New organometallic derivatives of early transition metals supported by carbazole ligation

We have recently begun to explore the organometallic chemistry of ligands derived from the carbazole nucleus. The choice of the carbazole ligand was stimulated by an expectation that the presence of the two coplanar aryl rings would decrease nitrogen-p to metal-d [special characters omitted]-donation possibly leading to derivatives that exhibit different chemistry than found with more strongly [special characters omitted]-donating dialkylamido ligation. A mixed carbazole-amido compound was synthesized by the reaction of [Zr(NMe2)4] with carbazole to produce [(cb)2Zr(NMe2)2(NHMe2)]. Inspection of the bond distances between the Zr-N(cb) and Zr-N(NMe2) reveals a difference of >0.15 Å, which demonstrates considerably less [special characters omitted]-bonding by the carbazole to the metal center. The addition of carbazole to [Ti(CH2Ph)4] lead to the bis(benzyl) compound [(cb) 2Ti(CH2Ph)2] in moderate yield. Solutions of [(cb) 2Ti(CH2Ph)2] react with two equivalents of 2,6-dimethylphenylisocyanide (xyNC) to produce the bis([special characters omitted]-iminoacyl) complex [(cb)2Ti(xyNCCH2Ph) 2]. The reaction of [Ti(CH2SiMe3)4] with carbazole is slow at ambient temperatures. At 100°C, the reaction produces a sparingly soluble product identified as the alkylidene bridged dimer [(cb)2Ti([special characters omitted]-CHSiMe3)2Ti(cb)2]. In the 1H NMR spectrum of [(cb)2Ti([special characters omitted]-CHSiMe3)2Ti(cb)2] a singlet at [special characters omitted] 14.75 can be assigned to the alkylidene proton. Treatment of [(cb) 2Ti([special characters omitted]-CHSiMe3)2Ti(cb)2] with xyNC slowly (1H NMR) produces a single organometallic species [(cb)Ti([special characters omitted]-cb)[special characters omitted]-xyNCCSiMe3)[[special characters omitted]-xyNCC(SiMe3)CHNxy)Ti(cb)] and one equivalent of free carbazole. The reaction of [Cp*TaCl4] with potassiocarbazole (cbK) leads to the formation of [C5(CH3)4(CH2)Ta(cb) 2Cl] in which one of the ring methyl C-H bonds has been cleaved. [C 5(CH3)4(CH2)Ta(cb)2Cl] can be readily alkylated with LiCH2SiMe3 or MgBrCH 2Ph to yield [C5(CH3)4(CH2)Ta(cb) 2CH2SiMe3] and [C5(CH3) 4(CH2)Ta(cb)2CH2Ph] as yellow and red crystalline solids, respectively.