Cobalt complexes 6, 1,1-dithiolates

Ethylenediaminetetraacetic acid, analogs, complexes of, 3 277 chelation by, 3 276-277 cobalt complex of, 3 281 complexes, 3 277-278 formation constant of, 3 273-274 -nickel, 3 17-18 stability of, 3 266-267 reaction with metal ions, 3 62 Ethylene dibromide, irradiation of, 5 196 4,5-Ethylenedithio-1,3-dithiole-2-thione based supramolecular complexes, 46 200-204 Ethylene glycol, 32 4... 

A general account of this area is available.1158 These complexes include di- and tri-thiocarbonates (OCS2, SCS2 ), unsaturated alkene systems (R2C=CS2 ), and dithiocarbimates (RN=CS ). K2CS3 can be prepared as a yellow solid by adding CS2 to an alcoholic solution of KOH which has been saturated with H2S,1159 and as a solution in DMF by adding KOH to CS "60 Relatively few cobalt complexes of these localized dithiols are known (Table 98). 

Asymmetric hydroformylation of prochiral olefins has been investigated both for the elucidation of reaction mechanism and for development of a potentially useful method for asymmetric organic synthesis. Rhodium and platinum complexes have been extensively studied, and cobalt complexes to a lesser extent. A variety of enantiopure or enantiomerically enriched phosphines, diphosphines, phosphites, diphosphites, phosphine-phosphites, thiols, dithiols, P,A-ligands, and P,5-ligands have been developed as chiral modifiers of rhodium and platinum catalysts. - " ... 

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... 

Garner and Joule next adapted the protected dithiolene strategy to target heterocyclic dithiolene complexes. This approach, first reported in 1988 by Larsen et al is illustrated in Scheme 2.25 with the formation of a cobalt quinoxalyldithiolene complex. Reaction of [CoCp(COD)] (COD = 1,5-cyclooc-tadiene) with 4-(quinoxalin-2-yl)-l,3-dithiole-2-thione (26) affords a quinox-aline dithiolene complex (27) that has been structurally characterized. This cobalt complex undergoes extensive proton-coupled electron transfer process (see Section 2.3.4). This system was further elaborated when the pyrazine ring in 4-(quinoxalin-2-yl)-l,3-dithiole-2-thione 26 was selectively... 

Substituted thioureas have been extensively studied over the decades. Reaction of CoX2 (X = C1, Br) with substituted phenylthioureas yield a range of complexes involving halide and thiourea as ligands, characterized by spectroscopy and thermogravimetric analysis.503 Both [Co(Rtu)4(OH2)2]2+ (Rtu = thiourea, phenylthiourea, allylthiourea) and [Co(Rtu)2(OH2)4]2+ (Rtu = diphenylthiourea) have been prepared and characterized as low-spin octahedral species.504 The octahedral bis(phenylthiourea)bis(dithiolate)cobalt(II) complex, one of a number of complexes of phenylthiourea, chlorophenylthiourea and bis(diphenylphospinothioyl)methane prepared and characterized,505 proved the most biologically active of those tested. 

Modified spectrophotometric procedures are described for the quantitative determination of cobalt and molybdenum as the 2-nitrosonaphth-l-olate and toluene-3,4-dithiolate complexes in carbon tetrachloride. The extraction, chelation and phase separation steps permitted rapid sample handling, controlled interferences more effectively and provided accurate assays. The molar absorptivities for cobalt and molybdenum were 5.1 x 104 and 2.5 xl04mol/lcm, respectively, and the detection limits for both elements were 4 ng/g. 

Finally, a very simple molecular electronic component is benzene-1,4-dithiol, which is readily used as a linker between gold electrodes in the same way as the cobalt terpyridine complex shown in Figure 11.40. Benzene dithiol has been used to demonstrate the thermoelectric effect in molecular electronic systems as a linker between a gold surface and the gold tip of a modified atomic force microscope. Thermoelectricity (termed the Seebeck effect) is the generation of an electrical potential... 

Macrocycle LXXXVIII was prepared (13) in an 8% yield from the reaction of the disodium salt of ethane-1,2-dithiol with di(2-bromo-ethyl)amine in ethanol at high dilution, and it was found to complex with Ni(II) and Co(II) ions when these were added as salts. A macrocycle containing the same donor atoms (LXXXIX) has been obtained in the form of complexes (87) by the template reactions of l,2-bis(2-aminophenylthio)ethane and 1,4-bis (2-formylphenyl)-1,4-dithiabutane with Ni(II) and Co(II) perchlorates. Iron, cobalt, nickel, and zinc as their M(II) perchlorates have been used as templates in the formation of XC (55, 133). 

Table 98 Preparations Some 1,1-Dithiolate Complexes of Cobalt...

These complexes usually contain a ligand such as NO-or an alkyl group and the change from octahedral coordination, which is characteristic of cobalt(III) complexes, to five- and four-coordination, which is typical of cobalt(II) and (I) complexes, raises the problem of how to designate the oxidation state. This was first discussed in the case of the dithiolate complexes (114) and more recently for the alkyl complexes (70). The complexes will be treated not in chronological order, but in order of increasing difficulty in designating the oxidation state of the cobalt ion. 

Adducts of the l,2-dithiole-3-thione with silver nitrate and copper dichloride have been described, and for various l,2-dithiole-3-thiones, adducts containing iron, cobalt, nickel, and copper have been studied in more detail. The ligands (L) used are either unsubstituted l,2-dithiole-3-thione or its methyl- or aryl-substituted derivatives. If X represents a halogen atom, the following types of coordination compounds have been characterized CuXLj and CuXLa, FeXjLj, CoXaL, and NiX Lj. Complexes of titanium(III), tin(IV), antimony(III) and (V), and bismuth(III) have also been studied. ... 

Fig. 12. Hydrogen transfer reactions catalyzed by Lactobacillus lekhmannii ribonucleotide reductase via deoxyadenosylcobalamin. (Co) indicates the cobalt-corrin complex. Hydrogen isotopes ( H) are exchanged between water and coenzyme, or vice versa, in presence of enzyme and a dithiol (i.e., reduced enzyme, E(SH)2) and an allosteric effector (not drawn) by reactions 1-3. Reaction 4 indicates degradation of the radical pair (center) to 5 -deoxyadenosine and cob(II)alamin. Reduction of a ribonucleotide substrate is described in step 5 the nucleotide radical (proposed in >) is a hypothetic intermediate...

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