Transfer hydrogenation is widely practised across all segments of chemical industry, yet its application to aryl halide reductive cross-coupling is undeveloped because of competing hydrogenolysis. Here, exploiting the distinct reactivity of Pd^I species, an efficient catalytic system for the reductive cross-coupling of activated aryl bromides with aryl iodides via formate-mediated hydrogen transfer is described. These processes display orthogonality with respect to Suzuki and Buchwald–Hartwig couplings, as pinacol boronates and anilines are tolerated and, owing to the intervention of chelated intermediates, are effective for challenging 2-pyridyl systems. Experimental and computational studies corroborate a unique catalytic cycle for reductive cross-coupling where the Pd^I precatalyst, [Pd(I)(P^tBu₃)]₂, is converted to the dianionic species, [Pd₂I₄][NBu₄]₂, from which aryl halide oxidative addition is more facile. Rapid, reversible Pd-to-Pd transmetallation delivers mixtures of iodide-bridged homo- and hetero-diarylpalladium dimers. The hetero-diarylpalladium dimers are more stable and have lower barriers to reductive elimination, promoting high levels of cross-selectivity.

转移氢化在化学工业的所有领域都得到了广泛应用，但由于竞争性氢解，它在芳基卤化物还原交叉偶联中的应用尚未得到发展。在这里，利用 Pd 物种的不同反应性，描述了一种通过甲酸盐介导的氢转移实现活性芳基溴与芳基碘化物还原交叉偶联的高效催化系统。这些过程显示出与 Suzuki 和 Buchwald-Hartwig 偶联的正交性，因为频哪醇硼酸盐和苯胺是耐受的，并且由于螯合中间体的干预，对具有挑战性的 2-吡啶基系统有效。实验和计算研究证实了还原交叉偶联的独特催化循环，其中 Pd 预催化剂 [Pd（I）（P^tBu₃）]₂ 转化为二离子物质 [Pd₂I₄][NBu₄]₂，芳基卤化物氧化加成更容易。快速、可逆的 Pd-to-Pd 转金属得到碘化物桥的同元和异元二元钞二聚体的混合物。异二芳基钞二聚体更稳定，还原消除障碍更低，促进高水平的交叉选择性。