Title: Metal complex facilitated transport and activation of molecular oxygen
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Title: Metal complex facilitated transport and activation of molecular oxygen
Physical Description: xiii, 315 leaves : ill. ; 28 cm.
Language: English
Creator: Balkus, Kenneth John, 1960-
Publication Date: 1986
Copyright Date: 1986
 Subjects
Subject: Oxygen   ( lcsh )
Transition metal compounds   ( lcsh )
Chemistry thesis Ph.D
Dissertations, Academic -- Chemistry -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis (Ph.D.)--University of Florida, 1986.
Bibliography: Bibliography: leaves 277-289.
General Note: Typescript.
General Note: Vita.
Statement of Responsibility: by Kenneth John Balkus, Jr.
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Bibliographic ID: UF00099325
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000940980
notis - AEQ2514
oclc - 016656125

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METAL COMPLEX FACILITATED TRANSPORT AND
ACTIVATION OF MOLECULAR OXYGEN







By







KENNETH JOHN BALKUS, JR.


A DISSERTATION 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























To Ken and Brenda, my parents














ACKNOWLEDGEMENTS

First and foremost, I would like to thank my family, my

parents Ken and Brenda, brothers David, Michael and Chris, and

sister, Lisa for their encouragement and support over the years.

During my stay at Florida, I crossed paths with so many

people, who in one way or another, have influenced my life.

Whether for the better or worse, I feel the richer for it. I

certainly owe the most to Dr. Russell Drago, not only for his

wisdom and support but for teaching me what it takes to be

successful in the world of academia. I would also like to thank

his charming wife, Ruth, who on many occasions made Florida seem

like a home away from home.

I would also like to thank some of my predecessors, including

Dr. Dorth Hamilton, Dr. Dave "Go Michigan" Pribich, and Dr. Carl

Bilgrien, whose inspiration and friendship will last a long time.

Additionally, I would like to thank the dynamic personalities of

the Drago group for making my stay at Florida quite interesting,

especially the lunch club, including Andy Griffis, Jerry Grunewald,

Bobby Taylor, and Rich "Repo" Riley. I would also like to

acknowledge Dr. Iwona Bresinska, Jeff Clark and Andy Kortz for

their helpful discussions. Maribel Lisk deserves a special nod for

her continuous help and also for sharing her private drawers. I

would also like to thank Dr. Nicholas Kildahl for originally

instilling in me a love for chemistry.









Outside the realm of chemistry, I need to thank Chuck landoli,

and Thelva Jimenez for remaining close friends throughout this

ordeal. Finally, I would like to extend a special thank you to Ann

Balke who has become a very positive force in my life. Without her

love and patience, this dissertation might not have been possible.












TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ............................................. iii

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

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

ABSTRACT ..................................................... xii

CHAPTERS

I. GENERAL INTRODUCTION ................................ 1

II. THE PREPARATION OF METAL COMPLEXES THAT REVERSIBLY BIND
DIOXYGEN.............................................. 3

Introduction .................................... 3
Experimental .................................... 15
Results and Discussion .......................... 18

III. THE PREPARATION AND CHARACTERIZATION OF Cu(I) COMPLEXES
THAT REVERSIBLY BIND CARBON MONOXIDE ................ 51

Introduction .................................... 51
Experimental .................................... 55
Results and Discussion .......................... 57

IV. METAL COMPLEX FACILITATED TRANSPORT OF GASES IN POLYMER
MEMBRANES ........................................... 78

Introduction .................................... 78
Experimental .................................... 87
Permeation Apparatus ......................... 87
Permeation Procedure ......................... 92
Membrane Preparation ......................... 98
Membrane Characerization ..................... 102
Membrane Evaluation .......................... 102
Results and Discussion .......................... 110
Blank Polymers ............................... 110
PS/[P]-CoSDPT Membranes ...................... 117
PS/[PJ-CoBr2SDPT, -3FSDPT Membranes .......... 125
Cycling Experiments .......................... 130
PS/[SG]-SDPT Membranes ....................... 139
PS/Co(NaCN)-Y, Co(bipy)(terpy)-Y Membranes ... 140
Mechanism .................................... 145









V. THE PREPARATION, CHARACTERIZATION, AND CATALYTIC
PROPERTIES OF HETEROPOLYANIONS ...................... 155

Introduction .................................... 155
Experimental .................................... 165
Oxidation Apparatus .......................... 167
Oxidation Procedure .......................... 167
Catalyst Preparation ......................... 171
Results and Discussion .......................... 174
Reactivity in Nonaqueous Solvents ............ 174
Oxidations with Molecular Oxygen ............. 245
Oxidations with Alkylperoxides ............... 263
Mechanism ........... ......................... 265
1-hexene Oxidation .......................... 267


VI. CONCLUSION .......................................... 275

REFERENCES ................................................... 277

APPENDIX...................................................... 290

BIOGRAPHICAL SKETCH .......................................... 315









LIST OF TABLES


Table Title Page

2-1 Composition of A and Y Zeolites 27

2-2 Conditions for the Preparation of Co(CN)xn-
Containing Zeolite 30

2-3 Infrared Co(CN)x Zeolitea 31

2-4 Electronic Spectra for Cobalt(II) Cyano Complexes _35

4-1 Permeation Data for Two PS/[SG] Films 103

4-2 Partial Pressures of 02 and N2 for Two PS/[SG] Films 104

4-3 02 Enrichment Results for a PS/[SG]-CoSDPT Film 109

4-4 Blank Films 116

4-5 02 Enrichment for Various Co(II) Containing Films 131

4-6 02 Enrichment for PS/[SG]-CoSDPT Films 139

4-7 02 Enrichment for Cobalt Zeolite Films 140

5-1 HPA Colors in Toluene 175

5-2 (XMW1109)n- Catalyzed Oxidation of Olefins
After 24 Hours 186

5-3 HPA Infrared Results 198

5-4 W183 6 data for [(C8Hi7)3CH3N]6-2x[GeRh2L2Wi+xO38+x] 209

5-5 Results Cycletime Experiment 210

5-6 FABMS Results 224

5-7 Bands in Rh24+ Electronic Spectra 229

5-8 HPA Cylic Voltametry Results 244

5-10 RhHPA Oxidation of Cyclohexene 254

5-11 Effects of Additives 255









LIST OF FIGURES


Figure Figure Caption Page

2-1 Oxygen adduct of 2-methylimidazole meso-tetra
(a, a, a, a o-pivalamidophenyl) porphyrin iron(II). 10

2-2 X-band ESR of [P]-CoSDPTO2 at 80 OK. 20

2-3 X-band ESR of [P]-Co3FSDPTO2 at 96 OK. 22

2-4 X-band ESR of [SG]-CoSDPTO2 (0.1 mm/gm SG, methylated)
at 80 OK. 24

2-5 X-band ESR of [SG]-Co3,5Br2SDPT (0.1 mm/gm SG,
methylated) at 80 OK. 26

2-6 FT-IR (nujol mull) for
A. Co(NaCN)-Y-1
B. Co(NaCN)-Y-2
C. Co(NaCN)-Y-3
D. Co(NaCN)-Y-5. 34

2-7 Electronic Spectrum for Co-Y Zeolite. 38

2-8 Electronic Spectrum for Co(NaCN)-Y-1. 40

2-9 Electronic Spectrum for Co-(NaCN)-Y-2. 42

2-10 Electronic Spectrum for Co(NaCN)-Y-3. 44

2-11 X-band ESR of Co(NaCN)-Y-3 + 02 after 50
oxygenation/deoxygenation cycles at 83 OK. 46

2-12 X-band ESR of Co(NaCN)-Y-3 after 50
oxygenation/deoxygenation cycles at 83 K. 48

3-1 X-band ESR of [P]-DCEACuC12, at 93 OK. 60

3-2 X-band ESR of [PJ-DCEACuC12 (linear), at 90 OK. 62

3-3 FT-IR of [P]-DCEACuC1. Experiments with CO binding. 65

3-4 FT-IR of [P]-DCEACuCl after exposure to 25 psig CO. 67

3-5 FT-IR of [P]-N(CH3)2CuCl. Experiments with CO binding. 71

3-6 X-band ESR of [PJ-N(CH3)2CuC12 after exposure to air. 73

3-7 FT-IR of [PJ-DCEACuCl.CH3CN. Experiments with
CO binding. 75


viii









LIST OF FIGURES (continued)

4-1 Vertical crossectional view of the gas separation
apparatus. 94

4-2 Vertical crossectional view of the revised gas
separation apparatus. 96

4-3 Schematic diagram of the gas permeation experimental
set up. 101

4-4 Glass plate for membrane preparation. 101

4-5 A plot of ln(PH PL) vs. time for two
polystyrene membranes containing [SG]. 108

4-6 A plot of PO vs. time for a polystyrene
membrane containing [SGJ-CoSMDPT. 112

4-7 Polystyrene supported CoSDPT. 119

4-8 Plot of partial pressure 02 vs. time for a
polystyrene/ [P]-CoSMDPT film. 121

4-9 Plot of the difference in partial pressure of
02 between the calculated curve and experimental
curve in figure 4-7 vs. time. 124

4-10 Plot of partial pressure 02 vs. time for a
polystyrene/ [PI-CoBr2SDPT film. 127

4-11 Plot of the difference in partial pressure of 02
between the calculated curve and experimental
curve in figure 4-10 vs. time. 129

4-12 Plot of partial pressure 02 vs. time for a
PS/[P]-CoSDPT film. Cycling experiment. 133

4-13 X-band ESR of PS/[P]-CoBr2SDPT at 82 OK. 136

4-14 X-band ESR of PS/[SG]-CoSDPT at 88 OK. 138

4-15 Scanning Electron Micrograph, surface view of
PS/[SG]-CoSDPT high loading and low loading. 142

4-16 Scanning Electon Micrograph, crossectional view
of PS/[SG]-CoSDPT high loading and low loading. 144

4-17 X-band ESR of PS/Co(NaCN)-Y-3 at 105 OK. 147

4-18 Contributions to 02 permeation in supported metal
complex containing polystyrene membranes. 149

4-19 Plot of partial pressure 02 vs. time for a
PS/[P]-CoBr2SDPT film. 152








LIST OF FIGURES (continued)

