Metal complexes of meso-amino-octaethylporphyrin and the oxidation of NiII(meso-amino-octaethylporphyrin)

The crystal structures of meso-NH2-OEPH2, NiII(meso-NH2-OEP), and CuII(meso-NH2-OEP) (where OEP is the dianion of meso-amino-octaethylporphyrin) have been determined to examine the effects of the meso-substituent on the geometry of the ligand. CuII(meso-NH2-OEP) has a nearly planar geometry while the free ligand itself and NiII(meso-NH2-OEP) have ruf conformations. NiII(meso-NH2-OEP) is much less reactive toward oxidation than are (py)2FeII(meso-NH2-OEP), ClFeIII(meso-NH2-OEP), or NiII(meso-HO-OEP), which all undergo oxidation in pyridine solution when exposed to dioxygen. Treatment of NiII(meso-NH2-OEP) with iron(III) chloride in chloroform solution does result in oxidation of the ligand in two separate processes. One involves oxygenation at the trans-meso position, while the other results in ring cleavage and removal of the amino function. The open-chain tetrapyrrole complex, NiII(OEB-CO2Et), has been characterized by single-crystal X-ray diffraction and shown to contain a helical ligand with a four-coordinate nickel ion.     

Dioxadiazuliporphyrin: a near-IR redox switchable chromophore

The synthesis of dioxadiazuliporphyrinogen 7 and its oxidized forms: dioxadiazuliporphyrin 8 and dication 8(2+), is reported. These compounds were characterized in solution using UV-vis and 1H and 13C NMR spectroscopic means and in the solid state via single-crystal X-ray diffraction analysis. Dioxadiazuliporphyrin is a nonaromatic porphyrinoid, readily and reversibly oxidizable to its cation radical and to the aromatic carbaporphyrinoid dication, which can be viewed as a 21,23-dicarba-22,24-dioxaporphyrin with two fused tropylium rings. Further insight into the geometric and magnetic manifestations of aromaticity and antiaromaticity in the case of the redox couple 8, 8(2+) is obtained using density functional calculations and nucleus-independent chemical shifts.     

Dithiaethyneazuliporphyrin--a contracted heterocarbaporphyrin

Dithiaethyneazuliporphyrin, the first contracted carbaporphyrinoid, has been synthesized; the molecule contains an azulene moiety embedded in the [18]dithiacarbatriphyrin(4.1.1) macrocyclic framework.     

Temperature-programmed desoprtion of H2 from the surfaces of pd/support and Pd-Ag/support catalysts (support = Al2O3, SiO2)

Thermal desorption of H₂ from the surface of Pd/support and Pd-Ag/support (support = Al₂O₃, SiO₂) catalysts has been investigated. Two wide desorption peaks can be observed for the 5% Pd/support catalyst. The presence of these peaks in the thermogram indicates that several adsorption states exist, which is the result of occurrance of different adsorption centers of specific bond strengths for hydrogen. The addition of silver to the palladium catalysts causes a considerable decrease in the size of the high temperature desorption peak. It is also worth noting that the temperature of the maximum of the desorption rate remains practically constant for all bimetallic catalysts studied. This means that the activation energy of the hydrogen desorption process does not change after the introduction of silver to the palladium catalyst.     

Dithiadiazuliporphyrin: facile generation of carbaporphyrinoid cation radical and dication

Dithiadiazuliporphyrin is a nonaromatic porphyrinoid, readily and reversibly oxidizable to its cation radical and to the unprecedented aromatic carbaporphyrinoid dication, which can be viewed as a 21,23-dicarba-22,24-dithiaporphyrin with two fused tropylium rings.     

Hückel and Möbius Expanded para‐Benziporphyrins: Synthesis and Aromaticity Switching

The four expanded p‐benziporphyrins A,C‐di‐p‐benzi[24]pentaphyrin(1.1.1.1.1), N‐fused A‐p‐benzi[24]pentaphyrin, A,D ‐di‐p‐benzi[28]hexaphyrin(1.1.1.1.1.1), and A,C‐di‐p‐benzi[28]hexaphyrin(1.1.1.1.1.1) were obtained in three‐component Lindsey‐type macrocyclizations. These compounds were explored as macrocyclic ligands and as potential aromaticity switches. A BODIPY‐like difluoroboron complex was obtained from the A,C‐di‐p‐benzi[24]pentaphyrin, whereas A,C‐di‐p‐benzi[28]hexaphyrin yielded a Möbius‐aromatic Pd^II complex containing fused pyrrole and phenylene subunits. Conformational behavior, tautomerism, and acid‐base chemistry of the new macrocycles were characterized by means of NMR spectroscopy and DFT calculations. Free base N‐fused A‐p‐benzi[24]pentaphyrin showed temperature‐dependent Hückel–Möbius aromaticity switching, whereas the A,C‐di‐p‐benzi[28]hexaphyrin formed a Möbius‐aromatic dication.     

Thiaporphyrin with an Inverted Thiophene Ring – DFT Studies

The structure and electronic energy have been investigated applyingthe density functional theory (DFT) for two idealized 2-thia-21-carbaporphyrin, (SCP)H and (3H-SCP), 2-thia-21-carbaporphyrin anion (SCP)^- and 21-thiaporphyrin (SP)H. The analysis of calculated total electronic energies, using the B3LYP/6-31-G^* approach, demonstrates that the energy difference between 21-thiaporphyrin and its inverted isomer equals 10.34 kcal/mol [(SCP)H] and 52.08 kcal/mol [(3H-SCP)]. In contrast to 21-thiaporphyrin thethiophene fragments in (SCP)H and SCP^- present a geometry resembling that one of an isolated thiophene molecule.