Synthesis and structure of early transition metal NHC complexes

Abstract

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·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-ⁱPr₂-C₆H₃)Cl₂(NHMe₂)(IMes) (M = V (9), Zr (10)) are prepared from V(NR)Cl₂(NHMe₂)₂ or ZrCl₂(NMe₂)₂(IMes) synthons. Ionic imido complexes [M(N-2,6-ⁱPr₂-C₆H₃)Cl₃(IMes)]⁻[HIMes]⁺ (M = V (12), Ti (13)) are obtained in modest yields from the treatment of [M(NR)Cl₂(NHMe₂)₂] with 2 equiv. of IMes. Treatment of a toluene solution of V(NMe₂)₄ and an amide RC(O)NH₂ (R = ^tBu, Ph) in the presence of an excess of Me₃SiCl produces the terminal oxo complex V(O)Cl₂(NHMe₂)₂ (13), which reacts with two equiv. of IMes to give the bis-NHC oxo-complex V(O)Cl₂(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·HCl have further been confirmed by X-ray diffraction analyses.