Orthopalladated phosphinite complexes as high-activity catalysts for the Suzuki reaction
| Autor: | Robin B. Bedford, Peter N. Horton, Michael B. Hursthouse, Samantha L. Hazelwood |
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| Rok vydání: | 2003 |
| Předmět: | |
| Zdroj: | Dalton Trans.. :4164-4174 |
| ISSN: | 1477-9234 1477-9226 |
| DOI: | 10.1039/b303657j |
| Popis: | The synthesis of a range of phosphinite ligands PR2(OAr) (R = Ph, iPr), their simple complexes with palladium(II) and their palladacyclic complexes has been investigated. The crystal structure of one of the palladacyclic complexes, [{Pd(μ2-Cl){κ2-P,C-PiPr2(OC6H2-2,4-tBu2)}2], has been determined. The palladacyclic complexes show extremely high activity in the Suzuki coupling of aryl bromide substrates with phenylboronic acid and can also be used with alkylboronic acid substrates. A comparison of the phosphinite-based catalysts with equivalent phosphite- and phosphine-based systems highlights their superior activity. The orthometallation of the phosphinite ligand in the pre-catalyst appears to be crucial for optimal activity. While the phosphinite palladacycles are only moderately active in the coupling of activated and non-activated aryl chloride substrates, their tricyclohexylphosphine adducts prove to be highly active in the coupling of the deactivated substrate, 4-chloroanisole. This high activity compared with other palladacyclic systems is explained in terms of catalyst longevity. The orthometallated precatalysts appear to undergo a reductive activation process to generate zerovalent active catalysts via reductive elimination of the orthometallated ring with a phenyl introduced by the boronic acid. This implies that the true active catalysts contain 2-arylated ligands. Catalysts formed with such 2-arylated ligands tend to show markedly higher activity than their parent ligands. |
| Databáze: | OpenAIRE |
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