Ruthenium hydrogenation catalysts with P–N–N–P ligands derived from 1,3-diaminopropane and the formation of a β-diiminate complex by a base-induced isomerization

The complexes RuHCl{PPh2(2-C6H4)CHNCH2CH2CH2NCH(2-C6H4)PPh2} (RuHCl{prP2N2}, 7) and RuHCl{PPh2(2-C6H4)CH2NHCH2CH2CH2NHCH2(2-C6H4)PPh2} (RuHCl{prP2(NH)2}, 8) are prepared by reaction of RuHCl(PPh3)3 with a ligand derived from 1,3-diaminopropane and ortho-diphenylphosphinobenzaldehyde. They are active precatalysts for the hydrogenation of acetophenone and are moderately active for the hydrogenation of benzonitrile and imines. The related complex RuHCl{ethP2(NH)2} with a ligand derived from 1,2-diaminoethane provides a more active catalyst. Complexes 7 and 8 undergo an unusual base-promoted isomerization reaction that produces a ruthenium complex containing a novel β-diiminato ligand.

Graphical abstractThe complexes RuHCl{prP2N2} and RuHCl{prP2(NH)2} in the presence of KOtBu are catalysts under mild conditions for the H2 hydrogenation of acetophenone, imines and benzonitrile. Under Ar these precatalysts undergo an unusual imine isomerization/deprotonation reaction.Figure optionsDownload full-size imageDownload as PowerPoint slide