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

Abstract

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.

Co‐Catalyzed Hydrosilylation of Ketones under Base‐Free Conditions: A Convenient Route to Silyl Ethers or Secondary Alcohols

“…first-row transition metal complexes. [9][10][11][12][13] The major research area has intensified on manganese, [14][15][16][17] iron, [18][19][20][21][22][23][24][25] nickel, [25][26][27][28] and cobalt. [24,25,29,30] However, despite numerous protocols for the highly selective Co-catalyzed hydrosilylation of alkynes and alkenes, the modification of carbonyl groups seemed more challenging.…”