Cycloaddition reactions via "on water" protocol reactions: A density functional theory study

Area of Science:

• Computational Chemistry
• Organic Reaction Mechanisms
• Physical Chemistry

Background:

• Reactions involving quadricyclane with azodicarboxylates (DMAD, DEAD) are known to be accelerated by water.
• The underlying mechanism for water's catalytic effect remains unclear.

Purpose of the Study:

• To elucidate the reaction mechanism of quadricyclane with DMAD and DEAD in both gas and aqueous phases.
• To understand the role of water in accelerating these cycloaddition reactions.

Main Methods:

• First-principles investigation using auxiliary density functional theory (ADFT).
• Employed generalized gradient approximation and hybrid functional approximations.
• Performed frequency analysis, reaction profile calculations, electron density analysis, and charge analysis.

Main Results:

• Optimized structures for reactants, products, and transition states were determined.
• Calculated potential energy barriers show reactions are faster in water than in the gas phase, consistent with experimental data.
• A significant change in polarity of key carbon atoms was observed during the reaction.

Conclusions:

• Water stabilizes the transition states of these reactions, leading to a lower activation energy barrier.
• The water-molecule framework plays a crucial role in the reaction mechanism and energetics of DMAD and DEAD cycloaddition reactions with quadricyclane.