Extremely high activity catalysts for the Suzuki coupling of aryl chlorides: the importance of catalyst longevity

Abstract

The incorporation of a new pi-acidic, orthometallated phosphite ligand into a palladium pre-catalyst gives considerably enhanced catalyst longevity and thus extremely high activity in the Suzuki coupling of deactivated, activated and sterically hindered aryl chloride substrates.

High‐Turnover Palladium Catalysts in Cross‐Coupling and Heck Chemistry: A Critical Overview

“…1.3 Â 10 5 ). [105] Recently, Bedford et al have reported on the hydrolytic instability of these complexes under typical Suzuki conditions, although the mechanistic consequences of this observation are still unclear. [106] Arylamine-palladacycles [107,108] such as 6a, b have been studied also by Bedford and co-workers.…”

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“…38 Interestingly, palladacycle 23b, which is structurally related to 23a, but in which the two non-ortho-metalated aryloxide substituents are replaced by a single salicylate residue, showed in the presence of PCy 3 extremely high activity in the Suzuki cross-coupling of deactivated, activated and sterically hindered aryl chlorides. 39 In 14,44 In 1997, Shen 45 established that a bulky and electron-rich phosphine, PCy 3 , is an effective Pd catalyst ligand for the cross-coupling of phenylboronic acid with aryl chlorides bearing electron-withdrawing groups (Scheme 3).…”

Ultra‐Low Catalyst Loading as a Concept in Economical and Sustainable Modern Chemistry: The Contribution of Ferrocenylpolyphosphane Ligands

“…As a consequence, in the last decade the progress on ligand chemistry became a major goal in the community of the organic chemist, and creativity partnered with a better understanding of the mechanistic necessities led to the emergence of several families of useful ligands for high-turnover palladium catalytic systems. For instance, and nonexhaustively: bulky electron-rich trialkylmonophosphanes, [9] (biaryl)dialkylphosphanes, [10] di-and tridentate pincers, [11] heterostructures at the origin of various palladacycles, [12,13] carbenes, [14] or multidentate polyphosphanes (Scheme 2) were found to be very efficient catalytic auxiliaries. [15] On this basis and ongoing since the mid 1990s we developed the design, synthesis, and characterization of original di-, tri-, and tetraphosphanes built on the ferrocenyl backbone (some representative examples of the library of ligands developed are depicted in Scheme 3).…”

“…[13] The difficulties encountered in the coupling of halides other than iodides has often been ascribed to their reluctance to perform the oxidative addition to palladium. Improved catalytic activities were detected from systems that combine palladium to hindered strongly σ-electron-donating ligands (such as trialkylphosphanes); in addition, the success of bulky ligands has been suggested to be derived from the ability of these ligands to promote geometrically driven coordinative unsaturation important to the transmetalation and reductive elimination steps.…”

“…After 2000, a blooming of the high-turnover palladium catalysts for the reactions of Heck, Suzuki, Stille, and Sonogashira occurred in the literature, with systems based on, for instance, ligands such as trialkylmonophosphanes, [9] modified (biaryl)dialkylphosphanes, [10] oxime palladacycles, [12] strongly π-acidic orthopalladated diarylphosphite palladacycles, [13] or carbenes [14] (respectively, a, b, c, d, and e in Scheme 2). The use of ferrocenyl diphosphanes, such as the electron-rich josiphos (k; Scheme 5) was also successful in some other low catalyst loading cross-couplings, [22] following the seminal works published by Hayashi et al for the Kumada-Corriu reaction.…”