Crystal and molecular structure of unsymmetrical N-methyl-substituted μ-oxo diiron(III) tetraphenylporphyrin

The synthesis and crystal structures of two μ-oxo iron(III) porphyrin complexes

Two [Formula: see text]-oxo iron(III) porphyrin complexes, [Formula: see text]-oxo-bis[meso-tetra-[Formula: see text],[Formula: see text],[Formula: see text],[Formula: see text]-([Formula: see text]-nicotina-midophenyl)porphinatoiron(III)] ([Fe(TPyPP)]2O) and its copper adduct ([Fe(TPyPP)(CuCl)]2O[CF3SO3][Formula: see text], which are derived from Gunter’s porphyrin model for cytochrome [Formula: see text]oxidase are reported. The two complexes were isolated and characterized by single crystal X-ray diffraction, UV-vis and IR spectroscopies. Crystal structural analysis including comparisons to [Formula: see text]-oxo analogues and Hirshfeld surface calculations revealed several noteworthy structural features [Formula: see text] the various picket orientations which are partially attributed to intra- and/or inter-molecular nonbonded interactions.

The Simplest Iron μ-oxo Species. The Molecular Structure of {[Fe(porphine)]2O}

We have prepared a new [Formula: see text]-oxo iron(III) porphyrin complex based on the simplest possible porphyrin ligand, porphine. Our structure determination for {[Fe(porphine)]2O}shows that it has a decidedly different molecular structure compared to all other [Formula: see text]-oxo iron(III)porphyrin complexes with two independent porphyrin ligands. The Fe–O–Fe angle is 153.21 (16)[Formula: see text]which leads to a small interplanar angle of 22.7[Formula: see text]between the two porphine rings. This also leads to C[Formula: see text]C nonbonded contact as short as 3.35Å between the two rings. The twist angle of the two porphine rings is 16.8[Formula: see text]. Other structural features are in general accord with those expected for high-spin iron(III) porphyrinates.

(Hydr)oxo-bridged heme complexes: From structure to reactivity

Iron–porphyrins ([Formula: see text] hemes) are present throughout the biosphere and perform a wide range of functions, particularly those that involve complex multiple-electron redox processes. Some common heme enzymes involved in these processes include cytochrome P450, heme/copper oxidase or heme/non-heme diiron nitric oxide reductase. Consequently, the (hydr)oxo-bridged heme species have been studied for the important roles that they play in many life processes or for their application for catalysis and preparation of new functional materials. This review encompasses important synthetic, structural and reactivity aspects of the (hydr)oxo-bridged heme constructs that govern their function and application. The properties and reactivity of the bridging (hydr)oxo moieties are directly dictated by the coordination environment of the heme core, the nature and ligation of the second metal center attached to the (hydr)oxo group, the presence or absence of a linker, and the degree of flexibility around that linker within the scaffold. Here, we summarize the structural features of all known (hydr)oxo-bridged heme constructs and use those to categorize and thus, provide a more comprehensive picture of structure–function relationships.

Heterogeneous catalytic properties of unprecedented μ-O-[FeTCPP]2 dimers (H2TCPP = meso-tetra(4-carboxyphenyl)porphyrin): an unusual superhyperfine EPR structure

Solvent accessible volume of the active catalyst μ-O-[FeTCPP]₂·nDMF dimer revealing an unusual superhyperfine EPR structure.

On the Molecular Stereochemistry of the 21,22,23-trimethyl-5,10,15,20-Tetraphenylporphyrin Cation

The crystal structure of the triflate salt of the title compound, [ Me 3 TPP ][ CF 3 SO 3], was investigated to obtain structural information on the conformation of N-trimethylated 5,10,15,20-tetraarylporphyrins. The molecular stereochemistry of the cation is characterized by an up/down/up arrangement for the three N-methyl groups with significant pyramidalization at the nitrogen atoms. The macrocycle is severely distorted with an average deviation from planarity of 0.438 Å. The distortion mode is an asymmetric saddle with deviations from the 4 N plane of the C b atoms at N-methylated pyrrole rings exceeding 1.1 Å. The out-of-plane displacements of pyrrole ring IV are significantly smaller than those of the methylated pyrrole rings.

Iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin

The iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin (OTPP)H have been investigated. Insertion of iron(II) followed by one-electron oxidation yielded a high-spin, six-coordinate (OTPP)Fe(III)Cl(2) complex. The reduction of (OTPP)Fe(III)Cl(2) has been accomplished by means of moderate reducing reagents producing high-spin five-coordinate (OTPP)Fe(II)Cl. The molecular structure of (OTPP)Fe(III)Cl(2) has been determined by X-ray diffraction. The iron(III) 21-oxaporphyrin skeleton is essentially planar. The furan ring coordinates in the eta(1) fashion through the oxygen atom, which acquires trigonal geometry. The iron(III) apically coordinates two chloride ligands. Addition of potassium cyanide to a solution of (OTPP)Fe(III)Cl(2) in methanol-d(4) results in its conversion to a six-coordinate, low-spin complex [OTPP)Fe(III)(CN)(2)] which is spontaneously reduced to [OTPP)Fe(II)(CN)(2)](-) by excess cyanide. The spectroscopic features of [OTPP)Fe(III)(CN)(2)] correspond to the common low-spin iron(III) porphyrin (d(xy))(2)(d(xz)d(yz))(3) electronic configuration. Titration of (OTPP)Fe(III)Cl(2) or (OTPP)Fe(II)Cl with n-BuLi (toluene-d(8), 205 K) resulted in the formation of (OTPP)Fe(II)(CH(2)CH(2)CH(2)CH(3)). (OTPP)Fe(II)(n-Bu) decomposes via homolytic cleavage of the iron-carbon bond to produce (OTPP)Fe(I). The EPR spectrum (toluene-d(8), 77 K) is consistent with a (d(xy))(2)(d(xz))(2)(d(yz))(2)(d(z)(2)(1)(d[(x)(2)-(y)(2)])(0) ground electronic state of iron(I) oxaporphyrin (g(1) = 2.234, g(2) = 2.032, g(3) = 1.990). The (1)H NMR spectra of (OTPP)Fe(III)Cl(2), (OTPP)Fe(III)(CN)(2), ([(OTPP)Fe(III))](2)O)(2+), and (OTPP)Fe(II)Cl have been analyzed. There are considerable similarities in (1)H NMR properties within each iron(n) oxaporphyrin-iron(n) regular porphyrin or N-methylporphyrin pair (n = 2, 3). Contrary to this observation, the pattern of downfield positions of pyrrole resonances at 156.2, 126.5, 76.3 ppm and furan resonance at 161.4 ppm (273 K) detected for the two-electron reduction product of (OTPP)Fe(III)Cl(2) is unprecedented in the group of iron(I) porphyrins.

Dynamic study of metal-ion incorporation into porphyrins based on the dynamic characterization of metal ions and on sitting-atop complex formation

We succeeded in the detection of the sitting-atop (SAT) copper(II) complex of TPP (5,10,15,20-tetraphenylporphyrin) in acetonitrile (AN) as a solvent with a very low Brønsted basicity, where two pyrrolenine nitrogens in the Cu(II)-SAT complex coordinate to the metal ion and two protons still remain on the pyrrole nitrogens. The structure parameters around the copper(II) ion in the Cu(II)-SAT complex, as determined by a fluorescent EXAFS method, suggest an axially elongated and equatorially distorted six-coordinate geometry. We measured the rates of the formation reaction of the SAT complexes for a series of transition metal(II) ions in AN using the stopped-flow technique. We propose the mechanism where there is a rapid deformation equilibrium of the porphyrin ring prior to the rate-determining step of the bond rupture of a coordinated solvent molecule on the metal(II) ion. Furthermore, we measured the rates of the deprotonation reaction of the Cu(II)-SAT complex by some Brønsted bases and indicated that the rate-determining step is the attack of the base on the proton of the pyrrole nitrogen in the SAT complex. Finally, a unified mechanism relevant to the porphyrin metalation mechanism has been proposed.

