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Abstract

The study of main-group species for catalysis has emerged in recent years as an active field of study, promising a sustainable alternative to the precious transition metals, whose use comes attached with concerns of toxicity, abundance and costs. Through strategic choice of substituents, typically inactive p-block elements may be activated for challenging bond activations. Rigid, bidentate catecholate and amidophenolate scaffolds were identified as suitable ligands for this purpose, and their impact on germanium and phosphorus compounds studied in this work. In the first part, perhalogenated bis(catecholato)germanes were prepared, characterized and shown by theory and experiment to be the first neutral germanium Lewis superacids, entirely stable in water. Additionally, they are active catalysts for a wide variety of reactions. At phosphorus, catecholates propelled the element typically used as Lewis base to new heights of Lewis acidity. Theoretical and experimental scaling methods ranked the newly prepared catecholato-phosphonium ions among the strongest, isolable Lewis acids. The high Lewis acidity was achieved even without requiring perhalogenation or multiple charges, and energy decomposition analysis assigned structural constraint as the key contributing factor. Aside from being highly active Lewis acid catalysts, the juxtaposition of electrophilic phosphorus and nucleophilic oxygen facilitated phosphorus-ligand cooperative bond activations. This way, inert C(sp2)-H, as well as Si-H bonds were cleaved, and cooperative addition of alkynes and alkenes was observed. Further control over the electronic and steric profiles of the spirophosphonium ions was asserted with amidophenolate substituents, which allowed isolation of the strongest, monocationic phosphonium ion yet, as well as ligand-cooperative activation of alkynes and alkenes following a different mechanism. Combination of both substituents gave phosphonium ions with Lewis acidity dependent structures, which could activate CH bonds by a frustrated Lewis pair-type mechanism. Lastly, a series of structurally constrained phosphenium ions based on pyridylmethylamidophenolate ligands was prepared and characterized. Tuning the substituents of the ligand periphery enabled reversible oxidative addition of even unactivated arenes such as benzene, which was unprecedented reactivity for main-group compounds. The mechanism of the reaction was elucidated by computations and a cooperative C-H deprotonation identified as key step