Ligand substitution in 1,2-Os3(CO)10(MeCN)2 by the diphosphine (PhO)2PN(Me)N(Me)P(OPh)2: X-ray diffraction structure of 1,2-Os3(CO)10[(PhO)2PN(Me)N(Me)P(OPh)2] and DFT investigation of the isomeric Os3(CO)10[(PhO)2PN(Me)N(Me)P(OPh)2] clusters

The diphosphine 1,2-bis(diphenoxyphosphino)-1,2-dimethylhydrazine, (PhO)2PN(Me)N(Me)P(OPh)2, reacts with 1,2-Os3(CO)10(MeCN)2 (1) to afford the corresponding ligand-bridged cluster 1,2-Os3(CO)10[(PhO)2PN(Me)N(Me)P(OPh)2] (2b) in high yield. The product cluster has been characterized in solution by IR and NMR spectroscopy, and the solid-state structure determined by X-ray crystallography. Cluster 2b is thermally robust, and shows no evidence for formation of the corresponding chelated isomer 1,1-Os3(CO)10[(PhO)2PN(Me)N(Me)P(OPh)2] (2c) in refluxing toluene. The energetics for the bridged and chelated clusters have been evaluated by electronic structure calculations, and the thermodynamic preference for the ligand-bridged isomer has been confirmed. DFT calculations on the known bridged and chelated diphosphine isomers of Os3(CO)10(dppe) clusters have also been performed, and these data are contrasted with clusters 2b and 2c.