For applications in aqueous media, sulfonated tetrahydrosalen (sulfosalan, HSS) was synthesized by sulfonation of tetrahydrosalen in fuming sulfuric acid. The Pd(II) complex of this ligand, [Pd(HSS)], showed outstanding activity in hydrogenation and redox isomerization of allylic alcohols in homogeneous aqueous solutions or in aqueous-organic biphasic systems (for oct-1-en-3-ol TOF(hydrogenation) = 1580 h-1, TOF(redox isomerization) = 400 h -1). DFT calculations revealed that H2 is activated heterolytically, resulting in a Pd(II)-hydride complex, [Pd(H)(HSS-Hphen)], in which one of the phenolate oxygens is protonated. Both hydrogenation and redox isomerization take place via concerted transfer of a proton and a hydride from the hydrogenated catalyst to the allylic alcohol.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry