Synthesis, characterisation and redox behaviour of isocyanide incorporated, chalcogen stabilised mixed-metal clusters

Room temperature reaction of a benzene solution of [Cp2Mo2Fe2(CO)7(μ3-E)(μ3-E′)] (EE′=Se2 (1), STe (2), SeTe (3)) with PriNC or ButNC resulted in the formation of iron bonded isocyanide clusters [Cp2Mo2Fe2(RNC)(CO)6 (μ3-E)(μ3-E′)], [E=E′=Se, R=Pri (5) or But (9); E=S, E′=Te, R=Pri (6a, 6b) or R=But (10a, 10b); E=Se, E′=Te, R=Pri (7a, 7b) or R=But (11a, 11b)] and molybdenum bonded isocyanide clusters [Cp2(RNC)Mo2Fe2(CO)6(μ3-E)(μ3-E′)], [E=E′=Se, R=Pri(13) or But (17); E=S, E′=Te, R=Pri (14) or R=But, (18); E=Se, E′=Te, R=Pri (15) or R=But (19)]. Two isomers (a and b) were detected by 1H NMR spectroscopy for the mixed-chalcogen clusters 6, 7, 10 and 11, where the isocyanide group is bonded to an iron atom. Thermolytic reaction conditions were necessary for the reaction of [(η5-C5H5)2Mo2Fe2(CO)7(μ3-Te)2] (4) with Pri NC or But NC to give [Cp2Mo2Fe2(RNC)(CO)6(μ3-Te)2] (R=Pri (8) or R=But, (12)) and [Cp2(RNC)Mo2Fe2(CO)6(μ3-Te)2] (R=Pri (8)). Compounds 5–19 have been characterised by IR and 1H and 13C NMR spectroscopy. The Se- and Te-bridged compounds have been further characterised by 77Se and 125Te NMR spectroscopy. The structures of compounds 12 and 14 were determined by single crystal X-ray diffraction methods. Redox properties of the mixed-metal clusters, 2, 6, 8, 12 and 14 have been studied by cyclic voltammetry in the potential range ±2.5 V at 298 K, using a platinum working electrode.