Cobaltate, complex with water soluble

A number of metal porphyrins have been examined as electrocatalysts for H20 reduction to H2. Cobalt complexes of water soluble masri-tetrakis(7V-methylpyridinium-4-yl)porphyrin chloride, meso-tetrakis(4-pyridyl)porphyrin, and mam-tetrakis(A,A,A-trimethylamlinium-4-yl)porphyrin chloride have been shown to catalyze H2 production via controlled potential electrolysis at relatively low overpotential (—0.95 V vs. SCE at Hg pool in 0.1 M in fluoroacetic acid), with nearly 100% current efficiency.12 Since the electrode kinetics appeared to be dominated by porphyrin adsorption at the electrode surface, H2-evolution catalysts have been examined at Co-porphyrin films on electrode surfaces.13,14 These catalytic systems appeared to be limited by slow electron transfer or poor stability.13 However, CoTPP incorporated into a Nafion membrane coated on a Pt electrode shows high activity for H2 production, and the catalysis takes place at the theoretical potential of H+/H2.14... 

For a decade or so [CoH(CN)5] was another acclaimed catalyst for the selective hydrogenation of dienes to monoenes [2] and due to the exclusive solubility of this cobalt complex in water the studies were made either in biphasic systems or in homogeneous aqueous solutions using water soluble substrates, such as salts of sorbic add (2,4-hexadienoic acid). In the late nineteen-sixties olefin-metal and alkyl-metal complexes were observed in hydrogenation and hydration reactions of olefins and acetylenes with simple Rii(III)- and Ru(II)-chloride salts in aqueous hydrochloric acid [3,4]. No significance, however, was attributed to the water-solubility of these catalysts, and a new impetus had to come to trigger research specifically into water soluble organometallic catalysts. 

It is interesting to note that no specific study was devoted to the aqueous biphasic hydrogenation of aldehydes with water-soluble cobalt-phosphine complexes, although such a property has long been known from hydroformylation experiments [199,200]. 

As with most complexation and drug solubility situations, pH b a critical variable. Cocaine base b not soluble in water, and if the drug b in thb form rather than a soluble salt, no reaction occurs. Acid b needed to ensure that the cocaine b in the water-soluble ionic form to allow for the formation of a complex. The color b the result of an ion-pair compound formed from the cationic cocaine and the anionic cobalt complex. As with all amine bases, such as ammonia, the base becomes protonated in acidic solution. The pKg of the base determines the ratio of the protonated, ionized form to the neutral form. It is possible to add too much HQ, because cobalt forms a water-soluble pink complex with chloride [CoCy . The pH can also influence the type of complex and ion pair formed. Under acidic conditions, the ion pair favored b [Co(cocaine)2l(SCN)2 (which b pinkbh and soluble in water), while in the neutral-to-basic ranges, the ion pair b assigned the structure [cocaine-H ]2 [Co(SCN)4] (which b a blue solid and soluble in chloroform). The important points of the cobalt thiocyanate reaction with cocaine are summarized in Figures 7.24r-7.26. 

Other cationic pentacoordinate organocobalt complexes have been investigated, such as those obtained with water-soluble phosphines P[(CH2) C6H4- -S03Na]3 ( = 1, 2, 3, and 6). This type of phosphines reacted rapidly with Co2(CO)g in two-phase reaction conditions to yield the disproportionation products [Co(CO)3(P[(CH2) C6H4-/>-S03Na]3)2][Co(CO)4]. This series of complexes has been used as precursors to water-soluble cobalt hydroformylation catalyst. ... 

Cobalt(II) complexes of three water-soluble porphyrins are catalysts for the controlled potential electrolytic reduction of H O to Hi in aqueous acid solution. The porphyrin complexes were either directly adsorbed on glassy carbon, or were deposited as films using a variety of methods. Reduction to [Co(Por) was followed by a nucleophilic reaction with water to give the hydride intermediate. Hydrogen production then occurs either by attack of H on Co(Por)H, or by a disproportionation reaction requiring two Co(Por)H units. Although the overall I easibility of this process was demonstrated, practical problems including the rate of electron transfer still need to be overcome. " " ... 