5-1 The structure of the Keggin Ion, [PW12040]3. 157

5-2 The structure of [(T-C5Me5)RhSiW9Nb3040]5- 161

5-3 Pressure set up for the oxidation of organic
substrates. 169

5-4 X-band ESR of [GeMn(H20)W11039]6 in toluene
at 97 OK. 177

5-5 X-band ESR of [GeMnW11039 6- + tBHP in toluene
at 115 K. 181

5-6 X-band ESR of [GeMnW11039]- + (xs)tBHP in toluene
at 87 OK. 183

5-7 X-band ESR of [GeCo(H20)W11039]6- + (xs)tBHP in
toluene at 78 K. 185

5-8 FT-IR of [(C8H17)3CH3N]8[GeW11039]. 193

5-9 FT-IR of red-brown [butyl4N]5[GeRh(H20)W11O39]. 195

5-10 FT-IR of green [butyl4N]6_2x[GeRh2(H20)2W0I+x38+x]- 197

5-11 W183 NMR of [(n-butyl)4N]6_2x
[GeRh2(CH3CN) W10+x038+x] in 1:1 CD3CN/CH3CN. 202

5-12 W183 NMR of [(C8gH1)3CH3N]6_2xEGeRh2LnW1i+x038+x
in 1:1 CD3CN/CH3CN. 204

5-13 W183 NMR of [(C8H1) 3CH3 N]6-2xGeRh2L n10+x038+x3 206
in 1:1 CD3Cl3/CH3C 206*

5-14 W183 NMR of [(CsH17) CH N]6-2x[GeRh2L Wi0+x038+x
in 1:1 toluene-D8/toluene. 208

5-15 Positive ion FABMS of RhHPA sample A. 213

5-16 Expansion of positive ion FABMS of RhHPA sample A. 215

5-17 Positive ion FABMS of RhHPA sample B. 217

5-18 Expansion of positive ion FABMS of RhHPA sample B. 219

5-19 Positive ion FABMS of RhHPA sample C. 221

5-20 Expansion of positive ion FABMS of RhHPA sample C. 223









LIST OF FIGURES (continued)


5-21 The electronic spectrum of
[CH 7)3CH N]6-2x[GeRh2(H20)nW0+xO38+x]
in acetonitrile. 228

5-22 FT-IR of RhHPA + CO in CC14. 232

5-23 X-band ESR of Rh(IV)HPA powder at 293 OK. 236

5-24 X-band ESR of Rh(IV)HPA powder at 100 oK. 238

5-25 Cyclic Voltammogram for [GeW110398-
in acetonitrile. 241

5-26 Cyclic Voltammogram for [GeRh2W0+xO38+x] (6-2x)-
in acetonitrile. 243

5-27 Plot of product 2-cyclohexen-l-one vs. time for
RhHPA catalyzed oxidation of 5 mL cyclohexene. 250

5-28 Plot of mmoles of 02 and 2-cyclohexen-l-one vs. time. 253

5-29 Plot of mmoles 2-cyclohexene-l-one product vs. time.
Affects of molecular sieves. 257

5-30 FT-IR of deactivated RhHPA catalyst with reaction
with cyclohexene. 260

5-31 FT-IR of deactivated RhHPA catalyst with reaction
with cyclohexenol peroxide. 262

5-32 Proposed mechanism for the RhHPA catalyzed oxidation
of cyclohexene. 267

5-33 Proposed mechanism for the Rh(III)/Cu(II) catalyzed
oxidation of terminal olefins with molecular oxygen. 271









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

METAL COMPLEX FACILITATED TRANSPORT AND
ACTIVATION OF MOLECULAR OXYGEN

By

Kenneth John Balkus, Jr.

December 1986

Chairman: Professor Russell S. Drago
Major Department: Chemistry

The research reported in Chapters I-IV involves the synthesis

and spectroscopic characterization of synthetic 02 and CO carriers,

improvement of the stability and reversibility of these metal

dioxygen and carbonyl complexes by varying the supports and ligand

environment, and the incorporation of these complexes in

polystyrene membranes as part of a novel gas separation process.

Bis(salicylidene-Y-iminopropyl)methylaminocobalt(II) and

derivations thereof, supported on both polystyrene and silica which

bind 02 reversibly in the solid state, are described in detail.

The characterization of a novel zeolite encapsulated anionic

complex is also reported. This compound, proposed to be

Co(CN)42-Y, binds dioxygen reversibly, at least 400 cycles and is

stable to moisture. Several new Cu(II) complexes supported on

polystyrene were prepared and their reversible interaction with

carbon monoxide was investigated.

A new method for the separation of oxygen from air is

presented. The system involves the incorporation of supported

transition metal complexes that reversibly bind dioxygen into

polystyrene membranes in order to facilitate the transport of 02.









These films, subsequently employed in a closed volume experiment,

exhibited enhanced 02 permselectivity. The permeation apparatus,

experimental procedure and membrane characterization are presented

in detail. A mechanism of transport which involves a site to site

interaction between metal centers is discussed.

The work in Chapter V focuses on employing lacunary

heteropolyanions (HPAs) as oxidatively resistant ligands for

catalytically active metal ions. The reactivity in organic

solvents of [XMW11039]n-, where M = Co(II), Mn(II) and Fe(III), was

investigated. In the presence of alkyl peroxide or iodosylbenzene,

these HPAs were found to catalyze the oxidation of several organic

substrates. This research led to the discovery of a dirhodium

heteropolytungstate catalyst. This polyoxometallate is proposed to

be a metal-metal bonded Rh2 substituted Keggin ion. The

preparation and characterization of this compound are described in

detail. The RhHPA was found to be an effective catalyst for the

allylic oxidation of cyclic olefins by molecular 02. Unusual

selectivity for the production of the cx,- unsaturated carbonyl was

observed. A consideration of the general features of this reaction

led to a proposed mechanism which involves an ion free radical

decomposition of insitu generated peroxides.

















CHAPTER I
GENERAL INTRODUCTION

Understanding the binding and activation of molecular oxygen

by transition metals is of paramount importance to the scientific

community. When one considers all the life forms which respire in

some manner as well as all the chemical processes that depend on

oxygen, the magnitude of this task becomes clear. As we improve

our general knowledge of oxygen fixation there is an increase in

the number of applications for 02. Since oxygen comprises only 21%

of the earth's atmosphere, there is a need for inexpensive

processes for the production of pure oxygen and oxygen enriched

air. Part one of this dissertation addresses this problem and

presents a novel method for the enrichment of oxygen from air.

This method involves the incorporation of supported metal complexes

that reversibly bind 02 into flat polymer membranes. By applying a

partial pressure differential across the membrane, the metal

complexes facilitate the transport of oxygen which enhances the

ability of the polymer itself to transport 02. Chapter II

describes the preparation of these oxygen binding metal

complexes. Chapter III considers metal complexes that reversibly

bind other gases such as carbon monoxide. The results for the

metal complex containing membrane based gas separations as well as

a mechanistic model to describe this mode of 02 transport are

detailed in Chapter IV.










The utilization of molecular oxygen to effect a variety of

chemical transformations most often requires a transition metal

catalyst. A goal of researchers in this area is to develop

catalysts that impart a high degree of both selectivity and

activity to the reaction. Typically the most selective oxidation

catalysts suffer instability or conversely the most active

catalysts are generally the least selective. Part two describes an

effort to employ polyoxometalates as homogeneous oxidation

catalysts. Soluble metal oxides, more specifically

heteropolytungstates, were employed as oxidatively resistant

ligands and substituted with a catalytically active metal

centerss. The preparation, characterization and reactivity of a

rhodium heteropolytungstate are described in Chapter V.

Each chapter is preceded by a brief introduction which

provides the necessary background information to allow a better

understanding of the chapter material as well as the progression of

topics presented in this general introduction.
















CHAPTER II
THE PREPARATION OF METAL COMPLEXES
THAT REVERSIBLY BIND DIOXYGEN



Introduction

The reversible fixation of dioxygen by metal complexes has

attracted the interest of many not only because of the biological

implications but also for a more practical reason, namely the

separation of 02 from gas mixtures. Since the first synthetic

dioxygen complex, (NH3)5CoO2Co(NH3)5, was characterized in 1898,

many oxygen carriers and metal-02 complexes have been reported.

The term oxygen carrier can be defined as a metal complex which can

reversibly fixate or bind 02. Reversible in this case means the

oxygen can be bound and released upon a change in pressure or

temperature. This also implies that the oxygenation and

deoxygenation can be carried out numerous times or cycled

continuously without a change to the metal complex. In developing

effective synthetic oxygen carriers one must first have an

understanding of those factors which determine the nature of the

metal bound dioxygen. Molecular oxygen or the free 02 molecule has
3g-
a triplet, 3 ground state with the two unpaired electrons in the

T orbitals as shown in the molecular orbital diagram below.












3au



S30-u

























0 0O 0



As a result of the triplet ground state, molecular oxygen is

generally unreactive towards diamagnetic molecules since a change

in spin is kinetically unfavorable. The formation of oxygen

adducts with transition metals is often favorable owing in part to

spin orbit coupling which can serve to relax the restrictions to

spin pairing. The exact nature of the metal bound oxygen has been

the subject of much controversy. Drago's spin pairing model has

become a widely accepted description of this metal 02 bonding.2

This essentially involves pairing of one or both of the unpaired

electrons of oxygen with unpaired electrons on the metal. This is

best illustrated by a molecular orbital diagram for an oxygen

adduct of Co(II) shown below. EPR experiments have established





5





dx -y2



d22 -41--::''' -] -*

dxy

dxz,dyz --l





0
~t-----^_




CO o0
N oI








that the unpaired electron is in an essentially oxygen based

orbital. Therefore, the degree to which oxygen is reduced depends

upon the electron distribution in the a molecular orbital formed
2 *
from the d and i orbitals. By varying the ligand field

strength around the cobalt center the contribution of the dz2 to

the o bonding orbital will change and therefore the degree of

electron transfer to the oxygen will vary accordingly. Since the

difference between Co2+-020 and Co3 -02 is only relative to the

electron distribution in the o MO, no distinction will be made

between neutral oxygen and any of its reduced forms when referring

to metal dioxygen complexes that are reversible oxygen carriers.

Generally, oxygen will ligate to metals in one of three

different geometries: end on bonded (A), bridged (B), or ring

bonded (C) as shown below. Specific examples of the different










M
/o o/
0 0 0 0

M 0 M M

0



A B C



structural types as well as some of the chemistry associated with

these complexes can be found in several recent reviews and will not

be presented here.3-5 Suffice to say that most of the metal

dioxygen complexes to be discussed in this chapter will be of the

type A or end on variety.

