Ruthenium-catalysed hydrogenation of esters using tripodal phosphine ligands

The synthesis of a new tripodal phosphine ligand, N(CH2PEt2)3, N-TriPhosEt is reported, and the use of tripodal ligands of this type, N(CH2PR2)3 (R = Ph, Et), in conjunction with ruthenium for the catalysed hydrogenation of dimethyl oxalate (DMO) is reported and contrasted with catalysis using the MeC(CH2PPh2)3 (TriPhosPh) ligand. A different order of reaction with respect to the DMO substrate is found, and the rate is slower. A study of the kinetics and mechanism of the hydrogenation of DMO with Ru(acac)3/TriPhosPh is described, along with the effect of different additives to the system. The performance of Ru(acac)3/TriPhosPh/Zn system with unactivated ester substrates is probed and found to proceed significantly slower. Finally, based upon experimental observations, a mechanism is proposed for ester hydrogenation using ruthenium catalysts with tripodal phosphine ligands.

A study of carboxylic ester hydrogenation with ruthenium and tripodal phosphine ligands is described.Figure optionsDownload high-quality image (34 K)Download as PowerPoint slideHighlights
• The synthesis of a new tripodal phosphine ligand, N(CH2PEt2)3, N-TriPhosEt.
• Ru-catalysed ester hydrogenation using the tripodal ligands N(CH2PR2)3 (R = Ph,Et).
• The effect of additives on Ru–TriPhosPh-based ester hydrogenation.
• The kinetics of ester hydrogenation with Ru and tripodal phosphines.
• Contrasting ester hydrogenation with TriPhosPh and N-TriPhosPh.