A synthetic, electrochemical and kinetic study of polysiloxane-bound rhodium carbonyl complexes
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Date
2012
Authors
Sebitlo, Rahab Mametsi
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
English: Two ferrocene-containing β-diketonato ligands, FcCOCH2COR, as well as their dicarbonyl
rhodium(I) complexes, [Rh(FcCOCHCOR)(CO)2], were synthesized. Chloro/bromo functionalized
polysiloxanes of the type [(OSiMe2)2OSiMe{(CH2)mX}]n with X = Cl and Br as well as iodo
functionalized polysiloxanes, [(OSiMe2)2OSiMe{(CH2)mI}]n, were synthesized. The latter were
converted to phosphine-containing polysiloxanes, [(OSiMe2)2OSiMe{(CH2)mPPh2}]n and used as a
starting material to synthesize six new rhodium(I)-containing polysiloxane complexes of the type
[(OSiMe2)2OSiMe{(CH2)mPPh2(CO)(FcCOCHCOR)Rh}]n, with Fc = ferrocenyl, R = CH3 and CF3,
m = 3, 4, 5. Characterization techiniques included 1H and 31P NMR, electrochemistry, UV/vis and
FTIR. 1H and 31P NMR data showed the existence of two isomers for each of the rhodium(I)
polysiloxane complexes in solution. Elemental analysis confirmed the elemental composition of the
polymers and from the XPS, the binding energies of elements were determined. The inherent
viscosity for all polymers was found to be in the range of 0.011-0.28 g/dL.
The new rhodium(I) polysiloxane complexes as well as the free rhodium(I) compexes were studied
by cyclic voltammetry in CH2Cl2/[NnBu4][B(C6F5)4]. Two isomers were identified for the
rhodium(I) polysiloxane complexes. In a one broad oxidation peak, Rh(1) and Rh(2) was
electrochemically irreversibly oxidized first in a one-electron transfer followed by one-electron
electrochemical reversible oxidations of the two ferrocenyl groups, Fc(1) and Fc(2).
A pseudo-first order kinetic study of methyl iodide oxidative addition to rhodium polymer
[(OSiMe2)2OSiMe{(CH2)3PPh2(CO)(FcCOCHCOCF3)Rh}]n was monitored by FTIR and UV/vis
techiques. A two stage mechanism was identified wherein kinetically favoured Rh(III)alkyl1 and
Rh(III)acyl1 formed first at the same reaction rate in stage 1. The kinetically favoured products
converted in stage 2 to the thermodynamically favoured Rh(III)alkyl2 and Rh(III)acyl2 species.
Stage 1 was dependent on the CH3I concentration and stage 2 was independent thereof. The FTIR
results also showed possible existence of a rhodium(I) polysiloxane square pyramidal complex. The
UV/vis-determined second-order rate constant for the first stage (k1 = 0.1853 M-1.min-1) at 25 °C
was found to be in agreement with the FTIR-determined rate constant (k1 = 0.1499 M-1.min-1). The
influence of temperature on the reaction was studied at 15, 35 and 45 °C and the activation entropy
for stage 1 was found to be -97(6) J.mol-1.K-1 while for stage 2 it was 6(3) J.mol-1.K-1. Stage 1
reacted in an associative mechanism, while stage 2 involved geometrical isomerizations.
Keywords: Rhodium(I), polysiloxane, silane, phosphine, polymerization, ferrocene, β-diketone,
oxidative addition.
Afrikaans: Twee ferroseen-bevattende β-diketonato ligande, FcCOCH2COR, tesame met hul dikarbonielrodium(I) komplekse [Rh(FcCOCHCOR)(CO)2], is gesintetiseer. Chloro/bromo gefunksionaliseerde polisiloksane van die tipe [(OSiMe2)2OSiMe{(CH2)mX}]n waar X = Cl en Br, asook jodo gefunksionaliseerde polisiloksane, [(OSiMe2)2OSiMe{(CH2)mI}]n, is gesintetiseer. Laasgenoemde is omgeskakel na fosfor-bevattende polisiloksane, [(OSiMe2)2OSiMe{(CH2)mPPh2}]n en is verder gebruik om ses nuwe rodium(I) bevattende polisiloksaankomplekse van die tipe, [(OSiMe2)2OSiMe{(CH2)mPPh2(CO)(FcCOCHCOR)Rh}]n, te sintetiseer, waar Fc = ferroseniel, R = CH3 en CF3, m = 3, 4, 5. Karateriseringstegnieke het 1H en 31P KMR, elektrochemie, UV/vis en FTIR ingesluit. 1H and 31P KMR data het die bestaan van twee isomere vir elk van die rodium(I)polisiloksaankomplekse in oplossing aangedui. Elementanalise het die elementsamestelling van die polimere bevestig en vanaf XPS data is die bindingsenergie van die elemente verkry. Die inherente viskositeit van al die polimere is bepaal en val in die gebied van 0.02-0.28g/dL. Die nuwe rodium(I)polisiloksaankomplekse asook die vry rodium(I)komplekse is met sikliese voltammetrie in CH2Cl2/[NnBu4][B(C6F5)4] bestudeer. Twee isomere kon geïdentifiseer word vir die rodium(I)polisiloksaankomplekse. Een breë oksidasiepiek bevat die elektrochemies omkeerbare oksidasie van Rh(1) en Rh(2) as ’n enkelelektron-oordragproses, gevolg deur die enkelelektron, elektrochemiese-omkeerbare oksidasies van die twee ferroseniel groepe Fc(1) en Fc(2). ’n Pseudo-eerste orde kinetiese studie van die oksidatiewe addisie van metieljodied aan die rodiumpolimeer, [(OSiMe2)2OSiMe{(CH2)3PPh2(CO)(FcCOCHCOCF3)Rh}]n, is volg met FTIR en UV/vis tegnieke. ’n Tweefase meganisme is geïdentifiseer waartydens die kineties verkose Rh(III) alkiel 1 en Rh(III) asiel 1 teen dieselfde reaksietempo in fase 1 gevorm het. Die kineties verkose produkte is in fase 2 omgeskakel na die termodinamies verkose produkte R(III) alkiel 2 en Rh(III) asiel 2. Fase 1 is afhanklik van die CH3I konsentrasie, terwyl fase 2 onafhanklik is daarvan. Die FTIR resultate het getoon dat daar ook moontlik ‘n vierkantig piramidale rodium(I)polisiloksaankomplek bestaan. Die UV/Vis bepaalde tweede-orde tempokonstante vir die eerste fase (k1 = 0.1853M-1.min-1) by 25 °C stem ooreen met die FTIR bepaalde tempokonstante (k1 = 0.1499 M-1.min-1). Die invloed van temperatuur op die reaksie is bestudeer by 15, 35, en 45 °C en die aktiveringsenergie vir fase 1 is -97(6) J.mol-1.K-1, terwyl dit 6(3) J.mol-1.K-1 vir fase 2 is. Fase 1 het met ’n assosatiewe meganisme gereageer, terwyl fase 2 slegs betrokke was by geometriese isomerisasie.
