Chemistry of Group 4 metals supported by carbazole ligation

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Abstract
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 Å longer than the Zr–NMe2 distances. This is consistent with almost negligible nitrogen-p to metal-d π-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 δ 246.9 in the 13C NMR of which indicates η2-C,N binding. The reaction of the more bulky alkyl substrate [Ti(CH2SiMe3)4] with cbH at 100 °C the reaction produces a sparingly soluble, red crystalline product identified as the alkylidene bridged dimer [(cb)2Ti(μ-CHSiMe3)2Ti(cb)2] which was structurally characterized. Treatment of it with xyNC (>3 equivalents) produces a single organometallic species [(cb)Ti(μ-cb)(μ-xyNCCSiMe3){μ-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)Cl2] (structurally characterized) which can readily be converted into the dimethyl [TiCp(cb)Me2]. p

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