Synthesis and structural characterisation of dithiocarbamate-stabilised dimeric molybdenum(V) imido complexes via oxo substitution reactions with organic isocyanates

Abstract

Thermolysis of molybdenum–oxo complexes [MoO2(S2CNEt2)2]1, [{MoO(S2CNEt2)(µ-O)}2]2 and [Mo2O2(S2CNEt2)2(µ-O)(µ-S)]3 with organic isocyanates afforded a range of imido-substituted binuclear molybdenum(V) complexes. Reaction of complex 1 with 1 equivalent of RNCO gave terminally substituted mono(imido) complexes [Mo2O(NR)(S2CNEt2)2(µ-S)2]4a–4c(R = But, 2,6-Me2C6H3 or adamant-1-yl) and bridging bis(imido) complexes [{MoO(S2CNEt2)(µ-NR)}2]5a and 5c(R = Ph or p-tolyl). Reaction of complex 2 with an excess of RNCO afforded the tetraimido complex [{Mo(NR)(S2CNEt2)(µ-NR)}2]6b(R =o-tolyl) and the bridging ureato complex [Mo2(NPh)2(S2CNEt2)2(µ-NPh){µ-PhNC(O)NPh}]7a, while with PhNCO and complex 3 a further ureato complex [Mo2(NPh)2(S2CNEt2)2(µ-S){µ-PhNC(O)NPh}]7b resulted. Thermolysis of complex 7a gave the tetraimido complex [{Mo(NPh)(S2CNEt2)(µ-NPh)}2]6a, a reaction which is reversed in the presence of PhNCO. Acid-catalysed hydrolysis of complex 6b afforded the bis(imido) complex [{MoO(NR)(S2CNEt2)}2](R =o-tolyl)5b which upon thermolysis with o-tolyl isocyanate regenerated 6b. Addition of HBF4 to 5a resulted in oxo substitution by dithiocarbamate to give [Mo2O(S2CNEt2)3(µ-NPh)2][BF4]8. Six of these complexes, namely 4a, 4b, 5b, 6b, 7a and 8, have been characterised by X-ray crystallography. All are dimeric and contain relatively short molybdenum–molybdenum contacts (2.625–2.822 A) indicative of metal–metal bonding, the longer distances being associated with bridging sulfido ligands. Terminal imido ligands are all linear and bridging imido ligands planar.