Mechanism of Olefin Hydrosilylation Catalyzed by RuCl₂(CO)₂(PPh₃)₂: A DFT Study

Abstract

Density functional theory (DFT) was used to explore the different mechanistic possibilities for the hydrosilylation reaction between methyldimethoxysilane and methylvinyldimethoxysilane catalyzed by the Ru(II) complex dicarbonyldichlorobis(triphenylphosphine)ruthenium(II) (A1). Reaction enthalpy profiles of the Chalk-Harrod, modified Chalk-Harrod, and σ-bond metathesis mechanisms were computed for several different active forms of A1. A total of 10 different pathways with different catalytic cycles and different induction steps were compared. We predict that a σ-bond metathesis mechanism involving the formation of a hydride analogue of A1 is most favored, in contrast to the commonly accepted Chalk-Harrod mechanism of hydrosilylation. The B3LYP-calculated activation energy within the catalytic cycle (∆H act ) 21.8 kcal/mol) is small enough to make A1 a reasonable catalyst for this reaction under the normally applied experimental conditions.

Computational insights into the mechanism of iron carbonyl-catalyzed ethylene hydrosilylation or dehydrogenative silylation

“…Sakaki et al, elucidated the RhCl(PH 3 ) 3 -catalyzed hydrosilylation obey the modified Chalk-Harrod mechanism [30]. Alternatively, the r-bond metathesis mechanism [31], in which a initial formed MAC bond is cleaved by a SiAH bond of uncoordinated silane via the four-membered transition state to afford MAH and CASi bonds simultaneously, has been considered for the Ru-catalyzed hydrosilylation of alkenes [32,33] and the ethylene hydrosilylation catalyzed by ZrCp 2 [34] and bis-N-heterocyclic carbene rhodium complex [35]. In addition, Beddie and Hall [36] provided the first theoretical evidence for the Glaser-Tilley mechanism [7] involving the direct insertion of alkene into the SiAH bond of ruthenium silylene complex without direct interaction between the alkene and metal center.…”

Mechanism of olefin hydrosilylation catalyzed by [RuCl(NCCH3)5]+: A DFT study

“…In our previous study [19], this reaction was found to have a prohibitively high barrier (DH act = 53.6 kcal/mol) and a catalyst is therefore needed to lower the activation enthalpy for the hydrosilylation to occur under normal operating conditions.…”

“…More recently, it has also been shown to be active in a number of late transition metal catalysts as well [19,[41][42][43][44][45][46][47][48][49][50][51]. Finally, in 2003, Glaser and Tilley proposed another mechanism for a cationic silylene Ru(II) catalyst in the hydrosilylation of alkenes [11], and subsequent computational studies supported this proposal [10].…”

“…those based on ruthenium [10][11][12][13][14][15][16][17][18][19]. However, such catalysts generally suffer from a loss of activity and/or selectivity relative to platinum catalysts, and they may induce side reactions of the substrates including olefin isomerization, dehydrogenative silylation and hydrogenation.…”

Theoretical study on ligand exchange reaction mechanisms of iron(IV) complexes with two different group 14 element ligands, Cp(CO)FeH(EEt3)(E′Et3) with (HEEt3) (E, E′ = Si, Ge, Sn)

“…It should be noted here that the entropic contribution to the free energies based on the gasphase calculations is overestimated for those steps involving substrate association or dissociation. Recent discussions on the overestimation can be found in the literature [48,49]. …”