PNP pincer ligands in late transition metal nitrido chemistry and gold catalysis

In this dissertation 1) an investigation of the possibility of forming cobalt- and nickel-nitrido complexes by studying the activation of the corresponding metal-azido complexes, and 2) an investigation into a novel, bimetallic approach to selectively promote the σ,π-activation mode in dual-gold Au(I) catalysis are presented. A diarylamine phosphine (PNP) pincer ligand described in the introductory chapter is selected to form corresponding (PNP)M-parent complexes because of its capability to accommodate high-valent metal centers, its rigidity and its stability at elevated temperatures and under photolytic conditions.
The described research shows two new examples of transient Co- and Ni-nitrido complexes, which are proposed based on experimental results and DFT calculations. This has (further) established the accessibility of such species. The research can therefore serve as a foundation for future investigations into Co and Ni complexes with multiple bonded ligands (N, O or S). Spectroscopic characterization of the proposed species remains elusive and still requires attention in future studies.
Furthermore, the research described herein establishes that Au(I) catalysis by σ,π-activation can be used to obtain different product selectivity as compared to mononuclear gold chemistry. A new concept to enforce this activation mode through ligand preorganization of two Au(I) centers is successfully introduced. Selective two-electron oxidation of one gold center is shown to lead to a mixed-valent Au(I)Au(III)(PNP) complex. Its reaction with a Au(I)-salt leads to oxidative C-C bond formation in the ligand and two-electron reduction of the Au(III)-center. Research on the overall reaction sequence leads to the proposal of a mechanism of the conversion.