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Electron-Rich Trialkyl-Type Dihydro-KITPHOS Monophosphines: Efficient Ligands for Palladium-Catalyzed Suzuki–Miyaura Cross-Coupling. Comparison with Their Biaryl-Like KITPHOS Monophosphine Counterparts

Lookup NU author(s): Dr Simon Doherty, Dr Julian Knight, Nicholas Ward, Dr Corinne Wills, Emeritus Professor William McFarlane, Emeritus Professor Bill Clegg, Dr Ross Harrington

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Abstract

The Diels-Alder cycloaddition between dicyclohexylvinylphosphine oxide and anthracene or 9-methylanthracene affords the bulky electron-rich trialkyl-type dihydro-KITPHOS monophosphines 11-(dicyclohexylphosphinoyl)-12-phenyl-9,10-dihydro-9,10-ethenoanthracene and 11-(dicyclohexylphosphinoyl)-9-methyl-12-phenyl-9,10-dihydro-9,10-ethenoanthracene, respectively, after reduction of the corresponding oxide. Both phosphines are highly air-sensitive and rapidly oxidize on silica-gel during purification but have been isolated as air-stable cyclometalated palladium precatalysts of the type [Pd{k2-N2′,C1-2-(2′-NH2C6H4)C6H4}Cl(L)]. Both palladium precatalysts form highly active systems for the Suzuki-Miyaura cross-coupling of a range of aryl chlorides with aryl boronic acids, giving the desired products in good to excellent yield under mild conditions and a catalyst loading of 0.25 mol%. A comparison of the performance of catalysts based on dihydro-KITPHOS monophosphines against their first-generation biaryl-like KITPHOS counterparts revealed that the latter are consistently more efficient for the vast majority of substrate combinations examined, albeit by only a relatively small margin in some cases. This, together with the greater air-stability and ease of handling of biaryl-like KITPHOS monophosphines, renders them more practical ligands for palladium-based cross-coupling. The steric parameters of both classes of KITPHOS monophosphine and a selection of electron-rich biaryl monophosphines have been quantified using a combination of Solid-G to determine the percentage of the metal coordination sphere shielded by the phosphine (the G-parameter), and Salerno molecular buried volume calculations (SambVca) to determine the percent buried volume (%Vbur); the corresponding Tolman cone angles have also been determined from correlations and the relative merits of the two approaches discussed. The electronic properties of these phosphines have also been investigated using DFT to calculate the A1 n(CO) frequency in LNi(CO)3 (B3LYP/6-31G(2d,p)[LanL2DZ on Ni]); and the resulting computed electronic parameters (CEP) were used to estimate the corresponding experimental Tolman electronic parameters (TEP).


Publication metadata

Author(s): Doherty S, Knight JG, Ward NAB, Bittner DM, Wills C, McFarlane W, Clegg W, Harrington RW

Publication type: Article

Publication status: Published

Journal: Organometallics

Year: 2013

Volume: 32

Issue: 6

Pages: 1773-1788

Print publication date: 20/02/2013

ISSN (print): 0276-7333

ISSN (electronic): 1520-6041

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/om3011992

DOI: 10.1021/om3011992


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