PREPARATION AND REACTIONS OF [CPOS(CH3CN)(3)](- A USEFUL SYNTHETIC INTERMEDIATE FOR THE PREPARATION OF CPOSL(3) COMPOUNDS() )

A photochemical synthesis of [CpOs(CH3CN)(3)](+) is reported (Cp = eta (5)-cyclopentadienyl). Photolysis of [CpOs(Bz)](+) (Bz = eta(6)-benzen e) in acetonitrile solution gives [CpOs(CH3CN)(3)](+), but only 30% co nversion is achieved before significant photochemically induced decomp osition of [CpOs(CH3CN)(3)](+) occurs. Photolysis of acetonitrile solu tions of [CpOs(Bz)](+) that contain biphenyl eliminates this side reac tion and allows the high-yield preparation of [CpOs(CH3CN)(3)](+). Qua ntum yields for the photodearylation reaction are identical in the pre sence or absence of biphenyl, suggesting that biphenyl acta as a passi ve filter, slowing the photochemical decomposition of [CpOs(CH3CN)(3)] (+). [CpOs(CH3CN)(3)](+) reacts with arenes, CO, and polypyrazolylbora te ligands, providing a high-yield route to CpOsL(3) compounds under m ild conditions. Compounds that were synthesized and fully characterize d include [CpOs(eta(6)-anthracene)]PF6, [CpOs(eta(6)-rubrene)]PF6, CpO s(BPz(4)) (BPz(4)(-) = tetrakis(1-pyrazolyl)borate), CpOs(HBPz(3)) (HB Pz(3)(-) = hydrotris(1-pyrazolyl)borate), [CpOs(CH3CN)(2)CO]PF6, and C pOs(CO)(2)Br. H-1 NMR evidence for an additional species ([(CpOs)(CpOs (CH3CN))(mu-eta(6),eta(4)-anth)](2+)) that contains an eta(6) and an e ta(4) CpOs(+) group is presented. Intriguing differences between the r eactivity of [CpOs(CH3CN)(3)](+) and [CpRu(CH3CN)(3)](+) with rubrene are observed, with the osmium complex showing a remarkable kinetic pre ference for the naphthacene backbone relative to the pendant phenyl ri ngs.