IDENTIFICATION OF ISOMERIC MESO-DIOXO DERIVATIVES OF OCTAETHYLPORPHYRIN AND SEPARATION AND STRUCTURAL CHARACTERIZATION OF THE NICKEL(II) COMPLEXES

Oxidation of Zn(II)(OEP) (OEP is the dianion of octaethylporphyrin) with thallium(III) trifluoroacetate is shown to form the previously unknown cis-dioxooctaethylporphodimethene (cis-H2OEPO2) as well as the known, isomeric trans-dioxooctaethylporphodimethene (trans-H2OEPO2). While these have not been separated, their nickle (II) complexes are readily separated by chromatography on silica gel Electronic absorption and H-1 NMR spectra are reported for these diamagnetic planar complexes. Addition of pyridine to either Ni(trans-OEPO2) or Ni(cis-OEPO2) yields six-coordinate, paramagnetic (S = 1) adducts. Dark violet Ni(II)(cis-OEPO2), C36H42N4NiO2, crystallizes in the tetragonal space group I4(1)/a with a = 14.664(7) angstrom and c = 14.163(7) angstrom at 130 K with Z = 4. Refinement of 745 reflections and 102 parameters yields R = 0.039, R(w) = 0.043. The nickel is four-coordinate (Ni-N) distance is 1.912(3) angstrom), and its coordination geometry is planar, while the macrocycle displays a saddle-shaped distortion. The keto groups are disordered over the four meso positions. Crystallization of Ni(II)(trans-OEPO2) from pyridine yields dark orange (py)2Ni(trans-OEPO2), C46H50N6NiO2, which crystallizes in the triclinic space group P1 with a = 9.878(4) angstrom, b = 10.212(4) angstrom, c = 10.503(4) angstrom, alpha = 80.08(3)-degrees, beta = 89.28(3)-degrees, and gamma = 66.50(3)-degrees at 130 K with Z = 1. Refinement of 2149 reflections and 260 parameters yields R = 0.030, R(w) = 0.040. The structure consists of a six-coordinate nickel ion at the center of the nearly planar macrocycle with the oxygen atoms disordered unequally into two sites so that it is clear that the trans-dioxo unit is present.