Abstract

Organic hydroxylamine (C-NHOH) and nitroso (C-NO) species are reactive compounds that find application in organic synthesis, for example in C–N or C–O bond formation. These groups are redox active, interconverting via reduction or oxidation amidst the series of organic nitrogen substituents: NH2, NHOH, NO, and NO2. In order to expand the synthetic potential of hydroxylamine and nitroso species, an understanding their reactivity in the presence of a metal-based catalyst is required. In this thesis, we are studying how copper ions influence the reactivity of a NHOH group tethered to a coordinating ligand. This tethering strategy allows for controlled reaction and a precise characterization of the reaction products.
Chapter 1 introduces the redox chemistry of nitrogen groups, current organic applications of nitroso compounds, as well as current methods to convert a nitro group into a hydroxylamine moiety.
Chapter 2 covers design and synthesis of different ligands with a pendant NO2 group to provide a NHOH moiety by partial hydrogenation. The optimization of reduction reactions using zinc and ammonium formate helped us to obtain several NHOH-containing ligands in high yields.
Chapter 3 studies the interaction of the ligands with copper(II) ions. Spectroscopic titrations provided insight into the stoichiometry of complexation. In particular, reaction of a NHOH-containing ligand with copper(II) acetate yielded a neutral complex with a C-NO moiety that is N-bonded to Cu. The complex was analyzed by crystallography, NMR, magnetic measurements, electrochemistry and DFT calculations. The electronic structure is consistent with a strongly antiferromagnetically coupled Cu(II)-(nitrosyl anion) formulation. Therefore, copper(II) has transformed a NHOH group into a 1e– reduced NO moiety, C-(NO–), adding to redox versatility of the organic NO linkage.