Fulvene to cyclopentadienyl conversion with homoleptic complexes of zirconium and hafnium

Article abstract of DOI:10.1021/om990402j

The reaction of 6,6-dimethylfulvene with M(CH₂Ph)₄ (M = Zr, Hf) in benzene gives [η⁵-C₅H₄(CMe₂CH ₂Ph)]M(CH₂Ph)₃ (1, M = Zr; 2, M = Hf) without any observable byproducts. A similar reaction for M = Ti is not observed. The single-crystal X-ray study of 1 shows a three-legged piano-stool geometry with an η²-bound benzyl ligand. A second equivalent of 6,6-dimethylfulvene does not react with either 1 or 2. The bulkier 6,6-diphenyfulvene only reacts cleanly with the more Lewis acidic Hf(CH₂Ph)₄ to give [η⁵-C₅H₄(CPh₂CH ₂Ph)]Hf(CH₂-Ph)₃ (3). Using the tetraamido complexes M(NMe₂)₄ and 6,6-dimethylfulvene, one obtains dimethylamine and [η⁵-C₅H₄(CMeCH₂)]M(NMe ₂)₃ (4 for M = Zr) in good yield. These products are formally derived from the deprotonation of a fulvene methyl group and subsequent coordination of the resulting 2-propenylcyclopentadienyl fragment. Reaction of 4 and 6,6-dimethylfulvene affords the bent metallocene [η⁵-C₅H₄(CMeCH₂)] ₂Zr(NMe₂)₂ (5). Excess 8,8-dimethylbenzofulvene and M(NMe₂)₄ provides exclusively the product with only one coordinated indene.