Inorganic Chemistry, Vol.57, No.3, 1426-1437, 2018
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 [O-3] 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(But)]ZrCl3 have been obtained by metathesis of ZrCl4 with [To(MeBenz)]Na and [To(But)]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 degrees). 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(ButBenz)]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)](2)Zr-(CH2Ph)(2) and [Bo(AdBenz)](2)Zr(CH2Ph)(2).