Electron-Transfer-Induced Geometrical Isomerization of the Dinitrile Complexes cis-[Re(NCR)2(Ph2PCH2CH2PPh2)2][BF4]
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- 作者：M. Fá ; tima C. Guedes da Silva ; Joã ; o J. R. Fraú ; sto da Silva ; Armando J. L. Pombeiro ; Christian Amatore ; and Jean-Noë ; l Verpeaux
- 刊名：Inorganic Chemistry
- 出版年：1998
- 出版时间：May 18, 1998
- 年：1998
- 卷：37
- 期：10
- 页码：2344 - 2350
- 全文大小：115K
- 年卷期：v.37,no.10(May 18, 1998)
- ISSN：1520-510X
文摘
In an aprotic medium and at a Pt electrode,cis- andtrans-[Re(NCR)2(Ph2PCH2CH2PPh2)2]+(cis+ andtrans+,respectively; R = aryl or alkyl) undergo two successivesingle-electron oxidations to form the 17-electron(cis2+or trans2+) and 16-electron(cis3+ or trans3+)derivatives. The cis3+ complexesisomerize to the correspondingtrans3+ complexes which undergo a slowerdecomposition reaction, and the rate constants(ki3+ andkdec, respectively)have been determined by kinetic analysis of the cyclic voltammetricbehavior. For the aromatic nitrile complexes,both rate constants increase with the electron-withdrawing ability(Hammett's 
p constant) of R. The ratiosofthe isomeric equilibrium constants (cis3+ 
trans3+, cis2+ trans2+, and cis+ trans+), for the aromatic nitrilecomplexes, also increase with p, the thermodynamic gainin favor of the trans isomer is much higher upon thefirst oxidation than upon the second one, and it decreases with theincrease of p (higher sensitivity of theenergyof the HOMO of the trans isomers to the electronic effect of R).For the alkyl cyanide complexes, steric effectsplay a dominant role on their thermodynamic and kinetic behaviors, byshifting anodically the oxidation potentialand enhancing the isomerization rate. The significance of thosesystems in terms of developing a "molecularhysteresis" behavior is also discussed.
p constant) of R. The ratiosofthe isomeric equilibrium constants (cis3+ trans3+, cis2+ trans2+, and cis+ trans+), for the aromatic nitrilecomplexes, also increase with p, the thermodynamic gainin favor of the trans isomer is much higher upon thefirst oxidation than upon the second one, and it decreases with theincrease of p (higher sensitivity of theenergyof the HOMO of the trans isomers to the electronic effect of R).For the alkyl cyanide complexes, steric effectsplay a dominant role on their thermodynamic and kinetic behaviors, byshifting anodically the oxidation potentialand enhancing the isomerization rate. The significance of thosesystems in terms of developing a "molecularhysteresis" behavior is also discussed.