Model aryl halide macrocyclic substrates for the elucidation of coinage metal catalysed cross-coupling reaction mechanism

Resumo

Aryl-Cu(III) species have been often implicated as the intermediate species that operate Ullmann-type couplings. However, such species have long remained elusive and the fundamental pathways that govern Ullmann-type couplings, first discovered in the beginning of the last century, are still under debate. The first part of this thesis deals with the reactivity of a well-defined aryl-Cu(III) complex in the presence of sulphur, selenium and phosphorus-based nucleophiles. The results obtained demonstrate the plausibility of Cu(I)/Cu(III) redox cycles in copper-catalysed C-S, C-Se and C-P cross-coupling reactions. An aryl-Ag(III) complex analogous to the aryl-Cu(III) complex was synthesised and its coupling reactions in the presence of a broad range of nucleophile coupling partners of different nature via reductive elimination was shown. The results of this thesis validate for the first time the feasibility of oxidative addition and reductive elimination steps at silver centres and unravels a mechanism based on two-electron redox cycles Ag(I)/Ag(III) in silver-catalysed cross-coupling reactions.