Synthesis, characterization and protonation reaction of copper and palladium complexes bearing nitrite ligands in O,O-bidentate and N-monodentate bonding fashions

Cu(Ph2P(o-C6H4C(O)H))2(NO2) (3) has been prepared in high yield by treating [Cu(Ph2P(o-C6H4C(O)H))2(NCMe)]BF4 (2) with [Ph2PNPPh2]NO2 at ambient temperature. The nitrite ligand of 3 is coordinated to the Cu(I) center in an O,O-bidentate mode. Protonation of 3 releases NO molecule, which mimics the reactivity of the Type 2 Cu-NiRs. In contrast, reaction of [Pd(NCMe)4](BF4)2 and Ph2P(o-C6H4C(O)H) affords cis-[Pd(Ph2P(o-C6H4C(O)H))2](BF4)2 (4) with the Pd2+ ion chelated by two phosphino–aldehyde moieties. The hemilabile formyl ligands of 4 can be displaced by NO2− to produce trans-Pd(Ph2P(o-C6H4C(O)H))2(NO2)2 (5), of which the nitrite ligands present an N-monodentate bonding feature. Protonation of 5 with HBF4, however, regenerates compound 4, likely via elimination of nitrous acid. The structures of 3–5 have been determined by an X-ray diffraction study.