Alkyl exchanges

Carefully fractionated through a gauze-packed column. Redistil and collect in weighed glass vials and seal. Keep away from moisture. It undergoes alkyl exchange with alcohols and forms azeotropes, e.g. with MeOH the azeotrope consists of 70% (MeO)3B and 30% MeOH with b 52-54"/atm, d 0.87. [J Chem Soc 2288 7952 Chem Ind (London) 53 7952 J Am Chem Soc 75 213 7955.] Also dried with Na, then distilled. 

The first extensive kinetic study of these reactions was carried out by Ingold et a/.7I3b, who demonstrated that for the two-alkyl exchange reaction, i.e. the reverse direction of equilibrium (283), the kinetics in acetone and ethanol were cleanly second-order, viz. 

The tribromide anion would, however, be expected to increase the rate if the reaction occurred via the SE mechanism. The second-order kinetics and stereochemical retention of configuration were shown to apply to the one- and three-alkyl exchanges, and the retention of configuration for the two-alkyl exchange was confirmed by Jensen et a/.716. 

For a discussion of solvent effects on organotin alkyl exchange reactions, see Petrosyan, V.S. J. Organomet. Chem., 1983, 250, 157. 

Scheme 9. Competitive alkyl exchange and coupling in the reaction of [TpBut]MgMe with 13CH3I.

As inactive species, a binuclear complex with a CH3 bridge between the metal and A1 center is existent (Fig. 10) [20], For the regeneration of the binuclear inactive products to the active hafnocene cations, alkyl-exchange reactions are assumed between the M-CH2-A1- unit and MAO. 

Scheme 3 Relationship between alkyl exchange and reversibility (k k )...

Beyond the well-defined substitutions of the heterocyclic ring systems, numerous other transformations have been carried out that cannot be simply classified into the substitution category. These transformations involve side chain alkylations, exchange of substituents by more sophisticated methods, or ring closures carried out on the side chains. A set of such reactions are summarized in Table 3. 

Heating peralkylated derivatives 56a in BBr3 leads selectively to the 6-bromo derivatives 56b via Br/alkyl exchange [74], Among other transformations, the reaction of 56b with the sodium salt of a thioazadiiron cluster is an example of combining main group and transition metal clusters in one molecule (56c), which provided crystals for structural characterization (Scheme 3.2-29) [75]. 

It seems very likely that the initial addition of the alkyl amine takes place at the activated N-C(2) azomethine bond and that the reaction sequence occurs in a similar way to that described in Scheme IILl. When the reactions were carried out in boiling ethanol, besides the N -phenyl-N -alkyl exchange, deethoxycarbonylation occurs. Deethoxycarbonylation is the sole reaction that takes place on treatment of 3 with r-butylamine (82JOC498). 

The investigation of the exchange of organyl gronps between varions dialkylzinc complexes, ZnR 2 and ZnR"2, has been performed by El MS. The observation of M of the mixed componnds ZnR R" confirmed that the alkyl exchange took place in the gas phase. ... 

The transition state proposed for the alkyl exchange in dialkylzinc reagents shows also many analogies with that for other alkylmetals which are dimeric in the ground state... 

Another approach for the preparation of IZnCH2l involves the alkyl exchange reaction between EtZnI (prepared from Zn metal and EtI) and CH2l2 - This method is especially useful if the reagent has to be prepared on a large scale and if Et2Zn is not a viable option. 

When treated with iodine pentafluoride, triphenylbismuthane gives triphenylbismuth difluoride but no evidence for the formation of bismuth(V) derivatives was found in the reactions with tris(4-fluorophenyl)bismuthane and tris(trifluoromethyl)bismuthane. Fluorine-aryl (or alkyl) exchange takes place in these cases instead of oxidative fluorination.139140... 

Addition of hydrogen to terminate the chains is the most important and widely used industrial process to control molecular weight. Chain transfer with organometallic compounds (cocatalysts), which is basically an alkyl exchange, can take place with titanium-based and chromium-based systems ... 

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