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

Hydrogenation of bis­(trimethylsilylmethyl) zirconium complex [Zr­(Me₂TACD)­(CH₂SiMe₃)₂] (<b>1</b>), 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)] (<b>2</b>). According to NMR spectroscopic and single-crystal X-ray diffraction studies, <b>2</b> exhibits a <i>C</i>_<i>s</i>-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] (<b>3</b>) and the dicationic hydride complex [Zr­(Me₂TACD)­(THF)₂­(μ-H)₂Zr­(Me₂TACD)]­[B­(3,5-C₆H₃Cl₂)₄]₂ (<b>4</b>). X-ray crystallography of the cationic complexes <b>3</b> and <b>4</b> revealed a <i>C</i>_<i>s</i>-symmetrical dinuclear structure derived from that of <b>2