Abstract
A new method for the repetitive batch silylative coupling (trans-silylation) of vinylsilanes with vinyl boronates in the presence of Ru(CO)Cl(H)(PCy3)2 immobilized in poly(ethylene glycols) (PEGs) has been developed. Three PEGs (PEG600, PEG2000, and MPEG2000) with different molecular weights and end groups (MW = 600–2000) were tested as solvents and immobilization media, while an aliphatic solvent (n-hexane or n-heptane) or supercritical CO2 was used for product extraction. By applying 2 mol % of the Ru–H catalyst, it was possible to carry out up to 15 complete runs, with the predominant formation of 1-boryl-1-silylethenes. This immobilization strategy permitted for catalyst reuse and obtaining higher TON values (approximately 660–734) compared to the reaction in conventional solvents (∼50). Detailed kinetic studies of the most effective catalytic system were performed to determine catalyst activity and stability. Moreover, the reactions were carried out in an MPEG2000/scCO2 biphasic system, positively influencing the process sustainability.
Highlights
Unsaturated derivatives of metalloids, such as boryl, silyl, stannyl, and germylsubstituted olefins, are useful intermediates in the synthesis of organic compounds with defined structures and selectivities.[1−4] Such p-block element groups attached to C sp[2] or C sp atoms can be transformed into products possessing various functionalities or used in coupling reactions (Suzuki, Hiyama, or Stille), leading to the formation of new C−C bonds.1b,2b,c,3a,5Because of their high reactivity and air and moisture stability, boryl- and silyl-substituted compounds are often the reagents of choice
Ruthenium hydride complexes Ru(CO)Cl(H)(PCy3)[2] (A) and Ru(CO)Cl(H)(PPh3)[3] (B), which have previously been reported to be the most active catalysts in silylative coupling reactions, were used in the transformations that are the subject of this study.12a,c
The results proved the possibility of conducting the silylative coupling reactions in green media such as poly(ethylene glycols) (PEGs), and positively influenced process economy by reusing the catalyst
Summary
Unsaturated derivatives of metalloids, such as boryl, silyl, stannyl, and germylsubstituted olefins, are useful intermediates in the synthesis of organic compounds with defined structures and selectivities.[1−4] Such p-block element groups attached to C sp[2] or C sp atoms can be transformed into products possessing various functionalities (e.g., halogen, amine, and carbonyl groups) or used in coupling reactions (Suzuki, Hiyama, or Stille), leading to the formation of new C−C bonds.1b,2b,c,3a,5 Because of their high reactivity and air and moisture stability, boryl- and silyl-substituted compounds are often the reagents of choice. When vinyl boronate is used as an olefin, the formation of 2-boryl-1-silylethene or 1-
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