Spin Switching with Triazolate-Strapped Ferrous Porphyrins.

Fe(III) porphyrins bridged with 1,2,3-triazole ligands were synthesized. Upon deprotonation, the triazolate ion coordinates to the Fe(III) ion, forming an overall neutral high-spin Fe(III) porphyrin in which the triazolate serves both as an axial ligand and as the counterion. The second axial coordination site is activated for coordination and binds p-methoxypyridine, forming a six-coordinate low-spin complex. Upon addition of a phenylazopyridine as a photodissociable ligand, the spin state of the complex can be reversibly switched with ultraviolet and visible light. The system provides the basis for the development of switchable catalase- and peroxidase-type catalysts and molecular spin switches.

Insertion of Ni(I) into Porphyrins at Room Temperature: Preparation of Ni(II)porphyrins, and Ni(II)chlorins and Observation of Hydroporphyrin Intermediates.

Reduced Nickel porphyrins play an important role as enzymatic cofactors in the global carbon cycle (cofactor F430), and as powerful catalysts in solar-to-fuel-processes such as the hydrogen evolution reaction, and the reduction of CO and CO2. The preparation of Ni(II)porphyrins requires harsh conditions, and characterization of the reduced species is intricate. We present a very mild, convenient, and high yielding method of inserting Ni into electron rich, and electron deficient porphyrins which at the same time gives access to to Ni(II) phlorins and Ni(II)chlorins and Ni(II)porphyrins.

Preparation and isolation of isobenzofuran.

The synthesis, isolation and characterization of isobenzofuran are described in this publication. Isobenzofuran is of general interest in synthetic and physical organic chemistry because it is one of the most reactive dienes known. A number of synthetic pathways have been published which all suffer from disadvantages such as low yields and difficult purification. We present a synthetic pathway to prepare isobenzofuran in laboratory scale with high yields, from affordable, commercially available starting materials.

Photoswitchable Magnetic Resonance Imaging Contrast by Improved Light-Driven Coordination-Induced Spin State Switch.

We present a fully reversible and highly efficient on-off photoswitching of magnetic resonance imaging (MRI) contrast with green (500 nm) and violet-blue (435 nm) light. The contrast change is based on intramolecular light-driven coordination-induced spin state switch (LD-CISSS), performed with azopyridine-substituted Ni-porphyrins. The relaxation time of the solvent protons in 3 mM solutions of the azoporphyrins in DMSO was switched between 3.5 and 1.7 s. The relaxivity of the contrast agent changes by a factor of 6.7. No fatigue or side reaction was observed, even after >100,000 switching cycles in air at room temperature. Electron-donating substituents at the pyridine improve the LD-CISSS in two ways: better photostationary states are achieved, and intramolecular binding is enhanced.

Crystal structure of bis-(4-meth-oxy-pyridine-κN)(meso-5,10,15,20-tetra-phenyl-porphyrinato-κ4 N,N',N'',N''')iron(III) perchlorate.

In the crystal structure of the title compound, [Fe(C44H28N4)(C6H7NO)2]ClO4, the FeIII ions are coordinated in an octa-hedral fashion by four N atoms of the porphyrin moiety and two N atoms of two 4-meth-oxy-pyridine ligands into discrete complexes that are located on inversion centers. Charge-balance is achieved by perchlorate anions that are disordered around twofold rotation axes. In the crystal structure, the discrete cationic complexes and the perchlorate anions are arranged into layers with weak C-H⋯O inter-actions between the cations and the anions. The porphyrin moieties of neighboring layers show a herringbone-like arrangement.

Crystal structure of 210,220-bis-(2,6-di-chloro-phen-yl)-4,7,12,15-tetra-oxa-2(5,15)-nickel(II)porpyhrina-1,3(1,2)-dibenzena-cyclo-hepta-deca-phane-9-yne di-chloro-methane monosolvate.

