SYNTHESIS, CHARACTERIZATION, AND PHOTOCHEMISTRY OF BIS(ARENE) AND ACETONITRILE COMPLEXES OF OSMIUM(II)

Osmium complexes of arenes, acetonitrile, and chloride have been studi ed. The yield has been significantly increased for the synthesis of (e ta(6)-C6H6)Os(NCCH3)Cl-2, an excellent starting material for the synth esis of Osbenzene complexes. Reactivity studies with this complex show that one chloride is displaced by Ag+ in acetonitrile to give [(eta(6 )-C6H6)Os(NCCH3)(2)Cl](+) but both chlorides are displaced by Ag+ in a cetone to give [(eta(6)-C6H6)Os(acetone)(3)](2+). The actone ligands o f the latter complex can be displaced by acetonitrile to give [(eta(6) -C6H6)Os(NCCH3)(3)](2+) and by other arenes (1,3,5-triethylbenzene, he xamethylbenzene, durene, naphthalene) to give [(eta(6)-C6H6)Os(arene)] (2+) complexes. Studies of thermal ligand exchange with the [(eta(6)-C 6H6)Os(NCCH3)(3-x)Cl-x]((2-x)+) complexes indicate that chloride enhan ces the rate of thermal acetonitrile exchange. Photolysis of [(eta(6)- C6H6)Os(NCCH3)(3)](2+) and [(eta(6)-C6H6)Os(NCCH3)(2)Cl](+) in acetoni trile results in loss of benzene to produce the new complexes [Os(NCCH 3)(6)](2+) and [Os(NCCH3)(5)Cl](+) in high yield. Photolysis of (eta(6 )-C6H6)Os(NCCH3)Cl-2 initially results in the formation of Os(NCCH3)(4 )Cl-2, which subsequently undergoes photochemical loss of chloride to give [Os(NCCH3)(5)Cl]Cl. Examination of this reaction by H-1 NMR spect roscopy indicates that the cis isomer of Os(NCCH3)(4)Cl-2 is produced. The photolysis of [(eta(6)-C6H6)Os(P(Ph)(3))(NCCH3)Cl](+) in acetonit rile also leads to release of benzene to form the cis product. Electro chemical data acquired for the new acetonitrile complexes ([Os(NCCH3)( 6)](2+), [Os(NCCH3)(5)Cl](+), and Os(NCCH3)(4)Cl-2) show highly revers ible, one-electron oxidations with the potential a linear function of the stoichiometry. The osmium complexes are about 0.5 V easier to oxid ize than the corresponding ruthenium analogs.