Electronic Structure of Iron Chlorins:  Characterization of Bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(III)triflate and Bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(II)

Abstract

The synthesis and characterization of the two iron chlorin complexes [Fe(III)(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) and Fe(II)(TPC)[(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2))](2) (2) are reported. The crystal structure of complex 1 has been determined. The X-ray structure shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 2.034(4) A, and to the pyrrole trans to it N(2), 2.012(4) A, are longer than the distances to the two remaining nitrogens [N(1), 1.996(4) A, and N(3), 1.984(4) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole. The (1)H NMR isotropic shifts at 20 degrees C of the different pyrrole protons of 1 varied from -0.8 to -48.3 ppm according to bis-ligated complexes of low-spin ferric chlorins. The EPR spectrum of [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) in solution is rhombic and gives the principal g values g(1) = 2.70, g(2) = 2.33, and g(3) = 1.61 (Sigmag(2) = 15.3). These spectroscopic observations are indicative of a metal-based electron in the d(pi) orbital for the [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) complex with a (d(xy))(2)(d(xz)d(yz))(3) ground state at any temperature. The X-ray structure of the ferrous complex 2 also shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 1.991(5) A, and to the pyrrole trans to it N(2), 2.005(6) A, are slightly different from the distances to the two remaining nitrogens [N(1), 1.988(5) A, and N(3), 2.015(5) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole.

Spectroscopic Determination of Proton Position in the Proton-Coupled Electron Transfer Pathways of Donor−Acceptor Supramolecule Assemblies

“…The thermal ellipsoid plot of the X-ray crystal structure of 7 shown in Figure 1 is similar to that of other porphyrinic derivatives with partially reduced pyrrole subunits. [38][39][40][41][42][43][44][45] Specific hydrogen atoms of interest, including those localized on opposite pyrrole rings as well as that on the pyrrole ring adjacent to the isocyclic five-membered ring, are shown in Figure 1. Cyano purpurin 7 is largely planar, except for the sp 3 -hybridized tetrahedral center adjacent to the isocyclic five-membered ring on the macrocycle periphery (Figure 1).…”

NMR and EPR Studies of Chloroiron(III) Tetraphenyl-chlorin and Its Complexes with Imidazoles and Pyridines of Widely Differing Basicities

“…[1][2][3][4][5][6][7][8][9][10][11][12] There have been a number of previous studies of synthetic and natural iron chlorin and/or isobacteriochlorin complexes by magnetic resonance techniques, including the seminal paper of Stolzenberg, Strauss and Holm in 1981 13 and additional papers from these authors, 14-18 as well as other researchers. [19][20][21][22][23][24][25][26][27][28][29][30][31] Understanding the electronic properties of the iron(III) complexes of each of the individual "green" hemes is an important step in understanding their mechanisms of action.…”

61 The Structural Chemistry of Isolated Chlorophylls

“…132 Another examples is a hexacoordinated iron(II) species. 133 Many similar systems were obtained through β-addition reactions. 2,3-Dialkylated derivatives such as 57 134 and 58 135 were described by Senge and coworkers.…”