Fundamental reactivity of the Metal-Carbon bond in cyclometalated PNC-complexes

The activation of C-H bonds by transition metals and the reactivity of the corresponding metal-carbon bond are interesting research topics form different point of views. Catalytic C-H bond functionalization has emerged as a highly active research area for the development of green construction of Carbon-Carbon and Carbon-heteroatom bonds. Fundamental knowledge on the mechanism of stoichiometric activation and functionalization of C-H bonds can lead to improved catalytic reactions. Furthermore, the reversible nature of C-H activation could account for metal-ligand cooperativity.
This thesis describes the coordination chemistry and reactivity of P,N,C-ligands ( 2-(di-tert-butylphosphinomethyl)-2-phenyl-pyridine and 2-(di-tert-butylphosphinito)-6-phenyl-pyridine) in Rh(I) and Ni(II) complexes. The strong P,N-chelation to the metal brings the ortho-C-H of a flanking phenyl ring in proximity of the metal, which results in facile C-H activation in both metal complexes. Although the Metal-Carbon bond is easily formed, it is still reactive in presence of acids and strong electrophiles. Application of such cyclometalated complexes in cooperative base-free dehydrogenation of formic acid is reported. Another topic of this thesis is the isolation of complexes with Metal-(C-H) interactions, which are generally considered to precede the C-H activation step. Furthermore, the reactivity of the Metal-Carbon bond with respect to formation of Carbon-Carbon bonds is described.