Synthesis, characterization, and fiber-optic infrared reflectance spectroelectrochemical studies of some dinitrosyl iron diphosphine complexes Fe(NO)2L2 (L = P(C6H4X)3)

A series of iron dinitrosyl complexes of the form Fe(NO)2(P(C6H4X)3)2 (X = p-OMe (1), p-Me (2), m-Me (3), p-H (4), p-F (5), p-Cl (6), p-CF3 (7)) has been prepared from the reactions of Fe(NO)2(CO)2 and the respective triarylphosphines. Complexes 1–7 have been characterized by IR and 31P NMR spectroscopy, and by X-ray crystallography for 1 and 7. In general, the compounds with the more basic phosphines display lower υNO stretches in the IR spectra than those with the less basic phosphines, and the trends in υNO as a function of Hammett parameter and solvent donor/acceptor number were analyzed. The redox behavior of compounds 1–7 in CH2Cl2 were studied by cyclic voltammetry at a Pt electrode. In general, the compounds undergo one-electron oxidations. Infrared spectroelectrochemistry revealed that the oxidations generate the derivatives with υNOs that are ∼100 cm−1 higher in energy indicative of Fe(NO)2-centered oxidations.