Kevin T. Potts

Electrocatalytic reduction of CO2 and O2 with electropolymerized films of vinyl-terpyridine complexes of Fe, Ni and Co

Abstract We have prepared and characterized, by cyclic voltammetry in acetonitrile and DMF (under N 2 or CO 2 ) for CO 2 reduction, and in aqueous media for O 2 reduction, iron, nickel and cobalt complexes of a terpyridine (tpy) and vinyl-terpyridine (v-tpy). These materials exhibit electrocatalytic activity towards the reduction of CO 2 and the magnitude of the catalytic effect is a function of the metal center. In the case of electropolymerizable metal complexes (those incorporating v-tpy) electrodeposited films exhibited higher electrocatalytic activity than the corresponding tpy complexes in solution. In the case of electropolymerized films of [Fe(v-tpy) 2 ] 2+ , electrocatalysis for CO 2 reduction was observed at potentials below −1.0 V which represents a very significant diminution (of about 1 V) in the overpotential. In the case of oxygen, the electrocatalytic activity of the electropolymerized films as well as the predominant product (peroxide or water) was dependent on the surface coverage.

Conjugated and cross-conjugated mesomeric betaines. correlation of electroreduction with structure and physiological activity

Electroreduction studies were performed on several cross-conjugated mesomeric betaines containing the fused pyrazolium (2) and fused imidazolium (3) ring systems. Studies at acidic pH were of principal interest. Substituent effects for 2 were in line with prior findings, and reduction potentials were comparatively negative (-0.96 to -1.34 V). Reduction potentials fit the modified Hammett equation. Compound 3 was more readily reduced (-0.88 V). The related psi-oxatriazoles (6) gave values in the range of -0.85 to -1.22 V. The electrochemical characteristics are compared with those of the mesoionic sydnones (4) and sydnoneimines (5). These mesoionic compounds were generally reduced at more positive potentials than 2 and 3. A relationship between electroreduction and physiological activity is proposed. The overall results are in keeping with the hypothesis of widespread participation of iminium-type species in biological systems.

Regiochemical control in Diels-Alder routes to aza-anthraquinone derivatives

Quinoline- and isoquinoline-5,8-diones react with 1-methoxycyclohexa-1,3-diene at 80 °C, the former giving 8-methoxy-1-aza-anthraquinone regiospecifically and the latter 5-methoxy-2-aza-anthraquinone regioselectively; in similar cycloadditions, substituted naphtho- and azanaphtho-quinones react with 1-dimethylamino-3-methyl-1-azabuta-1,3-diene at room temperature forming substituted mono- and di-aza-anthraquinones in high yields with high selectivity.

Photoinduced ring opening and fragmentation of isomeric mesoionic anhydro-4(5)-hydroxythiazolium hydroxides and of anhydro-5-hydroxy-3-methyl-2-phe

Abstract Isoelectronic mesoionic thiazoles and oxazoles undergo photochemical ring opening to heterocumulenes as evidenced by trapping experiments with alcohols. A competing photolytic fragmentation to COS and CO 2 , respectively, also occurs. Irradiation of the anhydro -5-hydroxythiazolium hydroxide system in the presence of O 2 results in the formation of singlet oxygen which undergoes a 1,4-cycloaddition to the thiazolium system. Decomposition of this cycloadduct gives rise to COS.

1,2,4-Triazoles—XXXI: Photodimerization of s-triazoleo[4,3-a]pyridines: formation of cyclobutane dimers1

Abstract Irradiation of several methyl substituted s -triazolo[4,3-a]-pyridines and 3-hydroxy- s -triazolo[4,3-a]pyridines with UV light gave thermally labile cyclobutane photodimers by dimerization of the 5,6-double bond in one molecule with the 7,8-double bond in another.

Multimetallic, double-stranded helical complexes derived from hexa(n-propylthio)novipyridine: synthesis, structure and redox properties ☆

4′,4′′,4′′′,4′′′′′,4′′′′′′,4′′′′′′′-Hexa(n-propylthio)-2,2′;6′,2′′:6′′,2′′′:6′′′,2′′′′:6′′′′,2′′′′′:6′′′′′,2′′′′′′:6′′′′′′,2′′′′′′′:6′′′′′′′,2′′′′′′′′-novipyridine (L), a new nonadentate ligand, reacts with cuprous tetrakis(acetonitrile) hexafluoro-phosphate in oxygen-free methanol at room temperature to yield the black, crystalline cuprous complex [L2CuI5][PF6]5. In the presence of air the corresponding mixed-valence complex [L2CuIICuI3][PF6]5 is obtained. Reaction with CuII and CoII ions resulted in the formation of the corresponding trimetallic complexes [L2MII3][PF6]6. Molecular compositions were established from partial elemental analysis, FAB mass spectral data, and from electrochemical and electronic spectral data. [L2CuI5]5+ contains the most cuprous ions assembled in a oligopyridine complex to date and these complexes, analogous to others in this series, were assigned double-stranded helical structures. An intramolecular diastereotopic effect in the 1H NMR spectrum of the diamagnetic pentacuprous complex showed its chiral nature and its stability in solution. Electrochemical studies of these complexes showed appreciable metal–metal interactions, and redox-induced transformations among the copper helicates were established spectroelectrochemically.

Substituted biurets as uranophilic ligands: a facile DMSO-induced conversion of a 1:1 into a 2:1 uranyl-ligand complex

Abstract 1,5-Bis[6-(1-ethoxycarbonyl-3-thioureido)-2-pyridindiyl]biuret and uranyl acetate gave a crystalline 1:1 uranyl-ligand complex which, on crystallization from DMSO, underwent rearrangement to a crystalline 2:1 uranyl-ligand complex and a stoichiometric amount of the uncomplexed ligand. Spectral characteristics of these ligands and their uranyl complexes together with single crystal X-ray data for the uranyl-ligand complexes are described.

Annulation to the phthalazine ring system utilizing mesoionic ring systems

Cycloadditions de thiazolo [2,3-a] phtalazinioolates-3 avec des dipolarophiles acetyleniques et ethyleniques: obtention de pyrido- et pyrrolo [2,1-a] phtalazines

Intramolecular 1,3-dipolar cycloadditions with thiocarbonyl ylides

anhydro-2-(2-Allyloxyphenyl)-3,5-diphenyl-4-hydroxythiazolium hydroxide and related alkenic systems, together with the corresponding prop-2-ynyloxy and cyanomethyloxy derivatives, undergo ready thermal intramolecular 1,3-dipolar cycloadditions giving stable 1 : 1-cycloadducts, substituted 4H-thieno[3,2-c]-, and 4H-thiazolo[4,5-c]-chromenes, respectively; the structure of one of these has been determined by X-ray crystallography.

Carbon–carbon bond formation by intramolecular 1,4-dipolar cycloaddition: heterocyclic betaines generated in situ from amides and N-substituted amides

Reaction of benzamides and N-substituted benzamides with appropriate o-alkenyl and -alkynyl side-chains and (chlorocarbonyl)phenyl ketene gives transient anhydro-1,3-oxazinium hydroxides which readily undergo intramolecular 1,4-dipolar cycloaddition; loss of CO2 from these 1:1-cycloadducts, isolable with N-substituted systems and alkenyl side-chains, gives chromeno[4,3-b]pyridin-2-ones.