Cobalt complexes pyrazine

Garner and Joule next adapted the protected dithiolene strategy to target heterocyclic dithiolene complexes. This approach, first reported in 1988 by Larsen et al is illustrated in Scheme 2.25 with the formation of a cobalt quinoxalyldithiolene complex. Reaction of [CoCp(COD)] (COD = 1,5-cyclooc-tadiene) with 4-(quinoxalin-2-yl)-l,3-dithiole-2-thione (26) affords a quinox-aline dithiolene complex (27) that has been structurally characterized. This cobalt complex undergoes extensive proton-coupled electron transfer process (see Section 2.3.4). This system was further elaborated when the pyrazine ring in 4-(quinoxalin-2-yl)-l,3-dithiole-2-thione 26 was selectively... 

Kinetic parameters k, often also and AS, occasionally AV ) for formation and dissociation of several pentacyanoferrate(II) complexes [Fe(CN)5L]" have been established. Ligands L include several S- and A-donor heterocycles,4-methyl- and 4-amino-pyridines, a series of alkylamines, 3- and 4-hydroxy- and 3- and 4-methoxy-pyridines, several amino acids, nicotinamide, " 4-pyridine aldoxime, 3-Me and 3-Ph sydnones, several bis-pyridine ligands,neutral, protonated, and methylated 4,4 -bipyridyl, 1,2-bis(4-pyridyl)ethane and traTO-l,2-bis0-pyridyl)ethene, pyrazine- 4,4 -bipyridyl- and bis(4-pyridyl)ethyne-pentaammine-cobalt(III), edta-ruthenium(III), and pentaammineruthenium-(II)and-(III) complexes of... 

Cobalt-mediated C-H activation of pyrazone 287 with bis(trimethylsilyl) acetylene in the presence of cyclopentadienylcobaltbis(ethene) [CpCo (C2H4)2] afforded pyrido[l,2-a]pyrazin-4-one complex 288, and its decom-plexation with Fe3"" furnished 6,7,8,9-tetrahydro-4H-pyrido[l,2-a]pyrazin-4-one 289 (07CEJ7443). 

The X-ray crystal structures of pyrazine V.JV -dioxide (134) <02AX(E)1253>, the P-polymorph of phenazine (135) <02AX(C)181>, cobalt(III) complexes of pyrazine-2,6- and pyridine-2,6-dicarboxylic acids <02JIC458>, and bis-urea-substituted phenazines <02ZN(B)937> were reported. Fluorescent pyrido[l,2-a]quinoxalines 136 prepared as pH indicators were examined by X-ray crystallography <02JCS(P2)181>, as were macrocyclic quinoxaline-bridged porphyrinoids obtained from the condensation of dipyrrolylquinoxalines 137 and 1,8-diaminoanthracene... 

Infrared absorption spectra of pyrazine A -oxides and alkylpyrazine A -oxides have been recorded and discussed (575, 625, 626). The ligand 2,3-bis(pyridin-2 -yl)pyrazine 1,4-dioxide and its complexes with cobalt(II), nickel(II), and copper(II) have been prepared and are polymeric octahedral in structure (754). 

So, NMR spectra of 4,4 -bipyridyl, pyrazine, and ethylenediamine coordinated to undecatungstocobalto(III)silicate and -borate anions. Identification of 1 1 and dumbbell-shaped 12 complexes, Bull. Korean Chem. Soc, 14 759 (1993) (c) J.L. Samonte and M.T. Pope, Derivatization of polyoxotungstates in aqueous solution. Exploration of the kinetic stability ofcobalt(II)- and cobalt(III) derivatives of lacunary anions with pyridine and pyridine-type ligands. Can. J. Chem.. In press... 

The influenee of peripheral substituents at the phthalocyaninato moiety on the properties of the corresponding compounds was studied with a number of octa-substituted derivatives R PcM, R PcMLj and [R PcM(pyz)] (e.g. R = CH3, m = 8, M = Fe, L=py) [83]. Substituted mononuclear and bridged phthalocyaninatoiron pyrazine complexes R PcFe(pyz)2 and [R PcFe(pyz)] are accessible according to the procedure for the corresponding unsubstituted complexes [65]. With cobalt as central metal the tetra-substituted macrocycles R PcCo (m = 4 R = f-bu, NO 2) can be prepared. They coordinate with pyridine and substituted pyridines to form the adducts R PcCoL2 [84]. With pyrazine the binuclear complex (t-bu)4PcCo(pyz)CoPc(t-bu)4 and the oligonuclear [(N02)PcCo(pyz)]n can be isolated and characterized [84]. 

The product of reaction of pyrazinecarboxamide with Cr + is a dark green complex of chromiumCiii) and the pyrazinecarboxamide radical ion, first characterized in 1965 (see ref. 118 and references cited therein). Evidence has now been presented to show that in reactions with various cobalt(ni) complexes, the effective reducing agent is, not the radical-ion complex but free Cr + present in equilibrium with it (Pz = substituted pyrazine) ... 

The reaction between cobaIt(u) and pyridine-2-aldoxime takes place in several steps. The initial rapid complex formation is followed by a rate-determining redox reaction where oxidation of the cobalt(n) by the ligand provides a route to an inert cobalt(ra) species. The mode of reaction of some chromium(iii)-bound pyrazine radicals with cobalt(iii) complexes has been clarified. In the reaction shown in equation (3) the green complexed radicals formed have been... 

Jung, O.-S., and Pierpont, C. G., Photochemical polymers. Synthesis and characterization of a polymeric pyrazine-bridged cobalt semiquinonate-catecholate complex, J. Am. Chem. Soc., 116, 2229-2230 (1994). 

A study of photosubstitution in six (substituted) pyridine and pyrazine pen-tacyanocobaltate(III) complexes [Co(CN)5L]" complements an earlier study of similar pentacyanoferrate(II) complexes. Irradiation in ligand field bands results in 100% replacement of L by water quantum yields range from 0.12 to 0.40. The results are similar to those for the iron(II) complexes, with such differences as are observed assignable to the large difference in importance of tt back bonding to cobalt(III) and to iron(II). ... 

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