Scott, Neil Walter James, Ford, Mark, Schotes, Christoph et al. (2 more authors) (2019) The ubiquitous cross-coupling catalyst system ‘Pd(OAc)2’/2PPh3 forms a unique dinuclear PdI complex: an important entry point into catalytically competent cyclic Pd3 clusters. Chemical Science. pp. 1-8. ISSN 2041-6539
Abstract
Palladium(II) acetate ‘Pd(OAc)2’/nPPh3 is a ubiquitous precatalyst system for cross-coupling reactions. It is widely accepted that reduction of in situ generated trans-[Pd(OAc)2(PPh3)2] affords [Pd0(PPh3)n] and/or [Pd0(PPh3)2(OAc)]- species which undergo oxidative addition reactions with organohalides – the first committed step in cross-coupling catalytic cycles. In this paper we report for the first time that reaction of Pd3(OAc)6 with 6 equivalents of PPh3 (i.e. a Pd/PPh3 ratio of 1:2) affords a novel dinuclear PdI complex [Pd2(µ-PPh2)(µ2-OAc)(PPh3)2] as the major product, the elusive species resisting characterization until now. While unstable, the dinuclear PdI complex reacts with CH2Cl2, p-fluoroiodobenzene or 2-bromopyridine to afford Pd3 cluster complexes containing bridging halide ligands, i.e. [Pd3(X)(PPh2)2(PPh3)3]X, carrying an overall 4/3 oxidation state (at Pd). Use of 2-bromopyridine was critical in understanding that a putative 14-electron mononuclear ‘PdII(R)(X)(PPh3)’ is released on forming [Pd3(X)(PPh2)2(PPh3)3]X clusters from [Pd2(µ-PPh2)(µ2-OAc)(PPh3)2]. Altering the Pd/PPh3 ratio to 1:4 forms Pd0(PPh3)3 quantitatively. In an exemplar Suzuki-Miyaura cross-coupling reaction the importance of the ‘Pd(OAc)2’/nPPh3 ratio is demonstrated; catalytic efficacy is significantly enhanced when n = 2. Employing ‘Pd(OAc)2’/PPh3 in a 1:2 ratio leads to the generation of [Pd2(µ-PPh2)(µ2-OAc)(PPh3)2] which upon reaction with organohalides (i.e. substrate) forms a reactive Pd3 clusters species. These higher nuclearity species are the cross-coupling catalyst species, when employing a ‘Pd(OAc)2’/PPh3 of 1:2, for which there are profound implications for understanding downstream product selectivities, chemo-, regio- and stereoselectivities.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2019, The Author(s). |
Dates: |
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Institution: | The University of York |
Academic Units: | The University of York > Faculty of Sciences (York) > Chemistry (York) |
Depositing User: | Pure (York) |
Date Deposited: | 01 Aug 2019 09:50 |
Last Modified: | 21 Jan 2025 17:39 |
Published Version: | https://doi.org/10.1039/C9SC01847F |
Status: | Published |
Refereed: | Yes |
Identification Number: | 10.1039/C9SC01847F |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:149236 |
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