Steric, electronic, and secondary effects on the coordination chemistry of ionic phosphine ligands and the catalytic behavior of their metal complexes

Abstract

The effects of introducing ionic functionalities in phosphine ligands on the coordination chemistry of these ligands and the catalytic behavior of the corresponding metal complexes are reviewed. The steric and electronic consequences of such functionalizations are discussed. Apart from these steric and electronic effects, the presence of charged groups often leads to additional, supramolecular interactions that occur in the second coordination sphere of the metal complex, such as intramolecular, interligand hydrogen bonding and Coulombic repulsion. These interactions can significantly alter the behavior of the phosphine ligand in question. Such effects have been observed in phosphine-metal association/dissociation equilibria, ligand substitution reactions, and stereoisomerism in phosphine-metal complexes. By drawing general conclusions, this review offers an insight into the coordination and catalytic behavior of phosphine ligands containing ionic functionalities and their corresponding metal complexes. More than sterics and electronics: The introduction of charged groups in phosphine ligands (see scheme) not only alters their solubility and their steric and electronic properties, but often also leads to supramolecular interactions. These effects can significantly alter the coordination chemistry of the phosphine ligand with respect to a transition metal. Here, the different types of interactions that play a role, as well as their consequences with respect to catalysis, are reviewed. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.