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 L2 X [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 Cp2 ZrCl2 . 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(CH2 Ph)3 (R = Me, But , 1-Ad) have also been synthesized via the reactions of [ToRBenz ]Tl with Zr(CH2 Ph)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(CH2 Ph)3 (R = But , 1-Ad) may be achieved by treatment with [PhNHMe2 ][B(C6 F5 )4 ] to generate {[ToRBenz ]Zr(CH2 Ph)2 }[B(C6 F5 )4 ], which are catalysts for the polymerization of ethylene. The molecular structure of the ether adduct, {[ToBut Benz ]Zr(CH2 Ph)2 (OEt2 )}[B(C6 F5 )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 ]2 Zr(CH2 Ph)2 and [BoAdBenz ]2 Zr(CH2 Ph)2 .