Resolving a Sequential Post-Transition-State Bifurcation Mechanism in the Dimerization of 2,3-Diazacyclopentadienone

Area of Science:

• Organic Chemistry
• Reaction Dynamics
• Computational Chemistry

Background:

• Bifurcating reactions present challenges in product selectivity due to multiple products arising from a single transition state.
• Product selectivity in such reactions is often dictated by dynamic effects rather than transition state energetics.

Purpose of the Study:

• To investigate and report a rare instance of product selectivity in the bifurcating dimerization pathway of 2,3-diazacyclopentadienone.
• To elucidate the mechanism and driving forces behind this unprecedented selectivity.

Main Methods:

• Computational modeling of reaction pathways.
• Analysis of potential energy surfaces and transition states.
• Investigation of electronic structure and electron flow dynamics.

Main Results:

• The dimerization proceeds via a stepwise mechanism with two sequential unsymmetric bifurcations.
• Kinetic control favors an adduct via the N═N moiety through a closed-shell transition state.
• Thermodynamic control favors an adduct via the C═C moiety through a singlet biradicaloid transition state.

Conclusions:

• The study demonstrates unprecedented product selectivity in a complex bifurcating reaction landscape.
• The interplay of electronic structure and dynamic effects governs electron flow and drives selective dimerization.
• This work provides insights into controlling selectivity in complex chemical reactions.