How Electrophilic Are Cobalt Carbonyl Stabilized Propargylium Ions?
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- 作者：Oliver Kuhn ; Doris Rau ; and Herbert Mayr
- 刊名：Journal of the American Chemical Society
- 出版年：1998
- 出版时间：February 11, 1998
- 年：1998
- 卷：120
- 期：5
- 页码：900 - 907
- 全文大小：189K
- 年卷期：v.120,no.5(February 11, 1998)
- ISSN：1520-5126
文摘
The kinetics of the reactions of dicobalt-coordinatedpropargyl cations with 
-nucleophiles (e.g.,allylsilanes) and hydride donors (e.g., trialkylsilanes) have beenstudied conductometrically and/or photometrically. The reactions follow second-order kinetics withrate-determining CC-bond formation or hydridetransfer. It is found that phenyl and trimethylsilyl substituentsin the propargyl cation moiety reduce theelectrophilic reactivities of these cations by less than a factor of10. The electrophilicity is reduced by afactor of more than 105, however, when one CO ligand isreplaced by PPh3 (3a 
3e).The reactions of thedicobalt-coordinated propargyl cations with allylsilanes and-stannanes, silylated enol ethers and ketene actetals,and hydride donors (R3SiH, R3SnH)follow the linear free enthalpy relationship log k =s(E + N), whichallows one to calculate electrophilicity parameters E forthese carbocations and to rationalize their syntheticpotential.
-nucleophiles (e.g.,allylsilanes) and hydride donors (e.g., trialkylsilanes) have beenstudied conductometrically and/or photometrically. The reactions follow second-order kinetics withrate-determining CC-bond formation or hydridetransfer. It is found that phenyl and trimethylsilyl substituentsin the propargyl cation moiety reduce theelectrophilic reactivities of these cations by less than a factor of10. The electrophilicity is reduced by afactor of more than 105, however, when one CO ligand isreplaced by PPh3 (3a 3e).The reactions of thedicobalt-coordinated propargyl cations with allylsilanes and-stannanes, silylated enol ethers and ketene actetals,and hydride donors (R3SiH, R3SnH)follow the linear free enthalpy relationship log k =s(E + N), whichallows one to calculate electrophilicity parameters E forthese carbocations and to rationalize their syntheticpotential.