Heitz Drew R, Tellis John C, Molander Gary A
Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.
J Am Chem Soc. 2016 Oct 5;138(39):12715-12718. doi: 10.1021/jacs.6b04789. Epub 2016 Sep 21.
An iridium photocatalyst and visible light facilitate a room temperature, nickel-catalyzed coupling of (hetero)aryl bromides with activated α-heterosubstituted or benzylic C(sp)-H bonds. Mechanistic investigations on this unprecedented transformation have uncovered the possibility of an unexpected mechanism hypothesized to involve a Ni-Br homolysis event from an excited-state nickel complex. The resultant bromine radical is thought to abstract weak C(sp)-H bonds to generate reactive alkyl radicals that can be engaged in Ni-catalyzed arylation. Evidence suggests that the iridium photocatalyst facilitates nickel excitation and bromine radical generation via triplet-triplet energy transfer.
铱光催化剂和可见光促进了室温下镍催化的（杂）芳基溴化物与活化的α-杂取代或苄基C(sp)-H键的偶联反应。对这一前所未有的转化过程的机理研究揭示了一种意想不到的机理的可能性，该机理推测涉及激发态镍络合物的Ni-Br均裂事件。由此产生的溴自由基被认为会夺取弱的C(sp)-H键以生成可参与镍催化芳基化反应的活性烷基自由基。有证据表明，铱光催化剂通过三重态-三重态能量转移促进镍的激发和溴自由基的产生。
