Palladium Acetate Revisited: Unusual Ring-Current Effects, One-Electron Reduction, and Metal–Metal Bonding

Palladium(II) acetate (1) and two new complexes of the ligand α,α,α',α'-tetramethyl-1,3-benzenedipropionate (esp2-), C s-Pd3(esp)3 ( Cs-2) and C3 h-Pd3(esp)3 ( C3 h-2), are studied in the solid state and in solution. Variable-temperature NMR and DFT studies of C s-2 reveal an unusual shielding region above the Pd atoms. The compounds show a surprising quasi-reversible reduction between -880 and -1200 mV versus Fc/Fc+, and the Pd3(esp)3 complexes may be cleanly reduced electrochemically. EPR spectra of reduced samples show pseudo-axial signals with 105Pd hyperfine coupling, consistent with unprecedented, isostructural Pd35+ species with a valence-trapped PdII-PdII-PdI electronic structure.