Cleavage of C(sp3)–F Bonds in Trifluoromethylarenes Using a Bis(NHC)nickel(0) Complex

The first example of the oxidative addition of a C­(sp3)–F bond in trifluoromethylarenes to a nickel(0) complex is described. A nickel(0) complex that bears two N-heterocyclic carbene (NHC) ligands of low steric demand is able to cleave C­(sp3)–F bonds of tri­fluoro­methyl­arenes to afford the corresponding trans-difluorobenzyl nickel­(II) fluoride complexes. Isolation and characterization studies suggested that the cleavage of the C­(sp3)–F bond proceeds via an η2-arene nickel(0) complex. Taking advantage of the reactivity of these nickel­(II) fluoride complexes, we developed a catalytic hydro­de­fluorination of tri­fluoro­methylarenes using hydrosilanes. A computational study indicated that the electron-rich nickel(0) center supported by two relatively small NHC ligands cleaves the C­(sp3)–F bond via a syn-SN2′ mechanism.本研究首次报道了三氟甲基芳烃（trifluoromethylarenes）中碳(sp³)-氟键与零价镍（nickel(0)）配合物发生氧化加成（oxidative addition）的首例实例。一种搭载两个位阻较低的氮杂环卡宾（N-heterocyclic carbene, NHC）配体的零价镍配合物，可断裂三氟甲基芳烃的碳(sp³)-氟键，得到相应的反式二氟苄基氟化镍(II)配合物。分离与表征研究显示，该碳(sp³)-氟键的断裂过程经由η²-芳烃零价镍配合物中间体完成。利用这类氟化镍(II)配合物的反应活性，我们开发了以氢硅烷（hydrosilanes）为还原剂的三氟甲基芳烃催化加氢脱氟（hydrodefluorination）反应体系。计算研究表明，由两个位阻较小的氮杂环卡宾配体稳定的富电子零价镍中心，通过顺式SN2'机理（syn-SN2′ mechanism）实现碳(sp³)-氟键的断裂。