Catalytic Hydrodechlorination of Benzyl Chloride Promoted by Rh-N-heterocyclic Carbene Catalysts

The rhodium(I) complexes [Rh(Cl)(COD)(R-NHC-(CH2)(3)Si(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 potassium tert-butoxide (KtBuO) the formation of mixtures containing toluene together with 17-19mol% of the CC homocoupling product, namely PhCH2CH2Ph, is observed. A mechanism proposal based on experimental insights and theoretical calculations at the DFT level that allows explanation of the experimental findings is included. Moreover, the heterogeneous catalytic system based on catalyst 1a supported on MCM-41 has been demonstrated to be effective for the solvent-free hydrodechlorination of benzyl chloride using HSiEt3 and HSiMe(OSiMe3)(2).