Photochemical Reaction of [(CO)₄Co(SiEt₃)] with Ethylene: Implications for Cobaltcarbonyl‐Catalyzed Hydrosilation of Alkenes

Abstract

The insertion of a nonactivated alkene into the MSi bond of a catalytically active transition‐metal complex has been demonstrated for the first time. Furthermore, the formation of CH4 instead of SiMe4 in the reaction of [(CO)4CoMe] with Me3SiH is clearly inconsistent with the traditional Chalk–Harrod mechanism for the transition‐metal‐catalyzed hydrosilation of olefins. Both reactions are key steps in a new proposal for the mechanism of this reaction.

Silicometallics and catalysis

“…The first convincing results for mechanistic pathways involving this step were presented by Seitz and Wrighton (Scheme 2) and obtained in a photochemical study of the reaction with the Me 3 SiCo(CO) 4 complex. 15 The insertion of ethylene into the Co-SiMe 3 bond was confirmed spectroscopically. Duckett and Perutz used the same system but with CpRh(C 2 H 4 )(SiEt 3 )H as a precursor, finally proposing an alternative mechanism based on a 'two-silicon cycle' as illustrated in Scheme 3.…”

“…12,15,16 The reaction occurs via potential formation of a complex containing s-alkyl and s-silylalkyl ligands. The b-H transfer from the two ligands to the metal proceeding concurrently is a decisive step for two alternative reactions, i.e.…”

“…76 Examples of reactions catalyzed predominantly by palladium and platinum (some by nickel) complexes illustrate the reactivity of the Si-Si bond in intermolecular (Eqns [11]- [13] and intramolecular 79 (Eqns [14], [15]) bis-silylation reactions. …”

Iron‐Catalysed Hydrofunctionalisation of Alkenes and Alkynes

“…Iron-hydride complex 146 was also obtained, presumably formed following b-hydride elimination from iron-alkylsilane complex 147 to give a vinylsilane byproduct. Upon irradiation of iron-alkylsilane complex 145, in Modified Chalk-Harrod mechanisms have also been suggested in some cases for cobalt-, [83] rhodium- [84] and iridium-catalysed [85] hydrosilylation reactions. The thermal and photochemical activation of iron pentacarbonyl also results in the formation of higher iron carbonyl cluster analogues, such as [Fe 2 (CO) 9 ] and [Fe 3 (CO) 12 ].…”

Regioselectivity in the rhodium catalysed 1,4-hydrosilylation of isoprene. Aspects on reaction conditions and ligands

“…A typical example is the hydrosilylation of isoprene resulting in two regioisomers, tail-product (I) and headproduct (II), via Z-specific 1,4-addition (Scheme 1). Depending on the actual catalyst, several different mechanisms for the rhodium-catalysed hydrosilylation of alkenes and dienes have been proposed [8][9][10][11][12][13][14]. The two most common ones for 1,3-dienes (Scheme 1) [12][13][14], are based on the original proposal by Chalk and Harrod for the hydrosilylation of alkenes [15].…”