Decarboxylation metal complexes

Osmium, quinuclidinetetraoxime-stereochemistry, 44 Osmium, tetrachloronitrido-tetraphenylarsenate stereochemistry, 44 Osmium, tris( 1,10-phenanthroline) -structure, 64 Osmium(II) complexes polymerization electrochemistry, 488 Osmium(III) complexes magnetic behavior, 273 Osmium(lV) complexes magnetic behavior, 272 Osmium(V) complexes magnetic behavior, 272 Osmium(VI) complexes magnetic behavior, 272 Oxaloacetic acid decarboxylation metal complexes, 427 Oxamidoxime in gravimetry, 533 Oxidation-reduction potentials non-aqueous solvents, 27 Oxidation state nomenclature, 120 Oxidative addition reactions, 282 Oxidative dehydrogenation coordinated imines, 455 Oximes... 

A-Carboxy-a-amino acid anhydrides, also referred to as 4-substituted oxazolidine-2,5-diones, Leuchs s anhydrides, or N-carboxyanhydrides (NCA), are polymerized by bases and transition metal complexes. Polymerization proceeds with simultaneous decarboxylation to produce a polyamide... 

Several forms of bis(pentafluorophenyl)zinc have been observed65. The high temperatures employed in the decarboxylation route illustrate the thermal stability of the aryl zinc reagents. 1 1 Metal complexes, such as 2,2 -bipyridine and 1,10-phenanthroline, are... 

In addition to the above-mentioned reactions, metal complexes catalyze decarboxylation of keto acids, hydrolysis of esters of amino acids, hydrolysis of peptides, hydrolysis of Schiff bases, formation of porphyrins, oxidation of thiols, and so on. However, polymer-metal complexes have not yet been applied to these reactions. 

The decarboxylation of simple /f-ketoacids, such as acetoacetic acid, is not metal promoted (Fig. 5-22) - this is in part due to formation of the chelate complex, which is in the enolate form. Mechanistic studies have indicated that the enol or enolate is inactive in the decarboxylation reaction. The mechanism indicated in Fig. 5-21 is not applicable to the metal complex. 

In the autoxidation of neat hydrocarbons, catalyst deactivation is often due to the formation of insoluble salts of the catalyst with certain carboxylic acids that are formed as secondary products. For example, in the cobalt stearate-catalyzed oxidation of cyclohexane, an insoluble precipitate of cobalt adipate is formed. 18fl c Separation of the rates of oxidation into macroscopic stages is not usually observed in acetic acid, which is a better solvent for metal complexes. Furthermore, carboxylate ligands may be destroyed by oxidative decarboxylation or by reaction with alkyl hydroperoxides. The result is often a precipitation of the catalyst as insoluble hydroxides or oxides. The latter are neutralized by acetic acid and the reactions remain homogeneous. 

The generality of the rearrangement is further illustrated by the reaction of 2,2 -furil with hydroxide ion in dry ether (Table 1). Likewise, 2,2 -pyridil is rearranged in hot methanol solution (40 min) to give the sodium salt of 2,2 -pyridilic acid (86%). Acidification, however, affords bis(2-pyridyl)methanol by decarboxylation since 2,2 -pyridilic acid (16) is structurally similar to a -keto acid. Benzilic rearrangement of 2,2 -pyridil with methanolic nickel(ll) and cobalt(II) acetates results in the formation of metal complexes of 2,2 -pyridilic acid (17 92%). A plausible mechanism is summarized in Scheme 4. Rearrangement is also observed with 2,2 -quinaldil, but benzil, 2,2 -furil or 1-phenyl-2-(2 -pyridyl)ethane-1,2-dione are not susceptible to these metal template reactions. 

Scheme 1. Decarboxylation from hydroxycarbonyl- and C02-metal complexes.

Some metal carbonyl clusters such as HFe3(CO)n, Ru3(CO)i2 and Ir4(CO)i2 have been studied in an alkaline solution as possible catalysts for the water gas shift reaction. A plausible mechanism has been proposed that involves nuleophilic attack by H2O or OH on an electrophilic metal center of the cluster to form an unstable carbohydroxy metal complex, which is then decarboxylated to give a metal hydride from which H2 is eliminated. 

The chemistry of aqueous solutions of COj in the presence of aquated transition metal complexes has been extensively studied by a group of researchers led by Harris, Palmer and vanEldik, and they have presented extensive kinetic studies on the carboxylation and decarboxylation of a variety of bis(ethylenediamine)carbonato complexes of The decarboxylation of [Rh(en)2(C03)] ... 

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