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Orthopalladated phosphinite complexes as high-activity catalysts for the Suzuki reaction

Orthopalladated phosphinite complexes as high-activity catalysts for the Suzuki reaction
Orthopalladated phosphinite complexes as high-activity catalysts for the Suzuki reaction
The synthesis of a range of phosphinite ligands PR2(OAr) (R=Ph, Pr-i), their simple complexes with palladium(II) and their palladacyclic complexes has been investigated. The crystal structure of one of the palladacyclic complexes, [{Pd(mu2-Cl){kappa(2)-P, C-(PPr2)-Pr-i(OC6H2-2,4-Bu-t(2))}(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.
cross-coupling reactions, palladium catalysts, aryl chlorides, c-c, ligand, transformations, palladacycles, amination, mechanism, pd-0
0300-9246
4164-4174
Bedford, Robin B.
42532c45-cb80-48cd-9e93-8c2d5059eabe
Hazelwood (née Welch), Samantha L.
d9a04fa7-74c4-49f8-a6df-421b8dfdd745
Horton, Peter N.
154c8930-bfc3-495b-ad4a-8a278d5da3a5
Hursthouse, Michael B.
57a2ddf9-b1b3-4f38-bfe9-ef2f526388da
Bedford, Robin B.
42532c45-cb80-48cd-9e93-8c2d5059eabe
Hazelwood (née Welch), Samantha L.
d9a04fa7-74c4-49f8-a6df-421b8dfdd745
Horton, Peter N.
154c8930-bfc3-495b-ad4a-8a278d5da3a5
Hursthouse, Michael B.
57a2ddf9-b1b3-4f38-bfe9-ef2f526388da

Bedford, Robin B., Hazelwood (née Welch), Samantha L., Horton, Peter N. and Hursthouse, Michael B. (2003) Orthopalladated phosphinite complexes as high-activity catalysts for the Suzuki reaction. Dalton Transactions, (21), 4164-4174. (doi:10.1039/b303657j).

Record type: Article

Abstract

The synthesis of a range of phosphinite ligands PR2(OAr) (R=Ph, Pr-i), their simple complexes with palladium(II) and their palladacyclic complexes has been investigated. The crystal structure of one of the palladacyclic complexes, [{Pd(mu2-Cl){kappa(2)-P, C-(PPr2)-Pr-i(OC6H2-2,4-Bu-t(2))}(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.

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More information

Published date: 2003
Keywords: cross-coupling reactions, palladium catalysts, aryl chlorides, c-c, ligand, transformations, palladacycles, amination, mechanism, pd-0

Identifiers

Local EPrints ID: 19904
URI: https://eprints.soton.ac.uk/id/eprint/19904
ISSN: 0300-9246
PURE UUID: b3174c5c-e3db-4dc2-9bb8-08bf25075ad9
ORCID for Peter N. Horton: ORCID iD orcid.org/0000-0001-8886-2016

Catalogue record

Date deposited: 22 Feb 2006
Last modified: 06 Jun 2018 12:52

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