Carboxyl Graphene as a Superior Support for Bulky Ruthenium-Based Olefin Metathesis Catalyst

Abstract

A Hoveyda-type catalyst decorated with two quaternary ammonium tags was synthesized and noncovalently grafted on SiO2, SBA-15, and on carboxyl graphene. A comparative study showed that the efficiency of the dual-anchored heterogeneous catalysts was highly dependent on the properties of the supporting material with graphene outperforming silicate supports. The graphene-immobilized complex exhibited excellent efficiency reflected in turnover numbers obtained in ring-closing metathesis and in self-metathesis of 1-decene. Importantly, the solid-supported catalyst assured increased recyclability with no ruthenium leaching as confirmed by inductively coupled plasma mass spectrometry.

Advanced sol–gel process for efficient heterogeneous ring-closing metathesis

“…The control results of pore volumes shown that matrices prepared with TEOS had higher pore volumes than those prepared with TMOS, and exhibit better activity, Figures S4 and 3, respectively. Our results are in agreement with those of previous reports on the binding of these catalysts to other solid supports 34 , 37 . Pastva et al 34 and Kaczanowska et al 37 reported that heterogeneous catalyst activity tended to increase with the increase in the pore size of the support used for catalyst entrapment.…”

“…1 , A-C catalysts. We expected the quaternary ammonium group in the type 2 catalysts to strongly (but not covalently) bind to the silica surface by adsorption, probably via electrostatic bonds with the silanol groups and/or the oxides on the surface of the sol–gel matrix 34 , 35 , 37 , 67 . This bond should decrease catalyst leakage, even during a metathesis reaction conducted in a polar solvent.…”

“…When type 2 catalysts were entrapped in sol–gel matrices, the leakage of the catalyst from the matrix was significantly improved, and higher conversion rates were obtained, compared to these of type 1 catalysts in table S1 . The leakage improvement could be due to binding of the quaternary ammonium group, in the type 2 catalysts, to the silica surface by adsorption, probably via electrostatic bonds with the silanol groups and/or the oxides on the surface of the sol–gel matrix 34 , 35 , 37 , 67 . Another indication that catalysts A-C bind to the matrix—i.e., become entrapped within it, thus limiting their leakage – can be found in the surface area results.…”

“…One is to fix the ruthenium-based catalysts to a support material, such as mesoporous silica, using the catalyst ion ligand (for example, see catalysts A-C in Fig. 1 ) 34 – 37 . Another way is to use the sol–gel process.…”

SBA-15 as a Support for Effective Olefin Metathesis Catalysts

“…Especially in hybrid catalysts prepared by immobilization of well-defined Mo and Ru carbenes, these properties have proved particularly useful. Although some Ru carbenes have also been immobilized on other materials such as Metal-Organic Framework MOF [84], graphene [85,86], glass, wool, and paper [87], the data reported so far show that SBA-15 is the most promising support for effective, stable, and widely applicable catalysts.…”