Hydrophosphonylation of aldehydes catalyzed by cyclopentadienyl ruthenium(II) complexes

Abstract

This work reports the first method for the synthesis of α-hydroxyphosphonates from aldehydes catalyzed by cyclopentadienyl ruthenium(II) complexes. The best results were obtained using the system HP(O)(OEt)2/[RuClCp(PPh3)2] (5 mol%), affording the α-hydroxyphosphonates in good to excellent yields with high chemoselectivity. The catalyst [RuClCp(PPh3)2] can be used for at least 12 catalytic cycles with excellent activity and the reactions were carried out under solvent free conditions. DFT calculations were performed to rationalize the mechanism showing that the barriers associated with the H-phosphonate tautomer, HP(O)(OR)2 are unrealistically high. This led us to propose that the catalyst promotes the tautomerization towards phosphite, P(OH)(OR)2, via P-atom coordination, which accounts for the observed reactivity.