Abstract
A series of unsymmetrical palladacycles have been synthesised and evaluated as catalysts in aldol and vinyl epoxide coupling chemistry.
Highlights
Pincer palladacycles, where a tridentate ligand can coordinate to palladium were first synthesized by Shaw and Moulton in 1976.2 the field of palladacycle-mediated catalysis only truly gathered momentum after the seminal discovery by Herrmann and Beller et al.[3,4] that their eponymous palladacycle (Fig. 1) was highly active in catalytic C–C bond coupling reactions
Given some distinct advantages of employing unsymmetrical pincer palladacycles in catalytic applications,[17] such as the tandem catalysis reported by Szabó et al.[27] recent work in our group has focused on a robust synthetic route to useful, modular unsymmetrical ligands and their pincer palladacycles.[29]
It was found that Pd(dppf )Cl2 (Pd-118) was the catalyst of choice utilising microwave-mediated (MW) synthesis (Table 1, entry 4)
Summary
Palladacycles contain a covalent Pd–C bond intramolecularly stabilised by a coordinating group such as an amine, phosphine or thioether and have been extensively studied since their discovery in the mid-1960s.1 Pincer palladacycles, where a tridentate ligand can coordinate to palladium were first synthesized by Shaw and Moulton in 1976.2 the field of palladacycle-mediated catalysis only truly gathered momentum after the seminal discovery by Herrmann and Beller et al.[3,4] that their eponymous palladacycle (Fig. 1) was highly active in catalytic C–C bond coupling reactions. The synthesis of NCN pincers can be complicated compared with the analogous PCP and SCS pincers due to the hardligand (amine) soft-acid (metal) mismatch between palladium and nitrogen This results in competition in forming the kinetic product III or the thermodynamic pincer product IV (Scheme 1).[21] incorporating functional groups in the mutual ortho position such as SiMe3 or Br can be beneficial in their synthesis, compared with C–H activation routes.[8]. Given some distinct advantages of employing unsymmetrical pincer palladacycles in catalytic applications,[17] such as the tandem catalysis reported by Szabó et al.[27] recent work in our group has focused on a robust synthetic route to useful, modular unsymmetrical ligands and their pincer palladacycles.[29] The present work is focused on the synthesis of several new unsymmetrical nitrogen-based pincer ligands, denoted NCN′, their respective palladacycles, phosphinite PCN pincer palladacycles, and catalytic evaluation in aldol condensation and vinyl epoxide coupling reactions in comparison to a related SCN pincer palladacycle
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
