SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF DITHIOCARBAMATE-STABILIZED DIMERIC MOLYBDENUM(V) IMIDO COMPLEXES VIA OXO SUBSTITUTION-REACTIONS WITH ORGANIC ISOCYANATES

Thermolysis of molybdenum-oxo complexes [MoO2(S(2)CNEt(2))(2)] 1, [{MoO(S(2)CNEt(2))(mu-O)}(2)] 2 and [Mo2O2(S(2)CNEt(2))(2)(mu-O)(mu-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)(S(2)CNEt(2))(2)(mu-S)(2)] 4a-4c (R = Bu(t), 2,6-Me(2)C(6)H(3) or adamant-1-yl) and bridging bis(imido) complexes [{MoO(S(2)CNEt(2))(mu-NR)}(2)] 5a and 5c (R = Ph or p-tolyl). Reaction of complex 2 with an excess of RNCO afforded the tetraimido complex [{Mo-2(NR)(S(2)CNEt(2))(mu-NR)}(2)] 6b (R = o-tolyl) and the bridging ureato complex [Mo-2(NPh)(2)(S(2)CNEt(2))(2)(mu-NPh){mu-PhNC(O)}] 7a, while with PhNCO and complex 3 a further ureato complex [Mo-2(NPh)(2)(S(2)CNEt(2))(2)(mu-S){mu-PhNC(O)NPh}] 7b resulted. Thermolysis of complex 7a gave the tetraimido complex [{Mo(NPh)(S(2)CNEt(2))(mu-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) (S(2)CNEt(2))}(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(S(2)CNEt(2))(3)(mu-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 Angstrom) indicative of metal-metal bonding. the longer distances being associated with bridging sulfide ligands. Terminal imido ligands are all linear and bridging imido ligands planar.