Reactivity of 2-(diphenylphosphino)pyridine and 2-(diphenylphosphine oxide)pyridine towards iron nitrosyl complexes and its relevance to oxygen activation

The nitrosyl dimer [Fe(NO)2Cl]2 (1) in the presence of 2-(diphenylphosphino)pyridine (PN) yields the [Fe(NO)2Cl(PPh2py)] (2) complex in which the PN ligand is bound to iron monodentate through its phosphorus atom. 2 is unstable and rapidly evolves to [Fe(NO)Cl(OPPh2py)] (3): coordination of the nitrogen atom of the PN ligand results in NO substitution and oxygenation of the PN ligand to the bidentate 2-(diphenylphosphine oxide)pyridine (OPN). The same compound 3 is obtained when 1 is allowed to react with the OPN ligand. Oxidation by oxygen (1 atm) of the FeNO moiety in 2, 3 or 1 in the presence of PN or OPN, results in the formation of the nitrato complex Fe(NO3)2Cl(OPN) (4).