Molecular Heme-Cyanide-Copper Bridged Assemblies: Linkage Isomerism, Trends in nu(CN) Values, and Relation to the Heme-a(3)/Cu(B) Site in Cyanide-Inhibited Heme-Copper Oxidases

Bovine heart cytochrome c oxidase and related heme copper oxidases are inhibited by cyanide, which binds at the binuclear heme-a(3)/Cu(B) site where dioxygen is reduced to water. To determine the mode of cyanide binding, heme-based binuclear complexes containing iron-cyanide-copper bridges in different oxidation states have been prepared by the reaction of [(py)(OEP)Fe(CN)] with Cu(II,I) precursors and structurally characterized by X-ray methods. Structures of two precursor complexes and two binuclear Cu(I)-CN-Cu(I) species are reported. The assembly [(py)(OEP)Fe-CN-Cu(Npy(3))](2+) has a nearly linear Fe(III)-CN-Cu(II) bridge containing low-spin Fe(III). The assemblies [(OEP)Fe-NC-Cu(MeNpy(2))](+) and [(OEP-CH(2)CN)Fe-NC-Cu(Npy(3))](+) exhibit the high-spin bridges Fe(III)-NC-Cu(I) and Fe(II)-NC-Cu(I), respectively. These are the first title bridges in these oxidation states. Bridge atom sequences are obtained from structural refinements of both linkage isomers; those for the reduced bridges are consistent with the soft-acid nature of Cu(I). Cyanide stretching frequencies respond to metal oxidation state and bridge geometry and, using data for solution and solid states, fall into the following ranges: Fe(III)-CN-Cu(II), 2120-2184 cm(-)(1) (11 examples); Fe(III)-NC-Cu(I), 2072-2100 cm(-)(1) (2 examples); Fe(II)-NC-Cu(I), 2099-2107 cm(-)(1) (1 example). These data are compared with nu(CN) values for the enzymes in different oxidation states. A nonlinear Fe(III)-CN-Cu(II) bridge (Cu-N-C = 150-160 degrees ) is consistent with the 2146-2152 cm(-)(1) range found for the fully oxidized enzymes. Bands that can be assigned with some certainty as Fe-CN vibrations in partially and fully reduced enzymes do not appear to correspond to Fe(III)-NC-Cu(I) and Fe(II)-NC-Cu(I) bridges but rather to Fe(II)-CN modes. The current work complements and extends our previous investigation (Scott and Holm, J. Am. Chem. Soc. 1994, 116, 11357) of linear and nonlinear Fe(III)-CN-Cu(II) bridges and is part of an investigation directed at providing a molecular basis of cyanide toxicity. (MeNpy(2) = bis(2-(2-pyridylethyl))methylamine; Npy(3) = tris(2-pyridylmethyl)amine; OEP = octaethylporphyrinate(2-), OEP-CH(2)CN = N-(cyanomethyl)octaethylporphyrinate(1-).)

Cyclic Metalloporphyrin Trimers: (1)H NMR Identification of Trimeric Heterometallic (Iron(III), Gallium(III), Manganese(III)) 2-Hydroxy-5,10,15,20-tetraphenylporphyrins and X-ray Crystal Structure of the Iron(III) 2-Hydroxy-5,10,15,20-tetra-p-tolylporphyrin Trimer(1)

