Tunable Lewis Acidity of B(mdan): A Balance between Stability and Reactivity

Abstract The Lewis acidities of organoboron compounds are pivotal in determining the reactivity and selectivity of boron-based synthetic transformations. Moreover, the stability of organoboron compounds is closely linked to their Lewis acidities, which are significantly influenced by substituents such as pinacolato (pin) and naphthalene-1,8-diaminato (dan). This study introduces the adaptive nature of an untapped N,N′-dimethyl-1,8-diaminonaphthalene-substituted boron functionality, B(mdan), demonstrating its ability to modulate Lewis acidities between H–B(mdan) and Ar–B(mdan), which is unachievable with B(pin) and B(dan). Lewis acidity-diminished and thus robust H–B(mdan) is directly convertible into an array of Ar–B(mdan) upon treatment with Grignard and organolithium reagents. The resulting Ar–B(mdan) exhibits 1.5 times greater Lewis acidity and serves as sufficiently reactive carbon nucleophiles, facilitating efficient, weak base-promoted, palladium-catalyzed direct cross-coupling reactions. Deviations in Lewis acidities, arising from different substituents (mdan, pin, and dan) and organic groups (H and Ph), as well as a detailed mechanism of the key transmetalation are systematically studied through computational techniques, including ammonia affinity, deformation/interaction enthalpy, and IGMH analysis.