Fulvene to cyclopentadienyl conversion with homoleptic complexes of zirconium and hafnium

The reaction of 6,6-dimethylfulvene with M(CH2Ph)(4) (M = Zr, Hf) in benzene gives [eta(5)-C5H4(CMe2CH2Ph)]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 eta(2)-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 [eta(5)-C5H4(CPh2CH2Ph)]Hf(CH2Ph)(3) (3). Using the tetraamido complexes M(NMe2)(4) and 6,6-dimethylfulvene, one obtains dimethylamine and [eta(5)-C5H4(CMeCH2)]M(NMe2)(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 [eta(5)-C5H4(CMeCH2)](2)Zr(NMe2)(2) (5). Excess 8,8-dimethylbenzofulvene and M(NMe2)(4) provides exclusively the product with only one coordinated indene.