Catalytic Hydrodechlorination of Benzyl Chloride promoted by Rh-NHC Catalysts

The rhodium(I) complexes [Rh(Cl)(COD)(R-NHC(CH2)3Si(OiPr)3)] (COD = cyclooctadiene; R = 2,6-diisopropylphenyl (1a); n-butyl (1b)) are effective catalyst precursors for the homogeneous hydrodechlorination of benzyl chloride using HSiEt3 as hydrogen source. This reaction is selective to the formation of toluene. However, in presence of a stoichiometric amount of KtBuO the formation of mixtures containing toluene together with 17-19 mol% of the C-C homocoupling product, namely PhCH2CH2Ph, was observed. A mechanism proposal based on experimental insights and theoretical calculations at the DFT level which allows explanation of the experimental findings is included. Moreover, the heterogeneous catalytic system based on the supported catalyst 1aMCM-41 has demonstrated to be effective for the solvent-free hydrodechlorination of benzyl chloride with HSiEt3 and HSiMe(OSiMe3)2.