The first example of reversible oxygen adduct formation was

reported in 1938 by Tsumaki. The complex was N,N'

-bis(salicylidene)ethylenediamine cobalt(II) or Co(II)SALEN shown

below. Cobalt(II) Schiff base complexes of this type were studied




o 0


-N N






extensively as reversible oxygen carriers with the hope of

developing a light weight oxygen storage system. The U.S. Air

Force, currently employs liquid oxygen storage systems on military









aircraft, developed an 02 generating system based on a fluorinated

derivative of Co(SALEN). Unfortunately the oxygen carrying

capacity for complexes of this type was greatly diminished after a

number of cycles. The deactivation of oxygen carriers is usually

the result of either irreversible oxidation of the metal center,

such as p-peroxodimer formation, or degradation of the ligand by

02. Most of the efforts to enhance the stability of these

complexes, i.e. their resistance to irreversible oxidation, have

been in either one of two directions, namely supporting the metal

complexes or the preparation of sterically hindered chelate

complexes. Examples of the later are Collman's "picket fence"

porphyrin complexes and Busch's lacunar macrobycylic ligands.10

Supported metal complexes will be the focus of much of the work in

this chapter.

In general, there are relatively few metal complexes that

reversibly bind molecular oxygen in the solid state. Dioxygen

binding in the solid state requires a crystal lattice with pores or

channels such that 02 can diffuse freely through the solid.11 The

restraints of the crystal lattice often render potential oxygen

carriers unreactive towards 02. For those complexes that do bind

dioxygen in the solid state, determination of those thermodynamic

parameters associated with oxygen binding can be very

complicated. For example, phase changes or changes in the crystal

structure will have an effect on equilibrium measurements. Solid

state equilibria are often described by Langmuir kinetics such as

X P2
S P02
1 -x 02 = P









where X = mole fraction of oxygenated sites, 1-X = mole fraction of

unoxygenated sites, K = the dioxygen binding constant, P0 = the

partial pressure of 02 in the gas phase, and Py = the partial

pressure of 02 required to oxygenate half of the metal complexes.

Unusual solid state 02 binding properties are best illustrated by

the Fe(II) picket fence porphyrins. When a sterically constrained

axial base such as 2-methyl-imdazole was coordinated to the Fe(II)

picket fence porphyrin (Figure 2-1), the absorption of oxygen did

not display a simple langmuir isotherm.12'13 In other words, the

oxygen affinity of the metal complex did not remain constant with a

change in oxygen pressure but rather showed two distinct reversible

forms. This type of behavior has been compared to the cooperative

oxygen binding of hemoglobin. Apparently, the initial oxygenation

of some of the Fe(II) sites induces a reversible change in the

crystal lattice creating Fe(II) sites that have a higher affinity

for 02.

In light of the crystal lattice restrictions in solid state

oxygen absorption, a logical solution would be to attatch the metal

complex to the surface of a solid. The purpose of the support is

threefold: 1) the individual complexes can be bound to the support

eliminating crystal packing effects and either through high surface

area or a porous solid more of the complex per unit mass can be

exposed to oxygen; 2) in separating the metal complexes on the

support, irreversible oxidation that is multiordered in metal

complex may be prevented; and 3) various supports such as polymers

may influence the binding of oxygen by providing a hydrophobic

environment analogous to the solvation effects observed with

natural oxygen carriers such as myoglobin.






















Figure 2-1. Oxygen adduct of 2-methylimidazole meso-tetra
(a, a, a, a o-pivalamidophenyl) porphyrin iron(II).




10

















CH3 CH
KC 1CH, H3C, ICH
O
0 io
N HN




cHirC IojHs
N-- Fe --N

N N





CH,


H









Metal complexes can be supported on polymers in a number of

ways. For example, a polymer with a basic functionality such as

polypyridine or a polymer that has a monodentate ligand covalently

attached, such as polystyrene functionalized with imidazole,

provides an axial base for many metal complexes that require such a

ligand to bind oxygen. Chelate complexes such as Co(TPP),14

Fe(TPP)15 (TPP = tetraphenylporphyrin), Co(DPGB)2,16 (DPGB =

diphenylglyoximatodifluoroborate, and Co(SALEN),17 have been

supported in this fashion. This mode of attachment suffers in that

there can be dissociation of the axial ligand or coordination of

two proximal bases rendering the metal coordinately saturated. An

alternative is to covalently attatch the chelate ligand directly to

the polymer. To this end, many polymer bound bidentate,

tridentate, and tetradentate ligands have been prepared.119 Most

noteworthy was the report of synthetic procedure for attaching

multidentate amines to organic polymers.20,21 Such amines form the

basic building blocks for many chelate ligands. Of particular

interest is the preparation of polymer bound pentadentate Schiff

base ligands, such as polystyrene supported bis(3-

(salicylideneamino)propyl)methylamine or [P]-SDPT as shown below.

Polymer supported CoSDPT reversibly binds oxygen in the solid state

as compared with CoSDPT in solution which has a AH = -9.8 kcal;22

this translates into AG = +1.28 kcal and a Pi = 6.7x103 torr! The

oxygen binding ability of many covalently or coordinatively

attached metal chelate complexes has been investigated,23

especially in relation to their catalytic oxidizing

potential.21,24 Polystyrene supported CoSDPT (21% substituted) was

studied as a solid state oxygen absorbent.25 It was estimated that












[CH2-CH]n [CH2-CH]

NH(CH2CH2CN)2


CH2C1 CH2-N(CH2CH2CN)2



BH3.THF


[CH2-CH], [CH2-CHJ]

2-(HO)C6H4CHO

HO I

CH2NC(CH2)3N=CHC ]2 H2-N(CH2CH2CH2NH2)2


this system could be economically competitive with cryogenic or

pressure-swing absorption oxygen separation process. However, the

capacity of [P]-CoSDPT to uptake oxygen decreased with an

increasing number of capture/release cycles. By virtue of most

polymers being flexible in nature, it is a rather difficult task to

achieve site isolation of supported metal complexes.

A more ridgid support, such as an inorganic oxide, can hinder

the motions of the attached metal complexes providing a more

effective site separation. Silica, Si02, has a surface covered

with hydroxyl groups which can be modified in a large number of

ways with organo-silanes. For example, silica gel has been

functionalized with imidazole then used to stabilize Fe(II)TPP.26


SOCH3

Si

-0 CH2CH2CH2-N N-FeTPP
-'>3<-









The [SG]-FeTPP reversible binds oxygen (at 0C Pv = 230 torr)

compared with [P]-FeTPP which irreversibly oxidizes with formation

of a u-peroxodimer. Cobalt(II) phthalocyanine has been supported

on silica functionalized with pyridine and also shown to reversibly

bind 02.27 Site isolation on silica gel can be achieved in two

ways either by having a dilute concentration of functionalized

sites or by a new method which involves cofunctionalization of the

support with alkylsilanes.28 It is thought that organosilanes can

migrate across the surface of silica by exchanging protons with

adjacent silanol groups. This results in aggregation and

deactivation of the metal complexes. Alkylation of the surface

prevents this migration and allows a higher loading of metal

complexes. There are few examples of covalent attachment of metal

complexes to silica gel. There is a recent report of a cobalt(II)

hematoporphyrin complex immobilized via a peptide bond to

silica.29 However, the cobalt is irreversibly oxidized in air.

CoSDPT has been covalently supported on silica gel and shown to be

an effective oxygen carrier.30 To date this is probably the most

effective means for stabilizing such a complex on the surface of a

solid support. This chapter will describe the preparation of such

complexes.

Alternative supports gaining considerable attention are

zeolites or molecular sieves. The absorbative properties of

zeolites are well known and many commercial gas separation or

purification processes are based on these properties.31 In

particular, both oxygen and nitrogen are produced on a commercial

scale by pressure-swing adsorption (PSA) based on molecular









sieves. As a solid support, zeolites have many unique features.

The structures of zeolites include a variety of pores, channels and

cavities of fixed dimensions. The framework has both strong Lewis

acid and Bronsted acid sites. The ionic nature of the cavities can

be varied with the Si/Al ratio and a whole host of cations can be

exchanged into these cages. Therefore, the steric constraints

coupled with the electrostatic environment within the zeolite cages

create a unique solid support. There are relatively few examples

of oxygen binding metal complexes that have been encapsulated in

zeolites. A number of cobalt(II) amine complexes in X and Y

zeolites have been prepared.32-35 There is also a report of oxygen

binding by Cr2+ on an A zeolite36 and a Ru3 O2 adduct in a Y

zeolite.37 More recently a [Co(bipy)(terpy)]2+ complex was

prepared in a Y zeolite and found to reversibly bind 02.38 This

was subsequently employed to separate oxygen from air with a

separation factor (02/N2) a = 12.3.39 However, this complex was

extremely moisture sensitive, precluding any practical

application. Generally the approach to preparing these complexes

has been to use ligands that the cage will readily accommodate

resulting in cationic or neutral complexes. Ideally a metal

complex which is indifferent to water and possesses oxidatively

resistant ligands would be best suited for zeolite encapsulation.

Such a complex is [Co(CN)5]3- first reported by Adamson0 and the

oxygen adduct later characterized by Raymond and Brown.1,42 This

complex has been incorporated in both A and Y zeolites by Dr. Iwona

Bresinska and found to be a very stable oxygen carrier, the details

of which will be discussed in this chapter. This is a very









significant result, especially in light of the popular

misconception that anionic complexes cannot be prepared in the

zeolite cavities.32

The supported metal complexes to be discussed here hold

promise as solid state oxygen absorbents and their application to

facilitated transport in membranes is even more exciting.



Experimental

Solvents and Reagents

Dimethylformamide (DMF) was distilled over BaO, freeze pump

thawed and stored under nitrogen. Dioxane and tetrahydrofuran

(THF) were distilled over CaH2. All other solvents and reagents

were stored over 4A molecular sieves and used without further

purification.

Spectral Studies

Infrared spectra were recorded on a Nicolet 5DXB Fourier

transform infrared spectrophotometer using NaC1 discs for nujol

mulls. Electronic spectra were obtained with a Perkin-Elmer 330

spectrometer. Solid state spectra were recorded as nujol mulls on

Whatman No. 1 qualitative filter paper. X-band ESR spectra were

obtained with a Bruker ER 200D-SRC spectrometer.

[P]-DPT

Chloromethylated (90%), divinylbenzene crosslinked (4%)

polystyrene beads were obtained as a gift from Sybron

Corporation. Polystyrene bound dipropylenetriamine, [P]-DPT, was

prepared according to the literature.21









[P]-S)PT, -3,5Br2aPT and -3FSDPT


The polymer bound pentadentate ligand, [P]-SDPT, was prepared

according to the literature.21 The 3,5-dibromo and the 3-fluoro

substituted salicylaldehyde derivatives were prepared in a similar

manner. For example, a large excess of 3,5-dibromosalicylaldehyde

was slurried with [P]-DPT in benzene at reflux overnight. The

water of condensation was collected in a Dean-Stark trap. The

functionalized resin was suction filtered and dried under a vacuum

at 80 C. The 3-fluorosalicylaldehyde was obtained as a gift from

Olin Corporation.

