Organometallic Zirconium Compounds in an Oxygen-Rich Coordination Environment: Synthesis and Structural Characterization of Tris(oxoimidazolyl)hydroboratozirconium Compounds

A series of tris­(oxoimidazolyl)­hydroborato ligands, which serve as L₂X [O₃] donors, have been employed to obtain organometallic zirconium compounds in an uncommon oxygen-rich coordination environment. For example, Cp­[To^MeBenz]­ZrCl₂ has been synthesized via the reaction of [To^MeBenz]Na with CpZrCl₃ and bears a structural resemblance to the bent metallocene dichloride derivative Cp₂ZrCl₂. In addition, the half-sandwich counterparts [To^MeBenz]­ZrCl₃ and [To^{Bu^t}]­ZrCl₃ have been obtained by metathesis of ZrCl₄ with [To^MeBenz]Na and [To^{Bu^t}]­Na, respectively. The structurally related zirconium benzyl compounds [To^RBenz]­Zr­(CH₂Ph)₃ (R = Me, Bu^t, 1-Ad) have also been synthesized via the reactions of [To^RBenz]Tl with Zr­(CH₂Ph)₄, and X-ray diffraction studies demonstrate that the benzyl ligands in these compounds are conformationally flexible and exhibit a large range of Zr–CH₂–Ph bond angles (94.7–131.7°). Protolytic cleavage of one of the benzyl ligands of [To^RBenz]­Zr­(CH₂Ph)₃ (R = Bu^t, 1-Ad) may be achieved by treatment with [PhNHMe₂]­[B­(C₆F₅)₄] to generate {[To^RBenz]­Zr­(CH₂Ph)₂}­[B­(C₆F₅)₄], which are catalysts for the polymerization of ethylene. The molecular structure of the ether adduct, {[To^{Bu^tBenz}]­Zr­(CH₂Ph)₂(OEt₂)}­[B­(C₆F₅)₄], has been determined by X-ray diffraction. In addition to the use of tris­(oxoimidazolyl)­hydroborato ligands, bis­(oxoimidazolyl)­hydroborato ligands have also been used to obtain zirconium benzyl compounds in oxygen-rich environments, namely, [Bo^MeBenz]₂Zr­(CH₂Ph)₂ and [Bo^AdBenz]₂Zr­(CH₂Ph)<sub>2