N-confused Porphyrin Research Articles

Helical Bis(N-Confused Porphyrins) with Subunits Fused by Double Orthometalation with Platinum: Adaptability of an Apparently Rigid System

Helical Bis(N-Confused Porphyrins) with Subunits Fused by Double Orthometalation with Platinum: Adaptability of an Apparently Rigid System

Helical Bis(N‐Confused Porphyrins) with Subunits Fused by Double Orthometalation with Platinum: Adaptability of an Apparently Rigid System

Flexible yet rigid: The flexibility of the porphyrin rings makes racemization or chiral induction still possible with helical metalated bis(N-confused porphyrin) systems, even though the bipyrrole fragment itself is rigid. The porphyrins are peripherally doubly orthometalated with platinum(II), and a series of its oxidative addition products were also obtained (see structures of the iodomethyl adduct: gray and brown C; blue N; orange Pt; purple I).

Regioselective Amination of Carbaporpholactone and N-Confused Porphyrin

An efficient route to the direct amination at the inner carbon of carbaporpholactone is reported. A regioselectivity of substitution is enforced by activation of the embedded furanone fragment due to coordination of the highly oxidized silver(III) cation. A stepwise oxidation of the dimethylamine derivative leads to the internally bridged carbaporpholactones which contain respectively [5.7.5] tricyclic or [5.7.5.7.5] pentacyclic rings. The analogous reactivity of N-confused porphyrin has been also explored.

Theoretical Study on Rotation of Pyrrole Rings in Porphyrin and N-Confused Porphyrin

Rotation of pyrrole rings in regular porphyrins and N-confused porphyrins is theoretically investigated by DFT calculations. While the inversion of the pyrrole rings in the regular porphyrins requires high activation energies (36.5-49.1 kcal/mol), the inversion of the confused pyrrole rings in the N-confused porphyrins requires much lower activation energies (18.1-24.5 kcal/mol). This marked difference can be explained by the intramolecular hydrogen bondings and aromatic stabilization due to the [18]annulenic substructures, where confusion and NH tautomerism play an important role. In both of the macrocycles, 360 degrees rotation of their pyrrole rings would be difficult possibly due to the small cavity. Alternatively, a reaction pathway for the production of N-fused porphyrin from N-confused porphyrin is obtained, which is consistent with the experimental observation.

ChemInform Abstract: The Oxidation of Ni(II) N‐Confused Porphyrins (NCPs) with Azo Radical Initiators and an Unexpected Intramolecular Nucleophilic Substitution Reaction via a Proposed Ni(III) NCP Intermediate.

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Transformations of N-Confused Porphyrin Triggered by Insertion of Silicon(IV)

N-confused porphyrin, 5,10,15,20-tetraaryl-2-aza-21-carbaporphyrin, dissolved in triethylamine reacts with dichloromethylsilane yielding the methylsilicon(IV) complex of 5,10,15,20-tetraaryl-2-aza-21-hydroxy-21-carbaporphyrin. Addition of aldehydes or ketones (acetone, acetaldehyde acetophenone, butanone, propanal, benzaldehyde, p-methylbenzaldehyde, p-methoxybenzaldehyde, terephthaldehyde) into the insertion mixture triggered the profound transformation of N-confused porphyrin to form the methylsilicon(IV) complex of N-fused porphyrin derivative substituted at the inner C(9) position by a hydroxyalkyl moiety derived from aldehyde or ketone. The macrocyle is structurally related to an aromatic N-fused inner phlorin while the coordination polyhedron of bound silicon resembles the trigonal bipyramid. The macrocyclic ligand coordinates in the facial mode as the three pyrrolic nitrogen donors lie at the vertices of the single trigonal face. The meridional positions of the trigonal bipyramid are occupied by two pyrrolic nitrogen donors and a sigma-methyl ligand. The coordination sphere is completed by apical coordination of the alkoxy oxygen atom derived from alkanal or alkonone. The incorporation of aldehydes and ketones is stereoselective. Acidic desililation of alkanal compounds yields two aromatic N-confused porphyrin derivatives, that is, 3-(1-hydroxyalkyl)-5,10,15,20-tetraaryl-2-aza-21-carbaporphyrin and its oxidation product 3-alkanoyl-5,10,15,20-tetraaryl-2-aza-21-carbaporphyrin. The acid triggered desililation of ketone derivatives produces the equimolar amounts of N-confused porphyrin and ketone. The first spectroscopically identified step involves the protonation of the C(7) position affording the non-aromatic silicon(IV) complex. The density functional theory (DFT) has been applied to model the molecular and electronic structure of all species identified in the course of silicon insertion into the N-confused and N-fused porphyrin.

