Computationally Unravelling the Mechanism and Selectivity of Five and
Six membered N-Heterocyclic Carbene- Catalyzed Alkyne
Hydrochalcogenation
Abstract
The present work is intended to bring to the forefront a relatively less
explored area of N-Heterocyclic Carbene (NHC) catalyzed alkyne hydro-
thiolation and selenation reactions. The present work can be regarded as
the first ever computational investigation on the catalytic activity of
the NHC catalyzed hydro- thiolation and selenation reactions by
exploring the reaction mechanism. Reaction mechanism involves
chalcogenol activation followed by alkyne insertion and the second step
is found to be the rate determining step. A comparison with the reported
uncatalyzed gas phase reaction showed that a simple imidazol-2-ylidene
catalyst can lower the free energy barrier by 19.62 and 14.63 kcal/mol
respectively for acetylene hydro- thiolation and selenation reaction.
All the employed NHCs are proved to be better catalyst for both
hydrothiolation and hydroselenation. Effects of factors such as changing
the heterocycle, increasing the conjugation, ring expansion and
electronic/steric substitution were also investigated. Effect of solvent
polarity on the reaction energetics and selectivity has also been
analyzed employing THF, DMSO and MeOH as the solvents.