Cationic nitridoruthenium(VI) catalyzed hydrosilylation of ketones and aldehydes Thanh V. Truong, Erica A. Kastl, Guodong Du ⇑ Department of Chemistry, University of North Dakota, Grand Forks, ND 58202, United States article info Article history: Received 10 January 2011 Revised 26 January 2011 Accepted 27 January 2011 Available online 1 February 2011 Keywords: Hydrosilylation Ruthenium nitrido Catalysis Aldehydes and ketones abstract The first example of a ruthenium nitrido compound as hydrosilylation catalyst is described, using phen- ylsilane as reductant. A variety of ketones and aldehydes are reduced to alcohols with good to high iso- lated yields. Some mechanistic insight on this new system is provided on the basis of the available experimental findings. Ó 2011 Elsevier Ltd. All rights reserved. High oxidation state transition metal complexes are known for their activity in catalytic oxidation and oxygen atom transfer reac- tions. 1 Recently, a number of high valent rhenium and molybde- num complexes bearing terminal oxo- or imido-groups have been demonstrated to be efficient catalysts in a variety of reduc- tion reactions, 2,3 such as hydrosilylation of ketones and aldehydes, 4 reduction of imines 5 and amides, 6 and hydrogenation of alkynes. 7 Besides the synthetic utility of these reactions, they also pose some very interesting mechanistic questions as related to r-bond activation. 8,9 So far this new type of catalysts for reductions are derived exclusively from high valent rhenium and molybdenum with a d 0 or d 2 electronic configuration, specifically those of Re(V), Re(VII), Mo(VI) and Mo(IV) compounds. In an effort to expand the scope of catalysts and further our understanding on the novel mecha- nisms, we have become interested in investigating the use of other high valent metals in catalytic reductions. Herein we report the hydrosilylation of carbonyl compounds catalyzed by a cationic nitrido Ru(VI) complex, 1 (see Fig. 1). 10 To the best of our knowl- edge, this is the first example of hydrosilylation catalyst based on high valent Ru(VI) with a terminal nitrido group. The catalytic activity of RuN-salen compound 1 was examined using acetophenone as a representative substrate under different reaction conditions. Variations in solvents, silanes, and catalyst loading are summarized in Table 1. Among the solvents examined, non-polar toluene and benzene seem to be suitable for the reac- tion, although 1 is barely soluble in them. Since toluene has a high- er boiling point than benzene (110 °C vs 80 °C), we suspect that the reaction temperature plays a key role for the difference observed in toluene and benzene. In fact, it is found that benzene can be equally effective as solvent when the reaction is carried out in a sealed NMR tube where the reaction temperature can be higher 0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2011.01.139 ⇑ Corresponding author. Tel.: +1 701 777 2241; fax: +1 701 777 2331. E-mail address: gdu@chem.und.edu (G. Du). O N N O Ru N + O ClO 4 - H 3 C H Figure 1. Cationic nitrido-ruthenium(VI) salen. Table 1 Catalytic hydrosilylation of acetophenone a Entry Catalyst loading Silane Solvent Time (h) Conversion b (%) 1 5 mol % PhSiH 3 Benzene 48 90 2 5 mol % PhSiH 3 THF 48 67 3 5 mol % PhSiH 3 CH 2 Cl 2 48 68 4 5 mol % PhSiH 3 CH 3 CN 48 0 5 5 mol % Et 3 SiH Toluene 48 50 6 5 mol % Et 3 SiH Benzene 48 0 7 5 mol % PhSiH 3 Toluene 4 99 8 1 mol % PhSiH 3 Toluene 18 99 a Reaction conditions: 0.6 mmol acetophenone, 1.5 equiv of silanes, and RuN catalyst in refluxing solvents. b Determined by NMR. Tetrahedron Letters 52 (2011) 1670–1672 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet