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

Abstract

Olefin metathesis, a powerful synthetic method with numerous practical applications, can be improved by developing heterogeneous catalysts that can be recycled. In this study, a single-stage process for the entrapment of ruthenium-based catalysts was developed by the sol–gel process. System effectiveness was quantified by measuring the conversion of the ring-closing metathesis reaction of the substrate diethyl diallylmalonate and the leakage of the catalysts from the matrix. The results indicate that the nature of the precursor affects pore size and catalyst activity. Moreover, matrices prepared with tetraethoxysilane at an alkaline pH exhibit a better reaction rate than in the homogenous system under certain reaction conditions. To the best of our knowledge, this is the first study to present a one-step process that is simpler and faster than the methods reported in the literature for catalyst entrapment by the sol–gel process under standard conditions.

Dual Role of Silicon‐based Matrices in Electron Exchange Matrices for Waste Treatment

“…Solution pH during the sol‐gel process is known to affect the pore size, and therefore, it could also affect the conversion [16a–c,17,19] . Hence, EEMs were prepared at two pH values (EEMCu2/EEM2, with and without copper at pH 2 and EEMCu13/EEM13, with and without copper, at pH 13, (details are described in the Experimental Section).…”

“…Note that because the matrices contained very low amounts of copper (Table S2) its presence may have been screened by the matrix. Also, tri‐valent copper is known to be unstable, [27,33] and therefore, its binding to the matrix walls could have stabilized it, as indicated by the ΔG o values of reactions 9–9b (at pH 13, the matrices contained Si−O − groups [16a] that can bind electrostatically to the cations). Lastly, the observed electron density diverged from the typical value for the tri‐valent copper.…”

“…BET analyses reflected the tendency reported in the literature and showed that the sol‐gel particles prepared at an acidic pH have larger pore radius compared to those made under basic conditions, and at basic conditions, the surface area is larger (Figure 6). [16a,b,39] …”

“…The study comprised four main steps – Step 1 . Matrix preparation: EEMs were prepared by mixing water at different pH levels (2, 13) with TMOS using a published procedure [1g,16a,e] . After the matrix mass was stabilized, it was mixed with 100 ml of an aqueous solution of copper (1.00×10 −3 M).…”

Heterogeneous Electrocatalytic Oxygen Evolution Reaction by a Sol‐Gel Electrode with Entrapped Na3[Ru2(μ‐CO3)4]: The Effect of NaHCO3

“…Ruthenium complexes belong to one of the most diverse families of coordination compounds, in part thanks to the large number of formal oxidation states, ranging from −2 to +8, exhibited by ruthenium [47] . As such, ruthenium complexes have been used in various reactions, including a C−H bond activation reaction, [48] olefin metathesis, [49–53] and water oxidation [2,54–56] …”