Facile Nitrite Reduction and Conversion Cycle of {Fe(NO)}6/7 Species: Chemistry of Iron N-Confused Porphyrin Complexes via Protonation/Deprotonation

Facile nitrite reduction was achieved using [Fe(II)(HCTPPH)NO] as the starting compound to react with NaNO(2). Stoichiometric studies allow the isolation of both {Fe(NO)}(6) and {Fe(NO)}(7) nitrosyl complexes and provide insight into the proton and electron transfer processes during the nitrite reduction. Treating [Fe(CTPP)NO] with acid or oxidizing [Fe(HCTPP)NO] with AgClO(4) yields intermediate [Fe(HCTPP)NO](+). The conversion cycles starting from {Fe(NO)}(6) [Fe(CTPP)NO] to {Fe(NO)}(6) [Fe(HCTPP)NO][ClO(4)] then to {Fe(NO)}(7) [Fe(HCTPP)NO] and vice versa were constructed.

Programmed asymmetrical trimer formation of β-alkyl N-confused porphyrin zinc(II) complex

Self-coordination of β-alkyl N-confused porphyrin (NCP) zinc(II) complexes has been studied to reveal that asymmetrical trimers formed exclusively. A key factor to control the configuration of the trimers (symmetric or asymmetric) has been studied theoretically, and revealed that the steric environment around the peripheral nitrogen atoms as well as rotational angles of the confused pyrrole rings play a crucial role in trimer formation of β-alkyl NCP zinc(II) complexes.

The oxidation of Ni(ii) N-confused porphyrins (NCPs) with azo radical initiators and an unexpected intramolecular nucleophilic substitution reaction via a proposed Ni(iii) NCP intermediate

The oxidation of Ni(II) N-confused porphyrins (NCPs) with azo radical initiators resulted in an unexpected intramolecular nucleophilic substitution reaction via a proposed Ni(III) NCP intermediate, which could be detected by HRMS.

Anion responsive dyad system of porphyrin and N-confused porphyrin

A dyad of porphyrin and N-confused porphyrin is synthesized for the first time, in which an efficient excitation energy transfer as well as enhancement of emission quantum yield induced by anion binding is observed.

Pt(II) N-confused porphyrin: An expanded pyrrole that affords a stable π-anion

Pt(II) complex of meso-tetrakis(pentafluorophenyl) N-confused porphyrin (1-Pt) efficiently binds Cl(-), Br(-), and I(-) anions at the peripheral N-H, while deprotonation proceeds with F(-), H(2)PO(4)(-), and OH(-) in CH(2)Cl(2) solution; neutral and anionic structures of 1-Pt were characterized by single crystal X-ray diffraction analysis.

Endocyclic Extension of Porphyrin π‐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.

Facile Synthesis of Unsubstituted β,β′-Linked Diformyldipyrromethanes

Unsubstituted beta,beta'-linked diformyldipyrromethanes are promising precursors for the synthesis of novel poly dipyrromethene ligands and N-confused porphyrins. A strategy has been developed to selectively synthesize unsubstituted beta,beta'-linked diformyldipyrromethanes in moderate yields starting from 2-formylpyrrole.

Synthesis and Reactivity of N-Methyl and N-Phenyl meso-Unsubstituted N-Confused Porphyrins