[PI-CoSDPT, -3,5Br2SDPT and -3FSDPT


Cobalt(II) was incorporated into the SDPT ligands by slurrying

excess cobalt(II) acetate with the resins in DMF under argon at

room temperature for two days. The polymer supported cobalt

complexes were suction filtered, washed with DMF, and dried under a

vacuum at 80 C.

[SG]-DPT

Silica bound dipropylenetriamine was prepared according to the

method previously described.30

[SG]-CoSDPT, -3,5Br2SDPT and -FSDPT


The silica supported Cobalt(II)SDPT complexes were prepared

from [SG]-DPT in the same way as described above for the

polystyrene bound analogues.










Zeolite Complexes

The zeolite work described below was part of a joint research

effort by myself and Dr. Iwona Bresinska. Dr. Bresinska

synthesized the metal complex containing zeolites and determined

the elemental composition. The major contribution on my part was

the characterization of these complexes.

The notation employed to describe the zeolite encapsulated

metal complexes follows the general formula, Co(MCN)-Y-1 where the

Co represents a cobalt(II) exchaged zeolite, MCN represents the

alkali metal cyanide salt used in the complex preparation (note:

M is not necessarily the cation for the original zeolite starting

material), and Y is the type of zeolite and the final digit

represents a specific preparation.

The general preparatory procedure followed for the compounds

listed in Table 2-2 was as follows. The cobalt(II) exchanged

zeolite was slurried with an alkali metal cyanide salt in an

appropriate deoxygenated solvent, most often methanol, for a

designated time period. All syntheses were carried out at room

temperature. The complex containing sieves were then suction

filtered and washed with solvent until the filtrate tested negative

for cyanide ion. The cyanide solutions were disposed of by

treating with an FeC12/NaC1 methanol/water solution to generate the

innocuous iron cyano complex. The zeolite was dried under vacuum

and stored in a dessicator. Elemental determinations were

performed by the microanalysis service of the University of

Florida. Cobalt content was determined with a Perkin-Elmer Plasma

II emission spectrometer.









Results and Discussion

The polymer and silica supported Co(II)SDPT complex and its

derivatives did not exhibit an ESR signal as could be expected for

high spin Co(II). The liquid N2 temperature ESR for the oxygen

adduct of [PJ-CoSDPT, shown in Figure 2-2, has approximate g values

of 2.06, 2.02 and 1.99. This compares well with those g values

previously reported (gz = 2.08, g = 2.016, and gx = 1.99)21 The

other polystyrene supported complexes are very similar. For

example, [PJ-Co3FSDPT (Figure 2-3) has gz ~ 2.08, gy 2.03 and

gx 1.86. The [P]-CoSDPT was prepared with electron withdrawing

substituents on the salicylidene portion of the ligand in an effort

to enhance the reversibility of dioxygen binding. In other words,

by reducing the electron density at the cobalt center the Pi2 for

the complex should increase as predicted by the spin pairing

model.2 This was demonstrated by the fact that a solid [P]-CoSDPT

sample only needed to be exposed to air in order to observe a Co-02

ESR signal whereas [P]-Co3FSDPT required at least 20 psig 02 to

oxygenate the sample. This effect is also manifested in the fact

that the 3,5-dibromo and 3-flouro derivatives facilitated the

transport of 02 to a higher partial pressure of 02 than [P]-CoSDPT

videe infra).

The silica supported complexes were prepared with a loading of

either 0.1 mmoles Co complex/gram of silica gel or 0.5

mmoles/gram. In some cases the surface was alkylated. The ESR for

a 0.lmmoles/gram SG loading and methylated surface for [SG]-CoSDPT

and [SG]-Co3,5Br2SDPT are shown in Figures 2-4 and 2-5. The g

values are similar to the polymer supported complexes (gz ~ 2.08,




































CU
C














Cuj
N




0

















al

C) D
bO
(CD










I
4- N



oON




(CDI


CD






Cu







C'

('



























jI
CD


CL
< "
>> >
. <
> A
Et f


A<



































0

C"




bo
a





CMj
m

LO
N


NJ





0













z:
bD
cC
0




Cx,





o e






ow
'Ii






C'


C"




22
















I* ^--





































4
cn













cc
) I











0
'U









Cl) N
r-


















I X)
bo
oc~o





-Ct


00
F-'

CI)

0
I to

0






C I)



I1 0



><0


(Si



21
to




24



































I
N S






JY 0





































O









m
*0
C













0 O
VI 0C












ON
o


' m



C







ON
0
c/C



(a
W






I -
x m



(\j
(Ul





26










































N Y
60 -





\ ^
] 0
\ ""'









gy 2.02. gx 1.99 and gz 2.09, gy 2.00, gx 1.99). A 0.5

loading sample does not display the cobalt hyperfine splitting

observed in these spectra of more dilute samples which suggests

these samples are magnetically dilute. In other words, the cobalt

centers are well isolated. Site separation of the complexes should

enhance their stability in the presence of 02 provided irreversible

oxidation is a second order process. At this point, the only

measures of stability are a shelf life of at least two years and

irreversible oxidation of the SG support material has not been

observed in the polymer membranes.

The two types of zeolite supports studied were of the A and Y

variety as shown below. These zeolites are characterized by the














A Y

parameters in Table 2-1.

Table 2-1

Composition of A and Y Zeolites



Zeolite Unit Cell Pore Supercage

Composition Diameter Diameter

A Na12(A1)2)12(Si02)12 4.2 A 11.4 A

Y Na56(A102)56Si02)136 7.4 A 13.0 A









The A zeolite is composed of octahederal sodalite units connected

by cubes whereas hexagonal prisms connect the sodalite cages in the

Y zeolites. The Y zeolite, which has the larger cavity, has been

the focus of this research. There are several cation sites in the

faujasite (Y) framework. Of particular interest are those

positions commonly referred to as SII sites, which are located in

the hexagonal face of the sodalite cage extending into the

supercage. Cobalt(II) at these positions could form complexes

within the large cage taking advantage of the steric constraints

imposed by this site. This approach has proved successful in

preparing otherwise unstable metal complexes in zeolites. However,

up to this point only cationic and neutral complexes have been

isolated. Owing to the electrostatics of the cage, the generation

of an anionic complex inside the zeolite was deemed unlikely. It

was gratifying to prove the contrary by preparing Co(CN) n-

complexes in the zeolites. Additionally, these complexes are quite

effective oxygen carriers videe infra). The cyanide ion itself

could not be incorporated into the zeolite. This was evidenced by

the fact that slurrying NaCN with Na-Y zeolite in methanol for 15

hours results in no CN incorporation. This means that any CN-

detected in the Co-Y zeolites must be attributed to complex

formation with the cobalt. Generally, cyanide ion promotes the

formation of transition metal complexes with high coordination

numbers. For Co(II), the pentacoordinate anion Co(CN)53- is the

most stable. Except for polymeric materials the only other

isolable cyano cobaltate complex reported is (PNP)2Co(CN)4, where

PNP = bis(triphenylphosphine)iminium cation.43 This complex was









characterized by x-ray crystallography and found to be square

planer. There is evidence for the existence of cobalt(II)

complexes with from 1 to 5 cyanide ligands in solution.4445

Characterization of the zeolite encapsulated Co(CN)xn- complexes

was complicated by the strong affinity of these complexes for

molecular oxygen. Therefore, the spectral studies reported herein

are for the oxygen adducts.

The Co(II) in the Co-Y zeolite is probably coordinated to at

least two lattice oxygens. Upon complexation with cyanide, this

interaction is believed to be partially retained when four or less

cyanides are coordinated. As can be seen from Table 2-2 the extent

of complexation depends upon the amount of cyanide used, the

solvent and the reaction time. The N/Co ratio does not necessarily

represent the empirical formula of a cobalt complex, since not all

of the cobalt may be completed. Additionally, some of the

exchanged cobalt could get washed out during the reaction with

NaCN, whereas the N/Co ratio in Table 2-2 is relative to the

initial concentration of cobalt.

The IR spectra of these zeolites provide a good handle to the

degree of complexation under various conditions. The data in Table

2-3 summarizes the infrared bands observed in the CN stretching

region. These frequencies are similar to those reported for Co(II)

cyano complexes (2094-2134 cm-1 ).46 For example,

[(C2H5)4N]3Co(CN)5] has a vCN = 2080 cm-1, whereas the oxygen

adduct shows a vCN = 2120 cm- At low N/Co ratios a higher

frequency band is observed and may be attributed to a lower number

of cyanides coordinated to cobalt. Increasing the CN











Table 2-2

Conditions for the Preparation of Co(CN)xn- Containing Zeolite



Compound Solventa Time [Co] [CN]b N/Coc

(hours) (mmole/gm)(mmole/gm)



Co(NaCN)-Y-1 CH3OH 18 1.0 4.0 0.76

Co(NaCN)-Y-2 CH3OH 164 1.0 20.0 1.32

Co(NaCN)-Y-3 CH3OH 96 0.94 22.0 4.29

Co(NaCN)-Y-4 CH3OH 120 0.94 20.0 3.0

Co(NaCN)-Y-5 H20 120 0.94 20.0 0.99

Co(NaCN)-Y-6 H20 120 1.27 40.0 0.72

Co(NaCN)-Y-7 CH3OH 120 1.27 40.0 2.09

Co(NaCN)-Y-8 DMF 237 0.94 24.0 2.63

Co(NaCN)-Y-9 CH3OH 139 1.27 88.0 2.34

Co(NaCN)-Y-10 H20 117 1.10 90.9 1.60

Co(NaCN)-Y-11 H20 100 1.27 144.0 0.75

Co(KCN)-Y-1 CH OH 120 0.94 14.2 3.02

Co(LiCN)-Y-1 DMF 237 0.94 25 2.29

Co(NaCN)-A-3 CH30H 188 1.88 18.0 0.94





a solvent for CN incorporation
b concentration of CN used in the reaction
c ratio of nitrogen in the product to the initial
cobalt concentration









Table 2-3



Infrared Co(CN)x Zeolitea



CN frequencies (cm-1)


