Preparation of six isomeric bis-acylporphyrins with chromophores reaching the near-infrared via intramolecular Friedel-Crafts reaction

We describe the preparation of six diketones based on the frameworks of five bis-naphthoporphyrins and one perinaphthoporphyrin. All diketones derive from meso-tetraarylporphyrins having incorporated two carbonyl groups, each one connected to one beta-pyrrole carbon and one ortho carbon atom from a meso-aryl group. These compounds were all produced in good yield by intramolecular Friedel-Crafts acylation, either from porphyrins meso-substituted by o-carboxyphenyl or o,o'-dicarboxyphenyl substituents or from porphyrins bearing carboxy groups attached to the pyrrolic beta-positions. Although the former reaction does not show significant regioselectivity when run on nickel complexes, the opposite is true for the corresponding free bases. All diketones show a spectacular bathochromic shift of the UV-vis absorption, the longest wavelength bands absorbing in the 700-825 nm range. Two compounds were structurally characterized by X-ray diffraction. In the case of the diketone, whose carbonyl groups are attached to vicinal pyrrolic beta-positions, a significant intermolecular interaction between the two carbonyl groups and an aromatic hydrogen atom was detected.     

Synthesis of C5-substituted imidazolines

5-(Hydroxymethyl)-3-(t-butyloxycarbonyl)imidazoline 2 was prepared in four steps from 2,3-diaminopropionic acid in 72% overall yield. Mitsunobu reaction with a series of phenol derivatives gave the corresponding 5-(aryloxymethyl)-3-(t-butyloxycarbonyl)imidazolines 8a-l. Phthalimide and N-benzyl trifluoroacetamide also reacted.     

Synthesis of syn-facial (Cr,Mn) benzyl complexes by the stereoselective thermolytic coupling of unsymmetric diazomethanes with cyclomanganated (η-arene)tricarbonylchromium complexes

The heat-promoted reaction of 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene with cyclomanganated 2-[tricarbonyl(η⁶-phenyl)chromium]pyridine afforded, upon departure of a molecule of CO, a new stable manganese alkylidene complex in which, according to X-ray diffraction analyses, the heterocyclic ligand is anti-facial with respect to the Cr(CO)₃ moiety. Similar heat-promoted reactions of unsymmetrically substituted diazoalkanes such as (Me₃Si)(H)CN₂, (Ph)(Me)CN₂, (Ph)(t-Bu)CN₂ and (Ph)(FcCH₂CH₂)CN₂, which are precursors of more electrophilic alkylidenes, with cyclomanganated 2-[tricarbonyl(η⁶-phenyl)chromium]pyridine derivatives afforded new syn-facial heterobimetallic benzyl complexes. The stereoselectivity of these reactions depends on the steric demand of the substituents at the diazoalkane. A phenyl substituent at the diazoalkane favors the formation of syn-facial heterobimetallic benzyl complexes with the Ph group in the endo position. Combining this “phenyl directing effect” to the steric effect operated by a bulky group at the phenyldiazoalkane, like noticed with (Ph)(t-Bu)CN₂, led to total stereoselectivity. This study discloses four new X-ray structures of syn-facial Cr,Mn benzyl complexes, which all present the same short Cr-to-Mn distance of ca. 3.04 Å.     

Cation-directed synthesis of tungstosilicates. 2. Synthesis, structure, and characterization of the open Wells-Dawson anion alpha-[{K(H2O)2}(Si2W18O66)]15- and its transiton-metal derivatives [{M(H2O)}(mu-H2O)2K(Si2W18O66)]13- and [{M(H2O)}(mu-H2O)2K{M(H2O)4}(Si2W18O66)]11-

