Single-boron complexes of N-confused and N-fused porphyrins

Boron(III) has been inserted into N-confused porphyrin, (NCPH)H2 (1), and N-fused porphyrin, (NFP)H (2). The reaction of dichlorophenylborane and 1 yields sigma-phenylboron N-confused porphyrin (4). The boron atom is bound by two pyrrolic nitrogen atoms and the sigma-phenyl ligand. The N-confused pyrrole ring is not involved in the direct coordination because the C(21)-H fragment remains intact. A reaction between PhBCl2 and N-fused porphyrin produces sigma-phenylboron N-fused porphyrin (3+). 4 converts quantitatively into 3+ under protonation. In sigma-phenylboron N-fused porphyrin [(NFP)BPh]Cl, the coordinating environment of boron(III) resembles a distorted trigonal pyramid, with the nitrogen atoms occupying equatorial positions and with the phenyl ligand lying at the unique apex. Boron(III) is displaced by 0.547(4) A from the N3 plane. The B-N distances are as follows: B-N(22), 1.559(4) A; B-N(23), 1.552(4) A; B-N(24), 1.568(4) A; B-C(ipsoPh), 1.621(4) A. 3+ can be classified as a boronium cation considering a filled octet and a complete coordination sphere. 3+ is susceptible to alkoxylation at the inner C(9) carbon atom, yielding 5-OR. The addition of acid results in protonation of the alkoxy group and elimination of alcohol, restoring the original 3+. Density functional theory has been applied to model the molecular and electronic structure of 4, 3+, and syn and anti isomers of methoxy adducts 5-OMe.     

Iron(II) vacataporphyrins: a variable annulene conformation inside a regular porphyrin frame

5,10,15,20-Tetraaryl-21-vacataporphyrin (1), an annulene-porphyrin hybrid containing a butadiene fragment in the macrocycle perimeter, gives paramagnetic iron(II) complexes 2. The porphyrin 1 is devoid of one donor atom of the coordination core; hence, metal ion is bound in the macrocyclic cavity by only three pyrrolic nitrogen atoms. The coordination sphere in 2-X (where X = Cl, Br, I) is completed by a halide anion. The butadiene fragment flexibility and constraints of coordination lead to two stereoisomers with the chain oriented inward (2-i-X) or outward (2-o-X) of the macrocyclic center. Axial halide subtraction (AgBF(4) addition) leads to two new forms differing in the butadiene chain configuration. The (1)H NMR spectra of all complexes show characteristics typical for high-spin iron(II) complexes of porphyrinoids. The dependence of the relaxation times T(1) versus Fe(II)···H distances (estimated by MM+ models) for three of the isomers is in accordance with the in, out, and/or zigzag geometries. The 2-o-X complex is more reactive than 2-i-X and reacts at room temperature with dioxygen to form the iron(II) 21-oxaporphyrin complex, conserving the iron(II) oxidation state. After the addition of imidazole or excess of methanol to a mixture of 2-o-X and 2-i-X, single five-coordinate complexes with out annulene configuration and two axial ligands are formed.     

Geometry and solvent-polarity dependences of the relaxation dynamics of the singlet excited state of center-to-edge phosphorus(V) porphyrin heterodimers

Para- and meta-isomers of center-to-edge phosphorus(V) porphyrin heterodimers (p- and m-Pm-PCl2) composed of a phosphorus(V) tetraphenylporphyrin (P) and a phosphorus(V) tetrakis(4-methoxyphenyl)porphyrin (Pm) were synthesized to investigate the geometry and solvent-polarity dependences of the relaxation dynamics of the lowest singlet excited state (S1) of the porphyrin dimer. The geometrical difference between m- and p-Pm-PCl2 in solution was confirmed by 1H NMR on the basis of the porphyrin ring current model. By the photoexcitation of the dimers, only the fluorescence from 1Pm*-P was observed in both dimers because of the efficient singlet energy transfer from the higher energy 1P* to the lower energy 1Pm*. However, the 1Pm*-P fluorescence had features that differ from the typical fluorescence from monomeric 1Pm*, especially for the solvent-polarity dependence of the quantum yields. Furthermore, all the fluorescence decay curves of 1Pm*-P were double-exponential. The special fluorescence features of 1Pm*-P are due to the equilibrium between 1Pm*-P and the charge-transfer (CT) excited state of the dimer ((Pm-P)CT). By the excited-state equilibrium, 1Pm*-P is efficiently quenched through (Pm-P)CT in highly polar solvents. The contribution of (Pm-P)CT to the decay process of 1Pm*-P is more remarkable in m-Pm-PCl2 than in p-Pm-PCl2, depending on the interaction between the two porphyrin -systems in the heterodimer.     

