PALLADIUM COMPLEXES OF 21-THIAPORPHYRIN - SYNTHESES AND CHARACTERIZATION

Treatment of tetraphenyl-21-thiaporphyrin (STPPH) with palladium(II) chloride in acetonitrile yields diamagnetic [Pd-II(STPP)]Cl. The electronic and H-1 NMR spectra are reported. [Pd-II(STPP)]Cl undergoes one-electron reduction (E(1/2)(degrees) = 0.28 vs SCE) to give Pd(STPP). The product of the chemical reduction was isolated and characterized. The nature of the reduced species was examined by EPR and NMR spectroscopy. The EPR spectrum displays a rhombic pattern (g(1) = 2.042; g(2) = 2.009; g(3) = 1.962). This asymmetry suggests an electronic structure with a considerable ligand radical anion contribution. The spin density distribution has been established by H-2 NMR spectroscopy. The observed pattern of paramagnetic shifts (pyrrole positions -9.9, 7.1 ppm; 10,15 phenyl meta 17.7, ortho-8.2, para-1.2 ppm) is consistent with thiaporphyrin based localization of the unpaired electron. Pd(SDPDTP) crystallizes in the monoclinic space group P2(1)/c with a = 15.625(5) Angstrom, b = 16.039(4) Angstrom, c 15.519(6) Angstrom, and beta = 112.47(3)(degrees) at 130 K with Z = 4. Refinement of 3104 reflections and 409 parameters yielded R = 0.097. The palladium is four-coordinate with bonds to three pyrrole nitrogen atoms (Pd-N distances 2.085(11), 1.999(15), 2.061(11) Angstrom) and the thiophene sulfur (Pd-S 2.208(5) Angstrom). The palladium atom lies in the plane of the three nitrogen atoms while the thiophene is sharply tilted out of the plane. The thiophene group is bound to palladium through pyramidal sulfur in the usual eta(1)(S) fashion. The thiophene ring is bent so the dihedral angle between the CalphaSCalpha and CalphaCbetaCbetaCalpha planes is 15.6 degrees. The structure is compared to those of the related fours five-, and six-coordinate metallothiaporphyrins.