One‐Pot Desilylation/Dimerization of Terminal Alkynes by Ruthenium and Acid‐Promoted (RAP) Catalysis

Abstract

The dimerization of terminal arylalkynes promoted by the (p-cymene)ruthenium dichloride dimer/acetic acid system {[RuCl 2 A C H T U N G T R E N N U N G (p-cymene)] 2 / AcOH} can be performed starting from the trimethylsilylethynyl derivatives (12 substrates), deprotected in situ, to afford 1,4-disubstituted 1-en-3-ynes with high regio-and (E)-stereoselectivity, at room temperature. The extension of this unprecedented two-reaction sequence to a diyne substrate affords a fluorene-based conjugated oligomer. The reaction mixture resulting from the desylilation-dimerization process dimerizes additional aliquots of phenylacetylene. The one-pot protocol results in shorter reaction times due to the presence of acetate salts which increase the concentration of active catalytic species, in which the acetate ligand acts as base toward the bound alkyne. The ruthenium source is transformed into a new trihapto-hexa-1,3-dien-5-yn-3-yl complex, formed by metal-assisted coupling of the enyne product and the terminal alkyne, and still maintaining catalytic activity. Selectivity, endurance, medium and functional group compatibility are the key features of the catalytic system obtained from the p-cymene ruthenium dimer under the one-pot conditions.

Kinetics and Mechanistic Insights into the Acetate-Assisted Dimerization of Terminal Alkynes under Ruthenium- and Acid-Promoted (RAP) Catalysis

“…It can therefore reenter the catalytic cycle, though with poor efficiency. One likely pathway for the formation of 10 involves π coordination of the enyne 5a through the internal triple bond and insertion into an acetylide–ruthenium bond, as an effect of product competition for the catalytic species . The molecule is analogous to the corresponding m -trifluoromethyl complex isolated after the one-pot desilylation/dimerization of m -CF 3 C 6 H 4 CCSiMe 3 catalyzed by 1 .…”

“…Under analogous conditions, aromatic diynes can be transformed into polyaddition oligomers or polymers, as fluorescent materials soluble in organic solvents (Chart ). , The robustness of the catalytic system based on 1 in AcOH allows for the C–C coupling process to be performed in one pot after desylilation of (trimethylsilyl)­arylacetylene substrates (Me 3 SiCCAr) under either basic or acidic conditions . Moreover, the hexamethylbenzene ruthenium dimer [{RuCl­(μ-Cl)­(η 6 -C 6 Me 6 )} 2 ] ( 2 ) promotes the synthesis of enynes with high efficiency and trans selectivity in the mixed aqueous medium AcOH/H 2 O …”

“…Interestingly, during the course of these studies it was observed that the presence of acetate salts in the reaction mixture provided significant rate enhancements. , This evidence might account for the generation of acetate ruthenium complexes, which are presumably involved as catalytic intermediates facilitating the coupling process. Similarly, in the field of palladium- or ruthenium-catalyzed arylation or alkylation of substituted arenes, a base-assisted deprotonation of the C–H bond has been recognized to be crucial in the formation of active cyclometalated intermediates .…”

Recent Advances in Activation of Silicon Bonds by Fluoride Ion / Jaunākie Sasniegumi Silīcija Saišu Aktivācijās Ar Fluorīda Jonu

“…2) acid hydrolysis Protiodesilylation of alkynylsilanes in the presence of fluoride ion recently was described in some works [38][39][40]. Thus, treatment of trimethylsilylarylethynes 29 in with 1.1 equivalent of Bu 4 NF afforded alkynes 30 (Scheme 13) [38].…”

“…2) acid hydrolysis Protiodesilylation of alkynylsilanes in the presence of fluoride ion recently was described in some works [38][39][40]. Thus, treatment of trimethylsilylarylethynes 29 in with 1.1 equivalent of Bu 4 NF afforded alkynes 30 (Scheme 13) [38]. Interestingly, that treatment of alkynes R L R S CHCHRC≡CSiMe 3 with fluoride ion, followed by hydrogenation in the presence of Lindlar catalyst, leads to formation of alkenes R L R S C(OH)CHR-CH=CH 2 [40].…”