Hydrosilylation of Terminal Alkynes Catalyzed by an Air-Stable Manganese-NHC Complex.

In recent years, catalysis with base metal manganese has received a significant amount of interest. Catalysis with manganese complexes having N -heterocyclic carbenes (NHCs) is relatively underdeveloped in comparison to the extensively investigated manganese catalysts possessing pincer ligands (particularly phosphine-based ligands). Herein, we describe the synthesis of two imidazolium salts decorated with picolyl arms ( L 1 and L 2 ) as NHC precursors. Facile coordination of L 1 and L 2 with MnBr(CO) 5 in the presence of a base resulted in the formation manganese(I)-NHC complexes ( 1 and 2 ) as an air-stable solid in good isolated yield. Single-crystal X-ray analysis revealed the structure of the cationic complexes [Mn(CO) 3 (NHC)][PF 6 ] with tridentate N,C,N binding of the NHC ligand in a facile fashion. Along with a few known manganese(I) complexes, these Mn(I)-NHC complexes 1 and 2 were tested for the hydrosilylation of terminal alkynes. Complex 1 was proved to be an effective catalyst for the hydrosilylation of terminal alkynes with good selectivity toward the less thermodynamically stable β-( Z )-vinylsilanes. This method provided good regioselectivity ( anti -Markovnikov addition) and stereoselectivity (β-( Z )-product). Experimental evidence suggested that the present hydrosilylation pathway involved an organometallic mechanism with manganese(I)-silyl species as a possible reactive intermediate.