NMR spectroscopy. The appearance of 6-5 is

believed to have resulted from the use of a sample of 1,3-di-

tert-butylcyclopentadiene containing a minor amount of tert-

butylcyclopentadiene. A satisfactory carbon-hydrogen analysis

and high resolution mass spectrum were also obtained for the

compound 6-5.



+ n BuLi -

2-7 Li+





Rh Rh
[6-2] + ux+
2 + reflux


6-5 6-6

72% 5%


Fig.6-3. The synthesis of Cp**Rh(COD)(6-5)








NMR Spectroscopy


1H NMR and 13C NMR spectra of 6-5 and 6-6 reveal

similarities fashion in the resonances of the COD ligand as

shown in Table 6-1 and Table 6-2. The 1H NMR of COD ligand of

6-5 exhibits three sets of resonance; olefinic protons and

two sets(Ha and Hb) of methylene protons (Table 6-1). The

olefinic protons absorb at 83.87 with a broad singlet and two

kinds of resonance take place for the methylene protons(Ha

and Hb). The stereochemical assignment of those methylene

peaks(Fig.6-4) was based on the 1H NMR spectrum of 6-2.60b

which shows two different resonances for methylene protons.

The proton Ha, which is comparably closer to rhodium appears

as a doublet at 8 1.89 due to a 8.31 Hz coupling to Rh, and

Hb absorbs slightly downfield at 82.19 with a doublet(JRh-H=

9.71 Hz) as shown in Table 6-1 and Figure 6-5. The 13C NMR

spectrum of 6-5 indicates all four methylene carbons are in

equivalent resonances. Thus only two sets of carbons were

observed in the 13C NMR spectrum; a resonance at 8 62.58 for

olefinic carbons (d, JRh-c= 13.97 Hz) and a singlet at 8 32.51

for the methylene carbons as shown in Table 6-1 and Figure 6-

6. The resonances of the Cp** ring reveal a similar pattern

in both the 1H NMR and 13C NMR spectra as for other Cp**

complexes (3-2, 5-3 and 7-2).

The compound 6-6 exhibits 1H NMR and the 13C NMR spectra

similar to those of 6-5 except for the Cp** portion of the

spectrum; the 1H NMR spectrum of the Cp** ring exhibits two







sets of resonance for ring protons at 8 4.83 (J=1.95 Hz) and

at 8 5.05( J=1.08 Hz) respectively as listed in Table 6-2.







1NI$ %%Ha
S "Hb

Fig.6-4. The structure of Cp**Rh(COD)(6-5) for
NMR.assignments.


Table 6-1. NMR spectral data(ppm) for the compound 6-5
in CDC13


tert-butyl ring COD ligand


H7: 1.25,s, H2: 4.68, s, 1H Ha:1.89, d, 4H
JRh-H=8.31 Hz
1H NMR H4,5: 4.69, S, 2H
Hb:2.19, m, 4H
JRh-H=9.71 Hz

Hc:3.87, d, 4H
JRh-H=0.23 Hz


13C NMR C7: 32.24,s C2: 80.98, d ClO,11,14,15:
JRh-c=4.14 Hz 32.51, s

C4,5: 81.52, d C8,9,12,13:
JRh-c=3.51 Hz 62.58, d
JRh-c=13.97 Hz
C1,3: 119.25, d
JRh-c=4.20 Hz




























Fig. 6-5. 1H NMR spectrum of 6-5 in CDC13


Fig.6-6 13C NMR spectrum of 6-5 in CDC13

















Fig.6-7. The structure of 6-6 for NMR assignments.




Table 6-2. NMR spectral data(ppm) for the compound 6-6
in CDC13



tert-butyl ring COD ligand


H7: 1.25,s H2,5: 4.83, t, 2H Ha: 1.89, d
JH-H=1.95 Hz JRh-H=8.37 Hz
1H NMR
H3,4: 5.05, t, 2H Hb: 2.17, m
JH-H=1.08 Hz JRh-H=6.36 Hz


HC: 3.91, m
JRh-H=0.23 Hz




13C NMR C7: 32.07,s C2,5: 62.44, d C10,11,14,15:
JRh-C=3.96 Hz 32.44, s

C3,4: 77.59, d C8'9,12' 13:
JRh-c=6.38 Hz 62.40, d
JRh-C=13.88 Hz












CHAPTER 7
CHEMISTRY OF Cp**Rh(PINACOLATE)



