Ruthenium complexes with N-functionalized secondary amino ligands: a new class of catalysts toward efficient hydrogenation of esters.

A series of ruthenium complexes (o-PPh2C6H4NHR)2RuCl2 (R = Me, 3; Et, 4; CH2Ph, 5) and (o-PPh2C6H4NH2)[(CH2NHR)2]RuCl2 (R = Me, 7; Et, 8; iPr, 9) modulated with mono-N-functionalized secondary amino ligands were synthesized and demonstrated as efficient catalysts in the hydrogenation of esters into alcohols. The catalytic performances of these new complexes are much better than their corresponding primary amino ligand-constituted complexes (o-PPh2C6H4NH2)2RuCl2 (2) and (o-PPh2C6H4NH2)[(CH2NH2)2]RuCl2 (6). The significant improvement is attributed to the increased electron density of the secondary amino ligand in comparison with that of the primary amino ligand.