Synthesis and redox properties of trans-[MBr2(L)4] (M = Ru, Os, L = PPhH2, PPh2H; M = Os, L = PCy2H) and the crystal structure of trans-[OsBr2(PPh2H)4] · Et2O

Article abstract of DOI:10.1016/0277-5387(96)00053-8

The complexes [MBr₂(PPh₂H)₄], [MBr₂(PPhH₂)₄] (M = Ru or Os) and [OsBr₂(PCy₂H)₄] are obtained upon reaction of RuBr₃ or [OsBr₆]^2- with an excess of the appropriate primary or secondary phosphine in refluxing, deoxygenated EtOH. ³¹P-{¹H} and ³¹P NMR spectroscopy confirm the retention of the P-bound protons and indicate that the trans-dibromo arrangement occurs, except in the case of [RuBr₂(PPh₂H)₄], where both the cis and trans forms are seen. A crystal structure analysis on [OsBr₂(PPh₂H)₄] · Et₂O shows the Os^II ion occupying a crystallographic inversion centre and coordinated to a distorted octahedral arrangement of two trans Br^- ligands and four equatorial PPh₂H ligands, Os - Br = 2.5883(5), Os - P = 2.351(1), 2.358(1) A, Electrochemical studies reveal reversible M^II/III redox couples at easily accessible potentials in all cases, confirming that deprotonation of the P - H functions does not occur on the cyclic voltammetry time-scale even in the more electropositive M^III species. Copyright