[Re(5-C5H5)(CO)3]+ Family of 17-Electron Compounds: Monomer/Dimer Equilibria an
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- 作者：Daesung Chong ; Derek R. Laws ; Ayman Nafady ; Paulo Jorge Costa ; Arnold L. Rheingold ; Maria José ; Calhorda ; William E. Geiger
- 刊名：Journal of the American Chemical Society
- 出版年：2008
- 出版时间：February 27, 2008
- 年：2008
- 卷：130
- 期：8
- 页码：2692 - 2703
- 全文大小：304K
- 年卷期：v.130,no.8(February 27, 2008)
- ISSN：1520-5126
文摘
The anodic electrochemical oxidations of ReCp(CO)3 (1, Cp = 
5-C5H5), Re(5-C5H4NH2)(CO)3(2), and ReCp*(CO)3 (3, Cp* = 5-C5Me5), have been studied in CH2Cl2 containing [NBu4][TFAB] (TFAB =[B(C6F5)4]-) as supporting electrolyte. One-electron oxidations were observed with E1/2 = 1.16, 0.79, and0.91 V vs ferrocene for 1-3, respectively. In each case, rapid dimerization of the radical cation gave thedimer dication, [Re2Cp
2(CO)6]2+ (where Cp represents a generic cyclopentadienyl ligand), which may beitself reduced cathodically back to the original 18-electron neutral complex ReCp(CO)3. DFT calculationsshow that the SOMO of 1+ is highly Re-based and hybridized to point away from the metal, thereby facilitatingthe dimerization process and other reactions of the Re(II) center. The dimers, isolated in all three cases,have long metal-metal bonds that are unsupported by bridging ligands, the bond lengths being calculatedas 3.229 Å for [Re2Cp2(CO)6]2+ (122+) and measured as 3.1097 Å for [Re2(C5H4NH2)2(CO)6]2+ (222+) byX-ray crystallography on [Re2(C5H4NH2)2(CO)6][TFAB]2. The monomer/dimer equilibrium constants arebetween Kdim = 105 M-1 and 107 M-1 for these systems, so that partial dissociation of the dimers gives amodest amount of the corresponding monomer that is free to undergo radical cation reactions. The radical1+ slowly abstracts a chlorine atom from dichloromethane to give the 18-electron complex [ReCp(CO)3Cl]+as a side product. The radical cation 1+ acts as a powerful one-electron oxidant capable of effectivelydriving outer-sphere electron-transfer reactions with reagents having potentials of up to 0.9 V vs ferrocene.
5-C5H5), Re(5-C5H4NH2)(CO)3(2), and ReCp*(CO)3 (3, Cp* = 5-C5Me5), have been studied in CH2Cl2 containing [NBu4][TFAB] (TFAB =[B(C6F5)4]-) as supporting electrolyte. One-electron oxidations were observed with E1/2 = 1.16, 0.79, and0.91 V vs ferrocene for 1-3, respectively. In each case, rapid dimerization of the radical cation gave thedimer dication, [Re2Cp2(CO)6]2+ (where Cp represents a generic cyclopentadienyl ligand), which may beitself reduced cathodically back to the original 18-electron neutral complex ReCp(CO)3. DFT calculationsshow that the SOMO of 1+ is highly Re-based and hybridized to point away from the metal, thereby facilitatingthe dimerization process and other reactions of the Re(II) center. The dimers, isolated in all three cases,have long metal-metal bonds that are unsupported by bridging ligands, the bond lengths being calculatedas 3.229 Å for [Re2Cp2(CO)6]2+ (122+) and measured as 3.1097 Å for [Re2(C5H4NH2)2(CO)6]2+ (222+) byX-ray crystallography on [Re2(C5H4NH2)2(CO)6][TFAB]2. The monomer/dimer equilibrium constants arebetween Kdim = 105 M-1 and 107 M-1 for these systems, so that partial dissociation of the dimers gives amodest amount of the corresponding monomer that is free to undergo radical cation reactions. The radical1+ slowly abstracts a chlorine atom from dichloromethane to give the 18-electron complex [ReCp(CO)3Cl]+as a side product. The radical cation 1+ acts as a powerful one-electron oxidant capable of effectivelydriving outer-sphere electron-transfer reactions with reagents having potentials of up to 0.9 V vs ferrocene.