Placing two metal centers in close proximity offers an appealing strategy for engendering new properties that may not be accessible from only a single metal center. However, although this strategy has been widely studied with first-row transition metals, the tunable heterobimetallic chemistry of second-row transition metals, like palladium, has received far less attention than it deserves. Here, we report the assembly, characterization, and electrochemical properties of a series of new heterobimetallic complexes of palladium for the purpose of understanding the influence of Lewis acidic metals on such species. The redox-active Pd centers in the new macrocyclic complexes are bound to a Schiff base cavity and the redox-inactive Lewis acidic centers, M, occupy a crown ether-like site. Single-crystal X-ray diffraction analysis reveals that the [Pd---M] distance is dependent upon the Lewis acidity of the redox-inactive metals (as quantified by the pKa values associated with their corresponding aqua complexes), a feature we have not observed in analogous series of complexes containing first-row metals. Analysis of cyclic voltammetry data shows that the reduction potentials of the heterobimetallic complexes were shifted positively in comparison with that of the monometallic precursor, resulting in an average shift of 48 mV/pKa unit. In this presentation, we will discuss these results and address the question of understanding metal- versus ligand-centered reduction in heterobimetallic complexes.

Quantification of Lewis acid effects in heterobimetallic complexes of palladium assembled with a macrocyclic approach

ACS Fall 2021

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