Lanthanide Texaphyrins as Photocatalysts

Here, we report the use of gadolinium­(III)-, lutetium­(III)-, and lanthanum­(III)-texaphyrins as bioinspired photocatalysts that promote a novel approach to the degradation of curcumin, a 1,3-diketo-containing natural product. Complexation of curcumin to the lanthanide centers of the texaphyrins yields stable species that display limited reactivity in the dark or under anaerobic conditions. However, upon exposure to mWatt intensity light (pocket flashlight) or simply under standard laboratory illumination in the presence of atmospheric oxygen, substrate oxidation occurs readily to generate curcumin-derived cleavage products. These latter species were identified on the basis of spectroscopic and mass spectrometric analyses. The mild nature of the activation conditions serves to highlight a potential new role for photoactive lanthanide complexes

Expanded Rosarin: A Versatile Fullerene (C₆₀) Receptor

An expanded rosarian (<b>P</b>_<b>3</b><b>P</b>_<b>6</b>) with a bowl-like conformation has been prepared and characterized in a one-pot procedure that involves condensing a bispyrrole pyridine precursor (<b>P</b>_<b>1</b><b>P</b>_<b>2</b>) with benzaldehyde, followed by oxidation. Single crystal X-ray diffraction analysis reveals a bowl-like conformation in the solid state with an upper rim diameter defined by the <i>meso</i>-phenyl substituents of ca. 13.5 Å and a depth of roughly 6.3 Å. <b>P</b>_<b>3</b><b>P</b>_<b>6</b> forms both 1:1 and 2:1 complexes with C₆₀ in the solid state. DFT reveals similar energies for the two binding modes. A 1:1 binding stoichiometry dominates in 1,2-dichlorobenzene-<i>d</i>₄ at the millimolar concentrations dictated by solubility consideration. The solution phase interactions between rosarian and C₆₀ were studied using ¹H NMR, UV–vis, and femtosecond transient absorption spectroscopies in 1,2-dichlorobenzene-<i>d</i>₄ or toluene. To our knowledge, this is the first report of an unfunctionalized porphyrinoid that forms a well-defined complex with C₆₀ in solution as well as in solid state

Expanded Rosarin: A Versatile Fullerene (C₆₀) Receptor

An expanded rosarian (<b>P</b>_<b>3</b><b>P</b>_<b>6</b>) with a bowl-like conformation has been prepared and characterized in a one-pot procedure that involves condensing a bispyrrole pyridine precursor (<b>P</b>_<b>1</b><b>P</b>_<b>2</b>) with benzaldehyde, followed by oxidation. Single crystal X-ray diffraction analysis reveals a bowl-like conformation in the solid state with an upper rim diameter defined by the <i>meso</i>-phenyl substituents of ca. 13.5 Å and a depth of roughly 6.3 Å. <b>P</b>_<b>3</b><b>P</b>_<b>6</b> forms both 1:1 and 2:1 complexes with C₆₀ in the solid state. DFT reveals similar energies for the two binding modes. A 1:1 binding stoichiometry dominates in 1,2-dichlorobenzene-<i>d</i>₄ at the millimolar concentrations dictated by solubility consideration. The solution phase interactions between rosarian and C₆₀ were studied using ¹H NMR, UV–vis, and femtosecond transient absorption spectroscopies in 1,2-dichlorobenzene-<i>d</i>₄ or toluene. To our knowledge, this is the first report of an unfunctionalized porphyrinoid that forms a well-defined complex with C₆₀ in solution as well as in solid state

