Chemistry of Group 4 metals supported by carbazole ligation

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].

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