Phosphine ligands in the ruthenium-catalyzed reductive amination without an external hydrogen source

• A systematic study of the phosphine additives for the reductive amination without an external hydrogen source is provided. • Nonhindered triarylphosphines with electron withdrawing groups were found to be the most perspective ligands. • Aromatic amines – activation up to six times; aliphatic amines – no noticeable activation occurs. A systematic study of the phosphine additives influence on the activity of a ruthenium catalyst in reductive amination without an external hydrogen source was carried out. [CymeneRuCl 2 ] 2 was used as a reference catalyst, and a broad set of phosphines including Alk 3 P, Alk 2 ArP, Ar 3 P and X 3 P was screened. Three complexes of general formula (Cymene)RuCl 2 PR 3 were isolated in a pure form, and their catalytic activity was compared with the in situ generated complexes. Nonhindered triarylphosphines with electron acceptor groups were found to be the most perspective activating agents, increasing the activity of the catalyst approx. six times, Alk 2 ArP ligands have less noticeable influence, while trialkylphosphines strongly deactivate the ruthenium catalyst.