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

Abstract

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(μ-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)(η5:η5-C10H8)]+[BMe(C6F5)3]− (Cp′ = C5H53a, 1,3-tBu2-C5H33b) 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.