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

Abstract The synthesis and characterization of the perchlorato derivatives of bis(isocyanide)tetrakis(phenyl)porphynatoruthenium(III) [Ru(TPP)(RNC) 2 ]ClO 4 ( 1 , R= t Bu; 2 , R=2,6-xylyl) are reported. The 1 H-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 g II =1.99 at 4 K, Σ g 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.