Investigation on the mechanism of water-assisted palladium-catalyzed benzylic C–H amination by N-fluorobenzenesulfonimide
作者:Yiying Zheng、Tao Xiong、Yunhe Lv、Jingping Zhang、Qian Zhang
DOI:10.1039/c3ob41299g
日期:——
A combination of computational and experimental methods was carried out to elucidate the mechanism of palladium-catalyzed water-assisted benzylic CâH amination with N-fluorobenzenesulfonimide (NFSI), which involved the oxidative addition of PdII to PdIV-species as a rate-limiting step, followed by water-assisted concerted metalationâdeprotonation (CMD) of the PdIV complex and water-assisted reductive elimination (RE) processes, and then a nucleophilic addition process to generate the final product and complete the catalytic cycle. The stability of the PdIV complex could be ascribed to the suitable ligands with strong Ï-donors and resistance to decomposition, as well as being sufficiently bulky because the water-clusters assembled the ligands through hydrogen bonds to act as one multidentate ligand. Calculation results suggested that water also plays a crucial role as a proton transferring bridge in water-assisted CMD and RE processes. The corresponding experimental findings substantiate the expectation. Additionally, NFSI was found to act as both the oxidant and the nitrogen source to facilitate the reaction, while the steric effect of the bulky âN(SO2Ph)2 group contributed to circumventing the o-CâH amination. In this reaction, we investigated a novel spiro-cyclopalladation intermediate, formed by the reaction of the PdIV centre with pristine-carbon instead of ortho-carbon, which might be valuable for our understanding and further development of transition metal catalyzed CâH functionalization.
研究人员结合计算和实验方法,阐明了钯催化水辅助苄基CâH与N-氟苯磺酰亚胺(NFSI)胺化反应的机理,其中涉及PdII与PdIV-物种的氧化加成作为限速步骤、随后是 PdIV 复合物的水辅助协同金属化去质子化(CMD)和水辅助还原消除(RE)过程,然后是亲核加成过程,生成最终产物并完成催化循环。PdIV 复合物的稳定性可归因于合适的配体具有强Ï-捐赠者和抗分解性,同时由于水团通过氢键将配体组装成一个多同位配体,因此具有足够的体积。计算结果表明,水在水辅助的 CMD 和 RE 过程中还扮演着质子传递桥的重要角色。相应的实验结果证实了这一预期。此外,我们还发现 NFSI 同时作为氧化剂和氮源促进了反应的进行,而笨重的âN(SO2Ph)2 基团的立体效应则有助于规避 o-CâH 氨化反应。在这一反应中,我们研究了一种新型螺环钯化中间体,它是由 PdIV 中心与棱碳而不是正碳反应形成的,这对于我们理解和进一步开发过渡金属催化的 CâH 功能化可能很有价值。