UvA

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.