2019
DOI: 10.1039/c9sc02342a
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Internal acidity scale and reactivity evaluation of chiral phosphoric acids with different 3,3′-substituents in Brønsted acid catalysis

Abstract: NMR H-bond analysis reveals an offset of internal and external acidities of catalysts and allows for a detailed reactivity analysis.

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Cited by 31 publications
(79 citation statements)
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“…7B), which is a typical chemical shi for protons in strong hydrogen bonds and is similar to the hydrogen bond signals in CPA$imine complexes. 13,29 The detection of magnetization transfer between the H-bond proton and both quinoline and CPA further corroborated the assignment of this hydrogen bond signal (ESI Fig. S30 ‡).…”
Section: Nmr-spectroscopic Investigation Of Catalyst Dimerizationsupporting
confidence: 59%
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“…7B), which is a typical chemical shi for protons in strong hydrogen bonds and is similar to the hydrogen bond signals in CPA$imine complexes. 13,29 The detection of magnetization transfer between the H-bond proton and both quinoline and CPA further corroborated the assignment of this hydrogen bond signal (ESI Fig. S30 ‡).…”
Section: Nmr-spectroscopic Investigation Of Catalyst Dimerizationsupporting
confidence: 59%
“…For CPA$imine systems, a correlation between hydrogen bond strength and reactivity has been observed previously, giving lower reactivities for weaker hydrogen bonds. 13 This trend is also re-ected for the monomeric and dimeric reaction pathways in the investigated quinoline systems, as the dimeric reaction pathway featuring a weaker PO À /H$N + hydrogen bond shows lower reaction rates than the monomeric pathway (Fig. 8).…”
Section: Nmr-spectroscopic Investigation Of Catalyst Dimerizationmentioning
confidence: 56%
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“…1 Extensive NMR studies of the binary complexes between different CPAs and aromatic N -arylimines proved the formation of strong, charge-assisted hydrogen bonds in these catalyst/substrate complexes, supported by a network of CH−π and π–π interactions. 35 Thus, the induced stereoselectivity stems from the noncovalent interactions. 6,7 However, for some transformations, even stronger Brønsted acids are required or at least show higher activities.…”
Section: Introductionmentioning
confidence: 99%
“…All results were compared to the previously investigated less acidic CPAs. 35,20 Finally, the internal acidity of these different classes of catalysts was correlated to the reactivity in the transfer hydrogenation. (c) In contrast to the CPAs, not only two but five possible hydrogen bond acceptors exist for the DSIs.…”
Section: Introductionmentioning
confidence: 99%