Syntheses, X-ray Crystal Structures, and Fluxional Behavior of the Clusters Cp*3Co3(μ2-CO)(μ3-CO)(μ-H)2, Cp*3Co3(μ2-H)(μ3-η²-HC=NCMe3), and Cp*3Co3(μ2-H)(μ3-η²-HC=NCMe2CH2Me)

Cp*3Co3(μ2-H)3(μ3-H) (1) reacts with 2 equiv of CO to form the 48-electron dicarbonyl dihydride cluster Cp*3Co3(μ2-CO)(μ3-CO)(μ-H)2 (2), which was studied by X-ray crystallography. 2 consists of an equilateral triangle of cobalt atoms (Co-Co = 2.476(1) Å) capped on each face by a μ-CO ligand. Line-shape analysis of the CO region in the variable temperature 13C NMR of 2 allowed the barrier for interconversion of the μ2- and μ3-CO ligands to be measured (ΔG‡ = 8.6(1) kcal mol−1). Cluster 2 loses H2 at 80 °C (ΔG‡ = 26(1) kcal mol−1) to form the 46-electron dicarbonyl cluster Cp*3Co3(μ3-CO)2 (3). 3 reacts with 5.4 atm of H2 at 80 °C to form a 1.1:1 equilibrium mixture of 2 and 3 (AG = -2.6(1) kcal mol-1). tert-Butyl isocyanide reacts with 1 at ‒35 °C to form the bis(isocyanide) cluster Cp*3Co3(μ- CNCMe3)2(μ-H)2 (10), which was observed by low-temperature 1H NMR spectroscopy. A coordinated tert-butyl isocyanide ligand rapidly inserted into a cobalt-hydrogen bond of 10 to produce the formimidoyl cluster Cp*3Co3(μ2-H)(μ3-η2-CH=NCMe3) (4). Likewise, the reaction of tert-amyl isocyanide with 1 formed Cp*3Co3(μ2-H)(μ3-η2-CH=NCMe2CH2Me) (11). Clusters 4 and 11 were characterized by X-ray crystallography and were shown to consist of a triangle of cobalt atoms capped on one face by a μ3-η2-formimidoyl ligand and capped on the opposite face by a μ-hydride ligand. Line shape analysis of the Cp* region in the variable temperature 1H NMR of cluster 4 allowed the barrier for complete rotation of the formimidoyl ligand parallel to the tricobalt plane to be measured (ΔG‡ = 9.9(1) kcal mol−1). © 1994, American Chemical Society. All rights reserved.

Duke Scholars

Author Ross A. Widenhoefer Chemistry