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)2FeCl2 (1a; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and (IEtPh*)2FeCl2 (1b; IEtPh* = 1,3-bis((R)-1′-phenylethyl)imidazol-2-ylidene), were prepared in good yields from the reactions of Fe{N(SiMe3)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)2FeMe2 (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.