Metal–Ligand Cooperativity of the Calix[4]pyrrolato Aluminate: Triggerable C−C Bond Formation and Rate Control in Catalysis

Metal‐ligand cooperativity (MLC) had a remarkable impact on transition metal chemistry and catalysis. By use of the calix[4]pyrrolato aluminate, [1](−), which features a square‐planar Al(III), we transfer this concept into the p‐block and fully elucidate its mechanisms by experiment and theory. Complementary to transition metal‐based MLC (aromatization upon substrate binding), substrate binding in [1](−) occurs by dearomatization of the ligand. The aluminate trapps carbonyls by the formation of C−C and Al−O bonds, but the products maintain full reversibility and outstanding dynamic exchange rates. Remarkably, the C−C bonds can be formed or cleaved by the addition or removal of lithium cations, permitting unprecedented control over the system's constitutional state. Moreover, the metal‐ligand cooperative substrate interaction allows to twist the kinetics of catalytic hydroboration reactions in a unique sense. Ultimately, this work describes the evolution of an anti‐van't Hoff/Le Bel species from their being as a structural curiosity to their application as a reagent and catalyst.