Mechanistic Insights into Curvature and Coordination-Governed Site-Selectivity in the Multistep Diels–Alder Functionalization and Polymerization of Borospherene B ₄₀

A comprehensive density functional theory study of the Diels–Alder (DA) cycloaddition between cyclopentadiene (Cp) and borospherene B 40 is presented, in which the origin of site-selectivity and the feasibility of multistep functionalization are elucidated. By combining a curvature-based descriptor (θ p ), frontier molecular orbital analysis, and Fukui function calculations, the B[IV,IV] bond is identified as the preferred reactive site. Kinetic and thermodynamic analyses confirm that this site exhibits the lowest activation barrier and the most favorable reaction energy. Activation strain model and energy decomposition analysis further reveal that its superior reactivity arises from an optimal balance between strain and interaction energies. Successive cycloadditions are shown to readily proceed to a tetra-adduct stage. Beyond small-molecule functionalization, B 40 is demonstrated to undergo DA-based copolymerization with a bis-anthracene derivative, yielding linear polymers with intrinsic carrier separation. These findings establish borospherene as a versatile platform for selective functionalization and the design of functional materials.