Formation, Structure, and Dynamic Behavior of a Novel Dinuclear Cationic μ-2,4-Hexadiyne Bis(zirconocene) Complex

Bis(propynyl)zirconocene ( 1b ) reacts with 0.5 molar equiv of trityl tetraphenylborate by a propynyl group transfer to form Ph 3 CC⋮CCH 3 and Cp 2 ZrC⋮CCH 3 + . The in-situ-generated (propynyl)zirconocene cation is not stable under the reaction conditions but instantaneously reacts with the neutral starting material 1b to form the [(μ-C⋮CCH 3 )(μ-CH 3 C⋮CC⋮CCH 3 )(ZrCp 2 ) 2 + ][BPh 4 - ] salt, 9 . Complex 9 was characterized by an X-ray crystal structure analysis. It contains an unsymmetrically bridging hexadiyne ligand and exhibits a planar-tetracoordinate carbon center that is stabilized by a three-center two-electron interaction with the two adjacent zirconocene moieties. In solution, complex 9 exhibits dynamic NMR spectra that indicate a symmetrizing exchange of the bonding situations between the two ends of the μ-hexadiyne ligand. The Gibbs activation energy of the automerization reaction of 9 is Δ G ⧧ (190 K) ≈ 9.5 kcal mol - 1 .