Inorganic Bergman Cyclization: An Appeal From Theory

Area of Science:

• Computational Chemistry
• Organic Synthesis
• Inorganic Chemistry

Background:

• The Bergman cyclization is a key reaction in organic synthesis, involving the transformation of enediynes into reactive 1,4-didehydrobenzenes (para-benzyne).
• Understanding and controlling the activation energy of this reaction is crucial for its synthetic applications.
• Previous studies have primarily focused on carbon-based enediyne systems.

Purpose of the Study:

• To computationally explore the Bergman cyclization of inorganic boron-nitrogen (B,N) substituted derivatives.
• To investigate the effect of B,N substitution on the reaction's activation barrier and transition state polarity.
• To characterize the electronic properties and bonding nature of the resulting products.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model the Bergman cyclization.
• Analysis of natural charge distribution and electron delocalization was performed.
• Transition state structures and activation energies were computed for parent and B,N substituted analogues.

Main Results:

• B,N substitution introduced polarity into the transition state, significantly lowering the activation barrier.
• Single B,N substitution at terminal positions reduced the activation barrier by approximately 50%.
• A complete B,N analogue exhibited an even lower activation barrier and a shift from biradical to zwitterionic character in the product, with reduced electron delocalization.

Conclusions:

• The Bergman cyclization scope can be expanded to inorganic B,N systems, offering a novel pathway for reaction modification.
• Inorganic substitution provides an effective strategy to tune the energetics and electronic properties of the Bergman cyclization.
• These findings open new avenues for designing reactive intermediates with tailored characteristics.