Effects of Mesopore Internal Surfaces on the Structure of Immobilized Pd-Bisphosphine Complexes Analyzed by Variable-Temperature XAFS and Their Catalytic Performances

Ken Motokura,Marika Ikeda,Takuma Fukuda,Yohei Uemura,Daiju Matsumura,Masayuki Nambo,Wang-Jae Chun

doi:10.3390/catal8030106

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 σ2static 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.

Highlights

Mesoporous silica is an ideal support material for the preparation of highly active catalysts because of its high surface area, inert nature of silica, and functionalization ability [1,2,3,4,5,6,7,8,9,10]
For SiO2 /PdCl(η3 -allyl)]2 (Pd)(η -allyl)Cl]2 and a bisphosphine ligand (PP-Pd) compared to Mesoporous silica (MS)/PP-Pd in the range from 100 to 20 K. These results indicate that the contribution of σdynamic to SiO2 /PP-Pd is smaller than that to MS/PP-Pd
The effect of the support morphology on the attached Pd complex was evaluated by variable-temperature XAFS analysis

Summary

Introduction

Mesoporous silica is an ideal support material for the preparation of highly active catalysts because of its high surface area, inert nature of silica, and functionalization ability [1,2,3,4,5,6,7,8,9,10]. Despite the frequent use of silane-coupling reactions in the functionalization of mesoporous silica materials, it is still a challenge to obtain a detailed analysis of the effect that the internal surface curvature of mesoporous silica has on the structure of the immobilized functionality. This difficulty is mainly due to the generally weak interaction between the silica surface and the immobilized function, as well as their remote location with reference to one another. Catalysts 2018, 8, 106 static and dynamic disorders, i.e., σ2 = σ2 static + σ2 dynamic , the variable-temperature XAFS analysis of the supported Pd complex should reveal the contributions of these two functions. The catalytic activities of the supported catalysts were evaluated using the Suzuki-Miyaura coupling reaction as a typical Pd-catalyzed reaction

Results and Discussion

Synthetic route to catalysts

20 K suggests σ2static offrom

Variable-Temperature XAFS Measurements

Suzuki-Miyaura Cross Coupling Reaction

Conclusions