An efficient Pd–NHC catalyst system in situ generated from Na₂PdCl₄ and PEG-functionalized imidazolium salts for Mizoroki–Heck reactions in water

Abstract

Three PEG-functionalized imidazolium salts L1–L3 were designed and prepared from commercially available materials via a simple method. Their corresponding water soluble Pd–NHC catalysts, in situ generated from the imidazolium salts L1–L3 and Na2PdCl4 in water, showed impressive catalytic activity for aqueous Mizoroki–Heck reactions. The kinetic study revealed that the Pd catalyst derived from the imidazolium salt L1, bearing a pyridine-2-methyl substituent at the N3 atom of the imidazole ring, showed the best catalytic activity. Under the optimal conditions, a wide range of substituted alkenes were achieved in good to excellent yields from various aryl bromides and alkenes with the catalyst TON of up to 10,000.

Olefination with Sulfonyl Halides and Esters: E‐Selective Synthesis of Alkenes from Semistabilized Carbanion Precursors

“…13 C NMR (100 MHz, CDCl 3 ): δ = 137.3, 134.8, 133.7, 133.0, 129.0, 128.72, 128.69, 128.3, 128.0, 127.66, 127.64, 126.61, 126.5, 126.3, 125.9, 123.5 ppm. The 1 H and 13 C NMR spectra were consistent with reported data …”

Water-soluble SNS cationic palladium(II) complexes and their Suzuki–Miyaura cross-coupling reactions in aqueous medium

“…This has been achieved via microwave heating [ 7 – 15 ], ultrasonication [ 16 – 18 ], ligand-free methodologies [ 19 – 25 ] and the use of water-soluble palladium pre-catalysts/catalysts [ 26 – 30 ]. The latter is the preferred choice since it allows for the reusability of the catalyst for subsequent reactions after simple phase separation [ 31 ]. However, the commonly employed phosphorous and carbene ligand-based palladium(II) complexes are found to be in most cases sensitive to moisture and air limiting the scope of their catalytic application in aqueous reactions [ 32 – 33 ].…”