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Synthesis of Novel Chelating N-Heterocyclic Carbenes and Their Heavier Analogues as Tools in Coordination Chemistry

Subject Area Inorganic Molecular Chemistry - Synthesis and Characterisation
Term from 2015 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 279353839
 
Final Report Year 2025

Final Report Abstract

This project builds upon earlier advances in the development of N-heterocyclic carbene (NHC)-based and heavier group homologous chelating ligands to coordinate main-group elements (Si, Ge, Sn, Pb, B, Al, Ga) and 3d transition metals (Mn, Fe, Co, Ni). The main objective is to establish predictive models of coordination behavior and reactivity by synthesizing new ligand systems and studying their structure–reactivity relationships. The key achievements include: Synthesis of Bis(silylenes) and Related Ligands: Building on our synthetic experience with bis(silylenes), we developed the three new neutral bis(silylenes) featuring different spacers. Utilizing the acridine framework, we synthesized an anionic bis(silylene). Moreover, we developed the mixed silylene-phosphine, bis(germylenes) as well as the NHC-supported bis(phosphinidene). Attempts to synthesize bis(borylene) led to isolation of the first silylene-stabilized dibenzodiboraoxepin. Small Molecule Activation and Coordination Features of Bis(silylenes): The bis(silylenes) exhibit a remarkably rich reactivity, including: 1) Isolation of the first bis-silylene-supported nitreone. 2) Cooperative white phosphorus activation to form unique Si=P-containing compounds, P2 complexes, and polycyclic species. 3) Access to bis-silylene stabilized metallylones across group through reductions of halide precursors. 4)Synthesis of a rare planar tetracoordinate silicon. 5) Metal-catalyzed hydrogenation/hydroboration using Mn and Ni complexes, with record-high catalytic activities. Silylene-Phosphine Chemistry: Ligand enabled isolation of the novel Ge clusters and the P5-chain species through P4 activation, facilitated by ligand-centered electron donation and stabilization. Bis(germylene) Coordination: Complexes derived from bis(germylenes) showed applications in catalysis and redox chemistry: 1) NiGe electrocatalysts derived from complex for oxygen evolution reaction (OER), exhibiting superior durability and activity. 2) The Bi(I) complex stabilized via germylene-induced charge delocalization was reversibly oxidized to a Bi(II) radical. Bis(phosphinidene) and Diborene Chemistry: The NHC-supported bis(phosphinidene) ligand coordinated a range of main group and transition metal centers. The first silylenestabilized dibenzodiboraoxepin not only enable the interesting activation of P₄ and NH₃ under ambient conditions, the selective and mild reductive deoxygenation affords the 9,10-diboraphenanthrene derivatives, as diboron-containing PAHs with novel reactivity such as mediating the monodeoxygenation of CO₂. Overall, our work witnesses a versatile coordination and small molecule activation chemistry of novel bis(silylene), bis(germylene), phosphinidene, and diborene ligands. The results advance ligand design strategies and reveal pathways for developing functional materials and catalysts from main-group-based coordination complexes.

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