Challenges in adduct formation and frustration of Lewis acids and bases

This thesis describes the diverse use of Lewis acid and base chemistry, in adduct formation and maintaining their frustration to be able to react with other molecules. In Chapter 1 we provide an overview of diazonium salts seen as nitrogen-based Lewis acids. In donor-acceptor reactivity two electrons from the Lewis base are donated to the Lewis acid forming a classical Lewis adduct, yet in certain cases the diazonium salt is able to oxidize the Lewis base and form an aryl radical upon loss of N₂, called single-electron transfer (SET). Chapter 2 describes the synthesis of azophosphonium salts [(p-R-C₆H₄)N₂(PtBu₃)][BF₄] (R = electron donating or withdrawing), but switching from phosphine to amine resulted in the formation of a triazene. These reactions proceed via the donor-acceptor mechanism, yet SET is feasible with the stronger oxidizing agent [NO][BF₄]. Next (Chapter 3), we expanded the library of azophosphonium salts and investigated the influence of the phosphine and substituents on the aryl group which were rationalised using the σ⁺_para Hammett constant. In Chapter 4 the reactivity of frustrated Lewis pair tBu₂PCH₂BPh₂ towards molecules containing a triple bond was investigated. For terminal alkynes C-H bond splitting had occurred, whereas for the nitriles and nitrilium ions the five-membered heterocycle was afforded. In Chapter 5, we delineate on the cooperativity of the Lewis basic and Lewis acidic site in both metal-ligand cooperativity (MLC) systems and FLP chemistry. Sterically encumbered groups on the MLC prevents quenching of the active sites, similar to what is known in FLP chemistry.