Introduction


Several recent papers have described the photoinduced

retrocyclization of heterometallacycles to give reactive

organometallic species: coordinately unsaturated 14-electron

Pt(0) intermediates from oxalates,61 iridium alkylidenes from

2-oxametallacyclobutanes,62 and rhodium oxo complexes from

carbonates.63 These proved to be a very good and valuable

reactivity pattern to generate a typical coordinatively

unsaturated, low-valent metal fragment with concomitant

transfer of two electrons to a metal center. For example

ultraviolet irradiation of oxalato bis(tertiary phosphine)

complexes of platinum(II) and palladium(II), Pt(C204)L2,

Pd(C204)L2 result in the reductive elimination of the oxalate

ligand as CO2 and the production of the reactive

intermediates PtL2 and PdL2.61 Transfer of two electrons

(either simultaneously or in rapid succession) yields the

zerovalent state, Pt(0) or Pd(0). The net photochemical

reaction is shown in equation 7-1.


hv
M(C204)L2 ML2 + C02 Eq.7-1







These 14-electron fragments bind ligands such as olefins,

perfluoroethylene, acetylene, and trialkylphosphines to yield

zerovalent metal complexes. Substrates such as alkyl, allyl,

and aryl halides, organosilanes, alcohols, allyl acetate, and

hydrogen undergo oxidative addition reactions to yield Pt(II)

or Pd(II) derivatives. Study of synthesis and reactions of

these 14-electron intermediates is a worthwhile way to learn

more about reductive elimination and oxidative addition

chemistry. Adamson et a164 showed that irradiation of the

rhodium(III) oxalate complexes Rh(C204)X(py)3 (X=C1, Br;

py=pyridine) caused two-electron reduction to the corresponding

rhodium(I) species RhX(py)2.

We became interested in synthesizing a Rh(III) complex of

Cp** which could generate a reactive 14 electron Rh(I)

intermediate through the reductive elimination shown in Figure

7-1. The compound (Cp**RhCl2)2 (3-2) was chosen as a starting

material. For the study of reductive elimination and oxidative-

addition we needed a ligand which could easily dissociate from

a rhodium complex through photolysis. The pinacolate ligand was

chosen since related photochemical studies of the chemistry of




Rh(m) hv +2Y

Y Y


Fig.7-1. Reductive elimination of Rh(III) complex







organometallic glycolate complexes have been done by several

groups.65-69 Chisholm et al.70 reported the synthesis of

W(OR)4(OCPh2CPh20) form W2(OR)2(pY)2 (R=OCH2CMe3, O-CHMe2).

Willis et al71 have reported the synthesis of a number of

quite stable complexes that do not contain any hydrogen atoms
3 to the metal center. Of particular interest was the

photolysis of glycolate complexes. Photolysis of thermally

stable [1,2-bis(diphenylphosphino)ethane]Pt(II) glycolate was

reported.72 It was recognized that photolysis of Pt(II)

glycolates gave a Pt(0) fragment together with aldehydes or

ketones corresponding to glycolate cleavage. It was also

believed the the generation of reduced, coordinatively

unsaturated metal species by this technique should not be

limited to the conveniently illustrated L2Pt(0) example. For

example, Bergman and Glueck are reported to have found that

photolysis of(C5Me5)Rh(pinacolate) yields two equivalents of

acetone and a 14-electron (C5Me5)Rh(I) intermediate.a Although

this intermediate might be expected to be reactive toward

oxidative addition, no additional information has been

published.

Based on all of this information, it was expected that

the irradation of the Cp**Rh(pinacolate) would undergo

similar photochemical degradation to produce acetone and a

reactive coordinatively unsaturated fragment.


a Bergman, R., personal communication of unpublished
preliminary results











hv
MRh() Rh(I) +2 acetone


P9 THF \
Fig.7-2. The photolysis of Cp**Rh(pinacolate)(7-1)



Synthesis of Co**Rh(pinacolate)(7-1)


The desired complex 7-1 was prepared by treatment of

excess potassium pinacolate (4 equivalents) with 3-2 in THF

solution at room temperature for 4 hr as shown in Figure 7-3.

