Chiral phanephos derived catalysts and their application in asymmetric catalysis

Konrad, Tina Maria

doi:10.17630/10023-4499

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“…Since even palladium nanoparticles in the presence of Phanephos ligands and acids have been shown to promote methoxycarbonylation with similarly good e.r. , it is reasonable to assume that various different precatalyst formulations can lead to an active catalyst of the type [Pd(H)(X)(P^P)]. Such species have been used in other computational studies on the mechanism of alkoxycarbonylation or hydroxycarbonylation of other alkenes.…”

Section: Resultsmentioning

confidence: 99%

“…4a Furthermore, palladium dihalides are known to react with acids to form Pd-hydride species [Pd(H)(X)(P^P)]. 32 Since even palladium nanoparticles in the presence of Phanephos ligands and acids have been shown to promote methoxycarbonylation with similarly good e.r., 33 symmetry, leading to four inequivalent quadrants (Figure 2 and Table S3). The structure of Phanephos (Figure 2) is interesting due to the rigidity of the paracyclophane backbone and its proximity to the pseudo-axial aryl rings on the phosphorous atoms, thus hindering free rotation around the P-aryl bond.…”

Section: Methodsmentioning

confidence: 99%

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Understanding Catalyst Structure–Selectivity Relationships in Pd-Catalyzed Enantioselective Methoxycarbonylation of Styrene

et al. 2020

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Catalyst-controlled regioselectivity in palladium-catalyzed carbonylation of alkenes has been a long-standing goal of homogeneous catalysis. In general, monophosphines do favor branched regioselectivity, but lead to poor enantioselectivity, while diphosphines give mainly linear products. Previously, we reported the simultaneous control of regio-and enantioselectivity in the hydroxy-and methoxycarbonylation of vinyl arenes with Pd complexes of the Phanephos ligand. Herein, we present a density functional theory study (B3PW91-D3 level of theory) of the catalytic cycle, supported by deuterium labeling studies, to understand its mechanism. Alkene coordination to a Pd-hydride species was identified as the origin of asymmetric induction and regioselectivity in both the parent Pd/Xylyl-Phanephos catalyst and electron-deficient analogue, and rationalized according to a quadrant-diagram representation. The mechanism by which the preferentially formed pro-(S) Pd-alkene complex can isomerize via rotation around the palladium-(C=C) bond was investigated. In the parent system, this process is in competition with the methanolysis step that leads to the ester product, and is responsible for the overall loss of regioselectivity. On the other hand, the introduction of electron-withdrawing substituents on the catalyst framework results in the reduction of the methanolysis barriers, making the isomerization pathway energetically unfavorable and so leading simultaneously to high regiocontrol and good enantiomeric ratios. ASSOCIATED CONTENT Supporting InformationThe Supporting Information is available free of charge on the ACS Publications website.Computational details, 2 H and 13 C NMR spectra, deuterium labeling studies (PDF)Cartesian coordinates, electronic energies, zero-point energies, enthalpies, T×S, Gibbs free energies, basis set superposition energies (a.u.), imaginary frequencies (XYZ)

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%