Reductive Oligomerization of Carbon Monoxide by Rhodium-Catalyzed Reaction with Hydrosilanes

Abstract

The production of specific organic compounds via the hydrogenation of carbon monoxide represents an important pathway to row chemical material production and promises to be critically important in the coming decades, given the world situation relative to crude oil. 1,2 Extensive efforts have been made toward this goal, but the number of processes available remain limited and the mechanisms for these reactions remain unclear. 3,4 Many of the mechanisms proposed thus far are based on studies of stoichiometric reactions involving discrete isolable complexes, 4 such as acyl complexes, 5 R-oxyalkyl complexes, 6 and related materials. 7,8 Although stoichiometric approaches give useful and important information, they often deviate from actual catalytic processes. We have designed a novel catalytic reaction of CO using hydrosilanes in place of H 2 . The advantage of using hydrosilanes is that otherwise unstable intermediates, such as enols, can survive as a silyl derivative without isomerization to the stable keto isomer (e.g., tautomerization) at the experimental conditions used. Hydrosilanes have been used as a promoter for reductive coupling of CO to ethylene glycol from H 2 /CO 9 and used for a stoichiometirc model for the hydrogenation of CO. 5,8 To our knowledge, there has been only one report 10 on a transition-metal-catalyzed reaction of CO with a hydrosilane. We now report a novel Rh-catalyzed reductive oligomerization of CO with a hydrosilane. The reaction is intrinsically interesting and useful as a synthetic method. Moreover, the reaction provides an entirely novel model that may be useful for a better understanding of the mechanism of such catalytic reductions.A variety of transition-metal carbonyl complexes such as Mo-(CO) 6 , W(CO) 6 , PdCl 2 , Ru 3 (CO) 12 , RuCl 2 (PPh 3 ) 3 , Co 2 (CO) 8 , Rh 6 (CO) 16 , [RhCl(CO) 2 ] 2 , RhCl(PPh 3 ) 3 , and Ir 4 (CO) 12 have been examined for their catalytic activity with respect to reactions of CO with HSiEt 2 Me under a variety of reaction conditions (2.5 mol % of catalyst to HSiEt 2 Me, 100-180°C, CO 10-50 atm), but CO-incorporated products were not detected in GC. In most cases, the sole product obtained was MeEt 2 SiOSiEt 2 -Me. As a result of extensive examination of catalysts and additives, we have ultimately discovered that a reaction of CO with hydrosilanes can be achieved by using a Rh/amine catalytic system to give CO-incorporated products. Thus, the reaction of CO (50 atm) with HSiEt 2 Me (2.5 mmol) at 140°C in the presence of [RhCl 2 (CO) 2 ] 2 (0.05 mmol)/Et 3 N (7.5 mmol) in C 6 H 6 (5 mL) for 1 day in a 50-mL stainless steel autoclave gave MeEt 2 SiOSiEt 2 Me 11 as the main product (31% yield), along with reductive coupling of CO which gave diethylmethylsiloxymethane (1a, 2%), 1,2-bis(diethylmethylsiloxy)ethene 12 (2a, 18%, Z/E ) 93/7), and 1,2,3-tris(diethylmethylsiloxy)propene (3a, 5%, Z/E ) 10/1). In addition, products that corresponded to four and five molecules of CO were also observed by GCMS (eq 1). Yields are based on the HSiEt 2 Me charged. In...

Double carbonylation and beyond: systems at work and their organometallic models

“…It was then suggested that this new type of coupling could occur via a siloxycarbyne intermediate. 59 Indeed, the occurrence of this intermediate and further carbon-carbon coupling has been nicely documented by Lippard and coworkers, on niobium and tantalum complexes. 115 As all the compounds of Scheme 34 were reasonably well characterized, step c of the reaction clearly demonstrates a carbon-carbon coupling between a siloxy carbyne ligand and a terminal carbonyl.…”

Crossover Studies of Methyl Migration from Oxygen to Iron in the Iron−Manganese Methoxycarbyne Complex Cp(CO)Fe(μ-COCH3)(μ-CO)Mn(CO)MeCp

“…Several examples have been proposed in which a silicon group migrates from iron to an acyl oxygen to give a carbene, 43,44 while in two catalytic CO reductions by hydrosilanes, a step was proposed that is the reverse of our methyl migration, in which a silyl moiety migrates from metal to the oxygen of a bound carbonyl to give a terminal siloxycarbyne. 45,46 Decomposition of some silyl-substituted Fischer-type carbenes has been proposed to proceed by migration first of the silicon to the metal to give a terminal alkoxycarbyne, followed by migration of the alkyl group to the metal. 47,48 One conclusion from the above is that dinuclear systems with sufficient stability to exist both as the isomeric carbyne and methyl carbonyl compounds 32,41 may not exhibit interconversion of these species.…”

Transformation of Manganese Acyls (CO)5MnC(O)CH2R (R = H, CH3, OCH3) into Their Siloxyvinyl Derivatives (CO)5MnC(OSiEt3)CHR with Triethylsilane. An Approach to Double Carbonylation of Manganese Alkyl Complexes (CO)5MnCH2R

“…In a recent communication, Murai and co-workers documented the reductive oligomerization of carbon monoxide involving Rh(I)-catalyzed reactions with hydrosilanes. The presence of the C2 and C3 kinetic products, ( Z )-1,2-bis(siloxy)ethenes and ( Z )-1,2,3-tris(siloxy)propenes, was accounted for by the intermediacy of a hypothesized Rh(I) ( E )-1,2-bis(siloxy)vinyl intermediate, Scheme .…”