SYNTHESIS AND REDOX PROPERTIES OF TRANS-[MBR(2)(L)(4)] (M=RU,OS, L=PPHH(2),PPH(2)H, M=OS, L=PCY(2)H) AND THE CRYSTAL-STRUCTURE OF TRANS-[OSBR2(PPH(2)H)(4)]CENTER-DOT-ET(2)O

The complexes [MBr(2)(PPh(2)H)(4)], [MBr(2)(PPhH(2))(4)] (M = Ru or Os ) and [OsBr2(PCy(2)H)(4)] are obtained upon reaction of RuBr3 or [OsBr 6](2-) with an excess of the appropriate primary or secondary phosphin e in refluxing, deoxygenated EtOH. P-31-{H-1} and P-31 NMR spectroscop y confirm the retention of the P-bound protons and indicate that the t rans-dibromo arrangement occurs, except in the case of [RuBr2(PPh(2)H) (4)], where both the cis and trans forms are seen. A crystal structure analysis on [OsBr2(PPh(2)H)(4)]. Et(2)O shows the Os-II ion occupying a crystallographic inversion centre and coordinated to a distorted oc tahedral arrangement of two trans Br- ligands and four equatorial PPh( 2)H ligands, Os-Pr = 2.5883(5), Os-P = 2.351(1), 2.358(1) Angstrom. El ectrochemical studies reveal reversible M(II/III) redox couples at eas ily accessible potentials in all cases, confirming that deprotonation of the P-H functions does not occur on the cyclic voltammetry time-sca le even in the more electropositive M(III) species. Copyright (C) 1996 Elsevier Science Ltd