Endocyclic extension of porphyrin pi-system by interior functionalization of N-confused porphyrins

Internally alkynylated or cyanated N-confused porphyrins have been prepared, and these have been characterized by NMR, UV/Vis/NIR absorption, and X-ray analysis. The desired porphyrins have been synthesized by interconversion between an N-confused porphyrin and an N-fused porphyrin. In the case of terminal alkyne derivatives, intramolecular addition of a pyrrolic NH moiety to the triple bond occurred at ambient temperature to give etheno-bridged N-confused porphyrins. Significant bathochromic shifts in the absorbances of these compounds may be reasonably explained in terms of an increase in their HOMO energy levels due to effective overlap of the porphyrin pi-orbital and the bridged alkene pi-orbital. The corresponding rhodium(I) complexes have also been prepared, and these have been characterized by NMR and X-ray analysis.     

Synthesis, reactivity, and properties of N-fused porphyrin rhenium(I) tricarbonyl complexes

The thermal reactions of N-fused tetraarylporphyrins or N-confused tetraarylporphyrins with Re2(CO)10 gave the rhenium(I) tricarbonyl complexes bearing N-fused porphyrinato ligands (4) in moderate to good yields. The rhenium complexes 4 are characterized by mass, IR, 1H, and 13C NMR spectroscopy, and the structures of tetraphenylporphynato complex 4a and its nitro derivative 15 are determined by X-ray single crystal analysis. The rhenium complexes 4 show excellent stability against heat, light, acids, bases, and oxidants. The aromatic substitution reactions of 4 proceed without a loss of the center metal to give the nitro (15), formyl (16), benzoyl (17), and cyano derivatives (19), regioselectively. In the electrochemical measurements for 4, one reversible oxidation wave and two reversible reduction waves are observed. Their redox potentials imply narrow HOMO-LUMO band gaps of 4 and are consistent with their electronic absorption spectra, in which the absorption edges exceed 1000 nm. Theoretical study reveals that the HOMO and LUMO of the rhenium complexes are exclusively composed of the N-fused porphyrin skeleton. Protonation of 4 takes place at the 21-position regioselectively, reflecting the high coefficient of the C21 atom in the HOMO orbital. The skeletal rearrangement reaction from N-confused porphyrin Re(I) complex (8) to N-fused porphyrin Re(I) complex (4) is suggested from the mechanistic study as well as DFT calculations.     

Synthesis, structure, and aromaticity of the nickel(II) complex of pyricorrole, a molecular hybrid of porphyrin and corrole

Formal migration of one meso-carbon atom in the porphyrin ring into the pyrrole moiety results in an isomer "pyricorrole", a pyridine-containing corrole macrocycle. We prepared the nickel(II) complex of pyricorrole by the nickel(II)-induced cyclization of a linear precursor. Electronic absorption and proton NMR spectra of this compound revealed the presence of an 18π-electron circuit over the macrocycle, suggesting that aromaticity was retained after intensive rearrangement of the porphyrin core. X-ray crystallography of the nickel(II) complex confirmed the planar structure and demonstrated that it possesses hybrid properties of porphyrin and corrole.     

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.     

