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Date of Award

8-1974

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Supervisor

P.M. Maitlis

Abstract

The catalytic activity of a series of pentamethylcyclopentadienyl-rhodium and -iridium complexes was explored to determine which catalytic species were significant. The halide complexes [M(C₅Me₅)x₂]₂ ((=Cl, Br, I) were inactive and required the presence of base as co-catalyst for the homogeneous hydrogenation of olefins.

As a part of this investigation, a number of new mono-ρ-hydrido [(M(C₅Me₅))₂HX₃], di-ρ-hydrido [Ir(C₅Me₅)HX]₂, and related complexes were isolated and successfully synthesised and characterised.

The hydrido complexes [(M(C₅Me₅))₂HX₃] and [lr(C₅Me₅)HX]₂ catalysed the hydrogenation of olefins in the absence of base at 1 atm and ambient temperature. However, they did show some co-catalysis by base and the effect of base on catalytic activity of [M(C₅Me₅)Cl₂]₂, [(M(C₅Me₅))₂HCl₃] and [Ir(C₅Me₅)HCl]₂ was carefully examined. The iridium complexes showed some deactivation on addition of excess triethylamine due to the formation of the caralytically inactive cationic complex [(Ir(C₅Me₅))₂H₃]. No such deactivation and formation of cationic complex was observed for the rhodium system.

In general iridium complexes were better catalysts than rhodium ones. The hydrogenation appeared to be favoured by polar and weakly coordinating solvents, particularly isopropanol.

A premliminary study of the mechanism of the reactions catalysed by these complexes indicated that the mono-μ-hyrdrio complexes reacted mainly as dimers and dichlorides and di-μ-hydrido complex [Ir(C₅Me₅)HCl]₂ reacted predominantly as monomer; mechanisms are presented to account for these observations.

The hydrido complexes [(M(C₅Me₅))₂(D)HCl₃] and [Ir(C₅Me₅)HCl]₂ were also active catalysts for the isomerisation of olefins. During the isomerisation of 4-methylcyclohexene by [(Ir(C₅Me₅))₂DCl₃], appearance of a high field hydride resonance was observed and these reactions are explained in terms of a hydride addition-elimination mechanism.

ecies "cre stgnific.ant. The hal ide c~~lexes pl(CSMeS)xzlz ( =. Cl, B "
,I) ~e.re ina~tiv,e'and ,required the presence, of base as co~cata1.yst forth'
hC!':JQeneous 'hydroQen~ -.' .,
'I ,~a' part of thls investi~ation.a numb!J-r 0t, ne\~ oono-~-hydrido_
[(M(~SI~e5) i ZHX 3]. d;"-;,-hydr,ido [I~(C5Me5)HX]Z" and'Tflated complexes \~ere"
isola~e:1 and s,uccessfull y syntheslsed ~ni1 .c~aracteris:d. . .'
.Thehydrido comple~es ['M!Cs~es~)zHX3] and [l~(c5r~e's)HX}L c<1talysed
the hydrogenation of olefins in t~e absence of base at 1 atm and a~bient_
"temperature. However. they did show some co-catalysis by bas~ and ~he
effect Of, !and:[lr(C5~leS)HC.1]2wascarefully, exar.1ined. The iridium compl,,1.'!?s sho','led
'. some deactivation. on addit~on of ~xC:~ss trtethYl,ar.line due to t~o~!"'.ation
of thecatalytlC-:lly InactIve catlon'\ccomple~ [(!r(CS~1e5)12Hp'\""'iu-- .
such deactivation,and formation of cationic complex was observed for the
I'hod i urn .sys tem. "
In general iridium compleJones. The hydrogenation appea'red to be favoured 'by polar 'and weakly co-
I ,ordinating sOflvents. partic:ul.arl y isopropanol: ' I.
l,.- A prel.,jminary stud/of the ;,echaniS!:1of the reactlons catalysed
l' ,
'} by these ccmplexes indicated that the mono-~-hydrido complexes reacted mainly as ,dimers and dichlorides ~nd di-u-,hydridocomplex [Ir(CSf.leS)HC1]Z
. \ ' 'reacted predominantly 4S monomer; mec~anisms are. pres~nted to dCco~nt for
these observations, !. (0)
.'- The hydrido complexes [(H(CSMeS)i Z
HC1
3
] and [lr(.CSMeS)HC1]Z 4'e
.also active catafysts for the isomerisation of olefins, .During the isom- . . ~
eri sa ti on of 4-methylcyc Iohexene by ['(l r( CSfi,eS)) ZOeI
3
], a ppeari\nce of a
hi gh fi el d hydride resonance was observed and thes,e re&c t ions are ~xp I ai ned
in" terms of a hydride addition~eliminationinechanism.

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