The dimer alpha-[{K(H2O)2}(Si2W18O66)]15- (1), synthesized by reacting K10A-alpha-[SiW9O34] with two equivalents of H+ in aqueous solution, has been characterized by polarography and 183W NMR spectroscopy. Nine resonance signals have been observed with the tetrabutylammonium salt in dimethylformamide/acetonitrile solution, in agreement with the crystal structure of the anion which consists of two A-alpha-[SiW9O34]10- associated through two W-O-W junctions. This anion derives from the Wells-Dawson structure by breaking four W-O-W junctions. The pocket between the two-half-anions can be filled by several metal cations. Reaction of transition-metal cations with 1 leads to the formation of [{M(H2O)}(mu-H2O)2K(Si2W18O66)]13- (1M) (M = Co, Ni, Cu) and [{M(H2O)}(mu-H2O)2K{M(H2O)4}(Si2W18O66)]11- (1M2) (M = Mn, Co, Ni) complexes. One potassium is always included in the pocket with one or two transition metals. Because of the shift of the potassium cation to one side of the anion, the coordination modes of the two transition metals are different. Crystals of 1, 1M, and 1Co2 potassium salts are triclinic (P-1, Z = 2) and crystals of 1M2 potassium salts are monoclinic (P2(1)/n, Z = 4). The symmetry of 1Mand 1M2 complexes is C1 and they are present in the crystal as racemate inversion pairs.     

A likely biogenetic gateway linking 2-aminoimidazolinone metabolites of sponges to proline: spontaneous oxidative conversion of the pyrrole-proline-guanidine pseudo-peptide to dispacamide A

A new spontaneous oxidative transformation of the associated pyrrole-proline-guanidine to the natural marine pyrrole 2-aminoimidazolinone derivative has been achieved. The sensitive reaction requires air oxygen and the N-acylation of proline by pyrrole-2-carboxylic acid. Proline metabolism and pyrrole 2-aminoimidazole secondary metabolites formation seem to be related and are utilized by sponges under stress conditions for their defense against predators. A plausible stress-induced oxidative chemical pathway that establishes dispacamide derivatives as the forerunners in the biogenetic synthesis of the key pyrrole 2-aminoimidazole oroidin is proposed. The mechanism of the reaction seems to be another development of the known luciferins' chemiluminescent reactions in bioluminescent marine organisms.     

Titanium-Oxo Clusters, Versatile Nanobuilding Blocks for the Design of Advanced Hybrid Materials

Summary. This review describes the major advances made on titanium-oxo clusters chemistry and their derived hybrid materials. The main synthesis procedures, the cluster structures presented in literature, and the relation between the titanium-oxo clusters condensation degree and poisoning ratio are discussed. The tuned organo-functionalisation of the titanium-oxo based nanobuilding blocks allows to develop a LEGO-like chemistry, able to direct the assembling of a large variety of structurally well defined complex hybrid architectures.     

Synthetic catalytic pores

Catalytic activity of a synthetic multifunctional pore is studied in large unilamellar vesicles under conditions where substrate and synthetic catalytic pore (SCP) approach the membrane either from the same side (cis catalysis) or from opposite sides (trans catalysis). A synthetic supramolecular rigid-rod beta-barrel with excellent ion channel characteristics is identified as SCP using 8-acetoxypyrene-1,3,6-trisulfonate (AcPTS) as model substrate. The key finding is that application of supportive membrane potentials increases the initial velocity of AcPTS esterolysis (v0). This results in an increase of Vmax beyond experimental error (+30%), whereas KM increases less significantly. Long-range electrostatic steering by the membrane potential, possibly guiding substrates into the transmembrane catalyst and, more importantly, accelerating product release (foff = 1.3) is discussed as one possible explanation of this global reduction of catalyst saturation. Control experiments show, inter alia, that similarly strong changes do not occur with opposing membrane potentials.     

Plasma Polymerization in a Nitrogen/Ethanol Dielectric Barrier Discharge: A Parameter Study

Plasma Chemistry and Plasma Processing - Plasma polymerization experiments are typically conducted by sustaining a non-thermal plasma in a gas flow containing monomer molecules. Recently, it was...