Co(NaCN)-Y-1

Co(NaCN)-Y-2

Co(NaCN)-Y-3

Co(NaCN)-Y-4

Co(NaCN)-Y-5

Co(NaCN)-Y-6

Co(NaCN)-Y-7

Co(NaCN)-Y-8

Co(NaCN)-Y-9

Co(NaCN)-Y-10

Co(NaCN)-Y-11

Co(LiCN)-Y-1

Co(KCN)-Y-1

Co(NaCN)-A-3

NaCN


2176.9(m), 2138(m)

2178.8(m-w), 2137(m-s)

2217(w), 2131.7(s), 2090(w)

2209(w), 2130.9(s)

2130.7(s)

2131.2(s)

2201(w), 2131(s)

2163(sh), 2133.5(w), 2090.2(m-w)

2205(m-w), 2131.8(s), 2097.9(w)

2197.9(sh), 2130.4(s)

2130.5(s)

2163(vw)

2124(s)

2135.7(s), 2108(vw), 2095(vw)

2090.7


a exposed to oxygen


Compound









concentration generates the band at 2131 cm-1, as illustrated in

Figure 2-6. Spectrum C shows three bands as might be expected for

a complex of C4v symmetry but compounds 5, 6 and 11 show only a

single band which would be consistent with D4h symmetry. The band

at 2090 cm- may coincide with the unoxygenated complex. This

would be in line with acetonitrile solutions having CN/Co ratios of

3 and 4 which display major peaks at 2096 and 2090 cm-

respectively.45

The counterion has been shown to have a profound effect on

complex formation. The CN stretching frequency has been observed

to increase with the probability of contact ion pairing.45 This

increase in vCN is thought to result from kinimatic coupling.47

This would be consistent with Co(NaCN)-Y (2131 cm-1) and Co(KCN)-Y

(2124 cm-1).

In order to better define the nature of the zeolite

encapsulated complexes, the electronic spectra were recorded by

placing a nujol/zeolite paste on a piece of filter paper in the

instrument sample light path. Likewise, a piece of paper with only

nujol was placed in the reference beam. The visible spectra

obtained in this fashion displayed broad and possibly overlapping

bands with low signal to noise ratios. Therefore, the assignments

of band maxima are tentative. The results for a series of Co(II)

cyano complexes are shown in Table 2-3. It should be pointed out

that Co(CN)53 exhibits only very weak absorptions in the 400 to

800 region and was excluded from Table 2-4. Although the maxima

have not been reported for the electronic spectrum of Co(CN)5023-,

the distinctive features appear below 500 nm. Additionally, the























Figure 2-6. FT-IR (nujol mull) for
A. Co(NaCN)-Y-1
2176.9 cm-
2138.0 cm-1
B. Co(NaCN)-Y-2
2178.8 cm-1
2137.0 cm1
C. Co(NaCN)-Y-3
2217.0 cm
2131.7 cm 1
2090.0 cm
D. Co(NaCN)-Y-5
2130.7 cm1.





34



















A









B


















D











Table 2-4



Electronic Spectra for Cobalt(II) Cyano Complexes


Complex


Bands (nm)


Co(NaCN)-Y-1c

Co(NaCN)-Y-20

Co(NaCN)-Y-3c

Co(NaCN)-Y-60

Co(KCN)-Y-1

Co-Y

[Co(CN)2(CH CN)2]

[Co(CN) (CH CN)]-

[Co(CN)4 2-/CH2C12

[Co(CN) ]2-/CH3CN)


514

514(sh), 648(sh)

514(sh), 560, 665

520(sh), 583(sh), 650(sh)

555(sh), 668(sh), 690(sh)

430, 530, 570, 624(sh)

605a, 625b, 690(sh)b

590a, 602b

563(sh)b, 594b

581(sh)b, 598(sh)b, 617b


a. reference 44
b. reference 45
c. oxygen adduct









other cobalt(II) cyano complexes listed in Table 2-4 have not been

reported as being reactive toward oxygen. The electronic spectrum

for Co(II) exchanged Y zeolite is shown in Figure 2-7. A violet

product is obtained after heating the pink hexaaquo complex under a

vacuum. The complex producing the violet color probably consists

of Co(II) bound to two lattice oxygens and two waters. Usually

tetrahedral complexes are characterized by intense low energy

transitions. Unfortunately, because of the solid state techniques

involved, the extinction coefficients were not accessible. All of

the spectra for the zeolite encapsulated Co(CN)xn- complexes were

characterized by large charge transfer bands with a number of low

energy transitions. Cobalt(NaCN)-Y-1 (Figure 2-8) is also violet

in color and has a single band at 514 nm. This zeolite shows a

very weak Co02 ESR signal indicating a very low concentration of

those complexes capable of binding 02. In comparison with

Co(NaCN)-Y-2 (Figure 2-9) and Co(NaCN)-Y-3 (Figure 2-10), the band

at 514 nm is reduced in intensity and a lower energy band grows

in. Cobalt(NaCN)-Y-3 is gray in color and is a very effective

oxygen absorbent. No discernable color change is observed during

oxygenation or deoxygenation. It should also be noted that

Co(CN)53 is yellow or pale green and the oxygen adduct is red-

brown.

The ESR of the oxygenated Co(NaCN)-Y-3 is shown in Figure

2-11. This is a typical Co02 signal with gi-2.01 and gll-2.07.

Evacuating the sample to below 10- torr produces the spectrum in

Figure 2-12 with gj-2.25 and gll-1.95. The sample has not been

completely deoxygenated as evidenced by the weak 02 signal at the























Figure 2-7. Electronic Spectrum for Co-Y Zeolite (nujol mull,
0-1 scale, 60 nm/min).




38

















I
LU
LU
CD
c3











350 40 550 650 750 80























Figure 2-8. Electronic Spectrum for Co(NaCN)-Y-1 (nujol mull,
0-1 scale, 60 nm/min).











































500 600


700 800























Figure 2-9. Electronic Spectrum for Co-(NaCN)-Y-2 (nujol mull,
0-1 scale, 60 nm/min).








































LCZ



00 600 00 800













500 600 700 800























Figure 2-10. Electronic Spectrum for Co(NaCN)-Y-3 (nujol mull,
0-1 scale, 60 nm/min).













































700 800

















































0
C


tC

N













ms



bo
C -x
C, C










03
(D
a~



E4 CJ
'o











I >1
x -4
7




(\i
;o c
ue,


Ox









C
IU
V C
CC







Cr,
2.~
CU





46






































C



cv


I

---A
to










57
o n
tn










0 x
DID





82 0


0
CC







o >
>0
ZiD











7
ox
o -
C~b

GN .4I




r.0


CM


C),












center of the spectrum. The relatively large anisotropy in the g

tensor supports the contention that the complex is not Co(CN)53-

2-
but rather Co(CN)4- with the axial position occupied by a lattice

oxygen as shown below. Additionally, for an acetonitrile solution



NC \ CN



NC I CN



Si Al



containing a 5:1 mixture of cyanide and Co(II) the gi-2.18 and

g|-2.00, whereas a solution containing a 3:1 mixture of cyanide

and Co(II) produces an ESR spectrum with gj~2.28 and g|l-2.00.

The oxygenation of the zeolite containing Co(II) complexes is

reversible and can be cycled at least 400 times. In fact, the

spectra shown in Figures 2-11 and 2-12 were taken after 50

cycles. However, the Pi for this complex must by very small since

reducing the pressure to below 10- torr did not completely

deoxygenate the sample. In terms of commercial applications as a

pressure swing adsorption catalyst, good reversibility is important

as well as the oxygen carrying capacity and the stability. The

ideal absorbent should have the capacity to absorb at least 10 mL

of oxygen per gram of catalyst. Such an absorbent would find

greater utility for large scale gas operations. On a smaller

scale, such as for a breathing apparatus which would require a

minimum of 30 liters of oxygen per minute, the 02 binding capacity









of the absorbent would have to be even greater. In a crude vacuum

line experiment, one gram of Co(NaCN)-Y-3 was placed in a tube of

known volume then degassed under less than 10-4 torr pressure. The

sample after exposure to 4 torr of 02, absorbed nearly 1 mL of

oxygen. This compares well with [Co(bipy)(terpy)]Li-Y which

absorbs 0.47 mL of 02 per gram of zeolite under 15 torr of 02.

A good PSA catalyst should be stable in the presence of H20,

C02, and S02. The cyanocobaltate complexes are stable to moisture

since they can even be prepared in water (Co(NaCN)-Y-5,6). In the

absence of moisture, CO2 and S02 have no effect on the 02 binding

properties of the complexes. However, if water was present, a

radical species was generated with SO2, probably S02* or SO2

and the capacity to bind oxygen was lost. Similar radicals are

formed with wet NaY zeolite itself under the same conditions.

In conclusion, stable cobalt(II) complexes have been supported

on polystyrene, silica gel, and zeolites. These complexes have

been demonstrated to be effective oxygen carriers. This property

has been exploited in Chapter IV, where these supported complexes

were employed as additives in polymer membranes to facilitate the

transport of oxygen.

The studies presented above were extended to include complexes

that reversibly bind carbon monoxide which are discussed in Chapter

III. Many of the complexes that bind 02 also react with CO,

forming complexes that are often more stable and less reactive than

the 02 complexes. Therefore, the CO carriers may provide good

models for the 02 carriers in the metal complex facilitated

membrane gas separations.














CHAPTER III
THE PREPARATION AND CHARACTERIZATION OF
Cu(I) COMPLEXES THAT REVERSIBLY BIND CARBON MONOXIDE



Introduction

The reversible fixation of carbon monoxide has been an area of

considerable interest for nearly a century. Some of the impetus

behind recent advances in CO chemistry has been a need for

efficient gas separation processes which is discussed in more

detail in Chapter IV. A primary application is the recovery of CO

from industrial byproduct gas streams which can then be used in

chemical production. Often the synthesis gas, CO/H2, used in

chemical production is obtained from steam reforming of natural

gas. However, this energy intensive process could be avoided and

our limited natural gas supply could be conserved if CO could be

supplied from byproduct gas streams. Tnere are many liquid

absorbtion processes for the separation of carbon monoxide from gas

mixtures, most of which are based on copper(I) chemistry. The most

notable commercial development, known as the COSORB process,

involves a CuAlC14 complex in an aromatic base.48'49 In comparison

with cryogenic separation, the COSORB process can produce 100.0

million pounds of CO per year versus 87.3 million with a purity of

99.83% versus 99.38% for nearly half the cost. It would appear

that the development of selective absorption processes could be a

profitable venture. The direction of current research efforts has

focused on solid absorbents and membrane separation which will be









discussed in Chapter IV. There are numerous metal complexes that

reversibly bind carbon monoxide in solution such as CH3Mn(CO)5,50

Vaska's complex IrCl(CO)(PPh3)2,51 the metal-metal bonded

bis-p-(bisdiphenylphosphinomethane)dihalodipalladium(II),52

phthalocyanatoiron(II),53 and the biologically significant metal

porphyrin complexes.54 A recent study of supported complexes for

the separation of gas mixture describes the attempt to support on

polystyrene Pd2(dmp)2C12, which rapidly binds CO in solution at

25 C.55 This complex could not be supported nor did the

crystalline complex bind CO, probably the result of lattice

constraints. As described in Chapter II, polymeric supports are

practical from the standpoint that they are easy to

functionalize. Site isolation of metal complexes is not important

for the fixation of carbon monoxide unlike the oxygen carriers.