Afrikaans: Twee ferroseen-bevattende β-diketonato ligande, FcCOCH2COR, tesame met hul dikarbonielrodium(I) komplekse [Rh(FcCOCHCOR)(CO)2], is gesintetiseer. Chloro/bromo gefunksionaliseerde polisiloksane van die tipe [(OSiMe2)2OSiMe{(CH2)mX}]n waar X = Cl en Br, asook jodo gefunksionaliseerde polisiloksane, [(OSiMe2)2OSiMe{(CH2)mI}]n, is gesintetiseer. Laasgenoemde is omgeskakel na fosfor-bevattende polisiloksane, [(OSiMe2)2OSiMe{(CH2)mPPh2}]n en is verder gebruik om ses nuwe rodium(I) bevattende polisiloksaankomplekse van die tipe, [(OSiMe2)2OSiMe{(CH2)mPPh2(CO)(FcCOCHCOR)Rh}]n, te sintetiseer, waar Fc = ferroseniel, R = CH3 en CF3, m = 3, 4, 5. Karateriseringstegnieke het 1H en 31P KMR, elektrochemie, UV/vis en FTIR ingesluit. 1H and 31P KMR data het die bestaan van twee isomere vir elk van die rodium(I)polisiloksaankomplekse in oplossing aangedui. Elementanalise het die elementsamestelling van die polimere bevestig en vanaf XPS data is die bindingsenergie van die elemente verkry. Die inherente viskositeit van al die polimere is bepaal en val in die gebied van 0.02-0.28g/dL. Die nuwe rodium(I)polisiloksaankomplekse asook die vry rodium(I)komplekse is met sikliese voltammetrie in CH2Cl2/[NnBu4][B(C6F5)4] bestudeer. Twee isomere kon geïdentifiseer word vir die rodium(I)polisiloksaankomplekse. Een breë oksidasiepiek bevat die elektrochemies omkeerbare oksidasie van Rh(1) en Rh(2) as ’n enkelelektron-oordragproses, gevolg deur die enkelelektron, elektrochemiese-omkeerbare oksidasies van die twee ferroseniel groepe Fc(1) en Fc(2). ’n Pseudo-eerste orde kinetiese studie van die oksidatiewe addisie van metieljodied aan die rodiumpolimeer, [(OSiMe2)2OSiMe{(CH2)3PPh2(CO)(FcCOCHCOCF3)Rh}]n, is volg met FTIR en UV/vis tegnieke. ’n Tweefase meganisme is geïdentifiseer waartydens die kineties verkose Rh(III) alkiel 1 en Rh(III) asiel 1 teen dieselfde reaksietempo in fase 1 gevorm het. Die kineties verkose produkte is in fase 2 omgeskakel na die termodinamies verkose produkte R(III) alkiel 2 en Rh(III) asiel 2. Fase 1 is afhanklik van die CH3I konsentrasie, terwyl fase 2 onafhanklik is daarvan. Die FTIR resultate het getoon dat daar ook moontlik ‘n vierkantig piramidale rodium(I)polisiloksaankomplek bestaan. Die UV/Vis bepaalde tweede-orde tempokonstante vir die eerste fase (k1 = 0.1853M-1.min-1) by 25 °C stem ooreen met die FTIR bepaalde tempokonstante (k1 = 0.1499 M-1.min-1). Die invloed van temperatuur op die reaksie is bestudeer by 15, 35, en 45 °C en die aktiveringsenergie vir fase 1 is -97(6) J.mol-1.K-1, terwyl dit 6(3) J.mol-1.K-1 vir fase 2 is. Fase 1 het met ’n assosatiewe meganisme gereageer, terwyl fase 2 slegs betrokke was by geometriese isomerisasie.
Description
Keywords
Rhodium(I), Polysiloxane, Silane, Phosphine, Polymerization, Ferrocene, β-diketone, Oxidative addition, Ligands, Electrochemistry, Chemical kinetics, Rhodium compounds -- Synthesis, Carbonyl compounds -- Synthesis, Dissertation (M.Sc. (Chemistry))--University of the Free State, 2012