Abstract
The first, recyclable protocol for the selective synthesis of (E)-alkenyl boronates via borylative coupling of olefins with vinylboronic acid pinacol ester in monophasic (cat@IL) or biphasic (cat@IL/scCO2) systems is reported in this article. The efficient immobilization of [Ru(CO)Cl(H)(PCy3)2] (1 mol%) in [EMPyr][NTf2] and [BMIm][OTf] with the subsequent extraction of products with n-heptane permitted multiple reuses of the catalyst without a significant decrease in its activity and stability (up to 7 runs). Utilization of scCO2 as an extractant enabled a significant reduction in the amount of catalyst leaching during the separation process, compared to extraction with n-heptane. Such efficient catalyst immobilization allowed an intensification of the processes in terms of its productivity, which was indicated by high cumulative TON values (up to 956) in contrast to the traditional approach of applying volatile organic solvents (TON = ~50–100). The reaction was versatile to styrenes with electron-donating and withdrawing substituents and vinylcyclohexane, generating unsaturated organoboron compounds, of which synthetic utility was shown by the direct transformation of extracted products in iododeborylation and Suzuki coupling processes. All synthesized compounds were characterized using 1H, 13C NMR and GC-MS, while leaching of the catalyst was detected with ICP-MS.
Highlights
Homogeneous catalysis has remained a key part of chemistry for several decades and is a powerful tool in the synthesis of valuable compounds
Homogeneous conditions generate notable problems in recovery and reuse of catalysts, which are mostly based on expensive noble transition metals (TM), for example, rhodium, iridium, platinum, palladium, or ruthenium
Having optimized the reaction and extraction conditions in hand, we have studied a scope of olefins, mainly electron-deficient, neutral or donating styrenes, in borylative coupling with in Having optimized the reaction and extraction conditions in hand, we have studied a scope of Having optimized the reaction and extraction conditions in hand, we have studied a scope of olefins, mainly electron-deficient, neutral or donating styrenes, in borylative coupling with in olefins, mainly electron-deficient, neutral or donating styrenes, in borylative coupling with in olefins, olefins, mainly mainly electron-deficient, electron-deficient, neutral neutral or or donating donating styrenes, styrenes, in in borylative borylative coupling coupling with
Summary
Homogeneous catalysis has remained a key part of chemistry for several decades and is a powerful tool in the synthesis of valuable compounds. The high activity and selectivity of molecular catalysts under mild reaction conditions, the lack of diffusion barriers in comparison to heterogeneous systems, and the variability of their electronic and steric properties tuned by the proper design and choice of ligands and metal centers lead to their application in the chemical industry in the production of advanced polymers and fine chemicals [1,2]. Homogeneous conditions generate notable problems in recovery and reuse of catalysts, which are mostly based on expensive noble transition metals (TM), for example, rhodium, iridium, platinum, palladium, or ruthenium. Homogeneous conditions require a considerable amount of volatile organic solvent to dissolve all reaction components: reagents and catalysts. Such an approach generates problems with the process economy resulting from the high solvent consumption within the process
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