Substituent Effects. Synthesis and Structural Characterization of Group 4 Metallacarboranes Containing (C₆H₅CH₂)₂C₂B₉H₉^2- and [o-C₆H₄(CH₂)₂]C₂B₉H₉^2- Ligands

Substituents on the carborane cage carbons affect not only bonding interactions between the group 4 metal ion and the carboranyl of the C2B9 system but also the reactivity pattern of the resulting metal complexes. Treatment Of MCl4(THF)(2) with 1 equiv of [(C6H5-CH2)(2)C2B9H9]Na-2(THF)(x) in THF at room temperature gave the bis(carboranyl) complexes {eta(4):eta(2)-[(C6H5CH2)(2)C2B9H9](2)MCl(THF)}{Na(THF)(3)} (M = Zr (1), Hf (2)). Under the same reaction conditions, interaction of TiCl4(THF)(2) with 1 equiv Of [(C6H5CH2)(2)C2B9H9]Na-2(THF)(x) led to the isolation of a small amount of TiCl3(THF)(3) and B-substituted zwitterionic compound (C6H5CH2)(2)C2B9H9(THF) (4). Reaction of 1 with 1 equiv of Li[N(SiMe3)(2)] resulted in the replacement of a Na+ by a Li+, giving the ionic complex [eta(3):eta(2)-{(C6H5CH2)(2)C2B9H9}(2)ZrCl-(THF)] [Li(THF)(4)] (3). ClZr[N(SiMe3)(2)](3) was isolated from the reaction of 1 with excess Li-[N(SiMe3)(2)]. Am equimolar reaction between M(NEt2)(4) and (C6H5CH2)(2)C2B9H11 afforded the monocarboranyl. complexes [eta(2)-(C6H5CH2)(2)C2B9H9]M(NEt2)(2)(NHEt2) (M = Ti (5), Zr (6)). It is believed that the additional N(p(pi))-->M(d(pi)) interactions stabilize this type of complex. Treatment of MCl4(THF)(2) with 1 equiv of less bulky yet rigid [{o-C6H4(CH2)(2)}C2B9H9]Na-2-(THF)(x) generated a bent-metallocene type of complex, [{o-C6H4(CH2)(2)}C2B9H9](2)M(THF)(2) (M = Zr (7), Hf (8)). These metallacarboranes were all fully characterized by various spectroscopic techniques and elemental analyses. Molecular structures of 1 and 3-5 were confirmed by single-crystal X-ray analyses.