Synthetic and NMR Studies of Neutral and Cationic Dinuclear Fulvalene Zirconium Complexes Containing the “Zr2(μ-CNtBu)” Unit

Abstract

Methylation of the previously described isocyanide-bridged complex [{Zr(η5-C5H5)Cl}2(μ-CNtBu)(μ-η5-C5H4-η5-C5H4)] with 2 equiv of MgClMe in toluene at 80 °C afforded the dinuclear dimethyl complex [{Zr(η5-C5H5)(CH3)}2(μ-CNtBu)(μ-η5-C5H4-η5-C5H4)], 1. The same reaction with 1 or 2 equiv of MgClMe at room temperature gave a mixture of compounds containing the dimethyl derivative 1 and two isomers of the monomethyl derivative [{Zr(η5-C5H5)}2(CH3)(Cl)(μ-CNtBu)(μ-η5-C5H4-η5-C5H4)], 2a, 2b, identified by NMR spectroscopy. Analogous methylation of the related compound [{Zr(η5-1,3-tBu2C5H3)Cl}2(μ-CNtBu)(μ-η5-C5H4-η5-C5H4)], 3, isolated by reaction of the zirconium(III) derivative [{Zr(η5-1,3-tBu2C5H3)(μ-Cl)}2(μ-η5-C5H4-η5-C5H4)] with 1 equiv of CNtBu in toluene, gave a mixture of unidentified compounds. Treatment of the dimethyl complex [{Zr(η5-C5H5)(CH3)}2(μ-CNtBu)(μ-η5-C5H4-η5-C5H4)], 1, with 1 equiv of the Lewis acid B(C6F5)3 in dichloromethane at −78 °C affords the new yellow crystalline zirconium cationic derivative [{Zr(η5-C5H5)}2(μ-CH3)(μ-CNtBu)(μ-η5-C5H4-η5-C5H4)][BMe(C6F5)3], 4. Hydrolysis of the μ-methyl compound 4 led to the μ-hydroxo cationic derivative [{Zr(η5-C5H5)}2(μ-OH)(μ-CNtBu)(μ-η5-C5H4-η5-C5H4)][BMe(C6F5)3], 5. Compound 4 reacts with an excess of isocyanides CNR in dichloromethane at −78 °C to give the cationic species [{Zr(η5-C5H5)}2(CH3)(CNR)(μ-CNR)(μ-η5-C5H4-η5-C5H4)][BMe(C6F5)3] (R = tBu, 6; 2,6-Me2C6H3, 7). All of the reported compounds were characterized by the usual analytical and NMR spectroscopic methods, which are discussed.