Department Chemie, Ludwig-Maximilians-Universität München , Butenandtstraße 5-13 (Haus F), 81377 München, Germany.
J Am Chem Soc. 2014 Oct 1;136(39):13863-73. doi: 10.1021/ja507598y. Epub 2014 Sep 19.
The kinetics of the hydride abstractions by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) from 13 C-H hydride donors (acyclic 1,4-dienes, cyclohexa-1,4-dienes, dihydropyridines), tributylstannane, triphenylstannane, and five borane complexes (amine-boranes, carbene-boranes) have been studied photometrically in dichloromethane solution at 20 °C. Analysis of the resulting second-order rate constants by the correlation log k2(20 °C) = sN(E + N) ( J. Am. Chem. Soc. 2001 , 123 , 9500 ) showed that the hydride abstractions from the C-H donors on one side and the Sn-H and B-H hydride donors on the other follow separate correlations, indicating different mechanisms for the two reaction series. The interpretation that the C-H donors transfer hydrogen to the carbonyl oxygen of DDQ while Sn-H and B-H hydride donors transfer hydride to a cyano-substituted carbon of DDQ is supported by quantum-chemical intrinsic reaction coordinate calculations and isotope labeling experiments of the reactions of D8-cyclohexa-1,4-diene, Bu3SnD, and pyridine·BD3 with 2,5-dichloro-p-benzoquinone. The second-order rate constants of the reactions of tributylstannane with different quinones correlate linearly with the electrophilicity parameters E of the quinones, which have previously been derived from the reactions of quinones with π-nucleophiles. The fact that the reactions of Bu3SnH with quinones and benzhydrylium ions are on the same log k2 vs E (electrophilicity) correlation shows that both reaction series proceed by the same mechanism and illustrates the general significance of the reactivity parameters E, N, and sN for predicting rates of polar organic reactions.
2,3-二氯-5,6-二氰对苯醌（DDQ）从 13C-H 供氢体（无环 1,4-二烯、环己-1,4-二烯、二氢吡啶）、三丁基锡烷、三苯基锡烷和五个硼烷配合物（胺硼烷、卡宾硼烷）中提取氢化物的动力学已在 20°C 的二氯甲烷溶液中通过光度法进行了研究。通过关联 log k2(20°C) = sN(E + N) ( J. Am. Chem. Soc. 2001, 123, 9500 )对得到的二级速率常数进行分析表明，从 C-H 供体一侧和 Sn-H 和 B-H 供体一侧提取氢化物遵循单独的关联，表明这两个反应系列具有不同的机制。C-H 供体将氢转移到 DDQ 的羰基氧，而 Sn-H 和 B-H 供体将氢转移到 DDQ 的氰基取代碳的解释得到了量子化学本征反应坐标计算和 D8-环己-1,4-二烯、Bu3SnD 和吡啶·BD3 与 2,5-二氯对苯醌反应的同位素标记实验的支持。三丁基锡烷与不同醌的反应的二级速率常数与醌的亲电性参数 E 呈线性相关，亲电性参数 E 先前是从醌与π-亲核试剂的反应中得出的。Bu3SnH 与醌和苯甲鎓离子的反应处于相同的 log k2 与 E（亲电性）相关表明，这两个反应系列通过相同的机制进行，并说明了反应性参数 E、N 和 sN 用于预测极性有机反应速率的普遍意义。
