A Waste‐Minimized Approach to Cassar‐Heck Reaction Based on POLITAG‐Pd0 Heterogeneous Catalyst and Recoverable Acetonitrile Azeotrope. Issue 16 (22nd July 2021)

• Record Type: Journal Article
• Authors: Valentini, Federica; Ferlin, Francesco; Tomarelli, Elena; Mahmoudi, Hamed; Bagherzadeh, Mojtaba; Calamante, Massimo; Vaccaro, Luigi
• Is Part Of: ChemSusChem. Volume 14:Issue 16(2021)
• Page Start: 3359
• Page End: 3366
• Publication Date: 2021-07-22
• Subjects: azeotrope -- C−C coupling -- Cassar-Heck -- polymer-supported catalyst -- waste minimization; Green chemistry -- Periodicals; Sustainable engineering -- Periodicals; Chemistry -- Periodicals; Chemical engineering -- Periodicals; 660
• DOI: 10.1002/cssc.202101052
• Languages: English
• ISSNs: 1864-5631

Abstract

Abstract: Three different Pd 0 ‐based heterogeneous catalysts were developed and tested in the Cassar–Heck reaction (i. e., copper‐free Sonogashira reaction) aiming at the definition of a waste minimized protocol. The cross‐linked polymeric supports used in this investigation were designed to be adequate for different reaction media and were decorated with different pincer‐type ionic ligands having the role of stabilizing the formation and dimension of palladium nanoparticles. Among the ionic tags tested, bis‐imidazolium showed the best performances in terms of efficiency and durability of the metal catalytic system. Eventually, aqueous acetonitrile azeotrope was selected as the reaction medium as it allowed the best catalytic efficiency combined with easy recovery and reuse. Finally, the synergy between the selected catalyst and reaction medium allowed to obtain highly satisfactory isolated yields of a variety of substrates while using a low amount of metal catalyst. The high performance of the designed POLymeric Ionic TAG (POLITAG)‐Pd 0, along with its good selectivity achieved in a copper‐free process, also led to a simplified purification procedure allowing the minimization of the waste generated as also proven by the very low E‐factor values (1.4–5) associated. Abstract : Waste not : The Cassar‐Heck reaction affords the synthesis of different alkynyl compounds in high isolated yields and low E‐factor values in a waste‐minimized protocol. The careful selection of POLITAG‐Pd 0 (POLymeric Ionic TAG) catalyst and the reaction medium lead to high turnover number (43500) and turnover frequency (2806 h −1 ) values. Most importantly, with the optimized protocol, the Eniluracil API intermediate was synthetized in high yield.