Because of the light sensitivity of the product, the reaction

was protected from light. Cp**Rh(pinacolate)(7-1) was

isolated as violet crystals in 83 % yield after being
recrystallized from CH2Cl2/pentane.



"&CK 2
Rh + THF Rh

C1 C1 2 excess

3-2 7-1

Fig.7-3. The synthesis of Cp**Rh(pinacolate)(7-1)




When only 2 equivalents of potassium pinacolate were

used, side products were formed along with major products. 1H







NMR spectroscopy revealed that there were two side products

in a 50:50 ratio. The nature of the side products will be

discussed in Chapter 10.



NMR Study



The 1H NMR spectrum of 7-1 shows variation in the

relative positions of the tert-butyl and pinacolate methyl

protons in the solvents CDCl3 and C6D6 as shown in Table 7-1.

In CDCl3 the tert-butyl group resonance appears at 81.39 with

the CH3 group of the C(CH3)2 moiety appearing at 8 1.04

(Fig.7-5). In C6D6 the tert-butyl protons absorb at 8 1.18 and

the pinacolate CH3 protons absorb at 8 1.38 (Fig.7-6). This

resonance could be interpreted as a magnetic anisotropy

phenomenon with the C6D6 coordinated to rhodium metal parallel

to the Cp ring under the tert-butyl group of Cp ring and

forming a shielding region for the tert-butyl group.

However this phenomenon was not observed in the 13C NMR

spectrum. The 13C NMR spectra in CDC13 and C6D6 were

similar(Table 7-2). Three peaks were found for the Cp ring

carbons and each of these is split by rhodium as was the case

in other Cp** complexes(3-2 and 5-2). The carbons bearing

tert-butyl groups are deshielded by the tert-butyl group.

That is why the C1'3 resonances appear downfield in the 13C

NMR spectrum compared to the other ring carbons.










Rh
*^8


Fig.7-4. Numbering of 7-1


Table 7-1. 1H NMR spectral data(ppm) for the compound 7-1

Solvent tert-Butyl Ring H CH3 of pinacolate

CDC13 1.39,s,18H H2: 4.78,s,lH H8: 1.05,s,12H

H4,5: 5.10,s,2H


C6D6 1.18,s,18H H2: 4.51,s,lH H8: 1.39,s,12H

H4,5: 4.57,s,2H





Table 7-2. 13C NMR spectral data(ppm) for the compound 7-1.

solvent ring C tert-Butyl C CH3 of pinacolate

CDC13 C2: 72.75, d C6: 29.74, s C8: 27.00, s
JRh-C=8.40Hz C7: 30.60, s C9: 84,88, s
C4,5; 84.89, d
JRh-C=4.04Hz
C1'3; 111.56, d
JRh-c=10.07Hz


C2: 72.42, d C6: 30.31, s C8:28.07, s
C6D6 JRh-C=6.23Hz C7: 29.62, s C9:86.05, s
C4,5: 75.47, d
JRh-c=7.90Hz
C1,3; 109.89, d
JRh-C=9,91Hz





























Fig.7-5. 1H NMR spectrum of 7-1 in CDC13


Fig.7-6. 1H NMR spectrum of 7-1 in C6D6





































Fig.7-7. 13C NMR spectrum of 7-1 in CDC13


0 .. .. .. 0 .. 46 2I
120 1do BO 64 20 P9M


Fig.7-8. 13C NMR spectrum of


7-1 in C6D6







X-ray Crystalloaraphy



An x-ray diffraction study has been performed on the complex

7-1, Cp**Rh(pinacolate). Recrystallization from benzene and heptane

gave light sensitive, violet crystals suitable for single crystal

x-ray diffraction. Data were collected at room temperature on a

Siemens R3m/V diffractometer equipped with a graphite

monochromator utilizing MoKa radiation (X = 0.710673A). Thirty two

reflections with 20.00 209 22.00 were used to refine the cell

parameters. Reflections(2435) were collected using the co-scan

method. Four reflections (223, 223, 212, 212) were measured every

96 reflections to monitor instrument and crystal stability

(maximum correction on I was < 0.98 %). Absorption corrections

were applied based on measured crystal faces using SHELXTL plus

(Sheldrick)31; absorption coefficient, g = 8.6 cm-1 (min. and max.

transmission factors are 0.909 and 0.943, respectively).

