Ewa Pacholska

A Direct Link between Annulene and Porphyrin Chemistry-21-Vacataporphyrin

A novel molecule, aza-deficient porphyrin 5,10,15,20-tetraaryl-21-vacataporphyrin has been synthesised by a substraction of a tellurium atom from 5,10,15,20-tetraaryl-21-telluraporphyrin under treatment of HCl. The new macrocycle is an annulene-porphyrin hybrid and at the same time is directly related to 21-heteroporphyrins but has a vacant space instead of heteroatomic bridge. The molecule preserves the fundamental structural and spectroscopic features of the parental 5,10,15,20-tetraarylporphyrin with three nitrogen atoms and two CH groups favorably prearranged for coordination.

Formation and reactivity of paramagnetic organometallic nickel complexes of 21-oxa- and 21-selenaporphyrins—1H NMR and EPR investigations

Abstract Addition of aryl Grignard reagents to a toluene solution of nickel(II) monohalide complexes of 5.20-bis( p -tolyl)-10.15-diphenyl-21-oxaporphyrin (ODTDPPH) and 5.20-diphenyl-10.15-bis( p -tolyl)-21-selenaporphyrin (SeDPDTPH) at 203 K resulted in formation of paramagnetic σ -aryl nickel(II) derivatives which were identified and characterized by means of 1 H NMR. The coordination of the aryl ligand has been unambiguously proven by the unique downfield pattern of the corresponding resonances. The ( σ -aryl)nickel(II) derivatives are in the high-spin electronic state: (d xv ) 2 (d vz ) 2 (d vz ) 2 (d z 2 ) 2 (d z 2 ) 1 (d x 2 y 2 ) 1 . A homolytic cleavage of the Ni 11 -C bond has been determined for (ODTDPP)Ni II (Ar) and (SeDPDTP)Ni II (Ar) in toluene with formation of low-valent nickel species: (ODTDPP)Ni and (SeDPDTP)Ni. One-electron reduction of (SeDPDTP)Ni II Cl to generate (SeDPDTP)Ni has been investigated by means of EPR, involving 61 Ni isotope enrichment and spectral simulations. A considerable increase in metal d-orbital contribution to the singly occupied molecular orbital has been observed upon coordination of 1-methylimidazole to (SeDPDTP)Ni.

An Unorthodox Conformation of [18]porphyrin‐(1.1.1.1) Heteroanalogue—21,23‐Ditelluraporphyrin with a Flipped Tellurophene Ring

Conformational flexibility of tetrapyrrole macrocycles is currently appreciated as an important factor in the fine-tuning of porphyrin and metalloporphyrin properties.[1] Thus, introduction of sterically demanding residues (including nitrogen atom protonation) in the porphyrin core or at the outer rim (alkylation, arylation), as well as coordination of metal ions, can result in a nonplanar porphyrin conformation. Coremodified porphyrins, formed by replacement of one or more nitrogen atoms by other heteroatom(s), also demonstrate severe nonplanar arrangements once the size and/or number of heteroatoms in the core increases, even though the basic framework of the porphyrin skeleton is preserved.[2] On the whole, [18]porphyrins-(1.1.1.1) and their heteroanalogues contain a similar framework of four essentially planar fivemembered rings linked by methine carbon atoms with all the nitrogen atoms or other heteroatoms pointing toward the center of the macrocycle. Even the most severe distortion of a macrocycle preserves such an TMin∫-macrocycle orientation of the five-membered rings.[1] An enlargement of the macrocycle by the addition of heterocyclic moiety(s) and/or methine carbon atoms introduces a novel structural motif. Thus a five-membered ring– axiomatic for porphyrins (heteroporphyrins)–can be oriented in such a way that one nitrogen or other heteroatom is located at the outer perimeter and two -atoms are found in the core or just over the center. An inversion of this type has been detected for the following expanded porphyrins and expanded heteroporphyrins:[3] tetrathia[22]porphyrin(2.2.2.2),[4] tetrathia[24]porphyrin-(2.2.2.2),[5] meso-substituted [22]pentaphyrin-(1.1.1.1.0) (sapphyrins)[6] and its heteroanalogues,[7, 8] [26]hexaphyrin-(1.1.1.1.1.1),[9] heteroanalogues of [26]hexaphyrin-(1.1.0.1.1.0) (rubyrin),[3, 10] and heteroanalogues of [30]heptaphyrins-(1.1.0.0.1.1.0) and [30]heptaphyrins-(1.1.0.1.0.1.0).[11] The lowest limit of the macrocycle size permitting the flipped geometry is exemplified by [18]annulene bridged by three sulfur atoms (which formally may be named trithia[18]porphyrin-(2.2.2)), but it behaves only as an array of isolated thiophene units which are totally out of plane in the solid state.[5] It was also postulated that a 180 rotation of the N-confused pyrrole ring of 2-aza-21-carbaporphyrin is necessary to produce the TMfused∫ porphyrin.[12] The conformation of 2-aza-21-carbaporphyrin with the flipped pyrrole ring is energetically accessible as demonstrated by DFT calculations.[13] Here we report on the synthesis and characterization of 5,10,15,20-tetraphenyl-21,23-ditelluraporphyrin (Te2TPP, 2) which is the first heteroanalogue of [18]porphyrin-(1.1.1.1) with the nonplanar macrocyclic conformation containing the flipped five-membered ring. The 21,23-ditelluraporphyrin 2 was synthesized by condensation of pyrrole and 2,5-bis(phenylhydroxymethyl)tellurophene[14c] (1 Scheme 1). This procedure follows the methodology previously used for the preparation of 5,10,15,20-

10,15-di(4-pyridyl)-5,20-di(4-tolyl)-21-thiaporphyrin as a building block for porphyrin coordination arrays

10,15-di(4-pyridyl)-5,20-di(4-tolyl)-21-thiaporphyrin, (SDPyDTP)H, was prepared by condensation of 2,5-bis(4-tolylhydroxymethyl)thiophene, pyrrole and 4-pyridinecarboxaldehyde in boiling propionic acid. The synthesis introduced two pyridyl substituents at two defined (opposite to thiophene) meso positions of the porphyrin periphery. The self-assembly of the angular 10,15-dipyridyl-21-thiaporphyrin modules with cis square-planar diphosphineplatinum(II) complex leads to a cyclic rhomboid dimer [Pt(DPPP)(SDPyDTP)H]2(OTf)4. The molecule acquires butterfly geometry. The 1H NMR studies confirmed the π-π stacking of the pyridyl ring with the equatorial phenyl rings of the phosphine fragment. The conformational equilibrium, interchanging the phenyl ring positions and affording the mixture of seven conformers in solution, has been considered. 1H NMR> spectroscopy was applied to identify oligomeric species, constructed by coordination of (SDPyDTP)H to the paramagnetic nickel(II) complex 5,10,15,20-tetra(4-tolyl)-21-thiaporphyrin, (STTP)NiIICl. (SDPyDTP)H acts as a mono- or bidentate ligand coordinating by meso-pyridyl substituents. Using the paramagnetically shifted resonances as an unambiguous spectroscopic probe, 1H NMR spectroscopy readily discriminated between five- {[(STTP)NiII]((SDPyDTP)H)} and six-coordinate {[(STTP)NiII]((SDPyDTP)H)2} oligomeric subunits. The applicability of 10,15-di(4-pyridyl)-5,20-di(4-tolyl)-21-thiaporphyrin as a suitable building block in construction of larger molecules was confirmed. The new route to modify the porphyrin coordination arrays, which preserves the overall architecture but modifies intrinsic chemical properties, using heteroporphyrin was demonstrated.