Studies of N-heterocyclic compounds with triosmium clusters: Formation of the heterocyclic-linked dicluster compound [Os-6(mu-H)(2)(mu(3)-C6H4N3)(2)(CO)(18)]

The cluster [Os-3(CO)(10)(MeCN)(2)] reacts with indazole (C7H6N2) to give two isomeric products [Os-3(mu-H)(mu-C7H5N2)(CO)(10)] in which the five-membered ring has been metallated with N-H cleavage to give an N,N-bonded isomer or with C-H cleavage to give a C,N-bonded isomer. These two isomers have very similar X-ray structures but can be clearly distinguished by H-1 NMR methods. They are shown to correspond to related clusters derived from pyrazole. Benzotriazole (C6H5N3) also reacts (as shown earlier by others) to give two isomers: an N,N-bonded species [Os-3(mu-H)(mu-C6H4N3)(CO)(10)] coordinated only through the five membered ring and a minor C,N-bonded isomer [Os-3(mu-H)(mu-C6H4N3)(CO)], metallated at the C-6 ring acid coordinated through both rings. The former isomer reacts with Me3NO in acetonitrile to give [Os-3(mu-H)(mu-C6H4N3)(CO)(9)(MeCN)] which thermally looses MeCN to produce the coupled product [Os-6(mu-H)(2)(mu(3)-C6H4N3)(2)(CO)(18)] which was shown by X-ray structure determination to have all six nitrogen atoms coordinated to osmium, a novel situation for coordinated benzotriazole. The two Os-3 units are Linked together by an OsNNOsNN ring in a boat conformation with the whole cluster adopting C-2 symmetry. (C) 1997 Elsevier Science S.A.