A Supramolecular Model for the Co-Catalytic Role of Nitro Compounds in Brønsted Acid Catalyzed Reactions.

Nitro compounds are known to change reaction rates and kinetic concentration dependence of Brønsted-acid-catalyzed reactions. Yet, no mechanistic model exists to account for these observations. In this work, an atomistic model for the catalytically active form for an alcohol dehydroazidation reaction is presented, which is generated by DFT calculations and consists of an H-bonded aggregate of two molecules of Brønsted acid and two molecules of nitro compound.

Ground-State Chemical Reactivity under Vibrational Coupling to the Vacuum Electromagnetic Field.

The ground-state deprotection of a simple alkynylsilane is studied under vibrational strong coupling to the zero-point fluctuations, or vacuum electromagnetic field, of a resonant IR microfluidic cavity. The reaction rate decreased by a factor of up to 5.5 when the Si-C vibrational stretching modes of the reactant were strongly coupled.

Nitro-Assisted Brønsted Acid Catalysis: Application to a Challenging Catalytic Azidation.

A cocatalytic effect of nitro compounds is described for the B(C6F5)3·H2O catalyzed azidation of tertiary aliphatic alcohols, enabling catalyst turnover for the first time and with a broad range of substrates. Kinetic investigations into this surprising effect reveal that nitro compounds induce a switch from first order concentration dependence in Brønsted acid to second order concentration dependence in Brønsted acid and second order dependence in the nitro compounds. Kinetic, electronic, and spectroscopic evidence suggests that higher order hydrogen-bonded aggregates of nitro compounds and acids are the kinetically competent Brønsted acid catalysts.

Breaking the dichotomy of reactivity vs. chemoselectivity in catalytic S(N)1 reactions of alcohols.

The inability to decouple Lewis acid catalysis from undesirable Brønsted acid catalysed side reactions when water or other protic functional groups are necessarily present has forced chemists to choose between powerful but harsh catalysts or poor but mild ones, a dichotomy that restricts the substrate scope of dehydrative transformations such as the direct SN1 reaction of alcohols. A systematic survey of Lewis and Brønsted acids reveals that the strong non-hydrolyzable Lewis acid B(C6F5)3 leads to highly chemoselective alcohol substitution in the presence of acid-sensitive alkenes, protecting groups and other functional groups without the typical compromise in reaction rates, substrate scope and catalyst loading.