A Robust, Moisture- and Air-Stable Phosphine Mono-Ylide Palladacycle Precatalyst: A Simple and Highly Efficient System for Mizoroki–Heck Reactions

Abstract

A palladacycle phosphine mono-ylide complex was identified as an efficient catalyst system for the Mizoroki-Heck cross-coupling reactions of aromatic or aliphatic olefins with a variety of aryl bromides and chlorides, including those containing electron-donating or electron-withdrawing substituents. The reactions, which proceeded in moderate to excellent yields, required relatively low loadings of palladium (10 ppm) and were performed under aerobic conditions. High catalyst activities with turnover frequencies of up to 20,000 h -1 were observed at 130°C.The palladium-catalyzed arylation of olefins, known as the Heck cross-coupling reaction, is one of the most versatile tools for forming carbon-carbon bonds. 1-6 Tolerance to a wide spectrum of functional groups in both substrates makes this reaction very useful in total syntheses. Historically, palladium complexes with phosphine ligands have been widely used to catalyze these reactions. 7-10 The phosphine ligands act as stabilizers for catalytically active palladium(0) complexes that are generated in situ. Palladium complexes with bulky and strongly electrondonating trialkylphosphines are favored for carboncarbon coupling of aryl halides with styrene; 11,12 however, diphosphine ligands, because of their chelating effects, generally shows better coordination ability in stabilizing active palladium species in the catalytic cycle. Among the existing catalysts for these reactions, the most effective are homogeneous palladium-ligand systems. [13][14][15][16][17][18][19] The efficiency of a Heck reactions is greatly dependent on the reactivity of the palladacycle catalyst precursors. It is well established that palladacycle complexes containing phosphine ligands that combine both good donor strength and π-accepting capacity have high catalytic activities in Heck cross-coupling reactions. 20-22 Over the past ten years, we have studied phosphorus ylides and their palladium complexes, 23-28 and we have used some of these complexes in carbon-carbon coupling reactions. [29][30] Here, we describe the use of precatalyst 1 to promote the Mizoroki-Heck coupling reaction of aryl bromides or chlorides with olefins (Scheme 1). The reaction proceeds smoothly with deactivated aryl bromides or activated aryl chlorides and it gives good yields at low palladium loadings under aerobic conditions.The catalyst precursor 1 used for the Mizoroki-Heck cross-coupling reaction was prepared in high yield by reaction of 1-biphenyl-4-yl-2-[[(diphenylphosphino)-methyl](phenyl)phosphino]ethanone with dichloro(cyclooctadienyl)palladium in a 1:1 molar ratio at room temperature. 31The palladium-catalyzed Mizoroki-Heck reaction is among the most important carbon-carbon bond-forming processes for the vinylation of aryl or vinyl halides. As a result, considerable effort has been made to develop new and improved protocols for the Heck coupling reaction since the pivotal discovery of the reaction by Heck and Mizoroki in the early 1970s. [32][33][34][35] Many palladium phosphine complexes have been used as c...

C(sp2)–C(sp2) cross coupling reaction catalyzed by a palladacycle phosphine complex: A simple and sustainable protocol in aqueous media

“…54 By comparison, it can be seen that this Pd complex has displayed some outstanding superiority as catalyst such as green condition, low catalyst loading and short reaction times. Considering table 5, it is obvious that this Pd complex (entry 1) has shown good catalytic activity for the Heck coupling reaction in the presence of 0.001 mol% catalyst in green optimized condition compared to the other catalysts (0.002-1 mol%) (entries 2-6), [48][49][50][51][52] 53 reported previously. The activity of our catalyst in Heck coupling reactions is significantly improved.…”

“…The described Pd(II) catalyst was observed to be stable and showed high catalyst activity in Heck cross-coupling reactions in water/DMF (2 mL, 1:1) and water/NMP (2 mL, 1:1) solvent systems for styrene and ethyl acrylate, respectively. In comparison with previously reported catalysts, 48 the salient features of the proposed catalyst include high efficiency and simplicity, which leads to short reaction time, high yields and a cleaner reaction profile.…”

“…On the whole, it can be seen that results obtained by using this Pd complex in most Heck reactions are similar to or slightly better than those of related bidentate chelating Pd complexes. [48][49][50][51][52][53] The advantages associated with this complex is the freedom to easily modulate electronic and steric properties simply by changing (i) the size of metallocyclic ring, (ii) the nature of metallated carbon (aliphatic and/or aromatic groups), (iii) the type of donor group (C-, P-, S-, O-, N-coordinated) and (iv) the nature of the ligands (halides and bidentate ligands).…”

Phosphonium salts and P-ylides

“…Prof. Sabounchei's group reported several studies on the synthesis of complexes from a-keto-stabilised phosphorus ylides as mono and bidentate ligands. In particular, they focused on palladacycle complexes as catalysts for Mizoroki-Heck reactions 296 and Suzuki/Heck couplings. 297 The preparation of seven-membered Pd(II) complexes bearing symmetric bidentate phosphorus ylides was also remarkable.…”

Pallada‐ and platinacycle complexes of phosphorus ylides; synthesis, X‐ray characterization, theoretical and electrochemical studies and application of Pd(II) complexes as catalyst in Suzuki‐Miyaura coupling reaction

“…Pd(II) complexes bearing phosphine groups have been extensively applied as efficient catalysts in some cross‐coupling reactions . Specifically, the Suzuki‐Miyaura reaction which emerged as the most important and reliable method for construction of functionalized biaryl, have been catalysed with the P, C‐chelated Pd(II) complexes of such phosphorus ylides . Recently, it was reported a variety of catalytic systems for the Suzuki‐Miyaura coupling reaction using mixed aqueous media .…”