Reactions That Generate Aromatic Molecules: Is Aromatic Stabilization Less or More Advanced than Bond Changes at the Transition State? Kinetic and Thermodynamic Acidities of Rhenium Carbene Complexes
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- 作者：Claude F. Bernasconi ; Mark L. Ragains ; and Santanu Bhattacharya
- 刊名：Journal of the American Chemical Society
- 出版年：2003
- 出版时间：October 8, 2003
- 年：2003
- 卷：125
- 期：40
- 页码：12328 - 12336
- 全文大小：231K
- 年卷期：v.125,no.40(October 8, 2003)
- ISSN：1520-5126
文摘
A kinetic study of the reversible deprotonation of the rhenium carbene complexes 1H+(O), 1H+(S) and 2H+(O) by carboxylate ions, primary aliphatic and secondary alicyclic amines, water and OH- in50% MeCN-50% water (v/v) at 25 
C is reported. These carbene complexes are of special interest becausein their deprotonated form they represent derivatives of the aromatic heterocycles furan, thiophene andbenzofuran. Intrinsic rate constants (ko for 
lta.gif" BORDER=0 >G = 0) determined from appropriate Br
lash.gif">nsted plots for theserhenium carbene complexes and for the corresponding selenophene (1H+(Se)) and benzothiophene (2H+(S)) derivatives investigated earlier follow the orders furan < selenophene < thiophene and benzofuran 
lsim.gif">benzothiophene. These orders indicate that an increase in aromaticity leads to an increase in the intrinsicrate constant or a decrease in the intrinsic barrier. This is an unexpected result; it implies that, in contrastto common resonance effects, the development of aromaticity at the transition state is ahead of protontransfer, i.e., the percentage development of the aromatic stabilization energy at the transition state ishigher than the percentage of proton transfer.
C is reported. These carbene complexes are of special interest becausein their deprotonated form they represent derivatives of the aromatic heterocycles furan, thiophene andbenzofuran. Intrinsic rate constants (ko for lta.gif" BORDER=0 >G = 0) determined from appropriate Brlash.gif">nsted plots for theserhenium carbene complexes and for the corresponding selenophene (1H+(Se)) and benzothiophene (2H+(S)) derivatives investigated earlier follow the orders furan < selenophene < thiophene and benzofuran lsim.gif">benzothiophene. These orders indicate that an increase in aromaticity leads to an increase in the intrinsicrate constant or a decrease in the intrinsic barrier. This is an unexpected result; it implies that, in contrastto common resonance effects, the development of aromaticity at the transition state is ahead of protontransfer, i.e., the percentage development of the aromatic stabilization energy at the transition state ishigher than the percentage of proton transfer.