Bipyridine complexes

Ru 2,2 -bipyridine complexes can form a large number of colored compounds upon successive reduction, with the formal Ru oxidation state from +2 to -4. In the case of highly reduced complexes, proper representation of the electrochromic reaction is actually the reduction of the hgand, not that of the metal center. 

R. J. Watts, J. S. Harrington, and J. Van Houten, A stable monodentate 2,2-bipyridine complex of iridium (III) A model for reactive intermediates in ligand displacement reactions of tris 2,2-bipyridine metal complexes, J. Am. Chem. Soc. 99, 2179-2187 (1977). 

Recently, chloro-, bromo-, and iodoben-zenes have been subjected to electroreduction using Ni(0) complex mediators to yield biphenyl. NiCl2L2 and NiBr2L2 [L= P(Ph)3, (Ph)2PCH2CH2P(Ph)2] have been used as catalysts [259-265]. Pro-tic media such as alcohols, that is, methanol, ethanol or alcohol-water mixtures are found to be suitable solvents for achieving the electrosynthesis of biaryls from aryl halides according to a procedure that involves a catalytic process by nickel-2,2 -bipyridine complexes [266]. Electrochemical cross-coupling between... 

Fluorescent redox switches based on compounds with electron acceptors and fluorophores have been also reported. For instance, by making use of the quinone/ hydroquinone redox couple a redox-responsive fluorescence switch can be established with molecule 19 containing a ruthenium tris(bpy) (bpy = 2,2 -bipyridine) complex.29 Within molecule 19, the excited state of the ruthenium center, that is, the triplet metal-to-ligand charge transfer (MLCT) state, is effectively quenched by electron transfer to the quinone group. When the quinone is reduced to the hydroquinone either chemically or electrochemically, luminescence is emitted from the ruthenium center in molecule 19. Similarly, molecule 20, a ruthenium (II) complex withhydroquinone-functionalized 2,2 6, 2"-terpyridine (tpy) and (4 -phenylethynyl-2,2 6, 2"- terpyridine) as ligands, also works as a redox fluorescence switch.30... 

Other metal complexes such as 2,2 -bipyridine complexes of Rh and Ir are efficient electrocatalysts for the reduction of C02 in acetonitrile.134 In the production of formate the current efficiency is up to 80%. Electrochemical reduction catalyzed by mono- and dinuclear Rh complexes affords formic acid in aqueous acetonitrile, or oxalate in the absence of water.135 The latter reaction, that is, the reduction of C02 directed toward C-C bond formation, has attracted great interest.131 An exceptional example136 is the use of metal-sulfide clusters of Ir and Co to catalyze selectively the electrochemical reduction of C02 to oxalate without the accompanying disproportionation to CO and CO2-. 

The possibility of the practical application of the catalytic photode-composition of water based on the reactivity of the excited states of tris(2,2 -bipyridine) complexes of ruthenium(III) and ruthenium(II) has attracted considerable interest, but it is now clear that the efficiency of this process is limited not only by the lack of efficient catalysts, particularly for the dioxygen-evolving path, but also by both thermal and photochemical ligand oxidation 1,2) and ligand substitution reactions (3) of the 2,2 -bipyridine complexes. The stoichiometrically analogous tris(2,2 -bipyridine) and tris(l,10-phenanthroline) complexes of both... 

Mechanism 2 requires deprotonation of a ligand, and dissociation of the hydrogen bound to the C(3) atom was suggested to be the slow step for the reaction of tris(2,2 -bipyridine)ruthenium(III) in base (12). This would require a mechanism for the 1,10-phenanthroline complexes different from that of the 2,2 -bipyridine complexes, but, from the data in Table II as illustrated in Figs. 3-5, this seems unlikely. The requirement of a different mechanism is based upon the significant differences in rates of D/H exchange as measured by 1H NMR for the tris(diimine)... 

Ishiyama, T., Takagi, J., Hartwig, J.F. and Miyaura, N., A stoichiometric aromatic C—H borylation catalysed by iridium(I)/2,2 -bipyridine complexes at room temperature, Angew. Chem., Int. Ed. Engl, 2002, 41, 3056-3058. 

Although the ECL phenomenon is associated with many compounds, only four major chemical systems have so far been used for analytical purposes [9, 10], i.e., (1) the ECL of polyaromatic hydrocarbons in aqueous and nonaqueous media (2) methods based on the luminol reaction in an alkaline solution where the luminol can be electrochemically produced in the presence of the other ingredients of the CL reaction (3) methods based on the ECL reactions of rutheni-um(II) tris(2,2 -bipyridine) complex, which is used as an ECL label for other non-ECL compounds such as tertiary amines or for the quantitation of persulfates and oxalate (this is the most interesting type of chemical system of the four) and (4) systems based on analytical properties of cathodic luminescence at an oxide-coated aluminum electrode. 

The synthesis of a series of polyfluorene 18 incorporated with chloro-tricarbonyl rhenium(I) 2,2-bipyridine complexes was reported (Scheme 10).78 Suzuki cross-coupling reactions were used to construct the main chain, and the... 

In all the hydrazine complexes, the heterochiral are more stable than the corresponding homochiral ones. In one of the 3,3 -difluoro-2,2 -bipyridine complexes, the homodimer is more stable than the heterodimer, and finally, half of the homochiral bipyridine complexes are more stable than the corresponding... 

Nickel-2,2-bipyridine complexes are also used for the preparation of unsymmetrical biaryls such as 4-methoxy-4 -trifluoromethylbiphenyl by electroreduction of two aryl halides, one of which has electron-donating and the other electron-withdrawing groups in the aromatic ring as shown in equation 110. The reaction was carried out in N-methylpyrrolidinone at constant current in an undivided cell fitted with a sacrificial magnesium anode and excess of 2,2 -bipyridine167. 

A poorly characterized, insoluble, gray-black 2,2 -bipyridine complex formulated as [ReCl3-(bipy) 3/2H20] (the value of n is unknown) has been obtained from the reaction of (BuJN)2Re2Cls with bipy in n-butanol. It is paramagnetic (jt = 1.36 BM), but its spectral properties give few clues as to its structure.108... 

Veggel and coworkers [137, 138] first reported the use of ruthenium(II) tris(2,2 -bipyridine) complexes ([Ru(bpy)3] +) and ferrocene as light-harvesting chromophores for sensitization of NIR luminescence from Nd(III) and Yb(III) ions. The Ru-Ln complexes (Ln = Nd 104, Yb 105) resulted from incorporating [Ru(bpy)3] + with m-terphenyl-based lanthanide complexes. Upon excitation of the Ru(bpy)s chromophore absorption with visible light up to 500 nm, both Ru-Nd and Ru-Yb complexes exhibited typical NIR luminescence because of effective Ru Ln energy transfer with the rates of 1.1 x 10 s for Ru-Nd complex and <1.0 X 10 s for Ru—Yb species. 

---