The incorporation of redox-inactive Lewis acidic metals into redox-active compounds has sparked significant interest due to the potential for reliably modulating thermochemical properties and reactivity. On the other hand, understanding the roles of Lewis acids in the tuning of elements beyond the first row of the transition series remains a frontier area. In this poster, we will show that such Lewis acid effects can be effectively leveraged to tune the redox properties of palladium. The synthesis and characterization of the first series of heterobimetallic complexes of palladium has been carried out using a Reinhoudt-type heteroditopic ligand with a salen-like [N2,O2] binding site for Pd and a crown-ether-like [O6] site. Incorporation of a range of mono-, di-, and tri-valent Lewis acidic redox-inactive metal ions (Mn+) into new complexes will be discussed. NMR spectroscopy has confirmed the assembly of the desired compounds, and single-crystal X-ray diffraction analysis has revealed a trend in [Pd---M] distance on Lewis acidity (as measured by the pKa values of corresponding metal aqua complexes), a feature not seen in analogous series of complexes containing first-row metals. Analysis of cyclic voltammetry data shows that the reduction potentials of these complexes are shifted positively in comparison with the monometallic precursor, and that the reorganization energy associated with ET also depends on Lewis acidity, where the strongest integrated Lewis acids are related with the slowest heterogeneous electron transfer rates. This reduction was assigned as a ligand-centered reduction based on various experimental data. Overall, these findings suggest that interactions with Lewis acids are as effective for second-row transition metals as they are for their first-row analogues.

Macrocyclic approach for the quantification of Lewis acid effects in heterobimetallic complexes of palladium

ACS Spring 2022

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