R. Nasielski-Hinkens

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.

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.

Photoelectrochemistry of a new ruthenium complex, the Ru(II)-tris-(1,4,5,8-tetraazaphenanthrene) dication

Abstract It is shown that the excited states of Ru(TAP) 2+ 3 (TAP ≡ 1,4,5,8-tetraazaphenanthrene) and Ru(TAPMe 2 ) 2+ 3 (TAPMe 2 ≡ 2,7-dimethyl-1,4,5,8-tetraazaphenanthrene) are too weak reductants to be oxidized at SnO 2 electrodes. On the other hand, in the presence of a reducing agent such as hydroquinone, the photo-generated reduced complexes are able to inject electrons into the SnO 2 conduction band. The good agreement between the Stern-Volmer constants obtained by luminescence quenching and by photoelectrochemistry confirms this electron transfer process.

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.

Photochemistry of aromatic compounds—VII: The influence of aliphatic amines on the photochemistry of 5-bromopyrimidines in mathanol

Abstract The UV irradiation of 2-methoxy-, 2-phenyl- and 2-dimethylamino-5-bromopyrimidine in methanol yields the corresponding dehalogenated, methylated and hydroxymethylated compounds. Added diethylamine or triethylamine strongly increases the rate of dehalogenation. It is suggested that amines influence the photochemistry of these compounds by transfering an electron to the excited state of the bromopyrimidines.

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.

13C NMR spectra of chromium tetracarbonyl complexes of 1,4,5,8-tetraazaphenanthrene and 1,4,5,8,9,12-hexaazatriphenylene

Abstract The 13C NMR spectra of the chromium tetracarbonyl complexes (TAP)Cr(CO)4 and (HAT)Cr(CO)4 in both the carbonyl and the ligand region are assigned on the basis of substituent effects and 1H single frequency 13C spectra.