Conversion of OsH 2(CO)(PPh 3) 3 to [OsH(CO)(PPh 3) 2L 2] +(L = pyridine, 4-tert-butylpyridine) by oxidation, hydride abstraction and protonation

Abstract

Two bis(pyridine) analogues of the 2,2′-bipyridine complex [OsH(CO)(PPh 3) 2(bpy)] − have been synthesized from the dihydride OsH 2(CO)(PPh 3) 3 ( 1). Chemical or electrochemical oxidation of 1, even in the presence of excess pyridine, is an overall oneelectron process. The oxidation is proposed to involve the reaction of radical cations with the starting dihydride to form a 1:1 mixture of the 17-electron complex OsH(CO)(PPh 3) 3 and the trihydride [OsH 3(CO)(PPh 3) 3] +. Both oxidation of the 17-electron complex and reductive elimination of H 2 from the trihydride cation, both accompanied by pyridine coordination, would give [OsH(CO)(PPh 3) 3(Py)] +. Reaction of this proposed intermediate with excess pyridine yields [OsH(CO)(PPh 3) 3(Py) 2] + as the observed final product. This bis(pyridine) complex is also produced by hydride abstraction from 1 in the presence of pyridine and by protonation of 1 with HBF 4 followed by reaction with pyridine. 4-Tertbutylpyridine participates in the same reactions. The pyridine complexes 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 trans-oriented phosphines and cis-pyridines.