REGULAR ARTICLE Mechanism of ketone hydrosilylation using NHC–Cu(I) catalysts: a computational study Thomas Vergote • Thomas Gathy • Fady Nahra • Olivier Riant • Daniel Peeters • Tom Leyssens Received: 29 March 2012 / Accepted: 23 June 2012 / Published online: 13 July 2012 Ó Springer-Verlag 2012 Abstract The plausibility of the catalytic cycle suggested for the hydrosilylation of ketones by (NHC) cop- per(I) hydrides has been investigated by a theoretical DFT study. Model systems yield the necessary insight into the intrinsic reactivity of the system. Computations show the activation of the copper fluoride pre-catalyst, as well as both steps of the catalytic cycle to involve a 4-center metathesis transition state as suggested in the literature. These results show the reaction to be favored by the for- mation of van der Waals complexes resembling the tran- sition states. Stabilizing electrostatic interactions between those atoms involved in the bond-breaking and bond- forming processes induces the formation of these latter. Both steps of the actual catalytic cycle show a free energy barrier of about 14.5 kcal/mol for the largest NHC ligands, with respect to the isolated reactants, hereby confirming the plausibility of the suggested cycle. The large overall exo- thermicity of the catalytic cycle of about 35 kcal/mol is in agreement with experimental observations. Keywords N-heterocyclic diaminocarbene Á Copper(I) Á DFT Á Hydrosilylation Á Reactivity Á Catalysis 1 Introduction Carbonyl bond reduction, specifically of aldehydes and ketones, to the corresponding alcohol functionality via hydride transfer is a fundamental transformation in organic synthesis [1–5]. Transition metal catalysis has been suc- cessfully applied in the reduction of many carbonyl com- pounds via hydrogenation or hydrosilylation [1–5]. Hydrogenation reactions often proceed in good yields but require high pressure or elevated temperature. Moreover, if the reaction is part of a multistep synthesis, the resulting free alcohol often requires protection prior to the next synthetic step. In contrast, the softer reactions conditions of hydrosilylation turned out to be a major advantage, in addition to the fact that both the reduction and the pro- tection steps are performed in a single, atom-efficient step. The first catalytic hydrosilylation systems, based on rhodium, were developed in the early 1970s [6–8]. Tradi- tionally, catalytic hydrosilylation of the carbonyl func- tionality was performed with precious, heavy metals ranging from Re, Rh, and Ru to Ir [9–18]. As the main drawback of these systems is the cost affiliated with these metals, during the two last decades efforts were taken in finding an efficient alternative system using less-expensive metals such as titanium [19–26], iron [27–29], manganese [30, 31], or zinc [32–35]. In 1984, Brunner and Miehling reported the first asymmetric hydrosilylation using a cop- per-diphosphine catalyst [36]. Since many copper-diphos- phine catalytic systems were developed [37–43], the active species formed in situ was postulated to be a copper (I) hydride. Lipshutz and co-worker describe the formation of the CuH species in a system combining a catalytic quantity of CuCl/NaOt–Bu/diphosphine and a stoichiome- tric quantity ofhydrosilylating agent [44–48]. At the same time, Carreira et al. [49], as well as Riant et al. [41, 50–52], Published as part of the special collection of articles celebrating theoretical and computational chemistry in Belgium. Electronic supplementary material The online version of this article (doi:10.1007/s00214-012-1253-4) contains supplementary material, which is available to authorized users. T. Vergote Á T. Gathy Á F. Nahra Á O. Riant Á D. Peeters Á T. Leyssens (&) Institute of Condensed Matter and Nanosciences, Universite ´ Catholique de Louvain, Place Louis Pasteur 1, 1348 Louvain-la-Neuve, Belgium e-mail: tom.leyssens@uclouvain.be 123 Theor Chem Acc (2012) 131:1253 DOI 10.1007/s00214-012-1253-4