The structure was solved by the heavy-atom method in

SHELXTL plus (Scheldrick)31 from which the location of the Rh

atom was obtained. The rest of the nonhydrogen atoms were

obtained from a subsequent difference Fourier map. The

structure was refined in SHELXTL plus using full-matrix

least squares. The structure was refined in the space groups

Pna21 (noncentrosymmetric) and Pnma (centrosymmetric).

Although the R-value was slightly lower in the

noncentrosymmetric space group refinement, the bond lengths

and angles never refined to their expected values. As an

example, the equivalent bonds of the cyclopentadienyl ligand







varied from 1.09 to 1.61 A. Refinement in the centrosymmetric

space group required treatment of both C(CH3)2 moieties of

the pinacolate ligand as disordered around a mirror plane

passing through atoms Cl, Rh, 01 and 02. The latter

refinement, in spite of the disorder, resulted in a

chemically more accurate structure. Thus it was chosen as the

correct space group (all structural parameters reported are

derived from the centrosymmetric space group Pnma). The non-H

atoms were treated anisotropically. All H atoms were refined

with isotropic thermal parameters except the methyl H atoms

of the disordered pinacolate ligand which were calculated in

ideal positions and their isotropic thermal parameters were
fixed. 176 parameters were refined and ( IFoI IFcl)2 was

minimized; w=l/(aIFo )2, s( Fo) = 0.5 kI -1/2{[s( I )]2 +

(0.021)2 }1/2 I(intensity)= ( I peak I background)(scan

rate), and s(I) = (I peak + I background)1/2 (scan rate), k

is the correction due to decay and Lp effects, 0.02 is a

factor used to down weight intense reflections and to account

for instrument instability. The linear absorption coefficient

was calculated from values from the International Tables for

X-ray Crystallography 32. Scattering factors for non-hydrogen

atoms were taken from Cromer and Mann33 with anomalous-

dispersion corrections from Cromer and Liberman34, while those

of hydrogen atoms were from Stewart, Davidson and Simpson







Crystallographic data and data collection parameters are

summarized in Table 7-3. Thermal ellipsoids drawing showing

the atom-numbering schemes for 7-1 is presented in Figure

7-9, 7-10 and 7-11. Selected bond lengths and angles relevant

to Rh-cyclopentadienyl and Rh- pinacolate interactions are

shown in Figure 7-12 and 7-13. Tables 7-4 and 7-5 list the

non-hydrogen atom fractional coordinates, their equivalent

isotropic thermal parameters, and the non-Ha atoms anistropic

thermal parameters, while selected bond lengths and angles

for 7-1 are provided in Table 7-6 and 7-7 respectively.



Table 7-3. Crystallographic data of 7-1


A. Crystal data (298 OK)
a, A
b, A
c, A
V, A3
dcalc, g cm-3(298 K)
Empirical formula
Formula wt, g
Crystal system
Space group
z
F(000), electrons


B. Data collection (298 OK)
Radiation, X (A)
Mode
Scan range


I
11.309(1)
17.121(2)
10.354(1)
2004.8(3)
1.313
C19H3302Rh
396.4
Orthorhombic
Pnma
4
832


Mo-Ka, 0.71073
co-scan
Symmetrically over 1.20 about
Kal,2 maximum







Table 7-3 continued

Background offset 1.0 and -1.0 in cofrom
KaI,2 maximum
Scan rate, deg. min.-1 3 6
20 range, deg. 3 50
Range of h k 1 0 < h < 13
-1 < k < 20
-1 < 1 < 12


Total reflections measured 2436
Unique reflections 1981
Absorption coeff. p (Mo-Ka), cm-1 8.6


C. Structure refinement
S, Goodness-of-fit 1.15
Reflections used, I > 2a(I) 1390
No. of variables 176
R, (OR* (%) 3.49, 3.85
R, COR* all data (%) 5.48, 4.18
Rint. (%) 1.35
Max. shift/esd 0.001


min. peak in diff. four. map (e A-3) -0.37
max. peak in diff. four. map (e A-3) 0.53


* Relevant expressions are as follows, where in the footnote Fo
and Fc represent, respectively, the observed and calculated
structure-factor amplitudes.
Function minimized was 0(I|Fol IFc I )2, where (0= (s(F))-2
R = J( IIFol JFcl) / XIFol
(OR = [Y0(IFol IFcl)2 / IFol2]1/2
S = [YO(IFol IFc)2 / (m-n)]1/2























c6 W




C1




C7a



C6a C


C10


C3a C13a


C9o



C9


C12


C10l


C13


Fig.7-9. Thermal ellipsoids drawing for compound -I






























Fig.7-10. Thermal ellipsoids drawing for conformation
isomer 2-la of compound 7-1


Fig.7-11. Thermal ellipsoids drawing for conformation
7-lb of compound 7-1







Two conformations were observed as shown in Figure 7-9.