N-fused porphyrin with pyridinium side-arms: a new class of aromatic ligand with DNA-binding ability

N-fused porphyrin (NFP) is a porphyrin analogue with an 18π tetrapyrrolic macrocycle, in which a unique tripentacyclic ring is embedded. While the optical properties of NFP of absorbing and emitting near-infrared (NIR) light around 1000 nm are promising for its application to NIR technology, its unique structure is also attractive as a platform to construct a novel class of DNA-binding ligands. Herein, we have synthesized a water-soluble derivative of NFP (pPyNFP) possessing four cationic pyridinium substituents and examined its acid/base behaviors and interactions with various forms of DNAs in aqueous solution. pPyNFP interacts with ssDNA and dsDNA electrostatically. pPyNFP also interacts with a G-quadruplex DNA derived from the human telomeric sequence and causes a characteristic spectral change of the G-quadruplex DNA, which suggests that pPyNFP modulates the Na(+)-induced (2 + 2) antiparallel G-quadruplex to the all-parallel structure.     

The synthesis of isostructural Mo2+ porphyrin and N-confused porphyrin complexes

We have synthesized the first early transition metal N-confused porphyrin complex Mo(NCTPP)(pip)2; this species is isostructural to its normal porphyrin analog Mo(TPP)(pip)2 but exhibits significant electronic differences arising from the inversion of a single pyrrolic group.     

A strategy to design highly efficient porphyrin sensitizers for dye-sensitized solar cells

We designed highly efficient porphyrin sensitizers with two phenyl groups at meso-positions of the macrocycle bearing two ortho-substituted long alkoxyl chains for dye-sensitized solar cells; the ortho-substituted devices exhibit significantly enhanced photovoltaic performances with the best porphyrin, LD14, showing J(SC) = 19.167 mA cm(-2), V(OC) = 0.736 V, FF = 0.711, and overall power conversion efficiency η = 10.17%.     

Radiolysis of 5,10,15,20-tetrakis(N-methyl-4-pyridyl)-porphyrin or 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin in aqueous solution in the presence and in the absence of DNA or human serum albumin

The reduction of two free-base ionic porphyrins: 5,10,15,20-tetrakis(N-methyl-4-pyridyl)-porphyrin (TMPyP) and 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin (TSPP) by the hydrated electron was studied under neutral pH in aqueous solution in the absence and in the presence of biomolecules, DNA or HSA. Pulse radiolysis studies provided the spectra of the short-lived π-radical anions and steady-state radiolysis led to formation of stable phlorin or chlorin, the products of two-electron reduction and protonation at a meso and a pyrrolic nitrogen positions or at two β-pyrrole positions, respectively. Identification of the final reduction products was based on their reactivity to molecular oxygen—the phlorin, contrary to chlorine, was oxidized rapidly by O₂ to recover the original porphyrin. The stable product of TMPyP reduction was the phlorin, whereas for TSPP the chlorine and the phlorin were obtained. Addition of biomolecules to the solution resulted in changes of the porphyrins spectroscopic properties and in the decrease in rates of the occurring reduction processes proceeding with participation of the porphyrins.     

On the mass spectra of thallium(III) porphyrin chelates

Thallium(III) porphyrins show anomalous features in their mass spectra compared with other metalloporphyrins. The base peak in all of the spectra arises by loss of the thallium atom and its axial ligands with transfer of two hydrogens to the macrocycle; the liberated thallium undergoes ion-molecule interaction with the thallium porphyrin, resulting in the observation of ions containing two thallium atoms per porphyrin ligand.     

Three-Stage Aromaticity Switching in Boron(III) and Phosphorus(V) N-Fused p-Benziporphyrin

Insertion of PCl₃ or PhBCl₂ into 5,10,15,20-tetraaryl-p-benziporphyrin prompted an intramolecular fusion affording anti-aromatic phosphorus(V) and non-aromatic boron(III) complexes of two N-fused dihydro-p-benziporphyrin isomers. These macrocycles are classified as carbatriphyrin due to the common [CNN] coordination. A sequence of direct transformations, triggered by protonation or two-electron redox processes, afforded a set of three mutually convertible N-fused p-benziporphyrinoids, with distinct anti-aromatic, non-aromatic, and aromatic spectroscopic features.     