The asymmetric unit of the title compound, [Ni(C52H34Cl4N4O4)]·CH2Cl2, consists of two discrete complexes, which show significant differences in the conformation of the side chain. Each NiII cation is coordinated by four nitro-gen atoms of a porphyrin mol-ecule within a square-planar coordination environment. Weak intra-molecular C-H⋯Cl and C-H⋯O inter-actions stabilize the mol-ecular conformation. In the crystal structure, discrete complexes are linked by C-H⋯Cl hydrogen-bonding inter-actions. In addition, the two unique di-chloro-methane solvate mol-ecules (one being disordered) are hydrogen-bonded to the Cl atoms of the chloro-phenyl groups of the porphyrin mol-ecules, thus stabilizing the three-dimensional arrangement. The crystal exhibits pseudo-ortho-rhom-bic metrics, but structure refinements clearly show that the crystal system is monoclinic and that the crystal is twinned by pseudo-merohedry.

Crystal structure of a polymorph of µ-oxido-bis-[(5,10,15,20-tetra-phenyl-porphyrinato)iron(III)].

The title compound, [Fe2(C44H28N4O)2O], was obtained as a by-product during the synthesis of FeIII tetra-phenyl-porphyrin perchlorate. It crystallizes as a new polymorphic modification in addition to the ortho-rhom-bic form previously reported [Hoffman et al. (1972 ▸). J. Am. Chem. Soc. 94, 3620-3626; Swepston & Ibers (1985 ▸) Acta Cryst. C41, 671-673; Kooijmann et al. (2007 ▸). Private Communication (refcode 667666). CCDC, Cambridge, England]. In its crystal structure, the two crystallographically independent FeIII cations are coordinated in a square-planar environment by the four N atoms of a tetra-phenyl-porphyrin ligand. The FeIII-tetra-phenyl-porphyrine units are linked by a µ2-oxido ligand into a dimer with an Fe-O-Fe angle close to linearity. The final coordination sphere for each FeIII atom is square-pyramidal with the µ2-oxido ligand in the apical position. The crystal under investigation consisted of two domains in a ratio of 0.691 (3): 0.309 (3).

Crystal structure of 2-[2-(pyridin-3-yl)diazen-1-yl]aniline.

The crystal structure of the title compound, C11H10N4, comprises mol-ecules in a trans conformation for which all the atoms are located in general positions. The six-membered rings are coplanar and this arrangement might be stabilized by intra-molecular N-H⋯N hydrogen bonding. In the crystal, the mol-ecules are linked into helical chains parallel to the b axis via N-H⋯N hydrogen bonding. The mol-ecular packing shows a herringbone-like pattern along the a axis. Comparison of the X-ray powder diffraction with that calculated from single crystal data proves that a pure crystalline phase was obtained and UV-Vis measurements reveal that only the trans isomer is present.

One-Pot Approach to Chlorins, Isobacteriochlorins, Bacteriochlorins, and Pyrrocorphins.

A Diels-Alder strategy is reported to synthesize the complete set of hydroporphyrins: chlorins, bacteriochlorins, isobacteriochlorins, and pyrrocorphins. Porphyrins and Ni-porphyrins react with isobenzofuran in very high yields at 70 °C to form the corresponding chlorins. Electron-deficient porphyrins react with a second equivalent of isobenzofuran yielding exclusively bacteriochlorin (82%), and Ni-porphyrin gives only isobacteriochlorin (99%). All cycloadditions are completely regio- and stereoselective. The regiochemistry is correctly predicted using the ACID method.

Light-controlled switching of the spin state of iron(III).

Controlled switching of the spin state of transition metal ions, particularly of FeII and FeIII, is a prerequisite to achieve selectivity, efficiency, and catalysis in a number of metalloenzymes. Here we report on an iron(III) porphyrin with a photochromic axial ligand which, upon irradiation with two different wavelengths reversibly switches its spin state between low-spin (S = 1/2) and high-spin (S = 5/2) in solution (DMSO-acetone, 2:598). The switching efficiency is 76% at room temperature. The system is neither oxygen nor water sensitive, and no fatigue was observed after more than 1000 switching cycles. Concomitant with the spin-flip is a change in redox potential by ~60 mV. Besides serving as a simple model for the first step of the cytochrome P450 catalytic cycle, the spin switch can be used to switch the spin-lattice relaxation time T1 of the water protons by a factor of 15.