The Liquid Phase Hydrogenation of Cyanocobaltate(II)

King, N. Kelso; Winfield, ME

doi:10.1021/ja01477a003

Cited by 59 publications

(10 citation statements)

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“…The cis-[Co(diars)2(H)2] CIO4 complex readily reacts with aqueous perchloric acid to liberate 1 molar equiv of hydrogen gas, and the yellow trans-[Co(diars)2(H) H2O] (CIO4) 2 The complexes where X = Cl-, Br-, NO3-, and CF3COOcan also be obtained by treating the appropriate acid with the dihydrido complex. Prolonged heating of the dihydrido complex in moderately concentrated mineral acids does not remove the remaining FI group as a hydride; it is only removed, as a proton, in basic solutions.…”

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confidence: 99%

Dissymmetric arsine complexes. Cobalt hydrides

Bosnich¹,

Jackson²,

Lo³

1975

Inorg. Chem.

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General methods for the preparation of arsinecobalt hydrides are given and the problems associated with isolating them are discussed. It is shown that, electronically, all the derivatives are formally cobalt(III) complexes despite the dichotomous chemical properties observed with some of the hydrides. No correlation between the variations in the hydride chemical shifts and the ligand field strengths of the axial ligands is found and the possible reasons for this are suggested. An aquo group trans to a hydrido ligand is labilized to the extent that its exchange is observable on an NMR time scale. The presence of two hydrido ligands confers stereochemical nonrigidity to the cw-[Co(diars)2(H)2]C104 system at room temperature.Of the non-carbonyl-containing hydrido complexes of the elements Co, Rh, and Ir, those of the first have been the least studied even though the scattered data which exist1-5 suggest that these, in a number of ways, may be more interesting than the species derived from Rh and Ir. One of the major problems associated with the study of cobalt-hydrido complexes is that no general methods for their preparation have been developed. It is well-known that three of the distinguishing features of cobalt complexes are, first, the stability of the labile Co(II) state, second, its involvement in the catalytic substitution of the stable and nonlabile Co(III) complexes and, third, the propensity of cobalt complexes in different oxidation states to undergo rapid redox disproportionation reactions. In addition, it is probable that most (formally) cobalt(III)-hydrido complexes are weakly acidic, releasing protons and the highly5•6 reactive Co(I) species in basic media. Thus attempts at reducing Co(II) or Co(III) complexes with (basic) hydride ions in protic media, a procedure which is generally successful for Rh(III) complexes,3•7 can give Co(I) species in equilibrium with the parent cobalt(III)-hydrido complex. A number of unwanted side reactions may then occur; a redox disproportionation reaction may ensue8•9 Co (I) + Co(III)-2Co(II) the Co(II) species may catalyze the decomposition of the hydridocobalt(III) product,10-12 and, in the presence of trace amounts of oxygen, the Co(I) species undergo rapid oxidative addition reactions to produce stable dioxygen adducts.5•6 We have encountered all these problems here, where we describe the preparation and properties of a series of cobalt-hydrido complexes containing tertiary arsine ligands. The three arsines employed are diars, R,R:5,S-tetars (and R,-R-tetars), and R,S-tetars (Figure 1) where it will be noted that the chiral inner arsenic atoms of the tetars ligands are stable with respect to thermal inversion under the conditions employed. The one problem which we have not been able to avoid and which is inherent in some, but not all, of the pure species is their tendency to reduce "spontaneously" to the Co(II) state in various solvents, but this property appears to be characteristic of many cobalt(III)-arsine complexes12 without hydrido ligands.

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confidence: 99%

Dissymmetric arsine complexes. Cobalt hydrides

Bosnich¹,

Jackson²,

Lo³

1975

Inorg. Chem.

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“…I), simultaneously accompanied by a relatively much slower disproportionation reaction, (Eq. II), which results in the formation of the inactive hydroxocomplex as well, by several groups of workers (3,5,18,20) in this field:…”

Section: Micellar Effects On Hydrogenation Of Pentacyanocobaltate(lll)mentioning

confidence: 90%

“…Micellar effects on bydrogenation of sorbic acid. The reduction of 2,4-hexadienoic acid to 2-hexenoic acid by the pentacyanocobaltate(III)-hydride complex, in alkaline aqueous systems and in presence of K promoter cations, has been shown by earlier workers to proceed selectively and irreversibly as follows (3,5,20): In presence of a reducible species like sorbate anion, the net rates of hydrogenation of pentacyanocobaltate(II) in aqueous, as well as surfactant, micellar solvent systems were found to remain unaltered compared to the blank hydrogenation runs, until the equilibrium concentration of pentacyanocobaltate(llI)-hydride complex is reached (see Fig. 1).…”

Section: Micellar Effects On Hydrogenation Of Pentacyanocobaltate(lll)mentioning

confidence: 99%

Effect of surfactant micelles on homogeneous catalytic hydrogenation of 2,4‐hexadienoic acid with pentacyanocobaltate(III)‐hydride complex

Nagarajan¹,

Venkataraman²

1981

J Americ Oil Chem Soc

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The influence of anionic (SLS), cationic (CTAB) and nonionic (NP 9E0) surfactant micelles on the homogeneous catalytic selective hydrogenation of 2,4-hexadienoic acid to 2-hexenoic acid in alkaline aqueous solutions of pentacyanocobaltate(llI)-hydride complex was studied at 1 atm pressure and 30 C. The results indicate that, compared to the reactions in the aqueous medium, (a) surfactant micelles present in concentrations in the neighborhood of their critical micelle concentrations (CMC) enhance both the net rate of formation of the pentacyanocobaltate(lll)-hydride complex and its equilibrium concentration by factors of 2 to 5 and 1.1 to 1.5, respectively; (b) the neutral NP 9E0 surfactant micelles enhance the rate of hydrogenation of 2,4-hexadienoic acid by pentacyanocobaltate(llI)hydride complex by a factor of 3, and, (c) the SLS and the CTAB surfactant micelles totally inhibit the hydrogenation of 2,4-hexadienoic acid. Probable mechanistic reasons are also advanced in order to explain the observed activation of the well known pentacyanocobaltate(lll)-hydride complex by surfactant miceiles.

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“…The acidity of the hydride is emphasised by its reaction with diazomethane to give the methyl a n a l o g~e .~,~ These reactions of vitamin B12E suggest that this unstable reduction product can best be formulated as an equilibrium: cOI11 + cOI . 19 Although the results of magnetic measurements on the coenzyme reported from different schools are at variance,21 the observed chemical reactions of the coenzyme and its alkyl analogues are best interpreted by regarding them as complexes of trivalent cobalt. Quantitative hydrogenation of the methyl analogue in the presence of platinum resulted in the formation of vitamin BIzr and an increase in volume of 0.5 mole caused by the liberation of methane:…”

Section: The Cobalumins and Their Reduction Productsmentioning

confidence: 99%