Abstract The reaction of [C 6H 6OsI 2(P iPr 3]] ( 1) with Na[ON=CR 2] (R 2 = Ph 2, Me 2, C(CH 2) 5) in the presence of KPF 6 leads to the formation of the oximato osmium(II) complexes [C 6H 6Os(η 2-ON=CR 2)(P iPr 3)]PF 6 ( 6, 7, 8b) in almost quantitative yield. The mesitylene compounds [(mes)Os(η 2-ON=CR′R″)(PR 3)]PF 6 ( 9–14) have been prepared similarly using [(mes)Os(PR 3] ( 3–5) as starting materials. The synthesis of [C 6H 6Os(η 2-ON=CMe tBu)(P iPr 3)]PF 6 ( 17) has been achieved from [C 6H 6OsCl 2(P iPr 3)] ( 16) which in turn is prepared from [C 6H 6Os(η-O 2C=O)P iPr 3)] ( 15) and excess Me 3SiCl. Reaction of 1, [C 6H 6OsI 2(PMe tBu 2)] ( 2) and 3 (PR 3 = P iPr 3) with Na[ON = CMe tBu] in the presence of KPF 6, in methanol as solvent, unexpectedly yields the azavinylidene complexes [(arene)Os(=N=CMe tBu)(PR 3)]PF 6 ( 18b, 19, 20). The X-ray structural analysis of 18b reveals the presence of a nearly linear OS-N-C fragment with an OS-N distance that is in agreement with typical osmium-nitrogen double bond lengths. Related azavinylideneosmium compounds [(arene)Os(=N=CR′R″)(PR 3)]PF 6 ( 21–26) have been obtained on treatment of the corresponding oximato complexes, 7, 10 or 14 with either HN=CR′R″ or, for R′ = H and R″ Ph, the trimethyl derivative.