Fluorous Chemistry pp 247-273

Part of the Topics in Current Chemistry book series (TOPCURRCHEM, volume 308)

Fluorous Hydrosilylation

Chapter

Abstract

Graphical Abstract

In this review, we describe the papers and patents dealing with the fluorous biphasic system (FBS) hydrosilylation reactions reported to date. Despite the limited number of reports, the FBS hydrosilylation reaction has been extremely successful. In all cases fluorous monophosphines (either alkylic or perfluoroalkylsilyl-substituted derivatives of triphenylphosphine) have been employed as ligands to synthesize and inmobilize the metal catalysts (either rhodium(I) or gold(I) derivatives) in the fluorous solvent (including a fluorous ionic liquid). The hydrosilylation of alkenes, ketones and enones with fluorous rhodium analogs to the Wilkinson’s catalyst [RhCl(PPh3)3], have afforded high TON/TOF and a very efficient separation and recycling of the fluorous catalyst. Modification of the fluorous content and position of the fluorous tails in the aryl groups of the phosphines have allowed for further optimization of the process and a better recovery of the catalyst with minimal leaching of rhodium and fluorous ligand to the organic phase. Moreover, the use of the so-called second generation methods which eliminate the need of fluorous solvents by exploiting the temperature-dependent solubilities of fluorous catalysts in common organic solvents (thermomorphic properties) have permitted the use and separation of fluorous alkyl-phosphine rhodium catalysts in hydrosilylation reactions in conventional organic solvents. The addition of an insoluble fluorous support such as Teflon tape allowed for an exceptionally easy and efficient recovery of fluorous rhodium catalysts (“catalyst-on-a-tape”) in the hydrosilylation of ketones. In the case of the FBS gold-catalyzed hydrosilylation of aldehydes, new fluorous gold catalysts with alkylic phosphines have led to an efficient separation and recycling of the gold catalysts although the TON/TOF are lower than in the rhodium-catalyzed hydrosilylation of alkenes and ketones. A detailed study of the non-fluorous gold-catalyzed version has helped to explain how this catalytic system could be improved.

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Keywords

Fluorous phosphines Gold Hydrosilylation Recycling Rhodium 

Abbreviations

FBC

Fluorous biphasic catalysis

FBS

Fluorous biphasic system

DMF

Dimethylformamide

FC-72

Mixture of perfluorohexanes

GC

Gas chromatography

IR

Infra red

MALDI-TOF

MALDI: Matrix-assisted laser desorption/ionization; TOF: time-of-flight mass spectrometer

NMR

Nuclear magnetic resonance

PFMCH

Perfluoromethylcyclohexane

RT

Room temperature

TEM

Transmission electron microscopy

THF

Tetrahydrofuran

tht

Tetrahydrothiophene

TOF

Turnover frequency; turnover number per unit time

TON

Turnover number; number of moles of substrate that a mole of catalyst can convert before becoming inactivated

Tos

Tosyl

TXRF

Total reflection X-ray fluorescence

xantphos

4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene

Copyright information

© Springer-Verlag Berlin Heidelberg 2011

Authors and Affiliations

  1. 1.Department of Chemistry, Brooklyn College and The Graduate CenterThe City University of New YorkBrooklynUSA

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