Piotr J. Chmielewski

N-METHYLTETRAPHENYLPORPHYRIN WITH AN INVERTED N-METHYLPYRROLE RING: THE FIRST ISOMER OF N-METHYLTETRAPHENYLPORPHYRIN

In the course of the mild methylation of 5,10,15,20-tetraphenyl-21-carbaporphyrin (CTPPH2) a novel isomer of N-methyl-5,10,15,20-tetraphenylporphyrin with an inverted N-methylated pyrrole ring, i.e. 2-N-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrin (2-NCH3TPPH) has been synthesised. The protonation of 2-NCH3CTPPH proceeds stepwise including mono- and two di-cationic species. 2-NCH3CTPPH can be considered as a new anion-specific binding agent. The lability of the 21-CH proton afforded the easy insertion of nickel(II) to form a stable organometallic macrocyclic complex.

NICKEL COMPLEXES OF 21-OXAPORPHYRIN AND 21,23-DIOXAPORPHYRIN

The nickel(I) and nickel(II) complexes of 5,20-bis(p-tolyl)-10, 15-diphenyl-21-oxaporphyrin (ODTDPPH) and 5,10,15,20-tetraphenyl-21, 23-dioxaporphyrin (O2 TPP) have been investigated. These oxa analogues of 5,10,15,20-tetraarylporphyrin, where one or two pyrrole rings are replaced by a furan moiety, have been synthesized by condensation of the respective precursors, namely 2,5-bis(arylhydroxymethyl)furan, pyrrole, and arylaldehyde. Insertion of nickel(II) into ODTDPPH or O2 TPP yielded high-spin five- and six-coordinate ([(ODTDPP)Ni(II) Cl] and [(O2 TPP)NiIICl2 ]) complexes, which can be reduced with moderate reducing reagents. The EPR spectra of [(ODTDPP)Ni(I) ] and [(O2 TPP)Ni(I) Cl] revealed the Ni(I) oxa(dioxa)porphyrin rather than a Ni(I) anion radical electronic structure. In the structures of [(ODTDPP)Ni(II) Cl], [(O2 TPP)Ni(IICl) 2 ], and [(ODTDPP)Ni(I) ], determined by X-ray diffraction, the furan ring is planar and coordinates in the η(1) fashion through the trigonal oxygen atom; the nickel ion lies in the furan plane for the latter two complexes, but slightly outside it in [(ODTDPP)Ni(II) Cl]. The Ni-N and Ni-O bond lengths decrease upon reduction of high-spin five-coordinate [(ODTDPP)Ni(II) Cl] to four-coordinate [(ODTDPP)Ni(I) ]. The pattern of downfield pyrrole resonances in (1) H NMR spectra of [(ODTDPP)Ni(IICl) ] and [(O2 TPP)-Ni(II) Cl2 ] has been established. The downfield positions of furan resonances are unusual for Ni(II) heteroporphyrins; they have been accounted for by the nearly in-plane coordination of the furan moiety as opposed to the side-on coordination found for thiophene- or selenophene-containing heteroporphyrins. An example of ion-pair formation, [(O2 TPPH)2 ][Ni(II) Cl4 ], was produced from [(O2 TPP)Ni(II) Cl2 ] by acidification with HCl.

Synthesis and characterization of Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-salicydene-o-hydroxymethyleneaniline

Abstract The new Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes with tridentate Schiff base, the product of condensation of o-aminobenzyl alcohol with salicylaldehyde have been synthesized and characterized by elemental analysis, IR, electronic, EPR and Mossbauer spectra, thermal analysis, magnetic susceptibility and molecular weight measurements. Dimeric or polymeric structures for the investigated complexes were proposed. The interaction of the cobalt complex with dioxygen is also described.

Peripherally Fused Porphyrins via the Scholl Reaction: Synthesis, Self-Assembly, and Mesomorphism

Oxidative coupling of activated aryl groups attached to β-positions of the porphyrin ring provides convenient access to derivatives containing peripherally fused phenanthrene and benzo[g]chrysene units. Tetra(benzochryseno)porphyrin, reported here for the first time, contains a nonplanar, sterically locked π system and shows very intense electronic absorptions in the Q range of the electronic spectrum. Tetraphenanthroporphyrins show a tendency to aggregate in solution. In one case, a discrete dimer is formed, whose structure was investigated spectroscopically and theoretically. Derivatives bearing long alkyl chains are mesomorphic and exhibit columnar phases (tetraphenanthroporphyrins) and a monoclinic 3D phase (tetrabenzochrysenoporphyrin). The symmetry of column packing in the columnar phases is dependent on the number of alkyl chains per molecule. X-ray diffraction measurements show that, in spite of their nonplanarity, the aromatic cores in the mesophases are tightly stacked within the column. The corresponding stacking patterns were derived from the structure of the dimer, on the basis of geometrical analysis and molecular modeling.

