OSMIUM COMPLEXES OF THE HALF-SANDWICH TYP E WITH OXIMES, IMINES, AND AZAVINYLIDENES AS LIGAND

Azavinylideneosmium complexes of the general composition [(arene)Os(=N =CRR')(L)]X (L = PMe3, PMetBu2, PiPr3) have been prepared by two metho ds. The first one uses the hydrido compound [C6H6OsHI(PMetBu2)] (2) an d oximes HON=CRR' as starting materials and proceeds via the oxime com plexes [C6H6OsH{N(OH)=CRR'}(PMetBu2)]PF6 (10, 11) as intermediates. Th ey react with Al2O3 with elimination of water to give the final produc ts 6-9. The second method starts with the dichloro- or diiodoosmium(II ) compounds [(arene)OsX2(PR3)] (14, 16, 19, 21; arene = C6H6, 1,3,5-Me 3C6H3; R = Me, iPr) which upon treatment with HN=CPh2 or imine derivat ives XN=C(R)Ph (X = Li, SiMe3) afford the azavinylidene complexes 13b, 18, 23, 33. In the reactions with HN=CPh2, the corresponding imine co mplexes [(arene)OsX(NH=CPh2)-(PR3)]X (15, 17, 20, 22) are formed as th e primary products. Whereas nucleophilic addition of H- and CH3- to th e N=C carbon atom of [C6H60s(=N=CPh2)(PMetBu2)]+ (6) gives the imidoos mium(II) compounds [C6H6Os(=NCRPh2)(PMetBu2)] (24, 25), the reaction o f [C6H60s(=N=CPh2)(PiPr3)]PF6 (13b) with LiAlH(OtBu)3 yields the hydri do(imino) derivative [C6H6OsH(NH=CPh2)(PiPr3)]PF6 (26). The bis(azido) complex [C6H6Os(N3)2(PiPr3)] (27), which is prepared either from 13b or [C6H6OSI2(PiPr3)] (14) and NaN3, undergoes a [3 + 2] cycloaddition reaction with C2(CO2Me)2. Two isomeric (triazole)osmium compounds 28, 29 have been isolated. Treatment of [C6H60s(=N = CRPh)(PiPr3)]PF6 with HX (X = O2CCF3) leads to addition of the acid to the Os=N bond and, f or R = Ph (13b), by subsequent elimination of HX to the formation of a five-membered metallaheterocycle 31. The X-ray structural analysis of [C6H60s(=N=CPh2)(PMetBu2)]PF6 (6) reveals an allene-like arrangement of the ligands and substituents around the Os=N=C unit.