Hydrosilylation of Aldehydes and Ketones Catalyzed by a 2-Iminopyrrolyl Alkyl-Manganese(II) Complex.

A well-defined and very active single-component manganese(II) catalyst system for the hydrosilylation of aldehydes and ketones is presented. First, the reaction of 5-(2,4,6- i Pr 3 C 6 H 2 )-2-[ N -(2,6- i Pr 2 C 6 H 3 )formimino]pyrrolyl potassium ( KL ) and [MnCl 2 (Py) 2 ] afforded the binuclear 2-iminopyrrolyl manganese(II) pyridine chloride complex [Mn 2 {κ 2 N , N' -5-(2,4,6- i Pr 3 C 6 H 2 )-NC 4 H 2 -2-C(H)═N(2,6- i Pr 2 C 6 H 3 )} 2 (Py) 2 (μ-Cl) 2 ] 1 . Subsequently, the alkylation reaction of complex 1 with LiCH 2 SiMe 3 afforded the respective (trimethylsilyl)methyl-Mn(II) complex [Mn{κ 2 N , N' -5-(2,4,6- i Pr 3 C 6 H 2 )-NC 4 H 2 -2-C(H)═N(2,6- i Pr 2 C 6 H 3 )}(Py)CH 2 SiMe 3 ] 2 in a good yield. Complexes 1 and 2 were characterized by elemental analysis, 1 H NMR spectroscopy, Evans' method, FTIR spectroscopy, and single-crystal X-ray diffraction. While the crystal structure of complex 1 has been identified as a binuclear entity, in which the Mn(II) centers present pentacoordinate coordination spheres, that of complex 2 corresponds to a monomer with a distorted tetrahedral coordination geometry. Complex 2 proved to be a very active precatalyst for the atom-economic hydrosilylation of several aldehydes and ketones under very mild conditions, with a maximum turnover frequency of 95 min -1 , via a silyl-Mn(II) mechanistic route, as asserted by a combination of experimental and theoretical efforts, the respective silanes were cleanly converted to the respective alcoholic products in high yields.