Highly Reactive Late Transition Metal Complexes for Small Molecule Activation
Final Report Abstract
The electronic and steric properties of N-heterocyclic carbenes (NHC) were investigated. The experimental available values for Tolmans Electronic Parameter (TEP) show a reasonable correlation to the electrostatic potential (ESP) at the carbene ligand of the free NHC. Interpolation of these values enables one to predict TEP values of unknown NHCs. Furthermore, the energy decomposition analysis (EDA) of the corresponding metal-carbene bond in Ni-NHC model complexes is a useful tool to quantify the σ- and π-contribution to the metal carbene bond. As a proof of principle, the oxidative addition of H3C-Cl and H3C-H to [M(NHC)2] was calculated. In addition to this project, it was demonstrated, how σ-donation in MH2 complexes lead to bent structures (d0-MH2) or strongly prefers linear structures (d10-MH2). This observation can be transferred to other σ-donating ligands and is an intrinsic property of these systems. In a third project the relevance of Pauli repulsion and orbital interaction in metallophilicity was demonstrated. The MO analysis and EDA of M+ꞏꞏꞏM+ revealed a covalent attractive contribution to the metal-metal interaction. However, it is important to mention that if ligands are present, like in [H3P-M-X]2, Pauli repulsion is much more important than the orbital interaction term. In these cases, the electrostatic energy is the largest attractive interaction term. Still, attractive D-A interaction is present, but is overruled by two-orbital-four-electron repulsion. Nevertheless, mixing of acceptor orbitals into the 1σ, leads to a stabilization of [H3P-M-X]2 systems, which would otherwise be non-bonding. Thus, an effective tuning of these interactions could be achieved if the acceptor orbitals are significantly stabilized. Studies which focus on the influence of the ligand acceptor orbital(s) are currently under progress.
Publications
- “Relevance of Orbital Interactions and Pauli Repulsion in the Metal-Metal Bond of Coinage Metals” Inorg. Chem. 2018, 57, 2603-2608
Brands, M.; Nitsch, J.; Fonseca Guerra, C.
(See online at https://doi.org/10.1021/acs.inorgchem.7b02994)
