ISSN:
0947-6539
Keywords:
amine boranes
;
carbocations
;
kinetics
;
linear free enthalpy relationship
;
reductions
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The kinetics of the reactions of trialkylamine boranes and pyridine boranes with benzhydryl cations have been determined photometrically. Second-order rate laws are obeyed, first-order with respect to amine borane concentration and first-order with respect to carbocation concentration. As for other reactions of carbocations with neutral nucleophiles, the rates of these reactions are only slightly affected by solvent polarity. The structure - reactivity relationships and kinetic isotope effects are in accord with a polar mechanism proceeding through a transition state where the migrating hydride is partly bound to the entering carbon and to the leaving boron atom. The rate constants correlate linearly with the electrophilicity parameters E of the carbenium ions. It is therefore possible to use the linear free enthalpy relationship logk2 = s(E+N) for determining nucleophilicity parameters N for the amine boranes and to compare their hydride-donating abilities with those of other non-charged hydride donors (silanes, germanes, stannanes, and dihydropyridines).
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.19970030808
