Structure and Apparent Reactivity of the π-Cation Radical Derivatives of Zinc and Copper 5,10,15,20-Tetra(2,6-dichlorophenyl)porphyrinate

Abstract

The report that the π-cation radical complexes of 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrinates have a near degenerate 2 A1u/2A2u ground state has led us to examine their molecular structures. We wished to explore whether this near degeneracy leads to unusual structural features, namely, an alternating bond distance pattern in the 16-membered ring. The X-ray structure of the zinc complex of 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrinate has a possible alternating bond distance pattern that could result from a pseudo-Jahn−Teller effect of coupled A1u and the A2u electronic states. In our attempts to prepare and crystallize additional π-cation radicals, we found an unusual reactivity at the molecular periphery of these porphyrin derivatives. The copper complex of 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrinate reacts with thianthrenium perchlorate to give a β-thianthrenium derivative. The zinc complex reacts with iodine/silver perchlorate yielding neutral β-iodinated derivatives. We report the structure of the thianthrenium derivative [Cu(TCl2PPTh)]ClO4 and a symmetrically substituted β-tetraiodo derivative [Zn(TCl2PPI4)]. Crystal data: [Zn(TCl2PP•)OClO3 ]·CH2Cl2·2C6H14, monoclinic, space group Cc, a = 12.516(2) Å, b = 21.327(3) Å, c = 22.764(3) Å, β = 98.281(13)°, V = 6012.8(16) Å3, Z = 4; [Cu(TCl2PPTh)]ClO4·CHCl3·C6H5CH3, orthorhombic, space group Pca21, a = 14.7625(18) Å, b = 12.220(2) Å, c = 33.672(5) Å, V = 6074.6(16) Å3, Z = 4; [Zn(TCl2PPI4)(THF)2]·2THF, triclinic, space group P1̄, a = 9.941(2) Å, b = 11.615(2) Å, c = 14.340(3) Å, α = 99.11(3)°, β = 103.27(3)°, γ = 106.61(3)°, V = 1499.1(5) Å3, Z = 1.

Electrosynthesis, electrochemistry, and crystal structure of the tetracationic Zn-meso-tetrapyridiniumyl-β-octaethylporphyrin

“…The reactions of porphyrin p cation radicals and dications with nucleophiles to yield meso or b substitutions are now well established and have been used to attach substituents via nitrogen, phosphorous and sulfur as well as at the meso positions of other porphyrins [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Unlike the previous work in which one or two peripheral positions of the oxidized porphyrins react, the exhaustive oxidative electrolysis of ZnOEP at 1.30 V vs SCE in the presence of pyridine (and Et 4 NPF 6 ) results in a new complex in which all four meso positions of the starting ZnOEP are substituted by pyridiniums (via the nitrogen) to yield the tetracationic ZnOEP(py) solution show the four meso protons of the original ZnOEP to be missing and to be replaced by pyridinium substituents whose protons appear downfield as one doublet, one triplet and one double doublet which clearly identify the ortho, para and meta protons, respectively (Fig.…”

“…The work has led to elegant but multistep strategies which, by necessity, suffer from low overall yields of the desired products. An alternate approach takes advantage of the fact that porphyrin p cations and dications, generated by electrochemical or chemical oxidation, are inherently electron-deficient and will react with nucleophiles to yield novel porphyrins with meso or b substituents [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”

“…With few exceptions, the new arrays [6] or products of the oxidation reactions [22,23] have not been characterized crystallographically. This dearth of structural data becomes particularly important because multiple peripheral substitutions in porphyrins have been shown to induce significant conformational distortions of the porphyrin skeleton that minimize steric interactions between the substituents [24,25].…”

Explorations in metalloporphyrin stereochemistry, physical properties and beyond

“…Further, I would take notice of two bodies of work that have not been discussed in this paper, work on the other oxynitrogen-ligated porphyrins (the ligands NO 2 − and NO 3 − ) [112][113][114][115][116][117][118][119][120][121][122][123][124] and the work on the characterization of π-cation radical complexes [125][126][127][128][129][130][131][132][133][134][135][136][137][138][139]. Diagram Illustrating the effect of axial ligand orientation on the axial bond distances in iron (III) species.…”

Bismuth Complexes of Porphyrins and their Potential in Medical Applications

“…This conformation is certainly a consequence of the coordination of two axial THF molecules on the metal and obviously, the intramolecular coordination of the carbonyl is not possible anymore. Another consequence of the six-coordination of the zinc [29] is the fact that the ethylmalonyl residue is rejected outside of the pocket of the porphyrin. In 15Ni, it should be noted that the porphyrin is significantly ruffled and that the shortest distance between a carbonyl oxygen and the metal is 3.836 Å .…”