Self-Assembled Pyridine-Dipyrrolate Cages

An inherently nonlinear pyridine dipyrrolate ligand, namely 2,6-bis­(3,4-diethyl-5-carboxy-1<i>H</i>-pyrrol-2yl)­pyridine (compound <b>1</b>), is able to distinguish between different zinc­(II) cation sources, namely Zn­(acac)₂ and Zn­(OAc)₂, respectively. This differentiation is manifest both in terms of the observed fluorescent behavior in mixed organic media and the reaction chemistry. Treatment of <b>1</b> with Zn­(acac)₂ gives rise to a cage dimer, cage-<b>1</b>, wherein two molecules of compound <b>1</b> act as double bridging units to connect two individual cage subunits. As inferred from X-ray crystallographic studies, this cage system consists of discrete zinc dimers with hydroxide bridges that, with the assistance of bound DMF solvent molecules, serve to fix the geometry and orientation of the pyridine dipyrrolate building blocks. When a different zinc source, Zn­(OAc)₂, is used to carry out an ostensibly similar complexation reaction with compound <b>1</b>, an acetate-bridged 1D abacus-like cage polymer is obtained as inferred from X-ray diffraction analysis. This extended solid state structure, cage-<b>2</b>, contains individual zinc dimer cage submits and appears stabilized by solvent molecules (DMF) and the counteranion (acetate). Rod-like assemblies are also observed by DLS and SEM. This construct, in contrast to cage-<b>1</b>, proved fluorescent in mixed organic media. The structure of the ligand itself (i.e., in the absence of Zn­(II)) was confirmed by X-ray crystallographic analysis and was found to assemble into a supramolecular polymer. Conversion to a dimer form was seen upon the addition of TBAOAc. On the basis of the metric parameters, the structures seen in the solid state are stabilized via hydrogen bonding interactions involving solvent molecules

Self-Assembled Pyridine-Dipyrrolate Cages

An inherently nonlinear pyridine dipyrrolate ligand, namely 2,6-bis­(3,4-diethyl-5-carboxy-1<i>H</i>-pyrrol-2yl)­pyridine (compound <b>1</b>), is able to distinguish between different zinc­(II) cation sources, namely Zn­(acac)₂ and Zn­(OAc)₂, respectively. This differentiation is manifest both in terms of the observed fluorescent behavior in mixed organic media and the reaction chemistry. Treatment of <b>1</b> with Zn­(acac)₂ gives rise to a cage dimer, cage-<b>1</b>, wherein two molecules of compound <b>1</b> act as double bridging units to connect two individual cage subunits. As inferred from X-ray crystallographic studies, this cage system consists of discrete zinc dimers with hydroxide bridges that, with the assistance of bound DMF solvent molecules, serve to fix the geometry and orientation of the pyridine dipyrrolate building blocks. When a different zinc source, Zn­(OAc)₂, is used to carry out an ostensibly similar complexation reaction with compound <b>1</b>, an acetate-bridged 1D abacus-like cage polymer is obtained as inferred from X-ray diffraction analysis. This extended solid state structure, cage-<b>2</b>, contains individual zinc dimer cage submits and appears stabilized by solvent molecules (DMF) and the counteranion (acetate). Rod-like assemblies are also observed by DLS and SEM. This construct, in contrast to cage-<b>1</b>, proved fluorescent in mixed organic media. The structure of the ligand itself (i.e., in the absence of Zn­(II)) was confirmed by X-ray crystallographic analysis and was found to assemble into a supramolecular polymer. Conversion to a dimer form was seen upon the addition of TBAOAc. On the basis of the metric parameters, the structures seen in the solid state are stabilized via hydrogen bonding interactions involving solvent molecules

Synthesis and Characterization of a Binuclear Copper(II) Naphthoisoamethyrin Complex Displaying Weak Antiferromagnetic Coupling

The reaction between a naphthylbipyrrole-containing hexaphyrin-type expanded porphyrin and copper acetate affords a bench-stable dicopper­(II) complex. UV–vis spectroscopy, cyclic voltammetry, and X-ray crystallographic analysis measurements provide support for the conclusion that this complex displays aromatic features. A weak antiferromagnetic exchange interaction between the binuclear copper­(II) ions is evidenced by variable-temperature electron paramagnetic resonance and by fitting of the bulk magnetic susceptibility to a dimer model, yielding <i>J</i> = −5.1 cm^–1