Kinetics and mechanism of the reactions of amine boranes with carbenium ions

被引:55
作者
Funke, MA [1 ]
Mayr, H [1 ]
机构
[1] TH DARMSTADT,INST ORGAN CHEM,D-64287 DARMSTADT,GERMANY
关键词
amine boranes; carbocations; kinetics; linear free enthalpy relationship; reductions;
D O I
10.1002/chem.19970030808
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
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 ro 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 logk(2) = 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).
引用
收藏
页码:1214 / 1222
页数:9
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