DIMOLYBDENUM OXO-IMIDO COMPLEXES - REACTIVITY OF [(MEC5H4)2MO2O2(MU-O)(MU-NPH)] AND CRYSTAL-STRUCTURE OF [(MEC5H4)2MO2O(S)(MU-O)(MU-NPH)]

Reaction of hydrogen sulphide with [(MeC5H4)2Mo2O2(mu-O)(mu-NPh)] (1) results in substitution of one of the terminal oxo moieties to give [(MeC5H4)2Mo2O(S)(mu-O)(mu-NPh)] (2) in high yield. The crystal structure of 2 has been determined. Whereas 1 is stable to hydrolysis in neutral media, heating 2 in wet toluene gives 1 by substitution of the terminal sulphido ligand. Addition of mineral acid to either 1 or 2 results in hydrolysis of the bridging imido moiety to give [(MeC5H4)MoO(mu-O)]2 (3) or [(MeC5H4)Mo2O2(mu-O)(mu-S)] (4) respectively. The former reaction has been investigated by H-1 NMR spectroscopy utilising trifluoroacetic acid which shows that initial protonation of 1 occurs selectively at a terminal oxo site to give [(MeC5H4)2Mo2O(OH)(mu-O)(mu-NPh)][CF3CO2] (5). Reaction of 2 with phenylisocyanate gives [(MeC5H4)2MoS(NPh)(mu-NPh)2] (6) and 1 via competitive reactions involving the replacement of oxo or sulphido moieties respectively.