Stabilization of Super Electrophilic Pd+2 Cations in Small-Pore SSZ-13 Zeolite

<div> <p>The results of our combined experimental (FTIR, XPS, HAADF-STEM, EXAFS) and density functional theory study reveal that Pd ions in zeolites, previously identified as Pd<sup>+3</sup> and Pd<sup>+4</sup>, are in fact present as super electrophilic Pd<sup>+2</sup> species (ion pairs with the negatively charged framework oxygens). In this contribution we re-assign the spectroscopic signatures of these species, discuss the unusual coordination environment of “naked” (ligand-free) Pd<sup>+2</sup> in SSZ-13, and their complexes with CO and NO. With CO, non-classical, highly positive [Pd(CO)<sub>2</sub>]<sup>2+</sup> ions are formed with the zeolite framework acting as a weakly coordinating anion (ion pairs). Non-classical carbonyl complexes also form with Pt<sup>+2</sup> and Ag<sup>+</sup> in SSZ-13. The Pd<sup>+2</sup>(CO)<sub>2</sub> complex is remarkably stable in zeolite cages even in the presence of water. Dicarbonyl and nitrosyl Pd<sup>+2</sup> complexes, in turn, serve as precursors to the synthesis of previously inaccessible Pd<sup>+2</sup>-carbonyl-olefin [Pd(CO)(C<sub>2</sub>H<sub>4</sub>)] and -nitrosyl-olefin [Pd(NO)(C<sub>2</sub>H<sub>4</sub>)] complexes. Overall, we provide novel insight into the interactions of divalent metals with the zeolite framework, and show the new chemistry of Pd/SSZ-13 system with implications for adsorption and catalysis.</p> </div>