Diazo complexes of osmium: preparation of binuclear derivatives with bis(aryldiazene) and bis(aryldiazenido) bridging ligands

Depending on experimental conditions and the nature of the phosphite, the reaction of OsH2P4 [P=P(OEt)3 and PPh(OEt)2] with bis(aryldiazonium) salts [N2Ar–ArN2](BF4)2 [Ar–Ar=4,4′-C6H4–C6H4, 4,4′-(2-CH3)C6H3–C6H3(2-CH3), 4,4′-C6H4–CH2–C6H4 and 1,5-C10H6] afford the cis and the trans binuclear [{OsHP4}2(μ-HNNAr–ArNNH)](BPh4)21, 2 aryldiazene derivatives. These complexes 1, 2 further react with the mono(diazonium) (4-CH3C6H4N2)BF4 salt to give the bis(aryldiazene) [{Os(4-CH3C6H4NNH)P4}2(μ-HNNAr–ArNNH)](BPh4)43, 4 derivatives. Binuclear bis(aryldiazenido) [{OsP4}2(μ-N2Ar–ArN2)](BPh4)2 (6) [P=P(OEt)3; Ar–Ar=4,4′-C6H4–C6H4, 4,4′-C6H4–CH2–C6H4] complexes were prepared by deprotonating with NEt3 the nitrile-diazene [{Os(4-CH3C6H4CN)P4}2(μ-HNNAr–ArNNH)](BPh4)4 (5) derivatives. The aryldiazenido compounds 6 react with HCl to give the new aryldiazene [{OsClP4}2(μ-HNNAr–ArNNH)](BPh4)2 (7) derivatives. The characterisation of the complexes by IR and 1H, 31P, 15N NMR data is also discussed. The reaction of the hydride OsH2(PPh2OEt)4 with mono(diazonium) salts was also studied and led exclusively to the mono(aryldiazene) [OsH(ArN NH)(PPh2OEt)4]BPh4 (8) (Ar=C6H5, 4-CH3C6H4) derivatives. Spectroscopic data (1H, 31P, 15N NMR) on 15N-labelled derivatives suggest the presence of two isomers with the N-bonded and the π-bonded ArNNH ligand, respectively.