Formate anion

The formation of 1-and 2-aIkenes can be understood by the following mechanism. In the presence of formate anion, the 7r-allylpalladium complex 572 is converted into the 7r-allylpalladium formate 573. The most interesting feature is the attack of the hydride from formate to the more substituted side of the (T-allylic system by the cyclic mechanism shown by 574 to form the 1-alkene 575[367]. The decarboxylation and hydride transfer should be a concerted... 

This method has been used for the reduction of l-methyl-2-alkyl-.d -pyrrolinium and l-methyl-2-alkyl-.d -piperideinium salts by Lukes et al. (42,249-251) and for the reduction of more complex bases containing the dehydroquinolizidine skeleton by Leonard et al. (252). The formic add reduction may be satisfactorily explained by addition of a hydride ion, or an equivalent particle formed from the formate anion, to the -carbon atom of the enamine (253), as shown in Scheme 13. 

Electrostatic potential map for formate anion shows most negatively-charged regions (in red) and less negatively-charged regions (in blue). 

Most reactions are carried out with perchlorates or fluoroborates methylene dichloride is a convenient aprotic solvent for salts with the former anion. Among the various anions, the strongest nucleophile yet reported to give ionized salts (in the case of an isobenzopyrylium salt) is the formate anion (cf. also Section II,B,2,c). 

Smallwood, C. J., McAllister, M. A., 1997, Characterization of Low-Barrier Hydrogen Bonds. 7. Relationship Between Strength and Geometry of Short-Strong Hydrogen Bonds. The Formic Acid-Formate Anion Model System. An Ab Initio and DFT Investigation , J. Am. Chem. Soc., 119, 11277. 

Formic acid is a widely used hydrogen donor.240 Flowever, since the active species in formic acid is the formate anion, it has been demonstrated that formate salts are superior to formic acid. Ammonium formate is used frequently as a hydrogen donor.241-243... 

As can be seen from the data in Table 35.1, the maximum reaction rate is achieved at the 5 2 formic acid triethylamine ratio that is the commonly used azeotropic mixture known as TEAF. When more acid is present, the catalyst may be less active, but equally there may be less formate anion (i.e., the active reagent). The concentration of the latter also depends upon the solvent being used. When there is more triethylamine present the reaction rate also decreases, and there are some indications that triethylamine may deactivate the catalyst. However, the use of formic acid mixtures with ammonia, ethylamine or diethy-lamine is less effective than triethylamine. 

The IPA system does not require a co-solvent, but one can be used if this proves advantageous. In the TEAF system a solvent is normally used, though neat TEAF or formic acid can be used if required. The solvent can have a large effect on the reaction rate and optical purity of the product this may in part be because the substrate seems to bind by weak electrostatic interactions with the catalyst, and is also partly due to the pH of the system. Solvents have a dramatic effect on the ionization of formic acid for example, in water the piCa is 3.7, but in DMF it is 11.5. This is because formation of the formate anion becomes less favorable with less polar solvents (see Table 35.2). The piCa of triethy-lamine is far less sensitive. As a consequence, formic acid and triethylamine may remain unreacted and not form a salt. The variation in formic acid piCa can also have a significant impact on the catalyst and substrate, particularly when this is an imine. 

Water has been shown to enhance the activity of ruthenium and rhodium catalysts in both the TEAF and potassium formate systems [34, 36, 52]. The aqueous systems enable much simpler control of pH this is important, as Xiao has found that a low pH markedly slows the reaction [52]. The pH at which this occurs corresponds with the pKa of formic acid (i.e., 3.7), implying that the formate anion is required for complexation with the catalyst. Xiao has proposed two possible catalytic cycles - one that provides poor ee-values at low pH as a result of ligand decomplexation, and another that gives high ee-values at high pH. 

Tapia, O., Andres, J. and Cardenas, R. Transition structure for the hydride transfer reaction from formate anion to cyclopropenyl cation a simple theoretical model for the reaction catalyzed by formate dehydrogenase, Chem. Phys. Lett, 189 (1992), 395-400... 

Indeed, the equation is consistent with the observed experimental results, except in the case of [OH-]. They explained the discrepancy by the fact that the concentration of OH- is regulated by formate anion buffer via reaction with CO, thereby maintaining the overall water-gas shift reaction rate to be essentially independent of base. 

They focused their research on answering the question as to whether catalysis proceeds via formate anion as an intermediate, such that dissociation of a CO ligand is the first step in the mechanism Cr(CO)6 -> Cr(CO)5 + CO followed by nucleophilic attack by formate anion i.e., from CO + OH- -> HCOO-) to produce the formate species Cr(CO)5 + HCOO- > Cr(CO)5(OOCH) , according to King et al.5 in Scheme 18 or whether a metallocarboxylic acid forms upon... 

In reviews on formic acid decomposition, Mars and coworkers194,198 wrote that the formation and decomposition of formate anions were monitored by infrared spectroscopy. These studies were carried out by Fahrenfort, Sachtler, and coworkers188,193 for the case of formates on metals produced by formic acid adsorption—Cu, Ni, Pd, Rh, Pt, and Zn and in the case of metal oxides, Hirota et al. investigated ZnO,187,189,190,197 while Scholten et al. studied MgO.199,200 The infrared... 

They developed a kinetic model based on the proposed mechanism. They proposed that it is the migration of the formate anion from the support to the metal site that governs the kinetics of water-gas shift rate,229 such that ... 

A. Davydov, Molecular Spectroscopy of Oxide Catalyst Surfaces, ed. N. T. Sheppard, John Wiley Sons, Inc., 2003, pp. 56-78 (hydroxyl groups), 447 453 (formate anions). 

To provide an example of a reaction that is very different to electrophilic aromatic substitution, the oxidation of formic acid by bromine was also studied. This reaction, which involves electrophilic attack on the formate anion (15) (Cox and McTigue, 1964 Smith, 1972 Herbine et al., 1980 Brusa and Colussi, 1980), is catalysed by a-CD (/c /k2u = 11) (Tee et al., 1990a), and the degree of transition state stabilization (Xts = 0.18 mM) is similar to that for phenols (Table A4.2) and most of the other substrates (Table A4.4). 

Second step. The elements of CH4O3 are eliminated. The most likely by-products are H20 and HCOOH. Make None. Break C4-C5, C6-O8, 010-011. The base can deprotonate the OH on C5, and the lone pair on O can then push down to form a n bond with C5, causing the C4-C5 bond to break. The electrons keep getting pushed around until they end up on O again and the 0-0 bond is broken, providing the driving force for the step. A keto-aldehyde and formate anion are obtained. Now C7 (deprotonated) is nucleophilic and C6 is electrophilic, so an aldol reaction followed by dehydration gives the observed product. 

Related decarboxylation reactions have been used to synthesize magnesium hydride anions from formate anions and organocalcium, organobarium and organostrontium metallates. ... 

Standard stock solutions of formate anion were prepared from reagent grade sodium formate. Standard solutions of other organic anions were prepared for assessment of potential interferences. Injections of 3 mL were made to fill a sample loop of 100 yL volume. 

Scheme 7.7 Mechanism for hydrolysis of orthoformates by 1. The formate ester product is further hydrolyzed by base to formate anion and the corresponding alcohol.

Proton abstraction from a model carbon acid, hydroxyacetaldehyde, by formate anion has been examined theoretically for the gas phase and for aqueous solution.152 The reaction shows an early transition state, whereas its enzymatic equivalent has a late transition state. Solvation brings the transition state foiward. The factors that contribute to producing the later transition state in enzymes are discussed. 

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