In each isomer(7-la and 7-1b), C(CH3)2 moieties of the

pinacolate ligands disordered around the mirror plane passing

through atoms C(l), Rh, O(1) and 0(2). The oxygen atoms are

nearly symmetrically bound to the rhodium center with a Rh-

0(1) distance of 1.932(5) A, a Rh-O(2) distance of

1.929(5)A, and a 0(l)-Rh-0(2) angle of 81.80(Figure 7-13).

Bond lengths and angles of the two disordered pinacolate

ligands are in agreement with their expected values.

This complex exhibits a slight puckering within the

five-membered carbon ring. The puckering is proved by the

displacements from the plane defined by the five ring carbons

The Cp ring has a mirror plane that bisects the molecule by

passing through C(l) and a middle point of C(3a) and C(3) as

shown in Figure 7-12. Due to the tert-butyl group, the Cp

ring of 7-1 was expected to exhibit pronounced torsional

deformation. The tert-butyl bearing carbons C(2) and C(2a)

tip away from the rhodium. The distance between C(2) and

adjacent carbon C(l), C(3), C(2)-C(l) and C(3)-C(1), are

significantly longer than C(3)-C(3a), which are even longer

than typical value of 1.40 A for cyclopentadienylrhodium

complexes.74

The structure shows a negligible deviation from

planarity, the mean distance from the ring carbons to the

least-squares plane being 0.04 A- tert-Butyl-bearing carbons

C(2) and C(2a) tip away from the rhodium and the other three

carbons tip toward it. This deviation is smaller than the







0 0
deviation of 0.12 A in(Cp**RhC12)2, the deviation of 0.29 A
0
in Cp**Rh(PPh3)Cl2 and the deviation of 0.11 A in

Cp*Rh(CO)2.73 Table 7-7 shows the amount of deviation of each

substituent from their respective planes in terms of
distance(d) and in terms of angle (y) as well as angle (0) from

rhodium. As a result the rhodium atom is somewhat more

shielded in 7-1 than in the other rhodium complexes.





C7a C7
OC15 /34(8)
C6a 10 01.426(6) / C6
C4a C 28(8)
C2a 106.0(4) .498(7) .538(9)

][.454(6) 5
5 C3a 109.0
1.382(7)





Fig.7-12. Selected bond lengths(A) and angles(o) for
the cyclopentadienyl ligand of compound 7-1.







Rh


0
Fig.7-13. Selected bond lengths(A) and angles(o) for
the pinacolate ligand of compound 7-1.


Table 7-4. Fractional coordinates and equivalent isotropica
thermal parameters (A2) for the non-H atoms of compound 7-1.


x

0.37620(6)
0.4806(4)
0.2575(4)
0.2762(6)
0.3482(3)
0.4698(4)
0.3075(4)
0.3976(7)
0.1890(6)
0.2960(8)
0.4177(8)
0.5003(7)
0.375(3)
0.3073(8)
0.2146(7)
0.350(3)


0.75
0.75
0.75
0.75
0.6820(3)
0.7096(3)
0.5988(3)
0.5435(4)
0.5898(5)
0.5771(5)
0.7203(7)
0.7700(9)
0.640(2)
0.7747(7)
0.750(2)
0.863(2)


z

0.22804(4)
0.0803(5)
0.0942(5)
0.4040(6)
0.3978(3)
0.3953 (4)
0.4047(5)
0.3414(8)
0.3355(7)
0.5478(6)
-0.0389(8)
-0.1473(7)
-0.047(3)
-0.0327(8)
-0.1292(7)
-0.047(2)


U

0.03894(15)
0.095(3)
0.097(3)
0.042(2)
0.042(2)
0.048(2)
0.053(2)
0.077(3)
0.071(2)
0.082(3)
0.055(5)
0.062(6)
0.14(2)
0.060(6)
0.136(7)
0.14(2)


AFor anisotropic atoms, the U value is Ueq, calculated as Ueq
= 1/3 Xilj Uij ai* aj* Aij where Aij is the dot product of
the ith and jth direct space unit cell vectors.


