Cohesion in Coordination Chemistry

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This collaborative work addresses the issues of cohesion in coordination and organometallic chemistry fostered by a mutual effort in experimental and theoretical investigations of the role of predominantly non-covalent interactions (NCIs) in reactions involving d-block transition metals where intramolecular London dispersion forces are suspected to be essential to their stabilization. For years, NCIs have been overlooked in coordination chemistry. Recent research shows that accounting for the effect of these interactions was essential to produce a physically correct assessment of the importance of metals ligand retinue on association energies and on relative stabilities of intermediates. It is expected that in coordination reactions involving ligand-metal bond formation, as encountered in catalytic processes, remote organic fragments contribute to the ligand-metal association energy by way of a significant dispersion term. Recent advances in dispersion-corrected DFT (namely DFT-D3) renders the investigation of reactions involving large (100-200 atoms) transition metal complexes possible in the gas, solution, and the solid state. This constitutes a new framework for improving further the general understanding of reaction kinetic profiles, regio, chemo and stereoselectivities. However, two pitfalls remain. The first one is the lack of comprehensive accurate thermodynamic data for ligand-metal binding that could serve as standard for the evaluation of quantum chemical (QC) methods. The second, intimately bound to the improvement of the former, is rooted in the known limitations of continuum-based solvation models. The project proposes a solution based on the investigation of elementary reactions by means of isotherm titration calorimetry, a technique that allows the accurate measure of enthalpies of reactions as low as 1 kcal/mol. It targets the study of known transition metal reactions. Acquisition of thermodynamic information by ITC is to be confronted to the assessment of the same thermochemistry by theoretical methods based on DFT-D3 and coupled-cluster type wave function theory (WFT) in order to elaborate a new benchmark reference. The critical goal of this confrontation of theory with experiment is to evaluate on a systematic basis the performance of contemporary QC methods particularly for reactions occurring in solution. Further research will be focused on the joint experimental/theoretical assessment of the nature and strength of non-covalent interactions involved in so-called hemichelation by a systematic investigation of the thermochemistry of ligand interaction with hemichelates. Further research will target the synthesis of new cases of hemichelates bearing different electron-unsaturated metal centers.