Oligomerization of a mixture of monomeric iron(III) 2-hydroxy-5,10,15,20-tetraphenylporphyrin, (2-OH-TPP)Fe(III)Cl, manganese(III) 2-hydroxy-5,10,15,20-tetraphenylporphyrin, (2-OH-TPP)Mn(III)Cl, and gallium(III) 2-hydroxy-5,10,15,20-tetraphenylporphyrin, (2-OH-TPP)Ga(III)Cl, complexes affords the series of heterometallic cyclic trimeric species of the general formula {[(2-O-TPP)Ga(III)](n)()[(2-O-TPP)Fe(III)](3)(-)(n)()}, {[(2-O-TPP)Ga(III)](n)()[(2-O-TPP)Mn(III)](3)(-)(n)()}, and {[(2-O-TPP)Fe(III)](n)()[(2-O-TPP)Mn(III)](3)(-)(n)()} (n = 0-3). The (1)H NMR spectroscopic and mass spectrometric investigations indicate that these compounds have a head-to-tail cyclic trimeric structure. In the (1)H NMR spectra the interactions between paramagnetic, weakly coupled centers are reflected by marked variations of chemical shifts and line widths of pyrrole resonances. The characteristic upfield positions of the 3-H pyrrole resonances are diagnostic for the trimeric motifs. The structure of the prototypical molecule, [(2-O-TTP)Fe(III)](3), has been determined by X-ray crystallography. [(2-O-TTP)Fe(III)](3).3n-octane crystallizes in the monoclinic space groupP2(1)/n with a = 16.729(6) Å, b = 43.671(13) Å, c = 19.564(7) Å, beta = 105.83(3) degrees, and Z = 4 at 130 K. The refinement of 1612 parameters and 5072 reflections yields R(1)( )()= 0.089 and wR(2) = 0.1848. The trimeric iron(III) complex has a head-to-tail cyclic arrangement with the pyrrolic alkoxide groups forming bridges from one macrocycle to the metal in adjacent macrocycle. The three iron(III) porphyrin subunits are not equivalent but have typical geometry for high-spin five-coordinate iron(III) porphyrin complexes. The porphyrin skeleton of [(2-O-TTP)Fe(III)](3) is expected to be representative of the structures of the homometallic and heterometallic trimeric complexes of 2-hydroxytetraarylporphyrin with M(III) ions.

A Nearly Linear Single Hydroxo Bridge. Synthesis, Structure, and Magnetic Susceptibility of (&mgr;-Hydroxo)bis((tetraphenylporphinato)manganese(III)) Perchlorate

The synthesis, X-ray structure, and magnetic susceptibility characterization of a hydroxo-bridged complex, (&mgr;-hydroxo)bis((tetraphenylporphinato)manganese(III)) perchlorate, {[Mn-(TPP)](2)(OH)}ClO(4), are described. The complex is readily prepared by a controlled hydrolysis of monomeric diaquo(tetraphenylporphinato)manganese(III) perchlorate. Interestingly, the bridging hydroxo complex appears to be more stable than the putative &mgr;-oxo complex in halocarbon solvents. The X-ray structure determination shows a complex in which two five-coordinate manganese(III) ions are bridged by a single hydroxo ligand with an average Mn-O distance of 2.026(1) Å and a Mn-O(H)-Mn bridge angle of 160.4(8) degrees. The two porphyrin planes are nearly coplanar, and the two metal ions are separated by 3.993 Å. The average Mn-N(P) distance is 2.008(7) Å. The two manganese ions are displaced by 0.19 and 0.20 Å from their respective 24-atom mean planes. Both of the two porphyrin rings are moderately S(4) ruffled and have a near-staggered orientation (the N-Mn-Mn'-N' dihedral angle is 29.9 degrees ). The four inter-ring pairs of meso-phenyl groups of the binuclear cation are extremely crowded, with a nearly perpendicular orientation for each pair. The solid-state magnetic susceptibility was measured over the temperature range 2-300 K. The observed behavior is typical of an exchange-coupled binuclear complex. The data were fit to the total spin Hamiltonian (H(tot) = H(1) + H(2) - 2J&Svector;(1).&Svector;(2)) of a zero-field-split, high-spin d(4)-d(4) dimer in its actual crystallographic geometry, using numerical techniques. The hydroxide bridge supports a relatively strong antiferromagnetic coupling (2J = -74.0 cm(-1)) between two zero-field-split (D = -10.8 cm(-1)) manganese(III) ions. Crystal data: a = 16.807(7) Å, b = 17.061(6) Å, c = 17.191(5) Å, alpha = 85.64(3) degrees, beta = 79.75(3) degrees, gamma = 61.95(2) degrees, triclinic, space group P&onemacr;, V = 4281(3) Å(3), Z = 2, R(1) = 0.0707 for 14 802 observed data based on F(o) >/= 4.0sigma(F(o)), R(2w) = 0.2007 for 21 696 total unique data, least-squares refinement on F(2) using all data.