High-Nuclearity Osmium Carbonyl Cluster Complexes Containing (6-Methylpyrid-2-yl)imido Ligands. Synthesis of Hepta-, Octa-, and Nonanuclear Derivatives

Three high-nuclearity osmium carbonyl cluster complexes, [Os7(μ5-κ2-ampy)(μ-CO)2(CO)17] (1), [Os8(μ3-Η)(μ-H)(μ5-κ2-ampy)(μ-CO)(CO)19] (2), and [Os9O(μ4-κ2-ampy)2(CO)18] (3) (H2ampy = 2-amino-6-methylpyridine), have been prepared by heating [Os3(CO)12] with 0.5 equiv of H2ampy in decane at reflux temperature. The trinuclear complex [Os3(μ-Η)(μ3-κ2-Hampy)(CO)9] is an intermediate in this reaction. The metallic skeletons of 1 and 2 can be described as mono- (1) or bi-face-capped (2), basal-edge-bridged, square pyramids, whereas that of compound 3 consists of a pentagonal bipyramid with two equatorial edges spanned by metal atoms. In the three clusters, the ampy ligands are attached to edge-bridging Ru atoms through their pyridine N atoms, while they also cap metallic squares (in 1 and 2) or triangles (in 3) through their imido N atom. An additional feature of compound 3 is that it contains a terminal oxo ligand, unprecedented in osmium carbonyl cluster chemistry.