Atom


Rh
01
02
Cl
C2
C3
C4
C5
C6
C7
C8
C9
C10
Cl1
C12
C13







Table 7-5. Anisotropic thermal parametersa for the
non-H atoms of compound 7-1.


Atom



Rh

01

02

Cl

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C13


Ull



0.0269(2)

0.030(3)

0.029(2)

0.031(4)

0.032(3)

0.036(2)

0.050(3)

0.074(5)

0.068(4)

0.105(6)

0.050(5)

0.055(5)

0.20(2)

0.049(6)

0.063 (6)

0.33(4)


U22



0.0561(2)

0.219(3)

0.223(2)

0.063(4)

0.060(3)

0.073(2)

0.054(3)

0.061(5)

0.056(4)

0.078(6)

0.078(5)

0.090(5)

0.12(2)

0.093(6)

0.302(6)

0.06(4)


U33



0.0338(3)

0.036(8)

0.038(8)

0.031(5)

0.035(3)

0.036(4)

0.054(3)

0.097(4)

0.089(4)

0.063(5)

0.038(12)

0.04(2)

0.10(3)

0.04(2)

0.04(2)

0.04(2)


U12



0.0000

0.0000

0.0000

0.0000

0.004(2)

0.009(2)

0.007(2)

0.013(4)

-0.009(3)

0.004(4)

0.006(4)

0.001(3)

-0.03(2)

0.009(4)

-0.081(5)

0.06(2)


U13



-0.00169

-0.00105

-0.00587

0.0046

-0.000(2)

-0.003(2)

-0.000(2)

0.007(4)

-0.010(4)

0.004(4)

-0.004(4)

0.011(5)

-0.08(2)

-0.005(5)

-0.01(3)

0.029(10)


AThe Uij are the mean-square amplitudes of vibration in A2 from the
general temperature factor expression

exp[-2l72(h2a*2Ull + k2b*2U22 + 12c*2U33 + 2hka*b*Ul2 + 2hla*c*Ul3
+ 2klb*c*U23)]


U23



0.0000

0.0000

0.0000

0.0000

0.007(2)

0.002(2)

0.010(3)

0.002(5)

0.010(5)

0.023(4)

-0.003(5)

-0.003(4)

0.00(2)

-0.006(4)

-0.003(4)

0.026(11







Table 7-6. Bond lengths (A) and angles (0) for the non-H of
compound 7-1.


1 2


01
02
C1
C2
C3
C8
Cli
C2
C3
C3
C4
C3a
C5
C5
C5
C6
C6
C7
C9
C9
C9
C10
C10
CIl
C12
C12
C12
C13
C13
02


3


Rh
Rh
Rh
Rh
Rh
01
02
C1
C2
C2
C2
C3
C4
C4
C4
C4
C4
C4
C8
C8
C8
C8
C8
C8
C11
C11
Cll
C11
CII
C11


02






Rh
Rh
C2a
C4
C1
C1
C2
C6
C7
C2
C7
C2
C2
C10
C11
01
C11
01
01
C13
02
C8
02
C8
C8


1-2


1.932(5)
1.929(5)
2.144(6)
2.132(4)
2.144(4)
1.513(10)
1.491(10)
1.423(6)
1.454(6)


1.498(7)
1.382(7)
1.538(9)



1.528(8)


1.534(8)
1.689(14)



1.46(4)


1.559(15)
1.51(2)



1.60(3)


1-2-3


81.8(2)






111.0(4)
111.7(4)
109.8(5)
126.9(4)
106.0(4)
126.8(4)
109.0(4)
108.6(5)
108.6(5)
111.2(4)
110.7(5)
110.1(4)
107.6(5)
128.3(14)
99.8(8)
96.5(7)
107.7(15)
121.0(13)
98.2(7)
115. (2)
103.9(9)
111.0(14)
117.7(10)
108.9(14)
99.8(7)