Electronic structure of porphyrins with electronegative substituents

Using the MO LCAO method in Hückel's approximation, the -electronic charges and the bond orders of porphyrins containing ethoxycarbonyl and methyl substituents in the -positions have been calculated. A correlation has been observed between the frequencies of stretching vibrations of the C=O groups in the IR spectra and the orders of their bonds. Changes in the chemical shifts of the protons of the methyl groups with the introduction of ethoxycarbonyl substituents agree with the changes in the -electron charges.     

Mass spectra of porphyrins with ethoxycarbonyl substituents

The mass spectra of porphyrins with ethoxycarbonyl substituents in the positions were obtained. It was observed that the chief paths for fragmentation of the porphyrins are common to all of them, regardless of the number of ethoxycarbonyl groups.The authors sincerely thank A. I. Tishchenko for his assistance in carrying out this investigation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 49–50, January, 1971.     

Phosphorus (V) porphyrin diaxially substituted with Leu-enkephalin

Synthesis of the first phosphorus (V) porphyrin-peptide conjugate was successfully accomplished. A biologically active peptide, leucine enkephalin, was constructed on the phosphorus atom of the 5,10,15,20-meso-tetraphenylporphinato dichlorophosphorus (V) chloride. The method involved solution phase peptide synthesis. The first C-terminal amino acid in the sequence of the peptide was axially attached to the porphyrin through a linker, 3-aminopropanol, and the remainder of leucine enkephalin was synthesized by subsequent additions of amino acids. Leucine enkephalin-P(V) porphyrin conjugate represents a new group of compounds, and its synthesis broadens potential applications of P(V) porphyrine, e.g. in photodynamic therapy.     

Effects of peripheral substituents and axial ligands on the electronic structure and properties of cobalt porphyrins

The effects of peripheral substituents and axial ligands (L) on the electronic structure and properties of cobalt tetraphenylporphyrin (CoTPP) have been studied using DFT methods. Various density functionals were tested, and the ground state of each system was determined by considering several possible low-lying states. The ground states of the fully fluorinated CoTPPF28(L)2 complexes with L = THF, Py, and Im were identified to be high-spin (4E(g)) by the meta-GGA functional tau-HCTH, which contains the kinetic energy density tau, in agreement with experimental measurements. All the pure GGA functionals, including the recently developed mPBE, OPBE, and HCTH/407, show more or less overestimation of the relative energies of the high-spin states. The energy gap between the 2A(1g) and 4E(g) states is insignificant (approximately 0.1 eV) and varies in the order L = Py < L = THF < L = Im. The results and their trend are consistent with 19F NMR studies which show partial population of the 4E(g) state in CoTPPF28(THF)2 and CoTPPF28(Py)2 and a complete conversion to the high-spin state in CoTPPF28(1-MeIm)2. Upon coordination by two very strong field axial CO ligands, CoTPPF28(CO)2 becomes low-spin, as in unligated CoTPPF(x). The influence of the peripheral substituents and axial ligands on the ionization potentials, electron affinities, and CoTPPF(x)-(L)2 binding strength was also investigated in detail.     

Built-in axial base binding on phenanthroline-strapped zinc(II) and iron(III) porphyrins

In addition to the need for functional models of cytochrome c oxidase, structural models are still required for a better understanding of the small reorganizations occurring during the catalytic cycle. An efficient synthetic approach has been designed to prepare several phenanthroline-strapped porphyrins, two of them bearing two pendant imidazoles. These built-in bases are both potentially able to act as axial bases for the metalloporphyrin and as complementary ligands for copper if necessary. Diamagnetic zinc(II) was used to demonstrate that the distal/proximal selectivity demonstrated by exogenic bases binding studies can be extended to the coordination of iron(III). Combination of EPR and paramagnetic 1H NMR shows that the imidazole binding on the zinc species can be further extended to the iron(III) species in dilute conditions.     

A novel phthalocyanine with two axial fullerene substituents

A silicon phthalocyanine with two axial fullerene substituents was synthesized, and its electrochemical, absorption- and film-properties were characterized.     

