Photochemical two-electron reduction of a dinuclear ruthenium complex containing a bent tetraazatetrapyridopentacene bridging ligand: pushing up the LUMO for storing more energy.

The synthesis and characterization of a ditopic bridging ligand, 9,12,21,22-tetraazatetrapyrido[3,2-a:2',3'-c:3″2″-m:2''',3'''-o]pentaphene (tatppα) and its dinuclear ruthenium complex, [(phen)(2)Ru(tatppα)Ru(phen)(2)][PF(6)](4) (1(4+)), are described. The tatppα ligand is structurally very similar to 9,10,20,33-tetraazatetrapyrido[3,2-a:2',3'-c:3″,2″-l:2''',3'''-n]pentacene (tatppβ), except that, instead of a linear tetraazapentacene backbone, tatppα has an ortho (or α) substitution pattern about the central benzene ring, leading to a 120° bend. Complex 1(4+) shows tatppα-based reductions at -0.

Electroreduction of the ruthenium complex [(bpy)2Ru(tatpp)]Cl2 in water: insights on the mechanism of multielectron reduction and protonation of the Tatpp acceptor ligand as a function of pH.

The mononuclear ruthenium complex [(bpy) 2Ru(tatpp)] (2+) ( 1 (2+); bpy is 2,2'-bipyridine and tatpp is 9,11,20,22-tetra-aza-tetrapyrido[3,2-a:2'3'-c:3'',2''-l:2''',3''']-pentacene) undergoes up to four reversible tatpp ligand-based reductions as determined by electrochemistry in aqueous solution. Specific redox and protonation states of this complex were generated by stoichiometric chemical reduction with cobaltocene and protonation with trifluoroacetic acid in acetonitrile. These species exhibit unique UV-visible absorption spectra, which are used to determine the speciation in aqueous media as a function of the potential during the electrochemical reduction.

The role of monomers and dimers in the reduction of ruthenium(II) complexes of redox-active tetraazatetrapyridopentacene ligand.

A combination of electrochemistry, spectroelectrochemistry, and 1H NMR has been used to study the reduction and solution speciation in acetonitrile of two mononuclear Ru complexes containing the redox-active 9,11,20,22-tetraazatetrapyrido [3,2-a:2',3'-c:3' ',2' '-l:2' '',3' ''-n]pentacene (tatpp) ligand. These complexes, [(bpy)2Ru(tatpp)][PF6]2 (1[PF6]2), and [(phen)2Ru(tatpp)][PF6]2 (2[PF6]2) (where bpy is 2,2'-bipyridine and phen is 1,10-phenanthroline), form pi-pi stacked dimers (e.g.

Driving multi-electron reactions with photons: dinuclear ruthenium complexes capable of stepwise and concerted multi-electron reduction.

Using biological precedents, it is expected that concerted, multi-electron reduction processes will play a significant role in the development of efficient artificial photosynthetic systems. We have found that the dinuclear ruthenium complexes [(phen)(2)Ru(tatpp)Ru(phen)(2)](4+) (P) and [(phen)(2)Ru(tatpq) Ru(phen)(2)](4+) (Q) undergo photodriven 2- and 4-electron reductions, respectively, in the presence of a sacrificial reductant. Importantly, these processes are completely reversible upon exposure to air, and consequently, these complexes have the potential to be used catalytically in multi-electron transfer reactions.

Influence of pH on the photochemical and electrochemical reduction of the dinuclear ruthenium complex, [(phen)2Ru(tatpp)Ru(phen)2)Cl4, in water: proton-coupled sequential and concerted multi-electron reduction.

The dinuclear ruthenium complex [(phen)2Ru(tatpp)Ru(phen)2]4+ (P; in which phen is 1,10-phenanthroline and tatpp is 9,11,20,22-tetraaza tetrapyrido[3,2-a:2'3'-c:3'',2''-l:2''',3''']-pentacene) undergoes a photodriven two-electron reduction in aqueous solution, thus storing light energy as chemical potential within its structure. The mechanism of this reduction is strongly influenced by the pH, in that basic conditions favor a sequential process involving two one-electron reductions and neutral or slightly acidic conditions favor a proton-coupled, bielectronic process. In this complex, the central tatpp ligand is the site of electron storage and protonation of the central aza nitrogen atoms in the reduced products is observed as a function of the solution pH.