Highly Strained Nonclassical Nanotube End-caps. A Single-Step Solution Synthesis from Strain-Free, Non-Macrocyclic Precursors

Nonclassical nanotube end-caps have been constructed from strain-free heterocyclic precursors using a one-step synthetic procedure, involving multiple nickel-mediated Ullmann couplings. These systems consist of tubular macrocyclic sections that are tightly capped on one side with a bridging benzene ring, forming deep, chemically accessible cavities. The end-caps are characterized by exceptionally high internal strain energies reaching 144 kcal/mol. The optical absorption and emission properties of these molecules show a marked dependence on conjugation length and geometrical factors. The mechanism of end-cap formation, investigated using DFT calculations, relies on precise timing of transmetalation and reductive elimination events.

Expanded Hexapyrrolohexaazacoronenes. Near-Infrared Absorbing Chromophores with Interrupted Peripheral Conjugation

A family of azacoronenes containing up to two saturated bridges at the periphery was synthesized from substituted hexapyrrolylbenzenes using a two-step condensation-aromatization procedure. The introduction of peripheral bridges provides access to nonplanar, sterically crowded systems that display complex reactivity patterns, involving stereospecific aromatization of bridges and nucleophile additions. Despite the interrupted conjugation on the periphery, the new azacoronenes have easily accessible higher oxidation levels, and a quadruply charged species was chemically generated by reaction with SbCl5. These oxidized species show extensive π-electron conjugation and are efficient UV-vis-NIR absorbers, active up to ca. 2400 nm. Interruption of peripheral conjugation is shown to induce a tendency toward biradicaloid electron configurations in doubly oxidized species.

Synthesis of N-Confused Porphyrin Derivatives with a Substituted 3-C Position

Active methylene compounds such as 5,5-dimethylcyclohexane-1,3-dione, cyclohexane-1,3-dione, 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one, 1,3-dimethyl-1H-pyrazol-5(4H)-one, and 3-methylisoxazol-5(4H)-one react with the 3-C position of N-confused porphyrin in THF for 5 min to afford a novel type of N-confused porphyrin derivatives in good yield without the need of any catalyst.

Application of 2-ethylpyrrole for a direct synthesis of 3-substituted inverted porphyrins

Abstract 3-Ethyl-5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrin is the major macrocyclic product in the condensation of 2-ethylpyrrole, pyrrole, and benzaldehyde. Oxidation of the ethyl substituent leads to 3-(1′-hydroxyethyl)- and 3-acetyl-substituted inverted porphyrins.

An inverted porphyrin with a pendant pyrrole—identification of a tetraphenylsapphyrin isomer in the Rothemund synthesis

Abstract 2-Aza-3-(2′-pyrrolyl)-5,10,15,20-tetraphenyl-21-carbaporphyrin was identified among the products of a Rothemund synthesis and characterized. An alternative convenient method of its synthesis starting from 2-aza-5,10,15,20-tetraphenyl-21-carbaporphyrin was proposed.

Helical bis(N-confused porphyrins) with subunits fused by double orthometalation with platinum: adaptability of an apparently rigid system.

Modifications of the interior or periphery of porphyrins allow major alteration or fine tuning of the properties of the system, such as cationor anion-binding ability, redox potential, absorption, emission, as well as many other properties. Porphyrin subunits can be also relatively easily linked into larger twoand three-dimensional arrays, thus extending the possibility of their application as biomimetic models, catalysts, and materials for the transport of charge, molecules, and ions. Among the covalently and coordinately linked oligomers, the most attractive class is constituted by the systems in which the subunits are directly linked. The interaction between delocalized p-bond systems appears to be strongest when the b-pyrrole carbon atoms of the porphyrins are linked. An important feature of b–b-linked bis(porphyrins) is their intrinsic axial chirality. However, the stability of the configuration requires restriction of the rotation around the b–b-bond. This restriction can be provided by the appropriate choice of metal ion that coordinates within both macrocyclic cores. The external nitrogen atom of the confused pyrrole in N-confused porphyrin (NCP) 1 and some of its derivatives and complexes can act as a donor site. In the readily obtainable bis(N-confused porphyrin) 2, a cis-oriented system of two external nitrogen atoms can