Reactions of Five-Membered Metallacyclocumulenes Cp2M(η4-t-Bu-C4-t-Bu) (M = Ti, Zr) with Diisobutylaluminum Hydride

Reactions of the five-membered metallacyclocumulenes Cp2M(η4-t-Bu-C4-t-Bu) (M = Ti, Zr) with the Lewis Acid i-Bu2AlH were studied. Cp2Ti(η4-t-Bu-C4-t-Bu) (1) reacts with i-Bu2AlH to give a heterobimetallic complex which was isolated as the THF adduct Cp2Ti[μ-η1:η2-t-BuCC−CHC-t-Bu)(μ-H)(i-BuAl)(THF)] (4). The reaction of the corresponding zirconocene compound Cp2Zr(η4-t-Bu-C4-t-Bu) (2) with i-Bu2AlH results in a cleavage of the central CC bond of the metallacyclocumulene C4 chain and formation of the dinuclear complex 6 and the dinuclear acetylide [(Cp2Zr)2(μ-CC-t-Bu)2]. In addition to the formation of 6 and the acetylide species an elimination of the butadiyne takes place, which gives in the subsequent interaction with i-Bu2AlH the zwitterionic aluminum cluster 7. Alternatively, complex 7 is also formed in the direct reaction of the butadiyne with a 3-fold excess of i-Bu2AlH. The molecular structures of 4 and 7 were confirmed by X-ray analysis.