Therefore, relatively simple systems can be investigated without

the elaborate synthetic procedures used in the preparation of

oxygen carriers to insure stability. For example, simple



-(CH C-C C C
II II I I
IHON NO 0

polyoximes of the general formula impregnated with Fe(II) and Cu(1)

salts reversibly bind CO.56-58 These functionalized polymers were

subsequently employed in an unsuccessful attempt to facilitate the

transport of CO through a polymer membrane.59

Other supports recently investigated include zeolites and

carbon. Zeolitic molecular sieves containing Cu(I) cations were

found to have a high affinity for CO, even in the presence of









water.60 Unfortunately, small amounts of CO were absorbed because

of low exchange of copper in the zeolite. A serious drawback of

using CuAlCl4 in facilitated transport is that it is extremely

moisture sensitive and forms HC1 in the presence of water. The

COSORB process requires less than 1 ppm of H20 in the feed gas.

The active component of the COSORB process, CuAlC14, was recently

supported on active carbon.61,62 Also stable in the presence of

moisture, this complex is an effective absorbent for CO. It was

proposed that the CuAICI4 complex was located in polar micropores

of the active carbon, where the walls composed of condensed

aromatic rings interact with the Cu(I). This support apparently

inhibits the aggregation of the metal complexes since these

micropores are so small. As a result even Copper(I) chloride has

been supported on carbon and found to be an effective CO

carrier. 3 At 20 OC, the carbon supported CuAlCl4 complex adsorbs

slightly more than a 1:1 molar ratio of CO. Low pressure

(0.4 mmHg) and high temperature (180 OC) is required to desorb

nearly all of the CO. The influence of the aromatic rings of the

carbon in stabilizing the Cu+ complex is not unique but seemingly

an integrable part of a number of separation processes (ex. COSORB

process-aromatic base). Along these same lines, CuAlC14 was

observed to reversibly bind CO in a polystyrene/toluene

solution.64,65 In the absence of polystyrene, the CuAlC14 solution

displays a marked decrease in CO binding ability, especially in the

presence of water. It was proposed that polystyrene forms a

stronger charge transfer complex by virtue of a chelate effect

where two aromatic rings interact with the CuAlCl4 complex.









Seemingly there is little need for the aromatic solvent and indeed

it was very recently reported CuAlC14 supported on macroreticular

crosslinked polystyrene reversibly adsorbs CO.66 Linear or gel

type crosslinked polystyrene supported CuAlC14 are far less active,

which probably can be attributed to diffusional problems. These

functionalized polystyrene beads can adsorb as much as 69 mL CO per

gram at STP. The effects of the polymer support must be twofold:

1) provide a hydrophobic environment and 2) form a weak complex

with the Cu(I).

The CuAlCl4 complex supported on a macroreticular resin was

reported subsequent to the completion of the work described in this

chapter. The original goal of this research was to prepare polymer

supported ligands that would bind and stabilize copper(I) which

could effectively act as a CO carrier. Numerous copper(I)

complexes reversibly bind CO.67'8 Since the copper(I) prefers to

be four coordinate, a bidentate or tridentated ligand would be

advantagous. Several CO carrying copper(I) complexes with bi and

tridentate ligands have been reported, all of which contain one or

more unsaturated amines.69-74 Complexes with saturated amines are

far less stable and readily undergo a disproportionation.75

Herein the synthesis and reactivity of polystyrene supported

copper(I) chloride, dimethylamine copper(I) chloride and

dicyanoethylamine copper(I) chloride are described in detail as

well as attempts to prepare homogeneous solution analogues.









Experimental

All reagents were used as received unless otherwise

specified.

Copper(I) iodide. Copper(I) iodide (Aldrich Chemical Co.) was

dissolved in acetonitrile and precipitated with deionized water.

The white solid was dried in a vacuum at 60 OC then stored in a dry

inert atmosphere box unexposed to light.

Copper(I) chloride. Copper(I) chloride was prepared according

to the literature procedure and stored in a dry inert atmosphere

box sealed from light.

[P]-CH2Cl. The chloromethylated linear polystyrene as well as

the 4% divinylbenzene crosslinked, 90% chloromethylated polystyrene

beads were provided by Sybron Corporation.

[P]-DCEA. Bis(2-cyanoethyl)amine, (DCEA) supported on

crosslinked polystyrene beads was prepared as previously

described.

The linear polystyrene supported DCEA was prepared as

follows. Ten grams of the [P]-CH2Cl was dissolved in 150 mL of

dioxane in a 500 mL round bottom flask equipped with a reflux

condenser. Into the solution was stirred 30 mL of

3,3'-iminodiproprionitrile for 30 minutes at room temperature then

at low heat for two days. The solution was filtered and methanol

added to the filtrate until a gelatinous precipitate formed. The

solid was redissolved in CH2Cl2, filtered and methanol added to the

filtrate until a white precipitate formed. The isolated [PI-DCEA

was dried in vacuo. Calculated for 90% Substitution: C, 81.2;

H, 7.67; N, 11.2. Found: C, 73.8; H, 6.8; N, 7.0 which

corresponds to 81% substitution.









[P]-DCEACuX. Excess copper(I) halide dissolved in dry

acetonitrile was slurried with one gram [P]-DCEA for twelve hours

at room temperature in an inert atmosphere box. The resin was

suction filtered and washed with CH3CN then dried under N2. For

X = I- calculated: C, 41.4; H, 3.9; N, 9.1. Found: C, 68.7;

H, 6.6; N, 11.00 which corresponds to 42% complexation, taking into

account one coordinated CH3CN per copper ion.

For X = Cl- calculated: C, 53.0; H, 5.0; N, 11.6. Found:

C, 65.1; H, 6.2; N, 10.5 which corresponds to 67% complexation

assuming one molecule of solvation.

[P]-DCEACuCl (linear). In a dry inert atmosphere box 1 gram

of [P]-DCEA was stirred with 1 gram (XS)CuC1 in 80 mL of

acetonitrile at room temperature for 24 hours. The now sticky

orange resin was suction filtered and dried in vacuo.

BenzylDCEA. The 3,3'-benzyliminodiproprionitrile was prepared

according to the published procedure.21

[P]-N(CH3)2. Polystyrene bound dimethylamine was prepared as

follows. Twenty grams [P]-CH2Cl were slurried with 50 grams of

anhydrous dimethylamine under argon at room temperature for

20 hours. The resin was suction filtered, washed with dioxane,

50/50 dioxane/H20, H20, 50/50 H20/THF, and dried in vacuo at

80 OC.

[P]-N(CH3)2CuC1. In an inert atmosphere box 2 grams of

[P]-N(CH3)2 were slurried with excess CuC1 in 50 mL of acetonitrile

for 5 hours. The pale yellow resin was suction filtered, washed

with CH3CN and dried under N2.









[P]-CH2ClCuC1. In an inert atmosphere box 1 gram of [P]-CH2C1

was slurried with excess CuCl in 50 mL of acetonitrile for 24 hours

at room temperature. The resin was suction filtered, washed with

acetonitrile and dried under nitrogen.

[Cu(DCEA)2]C12. Was prepared according to the published

procedure.77



Results and Discussion

The potentially tridentate ligand HN(CH2CH2CN)2, DCEA, forms a

2:1 complex with CuC12 in the manner shown below. The nitrile-





N/C


212 2
NCCH2CH2 CH2CH2CN --
N --- Cu --- N
--N CCH2CH2' Cu N CH2CH2C EN

C C




copper bond is relatively weak as evidenced by a bond length of

2.70 A and a single weak vCN stretch in the IR at 2258 cm-1 (free

ligand 2250 cm 1). The shift in frequency to a higher value is

indicative of the nitrile being N bound rather than T bonded. The

amine-copper bond is somewhat stronger (2.10 A) with the vNH

stretch at 3202 cm-1 shifted to a lower value than the free ligand

(3335 cm-1).77 When copper(I) salts were reacted with DCEA in

acetonitrile under nitrogen, either rapid disporportionation

occurred as evidenced by the formation of a copper mirror on the

reaction vessel or a green solid was formed. The green compound









was a Cu2+ complex as evidenced by an ESR. The IR showed no shift

in the vCN but the vNH shifted to 3296 cm-1. The Cu(DCEA)2C12 was

a bright purple color. The green solid obtained from the Cu+

reactions is probably an amine complex of some sort. Covalent

attachment of the DCEA ligand to a solid polymeric support would

inhibit formation of complexes of the type formed with copper(II)

and also reduce the basicity of the amine functionality. When

[P]-DCEA is reacted with CuC12 in boiling ethanol, a yellow resin

results with the ESR shown in Figure 3-1 and a CN stretch at

2248 cm-1. For the linear [P]-DCEA and CuCI2 in boiling

acetonitrile, a yellow resin was recovered with the ESR shown in

Figure 3-2. The IR shows a vCN = 2257 cm-1 providing some evidence

for bound nitriles. When Cul or CuCl is reacted with [P]-DCEA, the

resulting resin shows no notable IR shifts in the nitrile region.

Placing the resin in ammonia solution turns it blue indicating the

presence of Cu(N2H3)42+, which is evidence for the incorporation of

copper. The [P]-DCEA has completed Cu+ since no ESR signal is

observed and it should be further noted that the functionalized

polymer remains ESR silent even upon exposure to air. This resin

which has only been dried under nitrogen, is unreactive towards

carbon monoxide. However, if the polymer beads are placed under a

vacuum then exposed to a CO atmosphere, CO binding is observed. It

is postulated that the Cu(I) complex is solvated prior to

evacuation rendering the Cu+ coordinatively saturated and inert

towards CO. Copper(I) forms complexes of the type [Cu(CH3CN)n]+,

where n = 1-3 depending upon the anion.78,79 The copper(I) halides

form 1:1 complexes with acetonitrile. Such complexes are very air
























































C.


c'


w


Cm

C()

C)

C)

0




0



C
.0





0
L




60














I
























































CM





L






a,

C)



0.

