Delaney Connor P, Lin Eva, Huang Qinan, Yu Isaac F, Rao Guodong, Tao Lizhi, Jed Ana, Fantasia Serena M, Püntener Kurt A, Britt R David, Hartwig John F
College of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA.
Department of Chemistry, University of California, Davis, Davis, CA 95616, USA.
Science. 2023 Sep 8;381(6662):1079-1085. doi: 10.1126/science.adi9226. Epub 2023 Sep 7.
Copper complexes are widely used in the synthesis of fine chemicals and materials to catalyze couplings of heteroatom nucleophiles with aryl halides. We show that cross-couplings catalyzed by some of the most active catalysts occur by a mechanism not previously considered. Copper(II) [Cu(II)] complexes of oxalamide ligands catalyze Ullmann coupling to form the C-O bond in aryl ethers by concerted oxidative addition of an aryl halide to Cu(II) to form a high-valent species that is stabilized by radical character on the oxalamide ligand. This mechanism diverges from those involving Cu(I) and Cu(III) intermediates that have been posited for other Ullmann-type couplings. The stability of the Cu(II) state leads to high turnover numbers, >1000 for the coupling of phenoxide with aryl chloride electrophiles, as well as an ability to run the reactions in air.
铜配合物广泛用于精细化学品和材料的合成中，以催化杂原子亲核试剂与芳基卤化物的偶联反应。我们发现，一些活性最高的催化剂所催化的交叉偶联反应是通过一种以前未被考虑的机制发生的。草酰胺配体的铜（II）[Cu（II）]配合物催化乌尔曼偶联反应，通过芳基卤化物与Cu（II）的协同氧化加成形成高价物种，该高价物种通过草酰胺配体上的自由基特性得以稳定，从而在芳基醚中形成C-O键。这种机制与其他乌尔曼型偶联反应中涉及Cu（I）和Cu（III）中间体的机制不同。Cu（II）状态的稳定性导致了高的周转数，对于酚盐与芳基氯亲电试剂的偶联反应，周转数>1000，并且能够在空气中进行反应。
