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

Abstract

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 Bu^tNC 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=Bu^t (10a, 10b); E=Se, E'=Te, R=Prⁱ (7a, 7b) or R=Bu^t(11a, 11b)] and molybdenum bonded isocyanide clusters [Cp₂(RNC)Mo₂Fe₂(CO)₆(μ₃-E)(μ₃-E')], [E=E'=Se, R=Prⁱ(13) or Bu^t (17); E=S, E'=Te, R=Prⁱ (14) or R=Bu^t, (18); E=Se, E'=Te, R=Prⁱ (15) or R=Bu^t (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=Bu^t, (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. 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=Bu^t (10a, 10b); E=Se, E'=Te, R=Prⁱ (7a, 7b) or R=Bu^t (11a, 11b)] and molybdenum bonded isocyanide clusters [Cp₂(RNC)Mo₂Fe₂(CO)₆(μ₃-E)(μ₃-E')], [E=E'=Se, R=Prⁱ(13) or Bu^t (17); E=S, E'=Te, R=Prⁱ (14) or R=Bu^t, (18); E=Se, E'=Te, R=Prⁱ (15) or R=Bu^t (19)].