Hydride Ion Abstraction from Titanocene Cyclic Organohydroborates, Cp₂Ti{(μ-H)₂BR₂} (R₂= C₄H₈, C₅H₁₀, C₈H₁₄), as a Function of Solvent

Abstract

Hydride abstraction reactions of titanocene cyclic organohydroborate complexes Cp2Ti{(μ-H)2BR2} (R2 = C4H8, C5H10, C8H14) with B(C6F5)3 were investigated as a function of solvent. It was determined that the coordinating ability of the solvent directed the course of these abstraction reactions. The reaction in toluene, a noncoordinating solvent, produced a metathesis product, Cp2Ti{(μ-H)2B(C6F5)2} (1), in which the cyclic organohydroborate H2BR2 was substituted by H2B(C6F5)2. In diethyl ether and THF, the salts [Cp2TiL2] [HB(C6F5)3] (2, L = Et2O; 3, L = THF) consisting of titanocene cations with solvent ligands were isolated. Salt 2 is the first structurally characterized [Cp2TiL2]+ cation containing diethyl ether solvent ligands. The diethyl ether molecules of the cation in 2 are weakly coordinated and are labilized in THF and toluene. Dissolution of 2 in THF afforded 3. The complex Cp2Ti{(μ-H)B(C6F5)3}(OEt2) (4) and the proposed 15-electron species Cp2Ti{(μ-H)B(C6F5)3} (5) were generated through the displacement of an ether molecule from 2 by the [HB(C6F5)3]- anion in toluene. Single-crystal X-ray structures of 1, 2, and 3 were determined.