FORMATION, STRUCTURE, AND DYNAMIC BEHAVIOR OF A NOVEL DINUCLEAR CATIONIC MU-2,4-HEXADIYNE BIS(ZIRCONOCENE) COMPLEX

Bis(propynyl)zirconocene (1b) reacts with 0.5 molar equiv of trityl te traphenylborate by a propynyl group transfer to form Ph(3)CC=CCH3 and Cp(2)ZrC=CCH3+. The in-situ-generated (propynyl)zirconocene cation is not stable under the reaction conditions but instantaneously reacts wi th the neutral starting material 1b to form the =CCH3)(mu-CH3C=CC=CCH3 )(ZrCp(2))(2)(+)][BPh(4)(-)] salt, 9. Complex 9 was characterized by a n X-ray crystal structure analysis. It contains an unsymmetrically bri dging hexadiyne ligand and exhibits a planar-tetracoordinate carbon ce nter that is stabilized by a three-center two-electron interaction wit h the two adjacent zirconocene moieties. In solution, complex 9 exhibi ts dynamic NMR spectra that indicate a symmetrizing exchange of the bo nding situations between the two ends of the mu-hexadiyne ligand. The Gibbs activation energy of the automerization reaction of 9 is Delta G (double dagger)(190 K) approximate to 9.5 kcal mol(-1).