Substituent Effects on Nitrosyl Iron Corrole Complexes Fe(Ar3C)(NO)

Abstract

A series of nitrosyl tris(5,10,15-aryl)corrolate complexes of iron(III) Fe(Ar3C)(NO) with different substituents on the aryl groups have been prepared, and certain spectroscopic and reaction properties were compared. The cyclic voltammetric analysis of the various Fe(Ar3C)(NO) complexes demonstrated that both the one-electron oxidation and one-electron reduction potentials respond in systematic and nearly identical trends relative to the electron-donor properties of the substituents. A similar pattern was seen in the nitrosyl stretching frequency, nu(NO), which modestly decreased with the stronger donor substituents. Flash photolysis of Fe(Ar3C)(NO) solutions in toluene leads to NO dissociation followed by rapid [NO]-dependent decay of the transients formed (presumably Fe(Ar3C)) to regenerate the original spectra. As was seen in an earlier flash photolysis study of Fe(TNPC)(NO) (TNPC3- = 5,10,15-tris(4-nitro-phenyl)corrolate; Joseph, C.; Ford, P. C. J. Am. Chem. Soc. 2005, 127, 6737-6743), the second-order rate constants, k(NO), are all much faster ((1-9) x 10(8) M(-1) s(-1) at 298 K) than those for analogous iron(III) complexes of porphyrins. However, on a more microscopic level there is no obvious pattern in these rates with respect to the donor properties of the aryl ring substituents. The high reactivity of the ferric triarylcorrolates with NO data is interpreted in terms of the strongly electron-donating character of the Ar3C3- ligand and the quartet electronic configuration of the Fe(Ar3C) intermediate.