Coordination of imines on Os3 clusters:: Effect of the solvent in addressing isomer formation

Imine ligands terminally bound to triosmium clusters have been prepared by the reaction of Os-3(mu-H)(2)-(CO)(10) with NH3 and a keto or aldhehydic substrate. However reactions in nonpolar solvents yield only one of the two possible isomers. In contrast, reactions in polar solvents, such as methanol, yield both isomers. Experimental methods are described that clearly demonstrate that the overall stereochemistry of the resulting complexes is dependent upon the competition between intra- and intermolecular hydrogen-bonding interactions. The isomers have been unambiguously assigned using N-15 and C-13 labeling as well as T-1 measurements.