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=CClR (Ar* = 2-iPrC 6H4,2,6-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-tri-imine form on complexation with M(CO)3 fragments (M = Cr, Mo, W). Facial isomers result. The ligands are weak σ-do nors, as adjudged by CO IR stretching frequencies in [LM(CO)3], Crystal-structure determination on the iso-structural pair [HC(2iPrC6H 4N=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 /V,/V,/V-ligands with finely tunable bulk have wide potential in coordination chemistry..© 2009 Wilcy-VCH Verlag Gmbh& Co. KGaA.