Protonation of anionic

The reduction of organic halides in the presence of aromatic hydrocarbons, the subject of detailed kinetic studies, provide rate constants for the homogeneous ET [147-150] and the follow-up reaction [151]. The theoretical basis for this kind of experiment ( homogeneous redox catalysis ) was laid by Saveant s group in a series of papers during the years 1978-80 [152-157]. Homogeneous ET also plays an important role in the protonation of anion radicals [158]. 

Alternative synthetic approaches include enantioselective addition of the organometallic reagent to quinoline in the first step of the synthesis [16], the resolution of the racemic amines resulting from simple protonation of anions 1 (Scheme 2.1.5.1, Method C) by diastereomeric salts formation [17] or by enzymatic kinetic resolution [18], and the iridium-catalyzed enantioselective hydrogenation of 2-substituted quinolines [19]. All these methodologies would avoid the need for diastereomer separation later on, and give direct access to enantio-enriched QUINAPHOS derivatives bearing achiral or tropoisomeric diols. Current work in our laboratories is directed to the evaluation of these methods. 

Two reports of H2 formation upon acidification of anionic formyls 6 (31) and 19 (38) could not be reproduced (32, 47). Thus there are no documented examples of H2 evolution upon protonation of anionic formyl complexes. It is clear, however, that rapid reactions ensue in all cases (32, 47, 66) and that good yields of neutral metal carbonyl (H loss) products are obtained. 

The protonation of anion radicals and dianions derived from aromatic hydrocarbons has been studied in some detail by Hoijtink and co-workers 113-11 s). it was shown that apart from the reactions given above (Eqs. (42)—(46)) other disproportionation equilibria also play an important role. These are different for different anion radicals, making the whole picture very complex. Kinetic studies on the disproportionation of the nitrobenzene anion radical and some of its derivati-ves 116,u 7) jlave s 10wn that in aqueous solution at a pH > 11.5, reaction (41) is of great importance, whereas the protonated radical ion and the radical ion are the kinetically active species in the pH interval between 3.2 and 11.5. 

The complex mechanism of the protonation of anion radicals in DMF may have some bearing upon the mechanism proposed for the reaction of perylene radical anion with alcohols (Levin et a/., 1972) and anthracene radical anion with t-butyl alcohol (Rainus et a ., 1973). The disproportionation mechanism was proposed for these reactions in ethereal solvents with alkali-metal counter-ions. The principal evidence for the mechanism was the observation of rate laws of the form of (77) where was suggested to be... 

Table 1. Formation of Hydrides by Protonation of Anionic Transition-Metal Complexes ...

Rabideau, P. W., Huser, D. L. Protonation of anion intermediates in metal-ammonia reduction 1,2- vs. 1,4-dihydro aromatic products. J. Org. Chem. 1983,48,4266-4271. 

For salt type minerals, hydrolysis of cations and protonation of anions are taken into account in the calculation of their solubilities. Since the solubilities of these minerals are quite high, the protonation of dissolved anions from the mineral has a significant effect on pH. 

The protonation of anionic hydrides such as those in Table 1.1 produces neutral non-classical dihydrogen complexes such as M(Ti2-H2)(H)2(CO)(P Pr3)2,... 

Hydrido-clusters are usually prepared by protonation of anions. For example, the reaction of [Ru3(CO)i2] with aqueous KOH in THF solution results in cluster expansion to the octahedral dianion [Ru6(CO)ig] , protonation of which gives the monoanion [Ru6H(CO)i8] (in which the single H atom resides inside the Ru6 cavity), or the neutral dihydrido-cluster [H2Ru6(CO)ig] (in which the hydride ligands cap opposite faces of the octahedral metal cage), depending on the reaction conditions. 

Figure 53 Calculated geometries and selected atomic spin densities (BP86/TZVP) of three products resulting from protonation of anionic [(por)Fe(NONO)(lm)]x. Bond distances are in italics underline. See text for descriptions. Reproduced from Ref. (252) with permission from the Royal Society of Chemistry.

In contemporaneous studies by Kuwajima, the 1-silyloxy allyl anions were generated from 1-trimethylsilyl allylic alcohols such as 24. Treatment with a catalytic amount of base led to silyl enol ether 25 in excellent yield and (Z)-selectivity. The alkene geometry was proposed to arise from chelate 26, a structure consistent with Reich s results. Protonation of anionic intermediate 26 by alcohol 24, would provide product 25 and the alkoxide of 24, poised for Brook rearrangement. ... 

Taking into account that fact one concludes that protonation of anionic nucleotides may lead to significant changes in their conformations and energetic. It is... 

The complexity of subsequent and secondary reactions in the protonation of anionic clusters may be observed in the following equations that illustrate the protonation of the tetraanion [Rh6(CO)i4] under different reaction conditions. 

A representative list of rates of protonation of anions of pseudoacids is given in Table 3. These rates were obtained by dividing the observed rate of ionization, as measured by halogen uptake, by the observed acid dissociation constant. It is noteworthy that the site of... 

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