SYNTHESES AND X-RAY CRYSTAL-STRUCTURES OF THE TRICOBALT MONO(ETHYLIDYNE) CLUSTERS CP-ASTERISK-3CO3(MU-3-CCH3)(MU-3-CO)(MU-2-H), CP-ASTERISK-3CO3(MU-3-CCH3)(MU-3-CNCME3)(MU-2-H), AND CP-ASTERISK-3CO3(MU-3-CCH3)(MU-3-NO)

Cp3Co3(mu3-CCH3)(mu3-H) (3) reacted with CO to form the 1:1 carbonyl ethylidyne adduct Cp3Co3(mu3-CCH3)(mu3-CO)(mu2-H) (5) in 82% yield. S imilarly, tert-butyl isocyanide reacted with 3 to form the 1:1 isocyan ide ethylidyne adduct Cp3Co3(mu3-CCH3)(mu3-CNCMe3)(mu2-H) (6) in 87% yield. The reaction of 3 with NO formed the nitrosyl ethylidyne cluste r Cp3Co3(mu3-CCH3)(mu3-NO) (7) in 84% yield. The structures of cluste rs 5-7 were determined by X-ray crystallography. Each cluster consists of an equilateral triangle of cobalt atoms symmetrically capped on on e face by a mu3-CCH3 ligand and capped on the opposite face by a mu3-C O (5), mu3-CNCMe3 (6), or mu3-NO (7) ligand. Line shape analysis of th e Cp peaks in the variable-temperature H-1 NMR spectra of 5 and 6 all owed measurement of the barrier for migration of the hydride ligand be tween adjacent pairs of cobalt atoms in 5 [DELTAG(double dagger) = 10. 3(1) kcal mol-1] and 6 [DELTAG(double dagger) = 12.2(2) kcal mol-1].