Two pseudo-N3 ligands and the catalytic activity of their ruthenium(II) complexes in transfer hydrogenation and hydrogenation of ketones

Complex RuCl2(PPh3)(iBu-BTP) (5) was synthesized by the reaction of 2,6-bis(5,6-bis(iso-butyl)-1,2,4-triazin-3-yl)pyridine (iBu-BTP) and RuCl2(PPh3)3 in refluxing toluene, and its molecular structure was confirmed by X-ray crystallographic determination. Complex 5 was applied as a catalyst for transfer hydrogenation of ketones and exhibited catalytic activity comparable to RuCl2(PPh3)(Me4BPPy) (1) (Me4BPPy = bis(3,5-dimethylpyrazol-1-yl)pyridine) in some cases. The difference between the catalytic activity of 5 and 1 is attributed to the significantly different arrangement and positions of the PPh3 and chlorides and also to the different electron density on the N-heterocycles. Complex 1 exhibited good to excellent catalytic activity in hydrogenation of ketones under mild conditions. These results have suggested new applications of iBu-BTP and Me4BPPy as promising planar tridentate pseudo-N3 ligands to construct highly active transition-metal catalysts.

Complex RuCl2(PPh3)(iBu-BTP) (5) exhibited moderate to good and excellent catalytic efficiency in the transfer hydrogenation of ketones, and RuCl2(PPh3)(Me4BPPy) (1) showed good to excellent catalytic activity in hydrogenation of ketones. These results suggest that iBu-BTP and Me4BPPy are promising pseudo-N3 ligands to construct highly active transition-metal catalysts.Figure optionsDownload as PowerPoint slide