The surface of mesoporous silica was modified with a Pd–bisphosphine complex and/or a tertiary amine group for concerted acceleration of allylation reactions. Mesoporous‐silica‐supported catalysts with a 1.6 nm pore diameter showed higher performance than nonporous or larger mesoporous silica‐supported catalysts owing to the accumulation of active sites into a confined space. For the case in which allyl alcohol was used in the reaction, the presence of a silanol group on the surface was quite effective: the turnover number of Pd was nine times greater than that of the homogeneous Pd complex.

Although allylation using allylic alcohol is an environmentally‐friendly method because of water being the sole byproduct in such reactions, allylic alcohol is one of the most difficult allylating agents in Pd‐catalyzed allylation of nucleophiles. In this study, we successfully developed a mesoporous silica‐supported Pd complex as an efficient catalyst for the allylation of nucleophiles using allylic alcohols as allylating agents. The allylic alcohol is activated by the silanol group on the support surface, which easily undergoes a π‐allylpalladium intermediate formation. The catalytic activity of the supported Pd complex was ca. 9 times higher than that of its homogeneous precursor Pd complex. A highest turnover number of 4500 based on Pd was achieved. Various nucleophiles and allylic alcohol derivatives could be used as substrates. Not only the detailed catalyst structure but also the reaction mechanism including the concerted activation of allylic alcohol by the Pd complex and silanol were investigated by several spectroscopic techniques, such as Pd K‐edge XAFS, solid‐state NMR, and in‐situ FT‐IR measurements.

A concise synthesis of new oxy-tethered ruthenium complexes effective for the asymmetric transfer hydrogenation of aromatic ketones is described. The oxy-tether was constructed via a defluorinative etherification arising from an intramolecular nucleophilic substitution of a perfluorinated phenylsulfonyl substituent. The obtained tethered complexes exhibited desirable catalytic activity and selectivity, especially in the asymmetric transfer hydrogenation of functionalized aromatic ketones. The robustness and rigidity of the tether contribute to their superior catalytic performance relative to the nontethered prototype complex.

Abstract:In this study, mesoporous and nonporous silica-supported Pd complexes were synthesized and characterized. Variable-temperature XAFS measurements and a curve-fitting analysis showed a slightly larger contribution of σ 2 static when the Pd complexes were on a nonporous support in comparison to a mesoporous support. In contrast, the catalytic performance of the attached Pd complex in the Suzuki-Miyaura cross-coupling reaction was not affected by such small differences in the static disorder of the Pd complex.

The front cover artwork for issue 20/2018 is provided by Dr. Ken Motokura at Tokyo Institute of Technology (Japan) and collaborators. The image illustrates the concerted catalysis of a Pd complex and silanol on a mesoporous silica surface for the efficient activation of allylic alcohol in the allylation of nucleophiles. See the Full Paper itself at https://doi.org/10.1002/cctc.201801097.