1H-NMR and EPR studies of the electronic structure of low-spin ruthenium(III) isocyanide porphyrin complexes:: unusual (dxz,dyz)4 (dxy,)1 configuration

The synthesis and characterization of the perchlorato derivatives of bis(isocyanide)tetrakis(phenyl)porphynatoruthenium(III) [Ru(TPP)(RNC)(2)]ClO4 (1, R = ' Bu; 2, R = 2,6-xylyl) are reported. The H-1-NMR isotropic shifts at 298 K of the pyrrole protons of the two complexes, varied from -5.44 ppm for 1 to + 2.55 ppm for 2 rather than the expected -31 ppm, based on previously studied aryl complexes of low-spin ruthenium porphyrins. The EPR spectrum of 2 in solution is axial, with g(perpendicular to) = 2.07 and g(II) = 1.99 at 4 K, Sigmag(2) = 12.53. These spectroscopic observations are indicative of a metal-based electron for complex with a (d(xz), d(yz))(4) (d(xy))(1) ground state at any temperature. (C) 2001 Elsevier Science B.V. All rights reserved.