Synthesis and structure of early transition metal NHC complexes

The synthesis and structure of several new early transition metal (Ti, Zr, Hf, and V) NHC complexes supported by one or two IMes ligands is described. Reaction of M(NMe2)(4) with IMes center dot HCl gives compounds VCl2(NMe2)(IMes)(2) (2), and MCl2(NMe2)(2)(IMes) (M = V (3), Zr (4), Hf (5)). Treatment of TiCl3(THF)(3) with 2 equiv. of IMes and 1 equiv. of LiNMe2 affords the titanium(III) compound TiCl2(NMe2)(IMes)(2). Reaction of VCl3(THF)(3) with 2 equiv. of IMes in toluene produces the trivalent complex VCl3(IMes)(2) (6), while VCl2(Py)(4) gives the divalent compound VCl2(IMes)(Py)(3) (7), and ZrCl4(THF)(2) leads to ZrCl4(IMes)(2) (8). Imido compounds M(=N-2,6-Pr-i(2)-C6H3)Cl-2(NHMe2)(IMes) (M = V (9), Zr (10)) are prepared from V(= NR)Cl-2(NHMe2)(2) or ZrCl2(NMe2)(2)(IMes) synthons. Ionic imido complexes [M(=N-2,6-Pr-i(2)-C6H3)Cl-3(IMes)](-)[HIMes](+) (M = V (12), Ti (13)) are obtained in modest yields from the treatment of [M(=NR)Cl-2(NHMe2)(2)] with 2 equiv. of IMes. Treatment of a toluene solution of V(NMe2)(4) and an amide RC(O)NH2 (R = Bu-t, Ph) in the presence of an excess of Me3SiCl produces the terminal oxo complex V(=O)Cl-2(NHMe2)(2) (13), which reacts with two equiv. of IMes to give the bis-NHC oxo-complex V(=O)Cl-2(IMes)(2) (14). All new compounds have been characterised by various spectroscopic techniques, elemental analyses, and magnetism studies for paramagnetic compounds. The solid-state structure of 12 of these complexes and of IMes center dot HCl have further been confirmed by X-ray diffraction analyses.