Nonspectator Reactivity of Nontrigonal Tricoordinate Phosphorus Ligands

Abstract

This thesis describes novel ‘nonspectator’ reactivity of geometrically deformed tricoordinate phosphorus ligands that diverge from traditional supporting roles of phosphines in transition metal catalysis. Chapter 1 presents an overview of the chemistry of higher coordinate phosphorus ligands in transition metal complexes. Chapter 2 describes experiments validating the enhanced electrophilicity of nontrigonal Cₛ-symmetric P(III) compounds as compared to typical trigonal P(III) ligands with quasi-C₃ᵥ local symmetry. Specifically, phosphorus K-edge XANES spectroscopy combined with time-dependent DFT calculation reveal ca. 1.5 eV bathochromic shift in the position of P K-edge onset. In Chapter 3, the development of nonspectator reactivities of a novel chelating ligand containing a nontrigonal P(III) center with Group 8 Ru complexes is presented. In a first finding, a unique net insertion of nontrigonal P(III) ligand into a Ru–H bond, yielding a five-coordinate phosphorus center in which of the substituents is a transition metal (i.e. metallohydrophosphoranes). The mechanistic investigation of the net insertion shows an α-H-migration between Ru–P bond in a reversible and controllable fashion. Chapter 4 extends the nonspectator reactivity to metal–ligand cooperative bond activation to Group 9 metal systems. Various transformations, such as heterolytic splitting of carbon dioxide and cooperative O–H addition of phenol, are achieved by a designed Ir–P bond with a bifunctional reactivity. Finally, Chapter 5 presents results on the net insertion of nontrigonal P(III) ligands into Group 10 metal–carbon bonds, and the factors governing the insertion reactivity is discussed. Taken together, the versatile nonspectator reactivities provide a conceptually new role of higher coordinate phosphorus ligands as a viable platform for novel bond activation and group transfer processes.