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.

Improved Stability and Catalytic Activity of Palladium Nanoparticle Catalysts using Phosphine‐Functionalized Imidazolium Ionic Liquids

“…Important to this field in the context of catalysis is the influence, both steric and electronic, that the ionic group has on the coordination chemistry of the phosphine moiety. The steric effect of a phosphine is often evaluated by the Tolman cone angle, while the electronic influence can be estimated from the synthesis the phosphine selenides or the metal carbonyl complexes 24b. To this end, the influence of the PFIL parameters (i.e., N‐alkyl chain length and counter anion) on the electronic properties of the phosphine moiety were determined through the synthesis of the corresponding phosphine selenides and rhenium carbonyl complexes.…”

Water-soluble complexes MX2L2 (M = Pd, Pt; L = PPh2(C6H4-p-SO3K)): Synthesis, stereoisomerism, and catalytic activities for aromatic cyanation in n-heptane/water biphasic solution

“…The trans/cis ratio varies depending not only on electronic and steric features of constituents of metal complexes including phosphine and halide ligands, and metal but also on reaction mediums. For complexes with ion-paired phosphine ligands, contributions arising from either attractive or repulsive interactions between the ionic functionalities have to be incorporated with the factors [41]. The ratio of the cis/trans isomers of MX 2 L 2 complexes generally increases as the dielectric constant or the dipole moment of the solvent increases [42,43].…”

“…Since intramolecular interligand Coulombic repulsion is diminished at higher ionic strengths due to shielding of the charges [41,49], further experiments on the stereoisomers were performed in potassium halide solution of DMSO. Treatment of DMSO-d 6 solution of PdCl 2 {PPh 2 (C 6 H 4 -p-SO 3 K)} 2 (the trans/cis ¼ ca.…”

Carbon/Silicon Exchange at the Apex of Diphos‐ and Triphos‐Derived Ligands – More Than Just a Substitute?

“…While the metal will indeed be the center of reactivity, the ligand moiety plays a crucial role for tuning the electronic properties by changing donor ligands and/or controlling the sterics to provide selectivity or access to reactive sites. Even second‐sphere effects are of importance when designing metal complexes for catalytic applications While a detailed understanding of alterations in activity as a result of changing donor atoms on a metal center is provided in the literature and chemists are conscious of second‐sphere effects, there is no awareness that such changes can also be introduced by a stepwise replacement of C by Si in the ligand periphery. C/Si exchange, however, has been reported to have a significant influence on the chemical and physical properties of explosives and odorants as well as the biological properties of drugs .…”