A New, Flexible N,N,N‐Tripodal Facially Capping Ligand System: Synthesis and Structural Characterization of β‐Triketimines and Their M(CO)3 Complexes (M = Cr, Mo, W)

Abstract

AbstractReaction of imidoyl chlorides Ar*N=CClR (Ar* = 2‐iPrC6H4, 2,6‐iPr2C6H3, 2‐MeOC6H4; R = Me, Ph, tBu) with [Li(nacnac)] [nacnac = (Ar*NCMe)2CH] gives β‐triketimines L, most of which exist in solution in equilibrium with their imine/enamine tautomers. The route is highly modular, allowing independent variation of at least five parameters. The solution equilibria are very sensitive to such substituent pattern variation. Single‐crystal X‐ray diffraction analyses of examples of both tautomers and a geometric isomer in the solid state are presented, alongside solution NMR studies of the tautomerism. All examples revert exclusively to the β‐triimine form on complexation with M(CO)3 fragments (M = Cr, Mo, W). Facial isomers result. The ligands are weak σ‐donors, as adjudged by CO IR stretching frequencies in [LM(CO)3]. Crystal‐structure determination on the isostructural pair [HC(2‐iPrC6H4N=CMe)3M(CO)3] (M = Cr, Mo) revealed a hexagonal packing arrangement composed of aryl–aryl and carbonyl (CO)–H–C interactions which generates pseudocylindrical voids accounting for 6–9 % of the crystal volume. In only one case were these occupied by solvent molecules. This family of facially capping N,N,N‐ligands with finely tunable bulk have wide potential in coordination chemistry.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)