Synthesis, Characterization and Electrochemical Properties of Stable Osmabenzenes Containing PPh₃ Substituents

Treatment of [OsCl(2)(PPh(3))(3)] with HC[triple bond]CCH(OH)C[triple bond]CH/PPh(3) produces the osmabenzene [Os{CHC(PPh(3))CHC(PPh(3))CH}Cl(2)(PPh(3))(2)][OH] (2), which is air stable in both solution and solid state. The key intermediate of the one-pot reaction, [OsCl(2){CH=C(PPh(3))CH(OH)C[triple bond]CH}(PPh(3))(2)] (3), and the related complex [Os(NCS)(2){CHC(PPh(3))CH(OH)C[triple bond]CH}(PPh(3))(2)] (7) have been isolated and characterized, further supporting the proposed mechanisms for the reaction. Reactions of 3 with PPh(3), NaI, and NaSCN give osmabenzene 2, iodo-substituted osmabenzene [Os{CHC(PPh(3))CHCICH}I(2)(PPh(3))(2)] (4), and thiocyanato-substituted osmabenzene [Os{CHC(PPh(3))CHC(SCN)CH}(NCS)(2)(PPh(3))(2)] (5) respectively. Similarly, reaction of [OsBr(2)(PPh(3))(3)] with HC[triple bond]CCH(OH)C[triple bond] CH in THF produces [OsBr(2){CH=C(PPh(3))CH(OH)C[triple bond]CH}(PPh(3))(2)] (9), which reacts with PPh(3)/Bu(4)NBr to give osmabenzene [Os{CHC(PPh(3))CHC(PPh(3))CH}Br(2)(PPh(3))(2)]Br (10). Ligand substitution reactions of 2 produce a series of new stable osmabenzenes 11-17. An electrochemical study shows that osmabenzenes 2, 12, and 14-17 have interesting different electrochemical properties due to the different co-ligand. The oxidation potentials of complexes 2, 12, 16, and 17 with Cl, NCS, and N(CN)(2) ligands gradually positively shift in the sequence of Cl<NCS<N(CN)(2). Among the six compounds, only 12 and 17 undergo a well-behaved, nearly reversible and a quasi-reversible reduction process, respectively, indicating that two NCS or N(CN)(2) ligands contribute to the stabilization of their reduced states.