Mizoroki–Heck Reaction of Aryl Halides and Dialkyl Allylphosphonates in Water Catalyzed by Reusable Palladium Nanoparticles

Abstract

Commercial [PdCl 2 (NH 3 ) 2 ]w as appliedt oc atalyze the Mizoroki-Heck coupling of aryl halides with dialkyl allylphosphonates using iPr 2 NH as the base in water under aerobic conditions. The reactionw as conducted at8 08C( for aryl iodides) or 120 8C( for aryl bromides) for 36 h, giving the correspondinga ryl-substituted allylphosphonates in good to excellent yields, and both water-soluble and insoluble aryl halidesc ould be utilized in this reaction. After extracting the reaction solution with ethyl acetate, the residual aqueous solution was reused for the same reaction several times, and the true catalystwas found to be palladium nanoparticles. In addition, ao ne-pot synthesis of 1,4-diarylbuta-1,3-dienes, which combinedt his catalytic reactionw ith the Horner-Wadsworth-Emmons-Wittig reaction, was also performed. Results and DiscussionAt the outset, iodobenzene (1a)a nd diethyl allylphosphonate (2a)w eres elected as representativer eactants for optimization of the reactionc onditions (Table 1). When [PdCl 2 (NH 3 ) 2 ]a ssociated with aw ater-soluble cationic 2,2'-bipyridyl ligand [43] [a] W.

Mono and double Mizoroki–Heck reaction of aryl halides with dialkyl vinylphosphonates using a reusable palladium catalyst under aqueous medium

“…In previous studies, we found that i Pr 2 NH is the best base to employ for the coupling of aryl halides and dialkyl allylphosphonates; 92 therefore, it was also used as the base in the Mizoroki-Heck reaction of aryl halides and dialkyl vinylphosphonate. As shown in Table 1, iodobenzene 1a (1 mmol), diethyl vinylphosphonate 2a (2 mmol), i Pr 2 NH (1.1 mmol), and PdCl 2 (NH 3 ) 2 (5 mol%) were reacted in an open-air reactor at 80 C using water (3 mL) as the solvent.…”

“…Use of this catalyst without an auxiliary ligand to fulll the Mizoroki-Heck reaction has been described previously, in which Pd nanoparticles were formed during the coupling reaction. 92 The reaction rates of vinylphosphonates were faster than those of allylphosphonates, which may be due to the electron-withdrawing phosphonate group of 2a becoming attached directly to the vinyl carbon, which lowers the p* energy level of the olen, facilitating coordination of the p bond to palladium. Then, the catalyst loading was further reduced to 0.1 mol%, resulting in 68% and 70% product yields, respectively, with a prolonged reaction time (Entries 7 and 8).…”

“…When 5i was employed, we found that the catalytic activity decayed quickly, and the formation of palladium black on the glass reactor was observed due to the higher reaction temperature (Entry 2). 92 In reuse studies for the double Mizoroki-Heck reaction, 1p and 2a were chosen as the representative reactants. Aer extracting with ethyl acetate (3 Â 3 mL), a 54% isolated yield of 6p could be still achieved in the second reuse run (Entry 3).…”