N‐Confused Phlorin‐Prodigiosin Chimera: meso‐Aryl Oxidation and π‐Extension Triggered by Peripheral Coordination

An N‐confused phlorin isomer bearing a dipyrrin moiety at the α‐position of the confused pyrrole ring ( 1 ) was synthesized. Pd^II and B^III coordination at the peripheral prodigiosin‐like moiety of 1 afforded the corresponding complexes 2 and 3 . Reflux of 2 in triethylamine (TEA) converted the meso‐phenyl into the Pd^II‐coordinating phenoxy group to afford 4 . Under the same reaction conditions, TEA was linked to the α‐position of the dipyrrin unit in 3 as an N,N‐diethylaminovinyl group to afford 5 . Furthermore, peripheral coordination of B^III in 3 and 5 improved the planarity of the phlorin macrocycle and thus facilitated the coordination of Ag^III at the inner cavity to afford 3‐Ag and 5‐Ag , respectively. These results provide an effective approach for developing unique porphyrinoids through peripheral coordination.     

Isomerization and oxygen atom transfer reactivity in oxo-Mo complexes of relevance to molybdoenzymes

Both dioxo Mo(VI) and mono-oxo Mo(V) complexes of a sterically restrictive N2O heteroscorpionate ligand are found to exist as cis and trans isomers. The thermodynamically stable isomer differs for the two oxidation states, but in each case, we have isolated the kinetically labile isomer and followed its isomerization to the thermodynamically stable form. The Mo(VI) complex is more stable in the cis geometry and isomerizes more than 6 times faster than the Mo(V) complex, which prefers the trans geometry. In OAT reactions with PPh3, the trans isomer of the dioxo-Mo(VI) reacts approximately 20 times faster than the cis isomer. Thus, there are both oxidation state and donor atom dependent differences in isomeric stability and reactivity that could have significant functional implications for molybdoenzymes such as DMSO reductase.     

DFT survey of monoboron and diboron corroles: regio- and stereochemical preferences for a constrained, low-symmetry macrocycle

The structures of a number of mono- and diboron corrole complexes have been optimized using DFT methods in order to establish regio- and stereochemical preferences for bonding of one or two boron atoms to the corrole macrocycle. The formulations of the complexes were suggested either from preliminary experimental results (to be reported elsewhere) or by analogy with related diboron porphyrin compounds. The computational results suggest for the monoboron corroles BF(2)(H(2)corrole) and BPhH(H(2)corrole) that the regioisomer in which the boron is bound to a dipyrromethene site adjacent to the bipyrrole is preferred over the other possible regioisomers in which boron coordinates either in the bipyrrole or in the dipyrromethene site opposite the bipyrrole. In the N-substituted corrole complexes there are only two possiblities and, for each complex, the regioisomer with boron in the dipyrromethene site adjacent to the bipyrrole is lower in energy. For all four monoboron complexes the stereoisomers in which boron and both its substituents are displaced out of the mean N(4) plane are more stable than the boron in-plane stereoisomers. These regio- and stereochemical preferences are rationalised by an analysis of the deformations to the corrole macrocycle and the geometry at the boron atoms. The lowest energy structures in all cases correspond to the least strained configurations. In addition, all four complexes show significant BFHN hydrogen bonding and BHHN dihydrogen bonding interactions, which are maximised in the lowest energy configurations for each structure, indicating that these are important additional stabilising interactions. Three different regioisomers, each with cisoid or transoid stereochemistry were optimised for the diboron complex PhBOB(corrole) which contains a bridging BOB group. The dipyrromethene/dipyrromethene isomer is more stable than either of the dipyrromethene/bipyrrole isomers and cisoid stereochemistry is preferred over transoid. This contrasts with porphyrin complexes containing BOB groups for which both stereochemical possibilities are observed, and reflects the contracted size of the corrole macrocycle. Three further diboron corroles were investigated, the diboranyl cation [B(2)(corrole)](+) and its one- and two-electron reduced derivatives B(2)(corrole) and [B(2)(corrole)](-). These calculations were undertaken to determine whether the site of reduction of [B(2)(corrole)](+) is likely to be the diboron moiety or the macrocycle. The B-B bond lengths do not shorten upon reduction and an analysis of the molecular orbitals of each species indicates that reduction will be most likely to occur at the macrocycle, offering a potential route to an example of the two-electron reduced corrole ligand, an analogue of the 20-electron isophlorin ligand observed in the corresponding reduced porphyrin complex B(2)(porphine).     

