High-nuclearity ruthenium carbonyl cluster complexes derived from 2-amino-6-methylpyridine: synthesis of nonanuclear derivatives containing mu4- and mu5-oxo ligands

Nonanuclear cluster complexes Ru9(mu3-H)2(mu-H)(mu5-O)(mu4-ampy)(mu3-Hampy)(CO)21] (4) (H2ampy = 2-amino-6-methylpyridine), Ru9(mu5-O)2(mu4-ampy)(mu3-Hampy)2(mu-CO)(CO)20] (5), Ru9(mu5-O)2(mu4-ampy)(mu3-Hampy)2(mu-CO)2(CO)19] (6), and Ru9(mu4-O)(mu5-O)(mu4-ampy)(mu3-Hampy)(mu-Hampy)(mu-CO)(CO)19] (7), together with the known hexanuclear Ru6(mu3-H)2(mu5-ampy)(mu-CO)2(CO)14] (2) and the novel pentanuclear Ru5(mu4-ampy)(2)(mu-CO)(CO)12] (3) complexes, are products of the thermolysis of Ru3(mu-H)(mu3-Hampy)(CO)9] (1) in decane at 150 degrees C. Two different and very unusual quadruply bridging coordination modes have been observed for the ampy ligand. Compounds 4-7 also feature one (4) or two (5-7) bridging oxo ligands. With the exception of one of the oxo ligands of 7, which is in a distorted tetrahedral environment, the remaining oxo ligands of 4-7 are surrounded by five metal atoms. In carbonyl metal clusters, quadruply bridging oxo ligands are very unusual, whereas quintuply bridging oxo ligands are unprecedented. By using 18O-labeled water, we have unambiguously established that these oxo ligands arise from water.