Treatmentof OsCl2(PPh3)2(CHC(PPh3)CH(OH)-η2-CCH) (1) with PPh3and Bu4NCl in CH2Cl2under air gave paramagnetic osmacyclopentene [OsCl2(PPh3)2(CHC(PPh3)CH(OH)C(CH(PPh3)))]Cl (5). Heating the suspension of 5in CH2Cl2under a nitrogen atmosphere ledto the formation of η2-allene-coordinated osmacycleOsCl2(PPh3)(CHC(PPh3)CHCCH(P(C6H4)Ph2)) (6) and chloro-osmabenzene OsCl2(PPh3)2(CHC(PPh3)CHCClCH)(7) via disproportionation reaction. Oxidative transformationof 5under an oxygen atmosphere yielded osmafuran [OsCl(PPh3)2(CHC(PPh3)CHO)(CC(PPh3))]Cl (10). In addtion, complexes 6, 7, and 10can also undergo ligand substitutionreactions with NaSCN to afford more stable analogues. [ABSTRACT FROM AUTHOR]