The Role of Non-Covalent Interactions in the Reactions between Palladium Hydrido Complex with Amidoarylphosphine Pincer Ligand and Brønsted Acids

The interaction between (PNP)PdH (1); PNP = bis(2-diisopropylphosphino-4-methylphenyl)amide and different acids (CF3SO3H, HBF4∙Et2O, fluorinated alcohols formic acid) was studied in benzene or toluene as well neat by IR NMR spectroscopies. structures of hydrogen-bonded complexes were also optimized at the DFT/ωB97-XD/def2-TZVP level. nitrogen atom amidophosphine pincer ligand readily accepts proton not only from strong Brønsted but relatively weak alcohols. That suggests that binding to palladium(II) increases diarylamine basicity, making it a base. Nevertheless, H+ can be taken [(PN(H)P)PdH]+ (2) pyridine hexamethylphosphoramide (HMPA). These observations confirm need for shuttle base form result heterolytic splitting H2 [(PNP)Pd]+. At that, stoichiometric amount acid protonates hydride yielding an unstable η2-H2 complex rapidly converts into formate (PNP)Pd(OCHO), which loses CO2 restore (PNP)PdH, whereas high excess hampers this reaction through competitive protonation atom.