Preparation and Reactions of [CpOs(CH₃CN)₃]⁺. A Useful Synthetic Intermediate for the Preparation of CpOsL₃ Compounds

A photochemical synthesis of [CpOs(CH 3 CN) 3 ] + is reported (Cp = η 5 -cyclopentadienyl). Photolysis of [CpOs(Bz)] + (Bz = η 6 -benzene) in acetonitrile solution gives [CpOs(CH 3 CN) 3 ] +, but only 30% conversion is achieved before significant photochemically induced decomposition of [CpOs(CH 3 CN) 3 ] + occurs. Photolysis of acetonitrile solutions of [CpOs(Bz)] + that contain biphenyl eliminates this side reaction and allows the high-yield preparation of [CpOs(CH 3 CN) 3 ] + . Quantum yields for the photodearylation reaction are identical in the presence or absence of biphenyl, suggesting that biphenyl acts as a passive filter, slowing the photochemical decomposition of [CpOs(CH 3 CN) 3 ] + . [CpOs(CH 3 CN) 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(η 6 -anthracene)]PF 6, [CpOs(η 6 -rubrene)]PF 6, CpOs(BPz 4 ) (BPz 4 - = tetrakis(1-pyrazolyl)borate), CpOs(HBPz 3 ) (HBPz 3 - = hydrotris(1-pyrazolyl)borate), [CpOs(CH 3 CN) 2 CO]PF 6, and CpOs(CO) 2 Br. 1 H NMR evidence for an additional species ([(CpOs)(CpOs(CH 3 CN))(μ-η 6,η 4 -anth)] 2+ ) that contains an η 6 and an η 4 CpOs + group is presented. Intriguing differences between the reactivity of [CpOs(CH 3 CN) 3 ] + and [CpRu(CH 3 CN) 3 ] + with rubrene are observed, with the osmium complex showing a remarkable kinetic preference for the naphthacene backbone relative to the pendant phenyl rings.