The Sixteen CB11HnMe12-n- Anions with Fivefold Substitution Symmetry: Anodic Oxidation and Electro
详细信息 查看全文
- 作者：Benjamin T. King ; Stefanie Kö ; rbe ; Peter J. Schreiber ; Joshua Clayton ; Adriana Nmcová ; Zdenk Havlas ; Kamesh Vyakaranam ; Matthew G. Fete ; Ilya Zharov ; Jason Ceremuga ; Josef Michl
- 刊名：Journal of the American Chemical Society
- 出版年：2007
- 出版时间：October 31, 2007
- 年：2007
- 卷：129
- 期：43
- 页码：12960 - 12980
- 全文大小：476K
- 年卷期：v.129,no.43(October 31, 2007)
- ISSN：1520-5126
文摘
The 15 symmetrically methylated derivatives of the CB11H12- anion (1a) have been synthesizedand found to vary greatly in ease of oxidation. Cyclic voltammetry in liquid SO2 yielded fully reversibleoxidation potentials for five of those that have no adjacent unsubstituted vertices in positions 7-12; threeothers showed some indication of reversibility. The anions 1a-16a and the Jahn-Teller distorted neutralradicals 1r-16r have been characterized by ab initio and density functional theory calculations. In thestate average CASSCF(13,12)/6-31+G* approximation, the ground state potential energy surface of 1rcontains five symmetry-related pairs of minima. The computational results account for the reversible redoxpotentials very well when the solvent is included explicitly (RI-DFT(BP)/TZVP, COSMO). For display andfor a semiquantitative understanding of methyl substituent effects in terms of perturbation theory, themolecular orbitals of 1a have been expressed in the symmetry-adapted cluster basis. The results serve asan underpinning for a set of additive empirical increments for redox potential prediction. Relative to theusual hydrogen standard, a single methyl group facilitates oxidation by approximately 50, 70, 70, and 10mV in positions 1, 2, 7, and 12, respectively. This electron donor effect on the redox potential is due to a contribution, whereas those of (inductive and direct field) type are negligible.