Cooperativity in chiroptical sensing with dendritic zinc porphyrins

Zinc porphyrin-appended dendrimers, 12PZn, 18PZn, 24PZn, and 36PZn, containing 12, 18, 24, and 36 zinc porphyrin units, respectively, were synthesized using zinc porphyrin dyad (2PZn) and triad (3PZn) as precursors. Although these dye-functionalized dendrimers all serve as chiroptical sensors for an asymmetric bipyridine (RR- and SS-Py2), the sensing capability is highly dependent on the structure of the dendritic scaffold. 2PZn, which is chiroptically silent toward Py2, turns cooperative and displays a large ICD (induced circular dichroism) response in the visible region when incorporated into 12PZn. Judging from the extents of contribution of each zinc porphyrin unit to the CD amplitudes ([Deltaepsilonmax]), the cooperativity in 24PZn (112 M-1 cm-1) is lower than that in 12PZn (196 M-1 cm-1) and much lower in dendron 4PZn (59 M-1 cm-1). In contrast, 3PZn, which is ICD-active toward Py2, hardly shows such an enhanced cooperativity when incorporated into 18PZn and 36PZn and dendron 6PZn, as well. Absorption spectroscopy suggests some unique conformational characteristics of the zinc porphyrin units in highly cooperative 12PZn.     

Tuning the reactivity of dioxoruthenium(VI) porphyrins toward an arylimine by altering porphyrin substituents

Reaction of dioxoruthenium(VI) porphyrins [Ru(VI)(Por)O2] with arylimine HN=CPh2 in dichloromethane afforded bis(methyleneamido)ruthenium(IV) porphyrins [Ru(IV)(Por)(N=CPh2)2] for Por = 4-Cl-TPP and TMP; (methyleneamido)hydroxoruthenium(IV) porphyrins [Ru(IV)(Por)(N=CPh2)(OH)] for Por = TPP and TTP; and bis(arylimine)ruthenium(II) porphyrins [Ru(II)(Por)(HN=CPh2)2] for Por = 3,5-Cl2TPP and 3,5-(CF3)2TPP. In dichloromethane solution exposed to air, complex [Ru(II)(3,5-Cl2TPP)(HN=CPh2)2] underwent oxidative deprotonation to form [Ru(IV)(3,5-Cl2TPP)(N=CPh2)2]. The new ruthenium porphyrins were identified by 1H NMR, UV-vis, IR, and mass spectroscopy, along with elemental analysis. X-ray crystal structure determinations of [Ru(IV)(4-Cl-TPP)(N=CPh2)2], [Ru(IV)(TPP)(N=CPh2)(OH)], and [Ru(II)(3,5-(CF3)2TPP)(HN=CPh2)2] revealed the Ru-N(methyleneamido) or Ru-N(arylimine) distances of 1.897(5) A (average), 1.808(4) A, and 2.044(2) A (average), respectively.     

ChemInform Abstract: Phosphorus(V) Oxides.

On the basis of previously reported structural data it is suggested that the so-called crystalline polymorphs of P₂O₅ are in fact three distinct compounds with different structural characteristics but with the same empirical formula.     

Imido transfer from bis(imido)ruthenium(VI) porphyrins to hydrocarbons: effect of imido substituents, C-H bond dissociation energies, and Ru(VI/V) reduction potentials

[Ru(VI)(TMP)(NSO2R)2] (SO2R = Ms, Ts, Bs, Cs, Ns; R = p-C6H4OMe, p-C6H4Me, C6H5, p-C6H4Cl, p-C6H4NO2, respectively) and [Ru(VI)(Por)(NTs)2] (Por = 2,6-Cl2TPP, F20-TPP) were prepared by the reactions of [Ru(II)(Por)(CO)] with PhI=NSO2R in CH2Cl2. These complexes exhibit reversible Ru(VI/V) couple with E(1/2) = -0.41 to -0.12 V vs Cp2Fe(+/0) and undergo imido transfer reactions with styrenes, norbornene, cis-cyclooctene, indene, ethylbenzenes, cumene, 9,10-dihydroanthracene, xanthene, cyclohexene, toluene, and tetrahydrofuran to afford aziridines or amides in up to 85% yields. The second-order rate constants (k2) of the aziridination/amidation reactions at 298 K were determined to be (2.6 +/- 0.1) x 10(-5) to 14.4 +/- 0.6 dm3 mol(-1) s(-1), which generally increase with increasing Ru(VI/V) reduction potential of the imido complexes and decreasing C-H bond dissociation energy (BDE) of the hydrocarbons. A linear correlation was observed between log k' (k' is the k2 value divided by the number of reactive hydrogens) and BDE and between log k2 and E(1/2)(Ru(VI/V)); the linearity in the former case supports a H-atom abstraction mechanism. The amidation by [Ru(VI)(TMP)(NNs)2] reverses the thermodynamic reactivity order cumene > ethylbenzene/toluene, with k'(tertiary C-H)/k'(secondary C-H) = 0.2 and k'(tertiary C-H)/k'(primary C-H) = 0.8.     

