Electronic structure of iron chlorins: Characterization of bis(L-valine methyl ester)(meso-tetraphenylchlorin)iron(III)triflate and bis(L-valine methyl ester)(meso-tetraphenylchlorin)iron(II)

摘要

The synthesis and characterization of the two iron chlorin complexes [Fe-III(TPC)(NH2CH(CO2CH3)(CH(CH3)(2)))(2)]-CF3SO3 (1) and Fe-II(TPC)[(NH2CH(CO2CH3)(CH(CH3)(2))](2) (2) are reported. The crystal structure of complex 1 has been determined. The X-ray structure shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 2.034(4) Angstrom, and to the pyrrole trans to it N(2), 2.012(4) Angstrom, are longer than the distances to the two remaining nitrogens [N(1), 1.996(4) Angstrom, and N(3), 1.984(4) Angstrom], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole. The H-1 NMR isotropic shifts at 20 degreesC of the different pyrrole protons of 1 varied from -0.8 to -48.3 ppm according to bis-ligated complexes of low-spin ferric chlorins. The EPR spectrum of [Fe(TPC)(NH2CH(CO2CH3)(CH(CH3)(2)))(2)]CF3SO3 (1) in solution is rhombic and gives the principal g values g(1) = 2.70, g(2) = 2.33, and g(3) = 1.61 (Sigmag(2) = 15.3). These spectroscopic observations are indicative of a metal-based electron in the d(pi) orbital for the [Fe(TPC)(NH2CH(CO2CH3)(CH(CH3)(2)))(2)]CF3SO3 (1) complex with a (d(xy))(2)(d(xz)d(yz))(3) ground state at any temperature. The X-ray structure of the ferrous complex 2 also shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 1.991(5) Angstrom, and to the pyrrole trans to it N(2), 2.005(6) Angstrom, are slightly different from the distances to the two remaining nitrogens [N(1), 1.988(5) Angstrom, and N(3), 2.015(5) Angstrom], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole. [References: 62]