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)-benzene) in acetonitrile solution gives [CpOs(CH3CN)(3)](+), but only 30% conversion is achieved before significant photochemically induced decomposition of [CpOs(CH3CN)(3)](+) occurs. Photolysis of acetonitrile solutions of [CpOs(Bz)](+) that contain biphenyl eliminates this side reaction and allows the high-yield preparation of [CpOs(CH3CN)(3)](+). Quantum yields for the photodearylation reaction are identical in the presence or absence of biphenyl, suggesting that biphenyl acta as a passive filter, slowing the photochemical decomposition of [CpOs(CH3CN)(3)](+). [CpOs(CH3CN)(3)](+) reacts with arenes, CO, and polypyrazolylborate ligands, providing a high-yield route to CpOsL(3) compounds under mild conditions. Compounds that were synthesized and fully characterized include [CpOs(eta(6)-anthracene)]PF6, [CpOs(eta(6)-rubrene)]PF6, CpOs(BPz(4)) (BPz(4)(-) = tetrakis(1-pyrazolyl)borate), CpOs(HBPz(3)) (HBPz(3)(-) = hydrotris(1-pyrazolyl)borate), [CpOs(CH3CN)(2)CO]PF6, and CpOs(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 eta(4) CpOs(+) group is presented. Intriguing differences between the reactivity of [CpOs(CH3CN)(3)](+) and [CpRu(CH3CN)(3)](+) with rubrene are observed, with the osmium complex showing a remarkable kinetic preference for the naphthacene backbone relative to the pendant phenyl rings.