Understanding Ligand Effects on Bielectronic Transitions: Chemo‐ and Electroreduction of Rhodium Bis(Diphosphine) Complexes to Low Oxidation States

Angewandte Chemie International Edition, vol. 63, pp. e202408356

Abstract

Abstract Rhodium complexes in the −I and 0 oxidation states are of great potential interest in catalytic applications. In contrast to their rhodium +I congeners, however, the structural and electronic parameters governing their access and stability are far less understood. Herein, we investigate the two‐electron reduction of a parameterized series of bis(diphosphine) Rh complexes [Rh(d x p y ) 2 ]NTf 2 ( x =P‐substituent, y =alkanediyl bridging P atoms). Through (electro)reductions from the Rh I parents, Rh −I d 10 ‐complexes were obtained and characterized spectroscopically, including 103 Rh NMR data. The reductive steps convolute with structural rearrangements from square planar to tetrahedral coordination. We found that the extent of these reorganisations defines whether the first E 0 (Rh I/0 ) and second E 0 (Rh 0/−I ) reduction potentials are normally ordered, leading to monoelectronic stepwise transitions, or inverted, giving bielectronic events. Reductionist approaches based on Hammett parameters or the P−Rh‐P bite angles provide only partial correlations with the redox potentials. However, we identified the C−O stretch of analogue diphosphine complexes as an expedient computational parameter that enables these correlations through both electronic and geometric features, even in a predictive manner. Gaining control over two‐electron reduction behaviors through rationalized ligand effects has potential impact beyond Rh complexes, for molecular and enzymatic metal sites commonly exhibiting bielectronic transitions.

Authors 5

1. Anne‐Christine Kick Aachen Institut für Technische und Makromolekulare Chemie

   RWTH Aachen University

   Affiliation as printed

   Institut für Technische und Makromolekulare Chemie RWTH Aachen University Worringerweg 2 52074 Aachen

   Institut für Technische und Makromolekulare Chemie RWTH Aachen University Worringerweg 2 52074 Aachen

2. Thomas Weyhermüller

   Max Planck Institute for Chemical Energy Conversion

   Affiliation as printed

   Department of Molecular Catalysis Max Planck Institute for Chemical Energy Conversion Stiftstraße 34–36 45470 Mülheim an der Ruhr

   Department of Molecular Catalysis Max Planck Institute for Chemical Energy Conversion Stiftstraße 34–36 45470 Mülheim an der Ruhr

3. Markus Hölscher Aachen Institut für Technische und Makromolekulare Chemie

   RWTH Aachen University

   Affiliation as printed

   Institut für Technische und Makromolekulare Chemie RWTH Aachen University Worringerweg 2 52074 Aachen

   Institut für Technische und Makromolekulare Chemie RWTH Aachen University Worringerweg 2 52074 Aachen

4. Nicolas Kaeffer corresponding

   Max Planck Institute for Chemical Energy Conversion

   Affiliation as printed

   Department of Molecular Catalysis Max Planck Institute for Chemical Energy Conversion Stiftstraße 34–36 45470 Mülheim an der Ruhr

5. Walter Leitner Aachen Institut für Technische und Makromolekulare Chemie

   RWTH Aachen University · Max Planck Institute for Chemical Energy Conversion

   Affiliation as printed

   Department of Molecular Catalysis Max Planck Institute for Chemical Energy Conversion Stiftstraße 34–36 45470 Mülheim an der Ruhr

   Institut für Technische und Makromolekulare Chemie RWTH Aachen University Worringerweg 2 52074 Aachen

   Department of Molecular Catalysis Max Planck Institute for Chemical Energy Conversion Stiftstraße 34–36 45470 Mülheim an der Ruhr