Ladderenes as Covalently Condensed Acetylene: A DFT Investigation of Gold(I)-Catalyzed Mechanism, Substituent Effects and Energy Storage Potential.

Ladderenes, unique polymers composed of fused cyclobutane rings, exhibit promising properties for energy storage applications, including reversible redox behavior and structural tunability. This density functional theory (DFT) study investigates the formation of ladderenes via gold(I)-catalyzed alkyne-alkene coupling reactions. Our calculations reveal a step-wise chain propagation mechanism where the alkene product of each step reacts with a ligand-gold-alkyne complex, leading to the sequential addition of cyclobutene units. We demonstrate that electron-withdrawing substituents on the alkynes, such as chlorine, facilitate the dissociation of the gold catalyst (PMeAu) from the cyclobutene adduct, enhancing catalytic efficiency. Solvent effects are also shown to significantly influence the reaction energetics. This finding highlights the significant impact of alkyne substitution on the catalytic cycle. The inherent exothermicity of ladderene formation, coupled with their unique structural features, suggests their potential for storing energy in the form of "covalently condensed acetylene".