Condensations of 1-methyl and 1-phenyl-2,4-pyrroledicarbaldehydes with a tripyrrane in TFA-dichloromethane, followed by oxidation with aqueous FeCl(3), gave novel cross-conjugated meso-unsubstituted N-confused porphyrins (NCPs; 12). These porphyrin analogues showed significant diatropic ring currents that were enhanced upon protonation. Reactions with nickel(II) acetate in refluxing DMF, or palladium(II) acetate in acetonitrile, gave good yields of the corresponding nickel(II) or palladium(II) organometallic derivatives 18 and 19. These complexes were stable and the proton NMR spectra showed slightly increased downfield shifts to the external protons. Addition of TFA resulted in C-protonation at the internal carbon to give aromatic cations that showed the inner CH resonance between -2.5 and -4.0 ppm. The nickel(II) cations 20a and 20b slowly underwent demetalation but the related palladium cations 20c and 20d were quite robust and showed no loss of palladium after 1 week at room temperature. Reaction of NCPs 12 with silver(I) acetate gave silver(III) derivatives 21a and 21b where an oxidation had occurred at C-3 to afford a lactam unit. The silver complexes showed strong diatropic ring currents and porphyrin-like UV-vis spectra with a Soret band near 430 nm. N-Methyl NCP 21a also reacted with gold(III) acetate to give the gold(III) NCP 21c, albeit in low yield, and this species showed similar spectroscopic properties to silver(III) NCP 21a. Syntheses of N-phenyl NCP 12b were accompanied by the formation of the 3-oxo derivative 15b, and the related N-methyl product 16a could also be obtained when the reaction mixtures were oxidized with silver(I) acetate under acidic conditions. The proton NMR spectra for these aromatic NCPs in CDCl(3) show the internal CH shifted upfield to near -6.5 ppm, while the external meso-protons are strongly deshielded giving 4 singlets between 9 and 10 ppm. This study demonstrates that meso-unsubstituted NCPs have unusual reactivity and unique spectroscopic properties, and these results complement and extend the work on the much better known meso-tetraaryl NCPs.

Synthesis of N-Confused Tetraphenylporphyrin Rhodium Complexes Having Versatile Metal Oxidation States

A variety of N-confused tetraphenylporphyrin rhodium complexes were synthesized, and their structures and physical properties were investigated. Depending on the reaction conditions, the rhodium(I), -(III), and -(IV) complexes were produced, which exemplified the versatile coordination mode of N-confused porphyrin ligands.

N-confused porphyrin possessing glucamine-appendants: Aggregation and acid/base properties in aqueous media

A water-soluble derivative of N-confused porphyrin (NCP: 5,10,15,20-tetraaryl-2-aza-21-carbaporphyrin) was synthesized by introducing glucamine groups at the para-position of meso-aryl groups. The tetraglucamine-appended NCP ( TG-NCP) exists as monocation in aqueous solution containing 6 mM sodium dodecyl sulfate (SDS) but exists as freebase to form aggregates in pure water. These properties are distinct from those of corresponding regular porphyrin, which exists as freebase in the micellar solution and practically insoluble in water.

Synthesis, Structure and Spectroscopic Properties of Lanthanide Complexes of N‐Confused Porphyrins

AbstractA series of meso‐substituted N‐confused porphyrins (NCP) is synthesized using the modified Rothemund–Lindsey procedure. Lanthanide N‐confused porphyrinate complexes of the general formula [(NCP)Ln(LOMe)] [Ln3+ = Yb3+ and Er3+; L = (η5‐C5H5)Co{P(=O)(OMe)2}3–] are obtained in moderate yields upon interaction of N‐confused porphyrin free bases (H2NCP) with Ln[N(SiMe2)3]·x[LiCl(THF)3], followed by the addition of the tripodal anion L as an effective encapsulating agent for the lanthanide ions. The structural and spectroscopic data for these complexes provide evidence for an η2‐agostic interaction between the Ln3+ ion and the inner C–H bond of the NCP ligand. Methylation of [(NCTCPP)Yb(LOMe)] (H2NCTCPP = 2‐azo‐5,10,15,20‐tetracyanophenyl‐21‐carbaporphyrin) with methyl iodide yields the novel stable lanthanide complex of the N‐methylated derivative of N‐confused porphyrins, whose X‐ray structure also exhibits an η2‐agostic interaction between the metal center and the inner C–H bond of the NCTCPP ligand. The photophysical properties of the N‐confused porphyrins and their lanthanide complexes are investigated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Phosphorus Complexes of N-Fused Porphyrin and Its Reduced Derivatives: New Isomers of Porphyrin Stabilized via Coordination

