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

Abstract

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-iPr3C6H2)-2-[N-(2,6-iPr2C6H3)­formimino]­pyrrolyl potassium (KL) and [MnCl2(Py)2] afforded the binuclear 2-iminopyrrolyl manganese­(II) pyridine chloride complex [Mn2{κ2 N,N′-5-(2,4,6-iPr3C6H2)-NC4H2-2-C­(H)N­(2,6-iPr2C6H3)}2(Py)2(μ-Cl)2] 1. Subsequently, the alkylation reaction of complex 1 with LiCH2SiMe3 afforded the respective (trimethylsilyl)­methyl-Mn­(II) complex [Mn­{κ2 N,N′-5-(2,4,6-iPr3C6H2)-NC4H2-2-C­(H)N­(2,6-iPr2C6H3)}­(Py)­CH2SiMe3] 2 in a good yield. Complexes 1 and 2 were characterized by elemental analysis, 1H 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.

PCP Pincer Carbene Nickel(II) Chloride, Hydride, and Thiolate Complexes: Hydrosilylation of Aldehyde, Ketone, and Nitroarene by the Thiolate Complex

“…In all the 1 H NMR spectra, a resonance at 4.46 or 4.50 ppm was observed for H 2 formation and no resonance in the negative region for a nickel hydride species was observed, probably due to the transient nature of the hydrido-thiolate complexes A and B (Figure ). Moreover, metal-silyl complexes as active species have been proposed in several catalytic hydrosilylation reactions …”

Single-ion magnet behaviour in homoleptic Co(ii) complexes bearing 2-iminopyrrolyl ligands

“…We have been interested in the coordination chemistry of asymmetrical bidentate N , N ′-2-iminopyrrolyl and 5-substituted-2-iminopyrrolyl monoanionic chelates, which are ligands somehow reminiscent of porphyrins. In recent years, we have prepared a good number of mono(2-iminopyrrolyl) complexes of first-row transition metals (Mn, Fe, Co, Ni, Cu), 14 as well as of main-group elements (Na and B), 15 the first group being employed as catalysts for various important organic reactions, and the second one, in the case of boron, as luminescent materials for OLED optoelectronic devices. We have also synthesized and characterized homoleptic bis(2-iminopyrrolyl) complexes of Fe, Co, Ni, Cu and Zn.…”

Research on inorganic activators of dibromo Co-terpyridine complex precatalyst for hydrosilylation

“…Recently, due to their abundance, complex catalysts made from base metals, particularly first row transition metals, have been actively studied as alternatives to Pt-complex catalysts. 4,5 Since their success in the early 2010s, 3,6,7 many first row transition metal-complex catalysts, such as Mn, 5,8 Fe, 3,7,9–14 Co, 10,11,15,16 Ni, 17 and Cu complexes, 18,19 have been used in the hydrosilylation of alkenes (olefins), alkynes, ketones, and other similar compounds. The improvement of first row transition metal-complex catalysts has achieved high turnover numbers as well as high regio- and stereoselectivity.…”