Identification of isomeric meso-Dioxo derivatives of octaethylporphyrin and separation and structural characterization of the nickel(II) complexes

Abstract

Oxidation of ( ) (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 f/ww-dioxooctaethylporphodimethene (í/vms-H2OEPO2). While these have not been separated, their nickel (II) complexes are readily separated by chromatography on silica gel. Electronic absorption and NMR spectra are reported for these diamagnetic planar complexes. Addition of pyridine to either Nifirazir-OEPOz) or Ni(cfr-OEPO2) yields six-coordinate, paramagnetic (5=1) adducts. Dark violet Níii(ci'j-0EP02), C36H42N4N1O2, crystallizes in the tetragonal space group /4i/e with a = 14.664(7) A and c = 14.163(7) A at 130 K with Z = 4.Refinement of 745 reflections and 102 parameters yields R = 0.039, /?" = 0.043. The nickel is four-coordinate (Ni-N distance is 1.912(3) A), and its coordination geometry is planar, while the macrocycle displays a saddleshaped distortion. The keto groups are disordered over the four meso positions. Crystallization of Nin(irans-OEPO2) from pyridine yields dark orange (py^Nifí/ww-OEPCh), CseHsoNeNiOa, which crystallizes in the triclinic space group Plwith a = 9.878(4) A, b = 10.212(4) A, c = 10.503(4) A, a = 80.08(3)°, ß = 89.28(3)°, and = 66.50(3)°a t 130 K with Z = 1. Refinement of 2149 reflections and 260 parameters yields R = 0.030, Rv 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 fra/w-dioxo unit is present.

Unusual solvent dependent electronic absorption spectral properties of nickel(II) and copper(II) perhaloporphyrins

“…Similar behavior was reported for the ligation of piperidine to NiTPP [65] and other Ni(II) porphyrins [64]. In the solid-state, the Ni(II) porphyrins are known to exhibit six coordinate geometry [96][97][98][99][100][101][102].…”

Structural Consequences of Spin Conversion in a Sterically Encumbered Ni(II) Porphyrin

“…12 Halogenated and other electron-deficient Ni(II) porphyrins (including F430) readily bind axial ligands to form hexacoordinated high-spin Ni(II) complexes in which the d z 2 and d x 2 -y 2 orbitals are each singly populated. 1,[4][5][6][7][8] We report here that 1 does indeed bind two axial pyridines and compare the stereochemical parameters of the ligated high-spin Ni(II) derivative, 2, with those of the previously reported low-spin form. 12 In a different context, the structural consequences of the spin conversion, especially the expansion of the core surroundings of the metal described here, are particular relevant to the photodynamics of Ni porphyrins.…”

From Nanorods to Atomically Thin Wires of Anatase TiO2: Nonhydrolytic Synthesis and Characterization

“…The difference in the spectra could be explained as a result of the nickel core atoms changing from low spin four‐coordinate to a high spin six‐coordinate state. This is significant as the Ni–N bond length of the four‐coordinate nickel porphyrin is shorter than that of the six‐coordinate nickel compounds 60–63. The shorter bond length between the nickel and the nitrogen atoms translates into puckering of the macrocycle 64.…”