Reaction of ArNCO with syn-[MoO(µ-O)(S2CNR2)]2 or syn-[MoO(µ-NAr)(S2CNR2)]2 at 110 °C leads to the facile formation of bridging ureato complexes [Mo2(NAr)2(µ-NAr){µ-ArNC(O)NAr}(S2CNR2)2]
(Ar = Ph, p-tol; R = Me, Et, Pr), formed upon substitution of all oxo ligands and addition of a further equivalent of isocyanate across one of the bridging imido ligands. Related sulfido-bridged complexes [Mo2(NAr)2(µ-S){µ-ArNC(O)NAr}(S2CNR2)2] have been prepared from syn-[Mo2O2(µ-O)(µ-S)(S2CNR2)2]. When reactions with syn-[MoO(µ-NAr)(S2CNEt2)]2 were followed by NMR, intermediates were observed, being formulated as [Mo2O(NAr)(µ-NAr){µ-ArNC(O)NAr}(S2CNEt2)2], which at higher temperatures convert to the fully substituted products. A crystallographic study of [Mo2(N-p-tol)2(µ-S){µ-p-tolNC(O)N-p-tol}(S2CNPr2)2] reveals that the bridging ureato ligand is bound asymmetrically to the dimolybdenum centre—molybdenum–nitrogen bonds trans to the terminal imido ligands being significantly elongated with respect to those cis—a result of the trans-influence of the terminal imido ligands. This trans-influence also leads to a trans-effect, whereby the exchange of aryl isocyanates can occur in a regioselective manner. This is followed by NMR studies and confirmed by a crystallographic study of [Mo2(N-p-tol)2(µ-N-p-tol){µ-p-tolNC(O)NPh}(S2CNEt2)2]—the PhNCO occupying the site trans to the terminal imido ligands. Ureato complexes also react with PhNCS, initially forming [Mo2(NAr)2(µ-S){µ-ArNC(O)NAr}(S2CNR2)2], resulting from exchange of the bridging imido ligand for sulfur, together with small amounts of [Mo2(NAr)2(µ-S)(µ-S2)(S2CNEt2)2], containing bridging sulfide and disulfide ligands. The ureato complexes [Mo2(NAr)2(µ-S){µ-ArNC(O)NAr}(S2CNR2)2] react further with PhNCS to give [Mo2(NAr)2(µ-S)2(S2CNR2)2]n
(n
= 1, 2), which exist in a dimer–tetramer equilibrium. In order to confirm these results crystallographic studies have been carried out on [Mo2(N-p-tol)2(µ-S)(µ-S2)(S2CNEt2)2] and [Mo2(N-p-tol)2(µ-S)2(S2CNPr2)2]2.
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