Molybdenum(VI) imidodisulfur complexes formed via double sulfur-carbon bond cleavage of dithiocarbamates

Thermolysis of the bis(oxo) complexes [MoO2(S(2)CNR'(2))(2)] 1 with organic isocyanates afforded imidodisulfur complexes [Mo(NR)(eta(2)-S-2)(S(2)CNR'(2))(2)] 2 in moderate yields. Three of the latter, [Mo(NPh)(eta(2)-S-2)(S(2)CNEt(2))(2)] 2a, [Mo(NBu(1))(eta(2)-S-2)(S(2)CNMe(2))(2)] 2j and [Mo(NC6H3Pr2i-2,6)(eta(2)-S-2)(S(2)CNMe(2))(2)] 2k have been characterised by X-ray crystallography. All contain a distorted pentagonal-bipytamidal metal centre, the disulfur ligand lying in the equatorial plane while the linear imide ligand occupies an axial site. Reaction of 2a with P(OEt)(3) afforded the dinuclear molybdenum(v) complex [Mo2O2(mu-NPh)(mu-S)(S(2)CNEt(2))(2)] 3 which has also been crystallographically characterised. Thermolysis of 2a with an excess of the activated alkyne dimethyl acetylene dicarboxylate yielded three isomeric insertion products formulated as [Mo(SC(R)=C(Ri)NPh)-{eta(4)-SC(R)NPh}{eta(3)-SC(R)=C(R)=SC(NEt(2))}(S(2)CNEt(2))] 6 (R=CO(2)Me). The nature of the sulfur-carbon bond cleavage reaction was investigated in a series of experiments centred around the formation of 2a which is concomitant with that of [{MoO(mu-NPh)(S(2)CNEt(2))}(2)] 7a. Thermolysis of [MoO2(S(2)CNEt(2))(2)] 1a alone afforded the known molybdenum(v) complex [Mo2O2(mu-O)(mu-S)(S(2)CNEt(2))(2)] and, while addition of PhNCO to [MoO(eta(2)-S-2)(S(2)CNEt(2))(2)] afforded 2a, imido substitution was not noted with Bu(t)NCO, thus ruling out the general intermediacy of [MoO(eta(2)-S-2)(S(2)CNEt(2))(2)] in the dithiocarbamate cleavage process. Thermolysis of bis(imido) complexes [Mo(NR)(2)(S(2)CNEt(2))(2)]8 (R = Ph or C(6)H(4)Me-o) did not afford the respective disulfur complexes, however thermolysis of [MoO(NPh)(S(2)CNEt(2))(2)] did give 2a and 7a, thus implicating the oxoimidomolybdenum(VI) complexes as key reaction intermediates. These observations allow a general reaction scheme to be formulated.