DOUBLE-INSERTION REACTION OF ALKYNES WITH [CP'2ZRME]+ - FORMATION OF AN UNUSUAL DISTORTED ETA-5-PENTADIENYL LIGAND

Reaction of [Cp'2ZrMe(NMe2Ph)][X] (1; Cp' = C5H5 (a), (Me3Si)C5H4 (b), (Me3C)C5H4 (c), rac-C2H4(indenyl)2 (d); [X]- = [B(4-C6H4F)4]-) with excess 2-butyne gives [Cp'2Zr(eta(5)-CH2C(Me) = C(Me)C(Me) = CHMe)][X] (2a-d); an X-ray structure analysis of 2c shows that novel pentadienyl coordination occurs via a sigma-bond and two weak unconjugated eta(2)-interactions with the double bonds. The reaction proceeds via observable, but unstable, alkenyl and 1,3-alkadienyl complexes, followed by a 1,5-hydrogen shift. Double alkyne insertion is unfavorable for crowed (C5Me5)2ZrMe(X), which instead gives [C5Me5)2Zr(eta(3)-CH2C = CMe)][X] via a sigma-bond metathesis reaction.