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)

Reaction of imidoyl chlorides Ar*N=CCIR (Ar* = 2-iPrC(6)H(4), 2,6-iPr(2)C(6)H(3), 2-MeOC6H4; R = Me, Ph, tBu) with [Li(nacnac)] [nacnac = (Ar*NCMe)(2)CH] gives beta-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 beta-triimine form on complexation with M(CO)(3) fragments (M = Cr, Mo, W). Facial isomers result. The ligands are weak sigma-donors, as adjudged by CO IR stretching frequencies in [LM(CO)(3)], Crystal-structure determination on the isostructural pair [HC(2-iPrC(6)H(4)N=CMe)(3)M(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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)