Fukuzumi Shunichi, Ohkubo Kei, Okamoto Toshihiko
Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
J Am Chem Soc. 2002 Nov 27;124(47):14147-55. doi: 10.1021/ja026417h.
Rates of Diels-Alder cycloaddition of anthracenes with p-benzoquinone and its derivatives as well as rates of hydride-transfer reactions from 10-methyl-9,10-dihydroacridine to the same series of p-benzoquinones are accelerated significantly in the presence of metal ions in acetonitrile. An extensive comparison of the catalytic effects of metal ions in electron transfer from one-electron reductants (cobalt tetraphenylporphyrin and decamethylferrocene) to p-benzoquinones with those in the Diels-Alder reactions of the quinones as well as the hydride-transfer reactions has revealed that the catalysis of metal ions in each case is ascribed to the 1:1 and 1:2 complexes formed between the corresponding semiquinone radical anions and metal ions. The transient absorption and ESR spectra of the semiquinone radical anion-metal ion complexes are detected directly in the electron-transfer reduction of p-benzoquinone derivatives in the presence of metal ions. The catalytic reactivities of a variety of metal ions in each reaction are well correlated with the energy splitting values of pi(g) levels because of the complex formation between O(2)(.-) and M(n+), which are derived from the g(zz) values of the ESR spectra of the O(2)(.-)-M(n+) complex.
在乙腈中，金属离子存在下，蒽与对苯醌及其衍生物的狄尔斯-阿尔德环加成反应速率以及从10-甲基-9,10-二氢吖啶到同一系列对苯醌的氢化物转移反应速率都显著加快。对金属离子在从单电子还原剂（四苯基钴卟啉和十甲基二茂铁）到对苯醌的电子转移中的催化作用，与醌的狄尔斯-阿尔德反应以及氢化物转移反应中的催化作用进行了广泛比较，结果表明，在每种情况下，金属离子的催化作用都归因于相应的半醌自由基阴离子与金属离子形成的1:1和1:2配合物。在金属离子存在下，对苯醌衍生物的电子转移还原过程中直接检测到了半醌自由基阴离子-金属离子配合物的瞬态吸收光谱和电子自旋共振光谱。由于O(2)(.-)与M(n+)之间形成配合物，各种金属离子在每个反应中的催化活性与π(g)能级的能量分裂值密切相关，这些值来自O(2)(.-)-M(n+)配合物的电子自旋共振光谱的g(zz)值。
