Synthesis and structure of 1-metallacyclopent-3-yne complexes of group 4 metals

Five-membered metallacyclic alkyne complexes of titanium and hafnium, 1,1-bis(cyclopentadienyl)-1-titanacyclopent-3-yne (2) and trans-1,1-bis(cyclopentadienyl)-2,5-trimethylsilyl-1-hafnacyclopent-3-yne (6), were synthesized and structurally characterized. The structural analysis of titanium complex 2 implied a larger contribution of an η⁴-π,π-coordinated structure. The hafnium compound 6 has a similar structure to the corresponding zirconium analogue (1a), although slight differences in the bond lengths and angles were observed. A novel 1-zirconacyclopent-3-yne complex, 1,1-bis(methylcyclopentadienyl)-2,5-bis(trimethylsilyl)-1-zirconacyclopent-3-yne (5), was also prepared and the structure of the trans-isomer was determined.