Chemistry of Group 4 metals supported by carbazole ligation

A series of new derivatives of titanium and zirconium containing carbazole ligation have been isolated and studied. Treatment of [Zr(NMe2)(4)] with carbazole (cbH) leads to the adduct [Zr(cb)(2)(NMe2)(2)(NHMe2)]. Structural studies (trigonal bipyramidal with axial cb and NMe2) show the Zr-N(carbazole) distances to be 0.15 Angstrom longer than the Zr-NMe2 distances. This is consistent with almost negligible nitrogen-p to metal-d pi -bonding from the carbazole ligands. Treatment of [M(CH2Ph)(4)] (M = Ti or Zr) with cbH leads to the derivatives [Zr(cb)(4)] and [Ti(cb)(2)(CH2Ph)(2)]. The latter reacts with 2,6-dimethylphenyl isocyanide (xyNC) to generate the corresponding bis(iminoacyl) derivative, the iminoacyl carbon chemical shift of delta 246.9 in the C-13 NMR of which indicates eta (2)-C,N binding. The reaction of the more bulky alkyl substrate [Ti(CH2SiMe3)(4)] with cbH at 100 degreesC the reaction produces a sparingly soluble, red crystalline product identified as the alkylidene bridged dimer [(cb)(2)Ti(mu -CHSiMe3)(2)Ti(cb)(2)] which was structurally characterized. Treatment of it with xyNC (>3 equivalents) produces a single organometallic species [(cb)Ti(mu -cb)(mu -xyNCCSiMe(3)){mu -xyNCC(SiMe3)CHNxy)Ti(cb)] and one equivalent of free carbazole. The molecular structure could only be elucidated by a solid state structure that shows it to be dinuclear, containing a total of three equivalents of isocyanide within two distinct bridging units. Two terminal and one non-symmetrically bridged carbazole ligand are also present. The reaction of [TiCpCl3] with potassium carbazolate (Kcb) leads to formation of [TiCp(cb)Cl-2] (structurally characterized) which can readily be converted into the dimethyl [TiCp(cb)Me-2].