Dinuclear cationic zirconium complexes with the fulvalene ligand. Synthesis and reactivity

Article abstract of DOI:10.1016/S0022-328X(97)00212-X

The reaction of B(C₆F₅)₃ with the tetramethyl zirconium fulvalene derivative [Zr(C₅H₅)(CH₃)₂]₂(μ-η⁵:η⁵-C₁₀H₈) 1a in CH₂Cl₂ at -60°C gives the cationic compound [{Zr(C₅H₅)}₂(η-CH₃)(μ-CH₂)(μ-η⁵:η⁵-C₁₀H₈)]⁺[BMe(C₆F₅)₃]^- 2a. A similar reaction using the 1,3-di(tert-butyl) cyclopentadienyl derivative [Zr(1,3-^tBu₂-C₅H₃)(CH₃)₂]₂(μ,-η⁵:η⁵-C₁₀H₈) 1b affords a mixture of compounds, none of them being isolable as pure substances. However, monitoring the reaction of B(C₆F₅)₃ with 1b by variable temperature NMR spectroscopy, between -80°C and 25°C, permits the observation, at low temperature, of the intermediate dimethyl μ-methyl cationic species [{Zr(1,3-^tBu₂-C₅H₃)(CH₃)}₂(μ-CH₃)(μ-η⁵-η⁵-C₁₀H₈)]⁺ 8b which decomposes with evolution of methane to give the μ-methylene, μ-methyl complex [{Zr(1,3-^tBu₂-C₅H₃)}₂(μ-CH₃)(μ-CH₂)(μ-η⁵:η⁵-C₁₀H₈)]+[BMe(C₆F₅)3]^- 2b. In dichloromethane or chloroform complexes 2a and 2b undergo slow conversion to the μ-chloro, μ-methylene derivatives [{ZrCp′}₂(μ-Cl)(μ-CH₂)(μ-η⁵:η⁵-C₁₀H₈)]⁺[BMe(C₆F₅)₃]^- (Cp′ = C₅H₅ 3a, 1,3-^tBu₂-C₅H₃ 3b) by a halide abstraction process. Prolonged exposure of 3b to chlorocarbons gives the dichloro μ-chloro compound [{Zr(1,3-^tBu₂-C₅H₃)Cl}₂(μ-Cl)(μ-η⁵:η⁵-C₁₀H₈)]⁺[BMe(C₆F₅)₃]^- 9b. The addition of an excess of donor ligands to a solution of 2a in dichloromethane-d₂ at -60°C affords the cationic adducts [{Zr(C₅H₅)}₂(CH₃)L(μ-CH₂)(μ-η⁵:η⁵-C₁₀H₈)]⁺[BMe(C₆F₅)₃]^-[L = PMe₃ (4a), PMe₂Ph (5a), PPh₃ (6a), THF (7a)] obtained as a mixture of syn-and anti-isomers. The compound 5a can be isolated as an analytically pure sample when this reaction is carried out in CH₂Cl₂.