EXTENSION OF THE PREPARATION OF NEW OSMIUM SPECIES TO THE CIS-TETRAAMMINE MOIETY

A useful precursor cis-[Os(NH3)4(CF3SO3)2](CF3SO3) (1) has been synthe sized by oxidation of the dinitrogen complex cis-[Os(NH3)4(N2)2]Cl2 in CF3SO3H. While the reduction of 1 in aqueous solution leads to the et a2-dihydrogen complexes1 in high yield, in acetone, and at room temper ature, however, when reduced by Mg or Zn/Hg, 1 reacts rapidly with a v ariety of unsaturated ligands. In the presence of norbornadiene and 1, 5-cyclooctadiene, the corresponding eta4-diene tetraammine complexes w ere obtained in recovered yields of 30% and 80%, respectively. Traces of acid left in 1 lead to much reduced yields of these and of other sp ecies we have prepared, owing to the formation of the diacetone alcoho l complex as a side product in which the ligand bonds to Os(II) center in eta1-(HO-) and eta2-(O=C-) fashion. In the absence of a competing ligand, this chelate complex is the major product of the reaction. In the presence of the arenes, benzene, phenol and naphthalene, reduction of 1 was found to lead to the eta6-arene triammine complexes, the rea ction yields as determined by H-1 NMR being 64%, 68%, and 95%.