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The solution conformations of seven dodecasubstituted porphyrins, which generally show extremely nonplanar structures in the crystalline state, have been investigated using a method that combines proton NMR spectroscopy and molecular mechanics calculations. By comparison of the proton paramagnetic shifts measured for cobalt(II) complexes of these porphyrins with the dipolar shifts calculated using geometric factors obtained either from crystallographic data or from molecular mechanics structures, it is determined that the conformations of the macrocycles and their substituents are similar in solution and in the crystalline state. Thus, the nonplanar cobalt-(II) porphyrins that have well-defined cavity structures in the crystalline state retain these cavities in solution. Variable-temperature proton NMR spectroscopy is used to estimate the dynamic stabilities of the cavity structures. The porphyrins with cavities are found to behave differently from planar porphyrins without cavities with regard to the formation of {pi}-complexes with 1,3,5-trinitrobenzene. It is suggested that the cavities may modulate a range of porphyrin-substrate interactions, potentially making these porphyrins useful as regio- and stereoselective oxidation catalysts and in the preparation of complexes with well-defined ligand orientations.

The structures of two polymorphs of ({mu}-oxo)bis[(octaethylporphinato)iron(III)], [Fe(OEP)]{sub 2}O (C{sub 72}H{sub 88}Fe{sub 2}N{sub 8}O), have been determined by X-ray structure analyses using data collected with an area detector. The two [Fe(OEP)]{sub 2}O polymorphs (a triclinic and a monoclinic form) show strong structural similarities. The eight Fe-N{sub p} bond distances have average values of 2.077(3) {Angstrom} in the triclinic form and 2.080(5) {Angstrom} in the monoclinic form. The average displacements of the iron(III) atom from the mean porphinato core are 0.50 {Angstrom} in the triclinic form and 0.54 {Angstrom} in the monoclinic form. The most important structural feature of the molecule in the two crystal forms is the near-eclipsed intramolecular porphyrin ring orientation: the average N-Fe-Fe{prime}-N{prime} dihedral angles are 17.0(10){degrees} in the triclinic form and 16.8(6){degrees} in the monoclinic form. Molecular mechanics calculations have been carried out to explore the inter-ring orientation; these suggest that peripheral ethyl group interactions lead to the near-eclipsed orientation. Crystal data: triclinic form, a = 11.561(5) {Angstrom}, b = 12.299(8) {Angstrom}, c = 23.341(16) {Angstrom}, {alpha} = 82.56(3){degrees}, {beta} = 81.94(7){degrees}, {gamma} = 79.18(1){degrees}, space group P1, V = 3210(5) {Angstrom}{sup 3}, Z = 2,8931 observed data, R{sub 1} = 0.050, R{sub 2} = 0.056; monoclinicmore » form, a = 18.433(13) {Angstrom}, b = 15.104(6) {Angstrom}, c = 23.489(6) {Angstrom}, {beta} = 97.82(1){degrees}, space group P2{sub 1}/c, V = 6479(9) {Angstrom} {sup 3},Z = 4,6169 observed data, R{sub 1} = 0.054, R{sub 2} = 0.060.« less

Members of a new class of water-soluble, nonplanar porphyrins based on 5,10,15,20-tetraphenylporpyrin-2,3,7,8,12,13,17,18-octaacetic acid (OAATPPs) have been synthesized, and their physical and chemical properties as well as their interactions with complexing agents have been investigated using UV-visible absorption, EXAFS, nuclear magnetic resonance and resonance Raman spectroscopies. Red shifts of 19-36 nm in the major absorption bands are noted for Ni derivatives of OAATPP and its octamethyl ester (ME), meso-tetrakis(p-nitrophenyl)-porphyrinoctaacetic acid octamethyl ester, and octakis(hydroxyethyl)tetraphenylporphyrin relative to nickel tetraphenylporphyrin. These red shifts are indicative of a high degree of nonplanarity. The short Ni-N distances of 1.92(2) {Angstrom} for NiOAATPP-OME and 1.89(2) {Angstrom} for NiOAATNPP-OME from EXAFS experiments corroborate the nonplanar nature of these porphyrins. The decreased ring current effect and temperature-dependent NMR measurements also confirm that the porphyrins are nonplanar in solution. Resonance Raman studies also indicate nonplanar conformations for NiOAATPP and its derivatives by the characteristic downshifts in the frequencies of the structure-sensitive marker lines. At low pH(

X-ray crystal structures are reported for two sterically crowded porphyrins: 3,5,7,13,15,17-hexaethyl-2,8,12,18-tetramethylporphyrin (6, H{sub 2}DAP) and (3,5,7,13,15,17-hexaethyl-2,8,12,18-tetramethylporphinato)nickel(II) (Ni6,NiDAP). In the NiDAP structure, steric crowding is relieved by the usual mechanism of the porphyrin adopting a nonplanar conformation. The crystal structure of H{sub 2}DAP is unusual, as it shows an essentially planar conformation of the porphyrin macrocycle. In this case, steric crowding of the meso and pyrrole ethyl groups is relieved by a novel elongation of the porphyrin macrocycle. In this case, steric crowding of the meso and pyrrole ethyl groups is relieved by a novel elongation of the macrocycle among the 5,15 axis. A detailed study is made of the solution conformations of H{sub 2}DAP, NiDAP, and the corresponding zinc(II) complex (ZnDAP), using optical spectroscopy, variable-temperature proton NMR spectroscopy, and molecular mechanics calculations. It is suggested that the two species observed in low-temperature proton NMR studies of H{sub 2}DAP and ZnDAP correspond to cis and trans conformations of the methyl groups of the meso ethyls, and not the syn and anti structures proposed previously.