Internal acidity scale and reactivity evaluation of chiral phosphoric acids with different 3,3'-substituents in Bronsted acid catalysis.

ABSTRACT: The concept of hydrogen bonding for enhancing substrate binding and controlling selectivity and reactivity is central in catalysis. However, the properties of these key hydrogen bonds and their catalyst-dependent variations are extremely difficult to determine directly by experiments. Here, for the first time the hydrogen bond properties of a whole series of BINOL-derived chiral phosphoric acid (CPA) catalysts in their substrate complexes with various imines were investigated to derive the influence of different 3,3'-substituents on the acidity and reactivity. NMR 1H and 15N chemical shifts and 1 J NH coupling constants of these hydrogen bonds were used to establish an internal acidity scale corroborated by calculations. Deviations from calculated external acidities reveal the importance o

SUBMITTER: Rothermel K 

PROVIDER: S-EPMC6977555 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature