Syntheses, structures, and dynamic properties of M(CO)2(η3-C3H5)(en)(X) (M = Mo, W; X = Br, N3, CN) and [(en)(η3-C3H5)(CO)2M(μ-CN)M(CO)2(η3-C3H5)(en)]Br (M = Mo, W)

Mononuclear compounds M(CO)2(η3-C3H5)(en)(X) (X = Br, M = Mo(1), W(2); X = N3, M = Mo(3), W(4); X = CN, M = Mo(5), W(6)) and cyanide-bridged bimetallic compounds [(en)(η3-C3H5)(CO)2M(μ-CN)M(CO)2(η3-C3H5)(en)]Br (M = Mo (7), W(8)) were prepared and characterized. These compounds are fluxional and display broad unresolved proton NMR signals at room temperature. Compounds 1–6 were characterized by NMR spectroscopy at −60 °C, which revealed isomers in solution. The major isomers of 1–4 adopt an asymmetric endo-conformation, while those of 5 and 6 were both found to possess a symmetric endo-conformation. The single crystal X-ray structures of 1–6 are consistent with the structures of the major isomer in solution at low temperature. In contrast to mononuclear terminal cyanide compounds 5 and 6, cyanide-bridged compounds 7 and 8 were found to adopt the asymmetric endo-conformation in the solid state.