Palladium-Catalyzed C−C Coupling under Thermomorphic Conditions

Bergbreiter, David E.; Osburn, Philip L.; Wilson, and Allan; Sink, Erin M.

doi:10.1021/ja001708g

Cited by 280 publications

(164 citation statements)

References 49 publications

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“…[223] Immobilization of these pincer complexes on polyacrylamides allowed reaction under thermomorphic conditions. [224] P,C,P Pd(II) pincer complexes were also immobilized on silica, and achieved TONs of ca. 3,000 in the Heck coupling of iodobenzene with acrylates, with some recyclability.…”

Section: Scope and Synthetic Applicationsmentioning

confidence: 99%

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

2004

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This review discusses the problems associated with developing high-turnover catalysts for the cross-coupling and Heck reactions. New developments in the area, principally constituted by palladacycles and coordinatively unsaturated Pd catalysts featuring bulky phosphanes of high donicity, are reviewed from a mechanistic and synthetic standpoint, and compared with more traditional catalysts obtained from conventional mono-and polydentate Nand P-based ligands, as well as Pd catalysts without strong ligands, such as Pd colloids or heterogeneous catalysts. Carbene ligands are also briefly presented. Whereas a single, most promising approach to highturnover Pd catalysis cannot presently be defined, it is clear that the new "PdL 1 " catalysts (where L 1 is a monodentate bulky P ligand of high donicity) represent the latest, most important development in Pd research, certainly from the standpoint of scope and probably also from the standpoint of efficiency. High turnovers with these catalysts have been described and their use will certainly increase in the next few years. The review ends with a brief discussion containing practical considerations on how to choose a high TON catalyst for a given Heck or cross-coupling reaction of interest.

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Section: Scope and Synthetic Applicationsmentioning

confidence: 99%

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

2004

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“…[40] PNIPAM-based catalysts show good activities, high stability after several recycling runs and only little catalyst loss by phase separation. [38,40] On the other hand, it has to be questioned if it is reasonable to use these complicated and presumably expensive catalysts when, perhaps, classical catalysts would also operate using the concept of the UCST. This question will be discussed in Section 6.…”

Section: Thermoregulated Phase-transfer Catalystsmentioning

confidence: 99%

Thermoregulated Liquid/Liquid Catalyst Separation and Recycling

2006

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Considerable effort has been done to overcome the loss of catalyst in homogeneously catalysed processes. In this contribution we describe five recycling concepts for thermoregulated catalyst separation and recycling: fluorous biphasic systems (FBS), thermoregulated phase transfer catalysis (TRPTC), soluble polymer-based catalysis, thermoregulated microemulsions and temperature-dependent multicomponent solvent systems (TMS). Each of these concepts has its own special advantages like low catalyst leaching or simple process engineering but also drawbacks like usage of expensive special solvents or complex and expensive catalysts. In this context, TMS systems exhibit most advantages of the other concepts combined with the possibility to use common and cheap solvents as well as numerous classical molecular catalysts. Therefore, TMS systems are expected to be one of the most promising thermomorphic recycling concepts for industrial scale.

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“…[15] PNODAM-SCS (22) In 30 mL of tert-butanol, PNODAM-NASI 21 (300 mg, 0.089 mmol) was dissolved. Separately, amine-terminated SCS ligand 51…”

Section: Pnodam-nasimentioning

confidence: 99%

Mechanistic Studies of SCS-Pd Complexes Used in Heck Catalysis

Bergbreiter

Osburn

Frels

2005

Advanced Synthesis & Catalysis

150

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Air-stable SCS palladacycles that can be used to promote C À C coupling chemistry were studied mechanistically. Using a small library of electronically varied SCS ligands, a collection of palladacycles was synthesized. Kinetic studies showed that these complexes all had induction periods, induction periods that were effected by concentration of substrates, products and trace impurities. Hammet correlations showed that electronically diverse palladacycles had identical 1 values, values that suggested that aryl halide electrophilic addition to a Pd species was not the rate-determining step. Phosphine addition experiments led to increased reactivity of the starting palladacycles, possibly by trapping an in situ generated Pd(0) species. Studies that examined reactivity in biphasic thermomorphic reactions showed residual activity in phases that do not contain polymer-bound palladacycle and provided convincing evidence that palladacycles are not the actual catalyst. Poisoning experiments using mercury metal to test for the presence of a Pd colloid were very effective with low molecular weight palladacycles, completely suppressing Heck chemistry. Similar studies with polymer-bound palladacycles showed mercury poisoning too. However, since so little decomposition of the palladacycle occurred, the polymer-bound palladacycle could still be recycled multiple times. However, mercury poisoned subsequent cycles of the experiment too. The conclusion is that SCS palladacycles are actually reservoirs of a catalytically active but ill-defined form of palladium(0).

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Palladium-Catalyzed C−C Coupling under Thermomorphic Conditions

Cited by 280 publications

References 49 publications

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

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

Thermoregulated Liquid/Liquid Catalyst Separation and Recycling

Mechanistic Studies of SCS-Pd Complexes Used in Heck Catalysis

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