Cobalt complexes bipyridyl

Other, closely related, nicotinic acid derivatives and the unsubstituted system itself have also been studied and undergo similar reactions. Moreover, the approach may be extended to 2,2 -bipyridyls. Newkome and his collaborators have used the 2,2 -bipyridyl unit 19) as an electrophile in which ortho-hr ommes served as leaving groups. They have also used halomethyl systems and formed the macrocycles from these systems . A compound derived from the latter starting material 20) is reported to form a cobalt complex, in which both nitrogens and only one of the oxygen atoms participate in the binding . The two precursor units are shown below as 79 and 20, respectively. 

Telfer, S. G. Bemardinelli, G. Williams, A. F. Iron and cobalt complexes of 5,5 -di(methylene-A-aminoacidyl)-2,2 -bipyridyl ligands Ligand design for diastereoselectivity and anion binding. J. Chem. Soc. Dalton Trans. 2003, 435 40. 

Reduction of a cobalt(II) halide in presence of 2,2 -bipyridyl with zinc in THF-ethanol leads to cobalt(I)-bipyridyl complexes which hydrogenate butadiene to cis-2-butene at 25 °C and normal pressure of hydrogen. For different halides the rate decreases in the order I>Br>Cl. 1,10-Phenanthroline complexes were also active.64 Here again, the catalyst does not tolerate an excess of diene. The proposed mechanism for the hydrogenation is given in Scheme 4. 

However, the similarity in bond strengths of the peroxide linkage to molecular 02, the ease with which the known -peroxo Cobalt complexes liberate 02 (in contrast to /x-oxo bipyridyl Mn dimers) on photolysis, kinetic barriers on ju-oxo to peroxo dimer conversions led Sawyer et al.47 -49) to suggest peroxo binuclear complexes as the most probable intermediates. More studies with model compounds are needed to elucidate this point. Various mechanisms proposed for water oxidations are variations of these two principal types. 

Cobalt complexes, 635-882 ADP, 760 amides, 682 arsenates, 774 arsenic ligands, 767-775 ATP, 760 bipyridyl, 691 bis(dithiolates), 876 carboxylates, 790 cyanates, 679 cyanides reduction, 646 disulfides, 829... 

The neutral radical 11.12 is an interesting heterocyclic analogue of 2,2 -bipyridyl. This paramagnetic (spin-bearing) ligand forms an N, -chelated complex with bis(hexafluoroacetylacetonato)cobalt(ir). ... 

No cases of cis/trans isomerism have yet been reported among organo-cobalt(III) complexes, even among compounds not covered by this review. Complexes such as [R2Co(bipy)2] all have the cis configuration steric hindrance would be greatly increased by the coplanarity of the two bipyridyl ligands in the trans isomer 123). 

For instance, the (pentaphenylcyclopentadienyl) cobalt dicarbonyl anion-radical complex [(q-C5Ph5)Co(CO)2] has (n + 1) metal orbital populated with an unpaired electron, according to calculations by Connelly et al. (1986). In contrast, reduction of (bpy)Cr(CO)4 (bpy = 2,2 -bipyridyl) to its anion radical is known to occur without any major change in its structure or composition. 

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... 

Other aqueous preparative methods include aerial oxidation of an alkaline solution of CoS04 and NaCNO to give the fulminatocobaltate(III) anion [Co(CNO)6]3-, reduction of ruthenate(VI) by excess of fulminate to give [Ru(CNO)6]4, and displacement of 2,2 -bipyridyl or 1,10-phenan-throline from nickel(II) or cobalt(III) complexes to give [Ni(CNO)4]2 or [Co(CNO)6]3. Liquid ammonia may replace water as solvent [Ni(NH3) ]2+ and [Co(NH3)6]3+, for example, react with sodium fulminate in this solvent to form [Ni(CNO)4]2 and [Co(CNO)6]3. In all these reactions fulminate behaves very like cyanide with [AuClJ-, however, reduction to form the gold(I) complex [Au(CNO)2] takes place and no gold(III) complex can be isolated. 

Several studies of bimetallic complexes in which the donor and acceptor are linked across aliphatic chains have demonstrated that these are generally weakly coupled systems. " Studies of complexes linked by l,2-bis(2,2 bipyridyl-4-yl)ethane (bb see Figure 5), indicate that these are good models of the precursor complexes for outer-sphere electron-transfer reactions of tris-bipyridyl complexes. A careful comparison of kinetic and spectroscopic data with computational studies has led to an estimate of //rp = 20cm for the [Fe(bb)3pe] + self-exchange electron transfer. In a related cross-reaction, the Ru/bpy MLCT excited state of [(bpy)2Ru(bb)Co(bpy)2] + is efficiently quenched by electron transfer to the cobalt center in several resolved steps, equations (57) and (58). ... 

Irradiation of 118 in deoxygenated benzene solution gave an insoluble cobalt(II) complex which was not further characterized. Irradiation in the presence of O2 gave a clean photoreaction to yield an organometallic complex tentatively formulated as an alkylperoxo complex. Irradiation of dimethylcobalt complexes such as [(CH3)2Co(bipy)2]" (bipy = bipyridyl) 130) and (CH3)2Co(bdml,3pn) [bdml,3pn = bis-l,3-(diacetylmono-... 

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