Synthesis of bis(N-heterocyclic carbene) complexes of iron(II) and their application in hydrosilylation and transfer hydrogenation

Abstract

N-heterocyclic carbene (NHC) adducts of iron dichloride, (IMes) 2FeCl 2 (1a; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol- 2-ylidene) and (IEtPh*) 2FeCl 2 (1b; IEtPh* = 1,3-bis((R)-1′-phenylethyl)imidazol-2-ylidene), were prepared in good yields from the reactions of Fe{N(SiMe 3) 2} 2 with imidazolium salts. While the iron atom of 1a has a tetrahedral geometry, replacement of the chlorides by methyl groups via treatment of 1a with MeLi led to the formation of the square-planar complex trans-(IMes) 2FeMe 2 (2). The molecular structures of complexes 1a,b and 2 were identified by means of single-crystal X-ray diffraction analysis. Complexes 1a,b and 2 are good catalyst precursors in the transfer hydrogenation of 2′-acetonaphthone, and complex 2 also efficiently catalyzes the hydrosilylation of 2′-acetonaphthone. © 2012 American Chemical Society.