Petroporphyrins—II: The presence of porphyrins with extended alkyl substituents

The vanadyl porphyrins from Boscan oil (Cretaceous, W. Venezuela) were isolated as 3 fractions, and degraded to maleimides (1H-pyrrole-2,5-diones) by chromic acid. Analysis of the products by GC-MS, using multiple ion detection to enhance sensitivity, revealed a major homologous series of 3-Me components with n-alkyl side chains extending to C₁₁, and a minor series with branched alkyl side chains, the Me branch being at C-1. The origin of the extended alkyl groups is discussed.     

Cyclic Phosphorus(V) Compounds: Phosphazanes and Anhydrides

Abstract

³¹P n.m.r. has been extensively used to study the preparation and reactions of cyclic phosphorus-(V) compounds containing P-N-P and P-O-P linkages. Michaelis “Oxyphosphazobenzolchlorid”,[C₆H₅NPOCl]_n has been shown by ³¹P n.m.r. and mass spectroscopy to be the trimer (n=3), not the dimer as proposed by Michaelis. The competing reactions of aniline hydrochloride and POCl₃ to form the dimer (two isomers cis- and trans-) and the trimer have been elucidated. With PSCl₃ only the dimer [C₆H₅NPSCl]₂ is formed (both isomers).     

Phosphorus(V)-catalyzed deoxydichlorination reactions of aldehydes

A phosphine oxide-catalyzed conversion of aldehydes into 1,1-dichlorides is reported. The reaction proceeds via a phosphorus(V)-catalysis manifold in which phosphine oxide turnover is achieved using oxalyl chloride as a consumable reagent. The new method is applicable to a range of aldehydes and, in combination with palladium-catalyzed reductive dimerization, gives rise to a new catalytic approach to the synthesis of stilbenes and a short formal synthesis of resveratrol.     

Safer Pyrotechnic Obscurants Based on Phosphorus(V) Nitride

The potential of phosphorus(V) nitride, P₃N₅ , as a replacement for red phosphorus, P_R, in pyrotechnic obscurants has been theoretically and experimentally investigated. P₃N₅ can be safely mixed with KNO₃ and even KClO₃ and KClO₄ . The corresponding formulations are surprisingly insensitive to friction and only mildly impact‐sensitive. P₃N₅ /KNO₃ pyrolants with ξ=20–80 wt % P₃N₅ burn 200 times faster than the corresponding mixtures based on P_R and generate a dense smoke. Hence obscurants based on P₃N₅ /KNO₃ have a figure of merit that by far exceeds that of current state‐of‐the‐art P_R‐based obscurants. Furthermore, unlike P_R, which slowly degrades in moist air to phosphoric acids and phosphine (PH₃), P₃N₅ is stable under these conditions and does not produce any acids or PH₃ . P₃N₅ is hence a safe, stable, and powerful replacement for P_R for use in insensitive munitions.     

EPR spectra of V(IV) complexes and the structure of oil porphyrins

For natural bitumoids, the effects of the structure of vanadyl-porphyrin complexes on the EPR spectra were investigated. The ambiguity of the hyperfine structure (its presence or absence) corresponding to four nitrogen atoms in the spectra of oil vanadyl porphyrins correlates with the changes in the second coordination sphere of the nearest environment of the metal ion, namely, in methine bridges.     

Synthesis and 1H NMR studies of paramagnetic nickel(II) complexes containing bis(pyrazolyl)methane ligands with dendritic substituents

The substituted bis(pyrazolyl)methane ligands RCH(3,5-Me2pz)2(R=SiMe3, CH2Ph, G1, G2, and G3; Gn=Fréchet-type dendritic wedges of generation n) have been prepared starting from H2C(3,5-Me2pz)2. Reaction of these didentate ligands with [NiBr2(DME)] is a straightforward procedure that allows the synthesis of the nickel(II) complexes [NiBr2{RCH(3,5-Me2pz)2}]. The molecular structure of compound (R=CH2Ph) has been determined by X-ray diffraction studies. The nickel centre coordinates two bromine and two nitrogen atoms in a tetrahedral environment, and the metallacycle Ni(NN)2C adopts a boat conformation with the benzyl group in an axial position. 1H NMR studies have been carried out to characterize these paramagnetic nickel compounds in solution. Valuable information about the disposition of the ligands and dendritic wedges in solution has been obtained thanks to the influence of the paramagnetic centre on the proton resonances.