Synthesis of Osmapyridiniums by [4+2] Cycloaddition Reaction between Osmium Alkenylcarbyne and Nitriles.

A novel [4+2] cycloaddition reaction between osmium alkenylcarbyne complex [OsHCl2{CC(PPh3)CHPh}(PPh3)2]+BF4− ( 1) and nitriles (acetonitrile and benzonitrile) provided metallapyridiniums [OsCl2{CHC(PPh3)CPhCRNH}(PPh3)2]+BF4− (R=CH3 ( 2), Ph ( 3)) and OsCl3{CHC(PPh3)CPhCPhNH}(PPh3) ( 4). A possible mechanism was proposed. Treatment of 2 with n-BuLi and NEt3 afforded osmapyridines OsCl2{CHC(PPh3)CPhCCH3N}(PPh3)2 ( 5) and [OsCl{CHC(PPh3)CPhCCH3N}(C6H5N)(PPh3)2]+BF4− ( 6). The ligands of osmapyridiniums 2 and 4 were changed, thus providing a series of osmapyridiniums [OsCl(SCN){CHC(PPh3)CPhC(CH3)NH}(PPh3)2]+Cl − ( 7), OsCl(SCN)2{CHC(PPh3)CPhC(CH3)NH}(PPh3) ( 8), Os(SCN)3{CHC(PPh3)CPhC(CH3)NH}(PPh3) ( 9), [OsCl{CHC(PPh3)CPhC(CH3)NH}(CH3CN)(PPh3)2]+(BF4−)2 ( 10), [OsCl{CHC(PPh3)CPhC(CH3)NH}-( η2-1,10-phenanthroline)(PPh3)]+(BF4−)Cl− ( 11), [OsCl{CHC(PPh3)CPhC(CH3)NH}(η2-8-hydroxyquinoline) (PPh3)]+BF4− ( 12), and [Os{CHC(PPh3)CPhCPhNH}(CH3CN)3(PPh3)]+(BF4−)3 ( 13). Most of these products were characterized by NMR spectroscopy, elemental analysis and single crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]