N-fused isophlorin 3 and its tautomeric phlorin forms 4 and 5, the new constitutional isomers of porphyrin which preserve the basic skeleton of their maternal N-fused porphyrin, have been identified in the course of investigation of phosphorus insertion into N-fused porphyrin 2. N-fused porphyrin reacts with PCl3 in toluene yielding phosphorus(V) N-fused isophlorin 3-P wherein the macrocycle acts as a trianionic tridentate ligand. The identical product has been formed in the reaction of N-confused porphyrin 1 and POCl3 or PCl3. The coordinating environment of phosphorus(V) in 3-P as determined by X-ray crystallography resembles a distorted trigonal pyramid with the nitrogen atoms occupying equatorial positions with the oxygen atom lying at the unique apex. Phosphorus(V) is significantly displaced by 0.732(1) A from the N3 plane. The P-N distances are as follows P-N(22) 1.664(2), P-N(23) 1.645(2), and P-N(24) 1.672(2). All P-N(pyrrolic) bond lengths are markedly shorter than the P-N distances in phosphorus porphyrins. 3-P is susceptible to proton addition at the inner C(9) carbon atom, yielding aromatic 4-P. The modified macrocycle acts as a dianionic ligand and allows the efficient 18 pi-electron delocalization pathway. Two stereoisomers affording the syn (4-P syn) and anti (4-P anti) location of the H(9) atom with respect to the oxygen atom of the PO unit have been identified by (1)H NMR. A regioselective reduction of free base N-fused porphyrin 2 with NaBH4 yielded a nonaromatic isomer of 4, that is, N-fused phlorin 5 due to an addition of a hydride to the C(15) carbon and a proton to one of the pyrrolic nitrogens. The isomer 5 reacts with PCl 3 yielding phosphorus(V) fused isophlorin 3-P. Density functional theory has been applied to model the molecular and electronic structure of porphyrin isomers 3, 4, and 5 and their phosphorus(V) complexes.

Synthesis and Characterization of Transition Metal Complexes of Dimeric N-Confused Porphyrin Linked by an o-Xylene Fragment

Insertion of nickel(II), zinc, cadmium, or silver(III) into both macrocyclic crevices of 2,2'-o-xylene-bis(5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbaporphyrin) results in homometallic dimeric complexes which were isolated and characterized by NMR, UV-vis, mass spectrometry, and cyclic voltammetry. The 1H NMR study of these systems at low temperatures (203-233 K) allowed determination of most stable conformers with respect to a rotational freedom around the xylene bridge. An unfolded conformation for the dicationic bis(silver(III)) complex was determined on the basis of 2D nuclear Overhauser effect spectrometry experimentation. A mixture of nonequally populated diastereomers is observed for bis(zinc) and bis(cadmium) complexes due to a possibility of two different orientations of the apical anionic ligands with respect to the bridge. In a reaction of 5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbaporphyrinato nickel(II) with 2-(o-bromoxylene)-5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbaporphyrin in the presence of a proton scavenger, two isomeric bis(N-confused porphyrin) complexes with one subunit "empty" and the other metalated by nickel(II) were obtained. In the product 10, the o-xylene links external nitrogens of the subunits while product 11 consists of the xylene bridge between external nitrogen of the nonmetalated subunit and internal carbon of the fragment containing a nickel(II) ion. The products were characterized by mass spectrometry, UV-vis, NMR, and, in the case of complex 11, also by X-ray crystallographic analysis (space group P1, a =17.007(3), b = 18.130(3), c = 18.797(2) A, alpha = 105.856(13) degrees, beta = 107.447(13) degrees, gamma = 98.818(15) degrees, V = 5141.1(15) A3, Z = 2). Insertion of zinc or silver(III) into an empty crevice of 10 resulted in heterometallic zinc-nickel(II) or silver(III)-nickel(II) complexes 12 or 13, respectively, which were characterized by NMR, UV-vis, and cyclic voltammetry. The subunits in the bis(porphyrin) systems retain spectroscopic and redox properties typical for monomeric complexes.

Detection of unusual ΔHOMO < ΔLUMO relationship in tetrapyrrolic cis- and trans-doubly N-confused porphyrins

A plus-to-minus MCD sign in ascending energy has been detected for the Q bands of the copper(III) complexes of doubly N-confused porphyrin ( cis- and trans- 1). An unusual ΔHOMO < ΔLUMO relationship for tetrapyrrolic porphyrins was calculated using the HF, DFT, and semi-empirical methods. By applying the Michl’s perimeter model, the observed MCD pattern was successfully explained by the computational results.