α-Diimine Ligand Coordination and C-H Bond Activation in the Reaction of Os3(CO)10(MeCN)2 with 6-R-2,2'-Bipyridine (where R = Et, Ph): X-ray Diffraction Structures of the Ortho-Metalated Hydride Clusters HOs3(CO)9(N2C10H6-6-R)

The reactivity of the labile cluster Os-3(CO)(10)(MeCN)(2) (1) with the monofunctionalized heterocyclic ligands 6-R-2,2'-bipyridine (where R = Et, Ph) has been investigated. The alkyl-substituted heterocycle 6-Et-2,2'-bipyridine reacts with 1 in refluxing CH2Cl2 to give an isomeric mixture of HOs3(CO)(9)(N2C12H11) due to cyclometalation of the side-chain ethyl group (2) and ortho metalation of the unsubstituted bipyridine ring (3). The solid-state structure of the latter cluster, HOs3(CO)(9)(N2C10H6-6-Et) (3), has unequivocally established the site of the C-H bond activation in the product. Treatment of 1 with the aryl-substituted ligand 6-Ph-2,2'-bipyridine proceeds similarly with ortho metalation at the ancillary phenyl group and the C-6' ortho site of the unsubstituted bipyridine ring, as verified by H-1 NMR spectroscopy. The X-ray diffraction structure of the thermodynamically more stable bipyridine-metalated cluster HOs3(CO)(9)(N2C10H6-6-Ph) (5) has been determined. The course of these reactions is discussed with respect to our recent study involving the reaction of cluster 1 with the ligand 6-Me-2,2'-bipyridine.