The role of METAMORPhos ligands in transition metal complex formation and catalysis

Chemists are challenged to develop homogeneous transition metal catalysts that are faster, more selective, cheaper, safer, robust and environmentally benign. This is generally approached by varying the ligands that are coordinated to the applied metal to steer its properties. Traditionally, ligands functioned merely as spectators and affected the reactivity of a metal center via their electronic donating/accepting abilities and steric properties. However the role of ligands has been broadened and they can be designed such that they are actively involved during catalysis via for instance hydrogen bonding interactions, redox non-innocence or proton responsiveness. These types of ligands are commonly called bifunctional ligands.
This manuscript describes the preparation of several bifunctional (bis)METAMORPhos ligands and their coordination towards the transition metals Rh, Ir and Pd. Furthermore, the role of the ligand during complex formation and catalysis is outlined. For example, the development of several bisMETAMORPhos-iridium complexes and their application in base-free dehydrogenation of formic acid is described. The role of the ligand during catalysis is detailed based on experimental and computational results.