CONVERSION OF OSH2(CO)(PPH(3))(3) TO [OSH(CO)(PPH3)(2)L(2)](-TERT-BUTYLPYRIDINE) BY OXIDATION, HYDRIDE ABSTRACTION AND PROTONATION() (L EQUALS PYRIDINE, 4)

Two bis(pyridine) analogues of the 2,2'-bipyridine complex [OsH(CO)(PP h(3))(2)(bpy)](+) have been synthesized from the dihydride OsH2(CO)(PP h(3))(3) (1). Chemical or electrochemical oxidation of 1, even in the presence of excess pyridine, is an overall one-electron process. The o xidation is proposed to involve the reaction of radical cations with t he starting dihydride to form a 1 : 1 mixture of the 17-electron compl ex OsH(CO)(PPh(3))(3) and the trihydride [OsH3(CO)(PPh(3))(3)](+). Bot h oxidation of the 17-electron complex and reductive elimination of H- 2 from the trihydride cation, both accompanied by pyridine coordinatio n, would give [OsH(CO)(PPh(3))(3)(Py)](+). Reaction of this proposed i ntermediate with excess pyridine yields [OsH(CO)(PPh(3))(2)(Py)(2)](+) as the observed final product. This bis(pyridine) complex is also pro duced by hydride abstraction from 1 in the presence of pyridine and by protonation of 1 with HBF4 followed by reaction with pyridine. 4-Tert butylpyridine participates in the same reactions. The pyridine complex es are very similar to the previously reported 2,2'-bipyridine complex except that they do not display the bipyridine-localized reduction or metal-ligand charge transfer band. Their geometry is the same, with t rans-oriented phosphines and cis-pyridines.