Preparation and reactions of cyclic and acyclic allene complexes of zirconocene

• Published in: Tetrahedron Vol. 51; no. 15; pp. 4395 - 4406
• Main Authors: Yin, Jianguo, Jones, W.M.
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 10.04.1995; Elsevier
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; ALKENES; PROMOTED CYCLIZATION; TRANSITION-METAL COMPLEXES; CYCLOALKYNES; REACTIVITY; COORDINATION; IRON; DERIVATIVES; CYCLOHEPTATETRAENE; RAY CRYSTAL-STRUCTURE
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/0040-4020(94)01128-M

The zirconocene π-complex of 3-methyl-1,2-butadiene(1,1-dimethylallene) cannot be prepared by simple ligand substitution due to rapid coupling of the initally formed complex with the unreacted allene. This problem was circumvented by generating the allene complex by β-hydrogen elimination from a pre-formed sigma complex. This appears to be a potentially general way to prepare allene complexes of zirconocene if the allene precursor has no cis-vinyl hydrogen. This method has been successfully used to prepare zirconocene complexes of 3-methyl-1,2-cycloheptadiene, 3-methyl-1,2-cyclohexadiene and 4-phenyl-1,2,3-cyclohexatriene. Attempts to prepare a complex of 3-methyl-1,2-cyclopentadiene failed. Selected reactions of two of these cumulene complexes and their coupling products are reported. Zirconocene complexes of cyclic and acyclic allenes and cumulenes can be prepared by β-hydrogen elimination if alkyne formation is prevented by appropriate substitution.