Neutral and Cationic Zirconium Hydrides Supported by a Dianionic (NNNN)-Type Macrocycle Ligand

Hydrogenation of bis­(trimethylsilylmethyl) zirconium complex [Zr­(Me2TACD)­(CH2SiMe3)2] (1), prepared by reacting [Zr­(CH2SiMe3)4] with 1,7-dimethyl-1,4,7,10-tetraazacyclododecane (Me2TACD)­H2, gave dinuclear alkyl hydride complex [Zr­(Me2TACD)­(CH2SiMe3)2­(μ-H)2Zr­(Me2TACD)] (2). According to NMR spectroscopic and single-crystal X-ray diffraction studies, 2 exhibits a Cs-symmetrical structure with two distinct zirconium centers, one eight- and the other seven-coordinate, bridged by an amido donor and two hydrides. Abstraction of the trimethylsilylmethyl groups by the weak Brønsted acid [NEt3H]­[B­(3,5-C6H3Cl2)4] gave the monocationic mono­(alkyl) dihydride [Zr­(Me2TACD)­(CH2SiMe3)­(μ-H)2Zr­(Me2TACD)]­[B­(3,5-C6H3Cl2)4] (3) and the dicationic hydride complex [Zr­(Me2TACD)­(THF)2­(μ-H)2Zr­(Me2TACD)]­[B­(3,5-C6H3Cl2)4]2 (4). X-ray crystallography of the cationic complexes 3 and 4 revealed a Cs-symmetrical dinuclear structure derived from that of 2.