Cobalt catalysts such as HCo(CO)4 are widely used for hydroformyla-tion of higher alkenes, despite the higher temperatures and pressures required. The main reason for this is that these catalysts are also efficient alkene isomerization catalysts, allowing a mix of internal and terminal alkenes to be used in the process. Catalyst recovery is more of a problem here, involving production of some waste and adding significantly to the complexity of the process. A common recovery method involves treating the catalyst with aqueous base to make it water soluble, followed by separation and subsequent treatment with acid to recover active catalyst (4.3). 

Alkyne-nitrile cyclotrimerization is a powerful synthetic methodology for the synthesis of complex heterocyclic aromatic molecules.118 Recently, Fatland et al. developed an aqueous alkyne-nitrile cyclotrimerization of one nitrile with two alkynes for the synthesis of highly functionalized pyridines by a water-soluble cobalt catalyst (Eq. 4.62). The reaction was chemospecific and several different functional groups such as unprotected alcohols, ketones, and amines were compatible with the reaction.119 In addition, photocatalyzed [2+2+2] alkyne or alkyne-nitrile cyclotrimerization in water120 and cyclotrimerization in supercritical H2O110121 have been reported in recent years. 

Oxime 85 with sodium cobalt nitrite Na3Co(N02)6 forms a poorly water soluble Cobalt(III) complex CoL3 that, by contrast to 85, is relatively stable to acids. 

The crude substance is their recrystallised from water containing acetic acid. The compound was originally believed to exist in two isomeric forms, but Jorgensen found the crystalline form depends on the concentration of acetic acid used for crystallisation, inasmuch as rhombic leaflets separate from hot dilute acetic acid, and from hot concentrated acid the substance separates in yellow-brown needles. The complex is sparingly soluble in water, and gives no precipitate in aqueous solution with silver nitrate or potassium chromate. If treated with cold hydrochloric acid it is transformed into chloro-dinitro-triammino cobalt, [Co(NH3)3(N02)2Cl], and if warmed with concentrated hydrochloric acid gives diehloro-aquo-triammino-cobaltic chloride. 

It has long been known (93) that cobalt(II) complexes of phthalocyanines interact with molecular oxygen. The water-soluble tetrasulfonato derivative of the parent phthalocyanine selectively and catalytically oxidizes 2,6-di-tert-butylphenol to the benzoquinone and the dipheno-quinone in both homogeneous solution (94) and when polymer-supported (95). The active intermediate in the catalytic cycle is proposed to be the (as expected) mononuclear dioxygen complex of the cobalt-tetrasulfonatophthalocyanine system (92). It has been proposed that the formation of a peroxo-bridged dinuclear complex is responsible for the deactivation of the cobalt(II)-tetrasulfonatophthalocyanine system, since such a dinuclear system would be unable to further bind and activate dioxygen (96). Such deactivation results, ultimately, in loss of the catalyst and low turnover ratios. 

Alkali metal 1-methyl- and 1-phenyl-borinates are also available from bis(borinato)cobalt complexes (see below) on treatment with sodium or potassium cyanide in an aprotic solvent like acetonitrile. Cobalt cyanide precipitates and the alkali borinate remains in solution. After addition of thallium(I) chloride to some complexes, thallium 1-methyl- or 1-phenyl-borinate could be isolated as pale yellow solids, the only main group borinates isolated hitherto. They are insoluble in most organic solvents but readily soluble in pyridine and DMSO. The solids are stable on treatment with water and aqueous potassium hydride, but are decomposed by acids <78JOM(153)265). 

Wool and Polyamide Dyes. Water-soluble formazan complexes having sulfonamide, alkylsulfonyl, or sulfonic acid groups possess a high affinity to nitrogen-containing fibers. As with acid dyes, they can be used to dye wool and polyamide in neutral to weakly acid baths. Commercial dyes of this type are C.I. Acid Blue 267 and 297, and the 1 2 cobalt complex C.I. Acid Black 180, 13710 [11103-91-6] (29). 

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