C"




01
.0



CM

1)
L






62
























































o
C.

C0
0)









sensitive and the nitrile is easily lost. It is postulated that

the product of the acetonitrile synthesis is [P]-DCEACuX-S as shown

below. The Cul complex binds carbon monoxide with vCO = 2091 cm-.


_CCN
[P] -- N CuXCH CN
CN


Under similar conditions the CuCl complex also binds CO reversibly

with vCO = 2100 cm-1. The reversibility was demonstrated by

placing the resin in the apparatus described in Figure 5-3,

applying a vacuum of less than 1 mmHg, then exposing the polymer

beads to 15 psig CO. The CO could then be removed by again

reducing the pressure to less than 1 mmHg. A typical cycle is

shown in Figure 3-3. The absorption/desorption of CO can be cycled

at least five times without a loss in activity. Upon exposing the

resin to air after evacuation, the ability of the complex to fixate

CO was greatly diminished. Pumping on the air exposed sample

partially restores the ability to bind CO. The minimum conditions

necessary to absorb and desorb CO have not been determined but it

is known that at higher CO pressure the concentration of

carbonylated complexes increases. This is reflected in the IR

spectra where the CO streching band is noticeably more intense.

Figure 3-4 shows the IR for a [P]-DCEACuCl sample after exposure to

25 psig CO (vCO = 2094 cm-1). This can be compared to the spectra

in Figure 3-3. This suggests that complete complexation throughout

the crosslinked beads is a permeation controlled process. In other

words, at the higher pressure more CO will permeate through the

polymer faster and more Cu-CO adducts will be formed. This is also























Figure 3-3. FT-IR of [P]-DCEACuCi (nujol mull)
A. After evacuation
B. After exposure to 15 psig CO,
indicates CO stretch at 2100 cm1
C. After evacuation.




65










A















C^























Figure 3-4. FT-IR of [P]-DCEACuC1 (nujol mull) after exposure to
25 psig_ O (the arrow indicates the CO stretch at
2093 cm ').





67
































CO I
F--



















2200 1800

WAVENUMBERS CM-1









supported by the fact that the linear [P]-DCEACuX did not bind CO

under the same conditions. The porous nature of the macroreticular

resin provides diffusion pathways for the CO while the CO must

permeate through the amorphous regions of the linear polymer. The

importance of the nature of the polymeric support was further

demonstrated in an attempt to prepare a silica bound DCEACuX

complex. Even with careful preparative techniques, the Cu+ was

oxidized. This may attest to the importance of a hydrophobic

environment.

In order to discern the nature of the bound species in

[P]-DCEACuX the preparation of a solution analogue was attempted.

The ligand C6H5-N(CH2CH2CN)2, phenylDCEA, was unreactive towards

Cu2+ which was not surprising since it was later learned that

phenylDCEA is synthesized using a copper catalyst consisting of a

mixture of CuC1 and Cuo powder.80 Additionally, it could be

expected that the aniline type amine would be less basic than a

benzylamine. Acetonitrile solutions of CuCl and benzylDCEA are

unreactive towards CO at room temperature. However, at 0 C two CO

stretches are observed in the IR at 2025 cm-1 and 1994 cm-1

indicative of a strongly bound terminal CO and possibly a bridging

CO. Unfortunately an acetonitrile solution containing only CuCl

behaves in the same fashion. It is well known that copper(I)

halides absorb CO in organic solvents at room temperature

(CH3OH, 2070 cm-1; THF, 2085 cm-1)81 but apparently the

acetonitrile complex behaves in an unusual fashion. It is

sufficient to say that the polymer supported complexes react in a

manner unlike that of similar species generated in solution.









The weak interaction of the nitriles in complex formation, as

indicated by the infrared spectra, leads one to believe they may

not be necessary in order to stabilize the CO carrier. Keeping

this in mind, dimethylamine was supported on the crosslinked

polystyrene beads. The complex [P]-N(CH3)2CuCl CH3CN binds CO

(vCO = 2065 cm- ) much more strongly than [P]-DCEACuCl but is just

as reversible. A typical CO absorption/desorption cycle is shown

in Figure 3-5. It should be noted that CO is bound when the

complex is still solvated and the subsequent loss of the CN stretch

with repeated cycles appears to have no effect on the binding

ability of the complex. Exposing the tan colored resin to air

instantly changes the color to orange, resulting in the ESR

spectrum shown in Figure 3-6. The orange resin shows a very weak

peak at 2066 cm-1 upon exposure to CO. Pumping on the orange resin

at 10- mmHg for 5 hours reduces the intensity of the ESR signal.

If the orange resin is allowed to stand in air for several days it

will change to an olive green color accompanied by an increase in

intensity of the ESR signal but no changes occur in the general

features of the spectrum. The nature and reactivity of

[P]-N(CH3)2CuCl are clearly different than that observed for

[P]-DCEACuCl. However, as a further control CuCl was simply

adsorbed onto the polystyrene beads from an acetonitrile solution

and screened for its CO binding capacity. Keeping in mind that

solid copper(I) chloride binds CO only under extreme conditions and

that in the presence of moisture it is both light and air

sensitive, it came as somewhat of a surprise that

[P]-CH2ClCuCl-CH3CN reversibly binds CO at room temperature.

A typical cycle is shown in Figure 3-7. The CO is bound weakly























Figure 3-5. FT-IR of [P]-N(CH3)2CuC1
A. solitated complex after exposures to
25 psig CO (vCO = 2065 cm)
B. after evacuated
C. after exposure of 25 psig CO
D. after evacuated, exposure to air,
then 25 psig CO.





71














A




B







C -






D



















Figure 3-6. X-band ESR of [P]-N(CH )2CuC12 (orange) after exposure
to air, gi 2.09 and gl 2.28 (room temperature).












































300 G
I---
























Figure 3-7. FT-IR of [P]-DCEACuCl*CH3CN
A. After preparation
B. After exposure to 25 psig CO,
vCO = 2096 cm1
C. After evacuation
D. After exposure to CO
E. After evacuation, exposure to air,
then exposure to CO.




75





A








Il
B



A



C





D
*A

Ern1









(vCO = 2096 cm-1) and is not completely removed upon exposure to

reduced pressure. Interestingly enough, the CN stretch does not

decrease in intensity even after repeated cycling. The

acetonitrile is still weakly bound (vCN = 2252 cm-1) but apparently

stronger than for either [P]-DCEACuX-CH CN or

[P]-N(CH3)2CuCl*CH3CN. Even though the IR does not dictate a

stronger interaction one might rationalize these results as

follows. If the Cu(CH3CN)xCl forms a charge transfer complex with

the aromatic rings of polystyrene which would donate electron

density to the metal center, then there could be i backbonding from

the metal d orbitals to the 7f orbitals of the nitrile. This would

lower the frequency of the CN stretch. In the presence of air, the

ability of [P]-CH2ClCuCl-CH3CN to bind CO is drastically reduced

and an ESR signal is observed.

In conclusion it has been demonstrated that three different

copper(I) halide complexes supported on polystyrene are reversible

CO carriers. In comparing [P]-DCEACuC1 and [P]-N(CH3)2CuC1 it

appears that the nitrile groups of DCEA play a major role in

stabilizing the complex. The fact that the polymer supported

copper(I) acetonitrile complex binds CO leads to a study of the

unusual properties of metal complexes in polymer matricies which

will be developed in Chapter IV. The developments described above

directly relate to the goals outlined in Chapter II, namely the

preparation and characterization of supported metal complexes that

reversibly bind 02. Although the reactivity of the supported

copper(I) halide complexes with 02 was not firmly established, the

reversible binding of CO by these complexes was a significant





77



discovery. Eventually, inclusion of such complexes in the membrane

gas separations discussed in Chapter IV may provide important

mechanistic details related to the facilitated transport of 02,

especially in light of the wider range of physical methods

available to study CO complexes.
















CHAPTER IV
METAL COMPLEX FACILITATED TRANSPORT OF
GASES IN POLYMER MEMBRANES



Introduction

Gaseous oxygen constitutes 20.946% of the earth's atmosphere

and is essential to nearly all living creatures. Additionally,

many industries rely on 02, especially those which involve

combustion processes such as in primary metals manufacture (ex.

steel) and chemical production (ex. ethylene oxide). Oxygen

production in 1986 is expected to exceed 380 billion cubic feet to

the tune of over two billion dollars.82 Likewise the demand for

nitrogen is high at nearly 660 billion cubic feet or 3.3 billion

dollars worth. Many industries do not require high purity oxygen

but can get by with oxygen enriched air. This market is

continually growing and already includes waste water treatment

facilities, the pulp and paper industry, fermentation processes,

fish farming and fire flooding of oil reservoirs as well as

numerous applications in the medical industry. The large scale

production of oxygen is achieved by a cryogenic air separation

process or increasingly more often by pressure swing adsorption

which essentially involves N2 adsorption from air by zeolites. An

alternative separation method which has received considerable

attention as of late involves selective gas permeation through a

polymer membrane.









The separation of gases by polymer membranes is based on the

principle that different gases permeate differently where

permeability refers to the overall mass transport of a gas through

a membrane, as opposed to diffusion which only relates movement of

the gas inside the membrane. This was first noted in 1831 by

Mitchell, the inventor of the toy rubber balloon, who observed that

his balloons would deflate at different rates depending upon the

gas inside.83 It was not until 1866 that an understanding of this

process was advanced by Thomas Graham, who is credited as being the

father of gas separations. Graham proposed a solution-diffusion

model to describe the selective permeation of gases in polymer

8o
membranes. He also showed by employing a rubber membrane that

one could exploit the relative differences in permeabilities

between gases and separate a gas mixture by applying a partial

pressure differential across the membrane. Specifically, Graham

was able to produce a gas mixture containing 41% oxygen from air.

In 1879 von Wroblewoski quanitified Graham's work by adapting

Fick's law of diffusion to the permeation process85 as shown below



J = D SAp/l



where J is the flux of air flow as a mass quantity per unit time, D

is the diffusion coefficient, S is the solubility, Ap is the

partial pressure differential and 1 is the membrane thickness.