Macrocyclic Transformations from Norrole to Isonorrole and an N‐Confused Corrole with a Fused Hexacyclic Ring System Triggered by a Pyrrole Substituent

Three kinds of fused porphyrinoids, L2 – L4 , possessing different types of corrole‐based frameworks were synthesized from a pyrrole‐substituted corrole isomer (norrole L1 ). Oxidation of L1 afforded a unique N‐C_meso‐fused pyrrolyl isonorrole L2 , involving the fusion of an auxiliary pyrrolic NH moiety with a meso‐sp³‐hybridized carbon atom. Subsequently, L2 underwent macrocycle transformations to give singly and doubly N‐C_Ar‐fused N‐confused corroles, L3 and L4 , respectively. L3 and L4 contain fused [5.7.6.5]‐tetra‐ and [5.6.7.7.6.5]‐hexacyclic structures, respectively, prepared through lateral annulation. These skeletal transformation reactions from norrole to its isomer isonorrole and finally to N‐confused corrole indicate that multiply fused porphyrinoids could be readily synthesized from pyrrole‐appended confused porphyrinoids.     

水溶性锰卟啉体系催化氧化反应停流谱研究

采用快速混合停流技术,考察了pH=7.4,V(CH~3CN):V(H~2O)=1:1的混合溶剂中水溶性锰卟啉Mn^I^I^I(TMPyP)与单氧给体NaOCl及KHSO~5构建的细胞色素P-450模拟酶体系催化氧化活性物种的生成及催化烯烃DPBD环氧化过程。实验表明,在反应进行中存在着两种中间体：oxo-Mn^V(Por.)(1)和oxo-Mn^I^V(Por.)(2),但两者的催化活性有差异,在催化烯烃DPBD环氧化反应中,对于Mn^I^I^I(TMPyP)-NaOCl体系起催化作用的主要作用的主要是中间体1,而对于Mn^I^I^I(TNPyP)-KHSO~5体系两种中间体均与烯烃配位生成环氧化产物,并且该体系催化活性较高。     

Catalytic deoxygenation of pyridine N-oxides with N-fused porphyrin rhenium complexes

Deoxygenation reactions of pyridine N-oxide derivatives catalyzed by N-fused porphyrin rhenium(VII) trioxo complexes are developed, affording the corresponding pyridine derivatives in quantitative yields with excellent turnover numbers up to 340,000.     

Phosphacarborane chemistry: the 7,8,9,11-, 7,9,8,10- and 7,8,9,10-isomers of nido-P2C2B7H9--diphosphadicarbaborane analogues of 7,8,9,10-C4B7H11

The reaction between the carborane arachno-4,6-C2B7H13 (1) and PCl3 in dichloromethane in the presence of a "proton sponge" (PS = 1,8-dimethylaminonaphthalene) resulted in the isolation of the eleven-vertex nido-diphosphadicarbaboranes 7,8,9,11-P2C2B7H, (2) and 3-Cl-7,8,11-P2C2B7H, (3-Cl-2) in yields of 54 and 7%, respectively. Replacement of the PS by NEt3 in the same reaction gave diphosphadicarbaboranes 2 and 3-CI-2 together with the isomeric species nido-7,9,8,10-P2C2B7H, (3) in yields of 28, 15 and 3%, respectively. The reaction between the isomeric carborane arachno-4,5-C2B7H13 (4) and PCl3 in dichloromethane in the presence of PS gave the asymmetrical isomer, nido-7,8,9,10-P2C2B7H, (5). along with the chloro derivatives 4-Cl-7,8,9,10-P2C2B7H8 (4-Cl-5) and 11-Cl-7,8,9,10-PC2B7,H8 (11-Cl-5) (yields of 21, 1 and 13%, respectively). The structures of the chlorinated derivatives 3-Cl2 and 11 -Cl-5 were determined by X-ray diffraction analysis. In addition, the structures of all compounds isolated were geometry-optimised and confirmed by comparison of experimental 11B chemical shifts with those calculated by the GIAO-SCF/II//RMP2(fc)/6-31G* method. The calculations also include the structure and 11B NMR shifts of the isomer nido-7,10,8,9-P2C2B7H9 (6) which has not yet been isolated.