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 = Bu^t, 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 Å) 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.