What this implies is that the gas dissolved at the surface of a

rubbery polymer obeys Henry's law, C = Sp, and diffusion of the gas

obeys Fick's law where flux is proportional to the concentration









gradient or pressure differential. With the advent of World War I

came a resurgence in membrane research as it related to balloon and

airship fabrics. In 1918, Shakespear was able to show that the

permeability of a gas is independent of the presence of other

gases. He also developed the Kathrometer or thermal conductivity

detector (TCD) as part of a permeability tester.87 An enormous

amount of research was conducted up through the 1950's and 1960's

on the permeation properties of polymers which was prompted by the

use of plastics in the packaging industry. A considerable amount

of the engineering was developed during this period even though the

use of membranes in gas separations was commercially unfeasable at

the time.88 A more complete historical perspective as well as the

current status of membrane technology can be found in several

recent reviews.- In general, the simple solution-diffusion

model holds for nonswollen rubbery polymers. However, a vast

amount of literature is devoted to deviations from this model. It

will become evident in the following pages that simple changes in a

polymer membrane can result in large variations in the permeation

properties. The permeability of a gas is essentially a rate

measurement for movement of that gas through a polymer of thickness

1, with an applied pressure differential Ap. The permeability

coefficient P, is usually reported in units of

cm3(STP) cm/cm2sec cmHg or mmHg. The separation factor or the

ability of a polymer to separate two gases is given as a, where

a = P /P2 Since p = D*S, it is reasonable to assume those

molecules with a small molecular diameter (ex. He) would have high

permeabilities because of a high diffusion coefficient and those









molecules that are easily condensed (ex. CO2) would also have high

permeabilities because of a high sorption coefficient. Molecules

such as 02 and N2 which both have low diffusion and sorption

coefficients have low permeabilities and are particularly

difficult to separate. The ideal membrane material would exhibit

high selectivity and high flux as well as good mechanical

strength. Generally, the most selective membranes are the least

permeable and vice versa. Since nearly every polymer that can be

cast into a membrane has been evaluated for gas permeation

properties, the focus of many research efforts has been to enhance

the separability of polymer membranes. There has been an effort in

the area of module design in order to develop membrane systems

which provide high surface area and flux to polymers that are

selective but generally have low permeabilities. Another area

which is growing in interest involves the incorporation of

additives to modify the permeation properties. This approach has

been directed towards membranes that are highly permeable and

poorly selective.

There are essentially four types of membrane configurations,

namely the tube, flat, hollow fiber and liquid membranes. The tube

membrane finds little or no application in gas separations, but is

most often used in liquid filtration where there is a high

concentration of particulates.

The flat membrane can be packaged in a variety of ways. The

oldest and most commonly used module type in small scale gas

separations simply involves a flat plate or disc which may be

unsupported (i.e. the polymer itself), reinforced (i.e. the polymer









may contain a mesh screen for support), or a composite (i.e. either

one or both surfaces of the membrane may be attached to a support

material such as another polymer, paper or similar material).

These flat membranes can be secured in a gas separation cell

manifolded to a vacuum pump, then placed in a series of cascades or

stages to achieve a desired separation. Several oxygen enrichment

systems based on this type of membrane have been patented.9599

The application of such systems is for the small scale production

of oxygen enriched air. A major end use is in respiratory care. A

typical oxygen enrichment unit produces an air mixture containing

30-40% 02, depending upon the polymer employed, at a flow rate of

6 liters/minute.100 Because flat membranes of this type must be

relatively thick to be structurally stable to the applied partial

pressure differential, a low flow rate is obtained. In order to

obtain large flow rates a membrane must be extremely thin which is

incompatable with the need for thicker films to maintain structural

integrity. Much thinner flat films and subsequently higher flow

rates can be obtained with a spiral-wound element. This membrane

module consists of two retangular sheets of polymer membrane

(200-5000 A thick) separated by sheets of a porous supporting

material (100 p thick). This arrangement is a composite

membrane. The membranes are separated by a mesh channel spacer and

wrapped around a perforated hollow plastic tube. This high

pressure feed gas is directed through the end of this spiral and

the product gas permeates through the membranes and exits through

the hollow tube. Several oxygen enrichment plants based on this

technology have recently gone on line.101,102 Such plants have the









capacity to produce 200 ft3 per minute of air containing 29-30%

oxygen. Commercial units are now being offered that can supply as

much as 2000 ft3 per minute of oxygen enriched air. A single

8 inch spiral-wound element can produce nearly 177 liters per

minute of 02 enriched air compared with the thick flat membranes at

6 liters per minute.

Another type of membrane which has achieved commercial success

is the hollow fiber membrane. The hollow fibers are usually less

than 300 p in diameter which is finer than human hair. These

membranes are typically on the order of 1 p thick. The hollow

fibers suffer from the same problems as the ultra thin flat

membranes, a high flux but poor selectivity. This is because the

thin membranes are more likely to have micropores or pinholes.

This is a problem when one considers all a membrane needs is a

channel of 5-10 A in diameter to have most gas molecules of

interest flow through rather easily. This was resolved with the

development of composite hollow fiber membranes.103' 104 The

hollow fibers were lamenated with a thin layer (- 1 p) of a rubbery

polymer to plug the pinholes. Monsanto first commercialized these

membranes, known as PRISM separators, for the recovery of H2 and

CO2 in methanol synthesis.105 This technology was recently applied

to air separation by Dow Chemical.106 This hollow fiber membrane

system has the capacity to produce over 2000 ft3 per minute of 35%

oxygen enriched air. The advantage of hollow fibers over flat

spiral-wound membranes is that a higher separation surface area per

unit volume can be achieved. For example, for flat membranes the

area to volume ratio is typically on the order of a few









hundred ft-1 where as for the hollow fibers the ratio is several

thousand ft1.

Although the thin composite hollow fiber and flat membranes

can generate industrially acceptable fluxes the selectivities are

poor. The 02/N2 separation factor for polymers is generally less

than 3. A recent approach to enhancing the transport of a specific

gas through a membrane involves the encapsulation of a metal

complex containing solution into a porous polymer membrane. The

metal complex serves to facilitate the transport of a gas from one

boundary layer of the solution to the other. This type of membrane

is known as an immobilized liquid membrane, the primary advantage

of which is unsurpassed permselectivity.07-110 This system

differs from solvent extraction in that the facilitated transport

depends on the chemical reaction rate, diffusion rates in the

solution and the permeability in the polymer. Some of the early

efforts in this area employed simple metal salts of Cu+ and Ag+ to

separate aliphatic and unsaturated hydrocarbons.111-113 This was

extended to ion exchange membranes containing Ag+ which reacted

reversibly with ethylene under 90% humidity.114 Transition metal

complexes with organic ligands, especially multidentate ligands,

offer a wider variation of equalibrium and rate constants for

selectively binding a permeate gas. More than twenty years ago,

hemoglobin was observed to facilitate the transport of oxygen

across wet filter paper.1511 However, it was not until very

recently that this concept was applied to the separation of oxygen

from air. Bend Research, Inc. has obtained patent coverage on a

ligand membrane based oxygen enrichment process which involves a









metal chelate complex, solvent, axial base and membrane

support.117 The examples cited include; 1) Co(II) macrocyclic

amine complexes in DMSO with 1-methylimidazole as the axial base

and 2) Co(II) Schiff base complexes in DMSO and a-butyrolactone.

The best results were obtained with N,N'-bis(salcylideneimino)di-n-

propylamine cobalt(II) or CoS)PT in 1:1 DMSO and a-butyrolactone

encapsulated in 130 i thick microporous nylon 6,6 membrane. At

25 C, an air mixture containing 88% oxygen was produced in a

single pass through this membrane which corresponds to an 02/N2

selectivity of 30. This process is depicted below. Although the



High Pressure Side CoSDPT Low Pressure Side

160 mmHg 2 mmHg

02 r -02

N2-- CoSD PT-02

DMSO/a-butyrolactone



permselectivity of these membranes is quite remarkable there are

several features which may hinder its commercial development, such

as the need for a solvent and axial base. The mechanism of

facilitated transport in the liquid membrane involves diffusion of

the complexes, therefore, the solvent is a critical element to this

system. One positive aspect of the Bend patent claim is that it

was demonstrated that the incorporation of solutions containing

oxygen carriers in a polymer membrane enhances the permeation of

oxygen.









The results to be presented in this chapter represent a new

approach to enhancing the permeation properties of polymer

membranes and involves a novel method and mechanism of transport.

The goal of this work was to incorporate supported metal complexes

that reversibly bind dioxygen into solid nonporous polymer

membranes in order to enhance the selective permeation of 02 by a

mechanism unlike that in isotropic polymers or liquid membranes.

This could generally apply to any metal complex-polymer system in

which the complex has an affinity for a particular gas for which

there is a desired permselectivity. This was demonstrated by using

a flat polystyrene film containing a dispersion of supported Co(II)

Shiff base complex described in Chapter II.118 These metal complex

containing membranes show enhanced oxygen permeation relative to an

appropriate blank. This membrane system differs from the liquid

membrane in that the metal complexes are fixed and previously known

to bind 02 in the solid state. Only very recently has there been a

few reports of facilitated transport with oxygen carriers in

membranes. A cobalt porphyrin complex and 1-methylimidazole was

dispersed in a poly(butylmethylacrylate) film and found to separate

oxygen from nitrogen with a selectivity greater than ten.119

Similarly, CoSALEN and pyridine have been incorporated in a

polysulfone membrane to separate air.120 In both these cases the

metal complex is unsupported and can be viewed as being dissolved

in the polymer. Also, CoSALEN was dissolved in a

poly(octylmethylacrylate-Co-4-vinylpyridine) film and was observed

to facilitate the transport of 02.121 All of these results,

including the Bend patent, were reported subsequent to the start of









work reported here. Even though the various approaches taken to

enhance membrane separations with oxygen carriers are not strictly

analgous to the incorporation of the supported complexes described

herein, they do represent examples of facilitated transport which

serve to exemplify the importance of this work in the area of

membrane separation.

The concept of supported metal complex facilitated transport

of 02 polymer membranes depends upon the developments in Chapters

II and III. The ability of a supported metal complex to reversibly

bind 02 or CO in the solid state is an important consideration in

preparing the membranes for these experiments. The supported

CoSIPT complexes described in Chapter II were the complexes of

choice for demonstrating this novel method of membrane based gas

separation.

The results to be discussed include an evaluation of the

permeation experimental procedure, polystyrene as a membrane

material and metal complex containing membranes, including

permeation as well as structural properties. Additionally, a

transport mechanism will be discussed in light of these results.



Experimental

Permeation Apparatus

The design and construction of the permeation cell was

accomplished without knowledge of the prior art. During the course

of this research the apparatus underwent a series of revisions

which followed a progression of difficulties in the permeation

experiments. The evolution of the currently employed permeation




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