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[ToMeBenz]ZrCl2 has been synthesized via the reaction of [ToMeBenz]Na with CpZrCl3 and bears a structural resemblance to the bent metallocene dichloride derivative Cp2ZrCl2. In addition, the half-sandwich counterparts [ToMeBenz]ZrCl3 and [ToBut]ZrCl3 have been obtained by metathesis of ZrCl4 with [ToMeBenz]Na and [ToBut]Na, respectively. The structurally related zirconium benzyl compounds [ToRBenz]Zr(CH2Ph)3 (R = Me, But, 1-Ad) have also been synthesized via the reactions of [ToRBenz]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 [ToRBenz]Zr(CH2Ph)3 (R = But, 1-Ad) may be achieved by treatment with [PhNHMe2][B(C6F5)4] to generate {[ToRBenz]Zr(CH2Ph)2}[B(C6F5)4], which are catalysts for the polymerization of ethylene. The molecular structure of the ether adduct, {[ToButBenz]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, [BoMeBenz]2Zr(CH2Ph)2 and [BoAdBenz]2Zr(CH2Ph)2.