Synthesis of Bis(N-heterocyclic carbene) Complexes of Iron(II) and Their Application in Hydrosilylation and Transfer Hydrogenation

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.