J. Nasielski

A new heterocyclic ligand for transition metals: 1,4,5,8,9,12-hexaazatriphenylene and its chromium carbonyl complexes

Abstract The synthesis of 1,4,5,8,9,12-hexaazatriphenylene (HAT), a new ligand for low-valent transition metals, is described; it gives mono-, bis- and tris-chromium tetracarbonyl complexes. The CO stretching frequencies in (HAT)Cr(CO)4 show that HAT is a stronger electron acceptor than 1,10-phenanthroline.

Ruthenium polypyridyl complexes; their interaction with DNA and their role as sensitisers for its photocleavage

The excited state of the 1,4,5,8-tetra-azaphenanthrene complex, [Ru(TAP)3]2+, which unlike [Ru(phen)3]2+(phen = 1,10-phenanthroline) or [Ru(bipy)3]2+(bipy = 2,2′-bipyridyl) is strongly quenched upon binding to poly[d(G–C)], is found to be much more effective than either [Ru(phen)3]2+ or [Ru(bipy)3]2+ in causing cleavage of the DNA backbone.

Efficient coupling of 2-halopyrimidines to 2,2'-bipyrimidines

Abstract 2-chloropyrimidine, 2-chloro- and 2-bromo-4,6-dimethylpyrimidines, 2-chloro- and 2-bromo-4,6-diphenylpyrimidines have been dimerized to the corresponding 2,2′-bipyrimidines in good yields by Tieccos method using NiCl2, triphenylphosphine and zinc in DMF.

The photo-electrochemistry of the Rhodamine B-hydroquinone system at optically transparent bubbling gas electrodes

Abstract Use of the technique called ‘bubbling gas electrode’ yields very reproducible polarograms on solid electrodes. It is applied here to study the photoelectrochemistry of the Rhodamine B-hydroquinone system on optically transparent n -type SnO 2 and gold electrodes, in order to understand the operation of a photovoltaic cell based on due-supersensitizer couples. Rhodamine alone gives no photo-currents on gold, and weak ones on SnO 2 ; added hydroquinone gives rise to very intense photo-currents on both electrodes. Increasing supersensitizer concentrations lead to a plateau, allowing an estimate of the lifetime of an electro-active transient. Two mechanisms for supersensitization are envisioned: hydroquinone can donate an electron to the photo-electrogenerated oxidized rhodamine, reducing thus the cathodic tunnel-current; or the diphenol might transfer an electron to the photo-excited dye, producing thus a new oxidizable species. Taken alone, the second mechanism is unable to explain all findings. Action spectra, recorded for a large number of experimental conditions suggest a major contribution from adsorbed dye molecules; in the presence of hydroquinone, some contributions from the solution may be operative.

An unexpected course of the Meisenheimer reaction: aryl phosphates in the reaction of phosphoryl chloride with 2,3-diphenylquinoxaline-N1-oxide

Abstract Contrary to what is observed with other π-deficient heteroaromatic N-oxides, the reaction of 2, 3-diphenylquinoxaline-N1-oxide with OPCl3 gives only very poor yields of chlorinated quinoxalines. It is shown that the major product arises from an unprecedented attack by the nucleophilic oxygen atom of the reagent at a carbon atom of the homocycle of the O-phosphorylated N-oxide, leading ultimately to the corresponding mono- (or di-) aryl ester of phosphoric acid. Using a much smaller excess of OPCl3 and dilution of the medium with an inert solvent strongly increase the yield of chlorination products.

2,3-diphenyl- and 2,3,6,7-tetraphenyl-hexa-azatriphenylene, ligands for transition metals

Abstract 2,3-Diphenyl-1,4,5,8,9,12-hexa-azatriphenylene 2 and 2,3,6,7-tetraphenyl-1,4,5, 8,9,12-hexa-azatriphenylene 3 can be synthesized by the direct condensation of hexa-aminobenzene with glyoxal and benzil. It is, however, not possible to make specifically one of the compounds, which is always accompanied by the parent compound 1 and the fully substituted hexaphenyl-hexaazatriphenylene 4 . It is nevertheless possible to optimize the yields of 2 and 3 by a careful choice of the experimental conditions.

Group vib carbonyl complexes of pyrazino[2.3-f]quinoxaline or 1,4,5,8-tetraazaphenanthrene (tap)

Abstract 1,4,5,8-Tetraazaphenanthrenemetal tetracarbonyl complexes (metal = Cr, Mo, W) have been synthesized. The CO force constants show that there is more backbonding in these complexes than in the analogous 1,10-phenanthroline complexes, because of the two additional electron-withdrawing nitrogen atoms. The M→ L CT transitions show a strong bathochromic shift relative to the corresponding o -phenanthroline complexes.

Photochemistry of aromatic compounds—VII

Abstract Triethylamine accelerates the photodebromination of 5-bromopyrimidines, and much more so in methanol than in acetonitrile. The quantum yield in methanol is as high as 4, and additional data suggest that the amine-catalysed debromination is a photo-initiated free-radical chain reaction, the carrier being the .CH2OH radical; triethylamine acts as an electron donor in the initiation step and as a base catalyst in the chain reaction.

5-Amino-6-nitroquinoxalines from 6-Nitroquinoxalines by the Amination Reaction with Hydroxylamine

Abstract The yields of the direct amination of 6-nitroquinoxalines by hydroxylamine have been improved, opening thus a better access to 1,4,5,8-tetra-azaphenanthrenes.

The influence of cysteine solutions on the stability of CdS photoanodes

Abstract The influence of cysteine in aqueous alkaline solution as a reducing electrolyte is tested on the photoanodic behavior of polycrystalline CdS films. It is found that, compared to NaOH alone, cysteine increases the photo-oxidation currents, and shifts the zero photocurrent potential cathodically. At pH 11.5 at the beginning of the illumination, the photocurrents slowly increase by factors up to 4, thanks to some modification of the CdS surface, with some photocorrosion. At pH 9.2, the photocorrosion and the electrode modification are less important. However, even at this pH, cysteine does not seem to stabilize the electrode better than the sulfide. The advantage of the cysteine-cystine electrolyte is, unlike polysulfides, to be transparent in the CdS band gap region. Cystine alone has properties similar to those of cysteine at the very beginning of the illumination, but afterwards the photocurrent drops very quickly, until the CdS film is completely dissolved.