Syntheses, structures, and properties of phenyltrihydroborate complexes of zirconocene and titanocene

The phenyltrihydroborate complexes, Cp2ZrCl{(μ-H)2BHPh}, 1, and Cp2Zr{(μ-H)2BHPh}2 · (1/2 toluene), 2, were prepared from the reactions of Cp2ZrCl2 with one and two moles of LiBH3Ph. The Zr–H–B bonds in 2 are stable under vacuum at 100 °C for hours without significant decomposition. An inductive effect has been proposed for this strong interaction. This hydrogen bridge bond can be broken upon reacting with the Lewis base N(C2H5)3 to produce (C2H5)3N · BH2Ph and the zirconium hydride compound Cp2ZrH{(μ-H)2BHPh}, 3. Compound 3 also can be prepared from the reaction of Cp2ZrHCl with LiBH3Ph. The reaction of 1 with the Lewis acid B(C6F5)3 is solvent dependent, the metathesis product Cp2ZrCl{(μ-H)2B(C6F5)2}, 4, was formed in the toluene solution, whereas the ionic complex [Cp2ZrCl(OEt2)][HB(C6F5)3], 5, was isolated from the ether solution. The reaction of titanocene dichloride, Cp2TiCl2, with LiBH3Ph produced a 17-electron, paramagnetic complex, Cp2Ti{(μ-H)2BHPh}, 6. Single crystal X-ray structures of 1, 2, 3, 4, 5, and 6 were also determined. A coplanar structure of the four bridge hydrogens in 2 was observed.