Conversion of OsH2(CO)(PPh3)3 to [OsH(CO)(PPh3)2L2]+ (L = pyridine, 4-tert-butylpyridine) by oxidation, hydride abstraction and protonation

Article abstract of DOI:10.1016/0277-5387(95)00459-9

Two bis(pyridine) analogues of the 2,2'-bipyridine complex [OsH(CO) (PPh₃)₂(bpy)] have been synthesized from the dihydride OsH₂(CO)(PPh₃)₃ (1). Chemical or electrochemical oxidation of 1, even in the presence of excess pyridine, is an overall one-electron 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)(PPh₃)₃ and the trihydride [OsH₃(CO)(PPh₃)₃]⁺. Both oxidation of the 17-electron complex and reductive elimination of H₂ from the trihydride cation, both accompanied by pyridine coordination, would give [OsH(CO)(PPh₃)₃(Py)]⁺. Reaction of this proposed intermediate with excess pyridine yields [OsH(CO)(PPh₃)₂(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 HBF₄ 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.