H-1 NMR and EPR studies of the electronic structure of low-spin iron(III) phosphonite mesotetraphenylchlorin complexes: a (d(xz),d(yz))(4)(d(xy))(1) configuration from 293 to 4 K

摘要

The synthesis and characterization of the trifluoromethanesulfonato derivatives of bis(dimethylphenylphosphonite)tetrakis(phenyl)chlorinatoiron(III), and bis(diethylphenylphosphonite)tetrakis(phenyl)chlorinatoiron(III) are reported: [Fe(TPC)(P-Ph(OMe)(2))(2)]CF3SO3 (1) and [Fe(TPC)(PPh(OEt)(2))(2)]CF3SO3 (2). The H-1 NMR isotropic shifts at 20 degreesC of the different pyrrole protons of 1 varied from 10.9 and 5.55 ppm to -11.5 ppm rather than the expected 0.6 ppm to -57.8 ppm, based on previously studied dimethylphenylphosphine complexes of low-spin iron chlorins. The EPR spectrum of [Fe(TPC)(PPh(OMe)2)2]CF3SO3 (1) in solution is rhombic and shows the principal g-values g(1) = 2.44, g(2) = 2.16 and g(3) = 1.82, Sigmag(2) = 13.9. These spectroscopic observations are indicative of a metal-based electron for 1 with a (d(xz), d(yz))(4)(d(xy))(1) ground state at any temperature in contrast to [Fe(TPC) (PPh(Me)(2))(2)]CF3SO3 complex which showed a (d(xy))(2)(d(xz)d(yz))(3) ground state at any temperature. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 37]