Flexible Chelating Diphosphine Ligands and Their Interactions with Late Transition Metals

Ligand design plays an important role in the performance of transition metal catalysts. It is well known that the use of chelating ligands offer the metal center more stability, and additionally, chelating ligands can be tuned readily to influence the reactivity of the metal center. Many of these chelating ligands do not participate with the metal center throughout the course of chemical reactions, however interest has been increasing in the design of ligands that can cooperate with the metal center. Metal-ligand cooperation takes place in many forms including hemilability, charge switching, flexible coordination geometry, and ligand assisted substrate activations.

With these design features in mind, investigations centering around multidentate ligands possessing a central pi-system were carried out. These ligands allow for a variety of coordination modes to the metal center which are adaptable, and respond to the electronic requirements of the metal center. The coordination chemistry of the trans olefin ligands tPCR=CRP (R = H, Me), the cis olefin ligand, cPCMe=CMeP, and the o-terphenyl ligand, PterP, will be discussed. All the ligands, except for tPCMe=CMeP, showed versatility in their coordination modes, and were responsive to reaction conditions.

Furthermore, the ability of the ligands cPCMe=CMe and PterP to stabilize difficult to observe, non-heteroatom stabilized group 10 carbenes was assessed. The reactivity of the resulting palladium and platinum carbene species was investigated. These species proved to be competent at a variety of bond activation processes, consistent with their proposed reactivity in the literature. The presented work demonstrates the cooperative tendencies of p based chelating ligands, and how they can be used to elucidate intermediates not commonly observed in the literature.