One-electron reduction of aromatic nitrogen heterocycles in aqueous solution. 2,2'-Bipyridine and 1,10-phenanthroline

Abstract

Publication costs assisted by the National Science FoundationThe reaction of 2,2'-bipyridine (bpy), 1,lO-phenanthroline (phen), and their monoprotonated cations (bpyH+ and phenH+) with radiation-generated one-electron reducing agents yields radicals, the spectra, kinetics, and acid-base properties of which have been established. BpyH2+. has a pK, of 5.6 and exhibits an intense absorption maximum at 375 nm ( e 4.5 X lo4 M-l cm-' 1; bpyH. shows A, , , 365 nm ( E 3.0 X lo4 M-' cm-'). BpyH. decays via second-order kinetics (2h = 4.0 X lo9 M-' sd) representing primarily a disproportionation reaction. BpyH2+. appears to decay via concurrent first-and second-order reactions; the processes are complicated by unidentified dose-dependent sequences. Irrespective of pH, the final isolatable product is a pale yellow solid which can be identified by elemental analysis, molecular weight determination, and IR spectrum as a trimer of dihydrobipyridine isomers. PhenHz+. shows A,, 370 nm (e 7.8 X lo3 M-' cm-l ) and 510 nm ( e 3.8 X lo3 M-l cm-' ) and pK, = 6.3 while phenH. exhibits A, , , 350 nm ( E 5.8 X lo3 M-' cm-' ) and 475 nm (t 3.0 X lo3 M-' cm-l ).PhenH. protonates to form phenHz+-with k = 8.3 X lo9 M-' s-' a nd phenHz+. decays via second-order kinetics (2k = 1.6 x lo9 M-l s-l ). In alkaline solution (pH 10-13) the decay of phenH. is first order ( k = 2 X IO3 9-l).The bimolecular reaction appears to proceed predominantly via combination; a product has been isolated with the empirical formula C12HllN2C104. The behavior of the one-electron reduction products is compared with that of species believed to be similar arising from the photoreduction of bpy and phen in aqueous solution.

On the mechanism of formation and spectral properties of radical anions generated by the reduction of –[ReI(CO)3(5-nitro-1,10-phenanthroline)]+ and –[ReI(CO)3(3,4,7,8-tetramethyl-1,10-phenanthroline)]+ pendants in poly-4-vinylpyridine polymers

“…(5) implies the protonation of tmphen ÅÀ in the polymeric Re I complexes. Similar protonation processes have been observed in a variety of organic reactions involving radical anions [47], in the one-electron reduction of bpy and phen [48] by pulse radiolysis, in the electro-polymerization of Ru II poly-pyridinic complexes [49] and in pulse radiolysis reduction of several polymeric Re I complexes [1,10,37,50]. The process represented by Eq.…”

Electron Transfer between Guanosine Radical and Amino Acids in Aqueous Solution. 1. Reduction of Guanosine Radical by Tyrosine

“…This observation supported by the absence of degenerate electron exchange at pH 13.3 can be accounted for by a reaction sequence that changes the structure of the radicals in the primary pair. The anion DP -• has pK a > 14, 49 thus the protonation reaction DP -• + H 2 O f DPH • + OH -occurs very fast with changing the spin density distribution in one of the partners in the primary radical pair. The changing of the electron spin density distribution and of the g-factor in radical G(-2H) -• as compared to G(-H) • occurs upon deprotonation and may lead to the changing of the CIDNP enhancement factors and of the rate of paramagnetic relaxation.…”

Reactions of 2,4,6-tripyridyl-1,3,5-s-triazine and its Fe(ii) complex with OH· and eaq-

“…The free ligand tptz, similar to the complex Fe(tptz) 2 2+ , reacts with OH • or e aq − to form an adduct similar to terpy [9], bipy [6][7][8] and phen. Hence, the reaction may lead to an adduct, tptz(OH) • or Htptz(OH) •+ or H 2 tptz(OH) •2+ , depending on the pK a of tptz (2.19 and 3.40) [2].…”

“…OH • is a powerful oxidizing agent, while e aq − is a good reducing agent. OH • is known to react with metal complexes containing organic ligands forming an adduct in case of benzatopentammine cobalt(II) [5] and bipy [6][7][8].…”