Combined visible spectroscopy–conductance–electrospray mass spectrometry studies of paramagnetic catalysts. Speciation of Jacobsen’s manganese salen complex in the presence of σ-donor ligands, hydroxide sources, and cumyl hydroperoxide

Abstract

Combined multi-technique (visible spectroscopy, conductance, electrospray MS) experiments have been applied to the study of Jacobsen’s manganese salen complex, JCl. Equilibria between JCl and σ-donors L (heterocyclic amines and 4-phenylpyridine N-oxide) form labile octahedral salts [J(L)₂2]Cl as the major solution species. Many samples of JCl are found occasionally to contain small amounts of an impurity whose kinetic behaviour suggest it is JOH. The compound JOH may also be generated by Bu₄NOH addition to JCl. In the presence of an excess of cumyl hydroperoxide CHP and N-methylimidazole, JOH is converted into a green intermediate, characterised by mass spectrometry as [J₂2(O)]⁺+. This intermediate undergoes first-order decomposition in the presence of CHP regenerating JOH.