OSMIUM(II) COMPLEXES WITH THE HYBRID LIGAND 1-(DIPHENYLPHOSPHINO)-2-(2-PYRIDYL)ETHANE

Osmium(II) forms with 1-(diphenylphosphino)-2-(2-pyridyl)ethane (ppye) either mononuclear [OsX2-(ppye-P,N)2] 1 or binuclear [(ppye-P,N)2Os(mu-X)2Os(ppye-P,N)2] [PF6]2 2 (X = Cl or Br) derivatives, which have been characterized by UV/VIS, IR, and NMR spectroscopy. The six-co-ordinate 1 reacted with CO yielding either neutral [OsX2(CO)(ppye-P)(ppye-P,N)] or cationic [OsX(CO)(ppye-P,N)2]+ depending on the nature of the solvent. The latter can also be prepared by reaction between 2 and CO in dichloromethane. All the carbonyl derivatives initially formed have the CO group trans to a P atom and can be thermally converted into the isomer having mutually cis P and CO groups. The binuclear complexes 2 dissociate in solution to give five-co-ordinate [OsX(ppye-P,N)2]+ or the solvento species [OsX(solv)(ppye-P,N)2]+ depending on the solvent. With MeCN also the disolvento species [Os(MeCN)2(ppye-P,N)2]2+ is formed, which has been isolated in the solid state as the hexafluorophosphate salt. It undergoes substitution reactions with neutral ligands affording the mono-acetonitrile complexes [Os(MeCN)L(ppye-P,N)2]2+ [L = P(OEt)3, PMe2Ph or pyridine]. Complexes 2 also react with the same ligands giving cationic derivatives of the type [OsX(L)(ppye-P,N)2]+.