Promoter effect of bicarbonate in hydrogenation of cinnamaldehyde catalyzed by a water-soluble Ru(II)-phosphine complex

Article abstract of DOI:10.1016/j.ica.2017.06.061

The highly selective formation of cinnamalcohol in hydrogenation of trans-cinnamaldehyde with [{RuCl₂(mtppms)₂}₂] + mtppms as catalyst (mtppms = monosulfonated triphenylphosphine) in aqueous solution was substantially accelerated by NaHCO₃ (in 20–50 mol% quantities relative to cinnamaldehyde). More than double conversion compared to bicarbonate-free systems was observed at n(NaHCO₃)/n(Ru) = 20. Prehydrogenation of the reaction mixture before the addition of cinnamaldehyde resulted in further rate increase (45.3% conversion vs. 13.1% in water). ¹H, ¹³C and ³¹P NMR studies revealed that formate produced in hydrogenation of bicarbonate facilitated formation of trans-[Ru(H)₂(H₂O)(mtppms)₃], a better catalyst than cis-fac-[Ru(H)₂(H₂O)(mtppms)₃] which is the product of the reaction of [{RuCl₂(mtppms)₂}₂] + mtppms with H₂ in the absence of formate (or bicarbonate). Accordingly, NaHCO₂ produced even higher rate increase than the same amount of NaHCO₃.