Pyrazines transition metal complexes

Pyridine-based ligands which have been used for dendrimers are 2,2-bipyridine (bpy) 17,2,3-bis(2-pyridyl)pyrazine (2,3-dpp) 18 and its monomethylated salt 19, and 2,2 6, 2"-terpyridine 20. Their transition metal complexes possessing dendritic structures were first reported in the collaborative work of Denti, Campagne, and Balzani whose divergent synthetic strategy has led to systems containing 22 ruthenium centers. - The core unit is [Ru(2,3-dpp)3] 21 which contains three... 

Pyrazine derivatives were again popular as ligands in crystallographic studies of transition metal complexes. These complexes included silver(I) alkylpyrazine sulfonates 83 <07IC7299>, tetrakis[3-(pyrazin-2-yloxy)pyridinc-AiVJdithiocyanatomanganese <07AX(E)m441>,... 

The diazines also form metal complexes. Thus, pyrazine forms tetrahedral and octahedral complexes with Co11 and other transition metals it functions as a monodentate and also as a bidentate bridging ligand to give polymeric complexes. The stability of these complexes is increased by back-bonding. 

NH3)5]"+ (n = 4, 5, or 6) and [(bipy)2ClRu(pyz)RuCl(bipy)2]"4 (n = 2, 3, or 4).50 These studies reveal equivalent metal sites even in the mixed-valency Run-Ru,u species, despite the speed with which ESCA monitors electron distribution (10 17 s). Another investigation shows that the complex [Ru(NH3)5(pyz)]2+ can associate with several aqueous first-row transition-metal ions to form pyrazine-bridged dinuclear complexes.51 Equilibrium formation constants with Ni", Cu , and Zn11 were measured spectroscopically. 

Pyrazine and its alkyl derivatives are potentially useful bidentate ligands which form complexes with the following transition metals Cu, Co , Ni , Fe , Mo. and Some of this literature has been summarized by Cheeseman and Werstiuk (39). 

Carboxypyrazine catalyzes the chromic acid oxidation of primary and secondary alcohols (1305). The first-order, specific rates of reduction of Co(III) by Fe(ll) in complexes of the type [(NHj)(4ors)CoLFe(CN)sl with L as chelating 2-carboxylatopyrazine, pyrazine, and 2-methylpyrazine are 1.3 x 10", 5.5 x 10 , and 30 x 10 /sec, respectively, at 25°, pH 6-7, and fi = 0.15A/(1306). Complexes from 2-carboxypyrazine and lanthanide basic carbonates (1307) and from 2,3-dicarboxypyrazine and transition metals (1308) and its pentaamminechromium(III) complexes have been prepared (1309). 

Transition metal-catalyzed cross-coupling reactions of halogenopyrazines is an efficient synthetic method for alkyl-, alkenyl-, and alkynylpyrazines (Section 6.03.5.4.2). Palladium and nickel complexes are particularly effective as catalysts in this reaction. The Wittig reaction of halogenomethyl-pyrazines likewise leads to the formation of alkenylpyrazines (Section 6.03.8.1). Dehalogenation of halogeno pyrazines is a very practical synthetic method for alkyl- or aryl-substituted pyrazines. For example, phenylpyrazine has been prepared by catalytic hydrogenolysis of the 2-chloro-3-phenyl compound in the presence of triethylamine. This product is also obtained by decarboxylation of... 

Limiting rate constants for loss of pyrazine or of piperidine from their respective pentacyanoferrate(II) derivatives are affected to only a very small extent by the acetone content of binary aqueous mixtures.Probably here, as in the earlier case of the 4-cyanopyridine complex in aqueous alcohols, " this minor effect on rate constants conceals large but almost equal effects on the initial and transition states. This proved impossible to assess, due to the authors failure to find salts of appropriate solubility for the requisite measurements and transfer chemical potential derivations. It may be that the recently characterized transition metal(II) salts could lead to an answer. 

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