Water-mediated formation of hydride derivates from flexible Pd-salan complexes: A DFT study

Abstract

The formation of hydride derivatives of sulfonated palladium(II) salan (hydrogenated salen) complexes was studied with DFT methods. The non-hydrolytic property, chirality, and flexibility lead to a significant difference compared to salen derivatives. We made a detailed computational study to understand the relevance of the flexibility in contrast to the rigid salen complex. Two main pathways were investigated: one of them was a direct monohydride formation where the oxygen of the phenolate group was substituted by a hydrogen molecule followed by a proton transfer. Another was an indirect monohydride formation involving the substitution of phenolate arm by a solvent water molecule in the first step and subsequent reaction with H2 in the second. We focused on weak interactions among the Pd-complex and water molecules. Trigonal, square, and diamond motifs of H-bond networks were found around the oxygen atom of the phenolate arm which is crucial during the proton transfer step, however, substitution steps prefer chain type motifs.