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=tBu; 2, R=2,6-xylyl) are reported. The 1H-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⊥=2.07 and gII=1.99 at 4 K, Σg2=12.53. These spectroscopic observations are indicative of a metal-based electron for complex with a (dxz, dyz)4 (dxy)1 ground state at any temperature.