Low-Temperature <i>N</i>-Allylation of Allylic Alcohols via Synergistic Pd/Cu Catalysis: A Silica-Supported Dual-Metal-Complex Strategy
Shun-ichi Sakai, Shingo Hasegawa, Siming Ding, Ryota Osuga, Kiyotaka Nakajima, Shinji Tanaka, Wang‐Jae Chun, Ken Motokura
Abstract
N -allylation is an important method for constructing C–N bonds in fine chemical synthesis. Accumulation of catalytically active species on the same support surface is a promising approach for achieving high catalytic efficiency. In this study, we developed a catalyst comprising Pd and Cu complexes immobilized on a silica surface. The dual-metal-complex catalyst catalyzed the N -allylation of aniline using allyl alcohol at the low temperature of 30 °C with tunable selectivity toward mono- and disubstituted products. The coimmobilization of a Cu complex increased the turnover number of the Pd complex 5.3 times, which was much higher than those of reported heterogeneous catalysts used at reaction temperatures higher than 100 °C. A wide substrate scope, recyclability, and suppression of aggregation and leaching were also confirmed. Whereas synergy was scarcely observed for the simple mixture of homogeneous Pd and Cu complexes, the dual-complex catalyst exhibited significant synergy, indicating concerted catalysis on the solid surface. Spectroscopic analysis, including XAFS, in situ IR, and DNP-enhanced 15 N NMR, and density functional theory calculations indicated that an aniline molecule is activated by the Cu complex, resulting in the efficient nucleophilic attack to a π-allylpalladium intermediate.