Activation of single and multiple C–N bonds by Ru(II) catalysts in homogeneous phase

Abstract

The ruthenium(II) dihydro complexes RuH 2 (CO) 2 (P n Bu 3 ) 2 , RuH 2 (CO) 2 (PPh 3 ) 2 , and RuH 2 (PPh 3 ) 4 are able to hydrogenate/hydrogenolyse organic substrates containing single or multiple C-N bonds. The influence of several reaction parameters such as reaction time, temperature, hydrogen pressure and concentration of the catalyst were tested. A benzonitrile conversion of 76.5% was achieved after 24 h at 393 K. In the same conditions, N-benzylidenaniline is hydrogenated with a 92.1% conversion. Finally the activation parameters and the kinetic constants of these reactions were calculated. New ruthenium hydrido complexes containing a benzonitrile or an imine ligand were identified and spectroscopically characterized. A catalytic cycle was proposed to rationalize the results obtained, on the basis of the new complexes identified.

Catalytic activity of dihydride ruthenium complexes in the hydrogenation of nitrogen containing heterocycles

“…Synthesis of ruthenium complexes: RuH 2 (PPh 3 ) 4 , RuH 2 (CO) 2 (P n Bu 3 ) 2 , RuH 2 (CO) 2 (PPh 3 ) 2…”

“…In this paper, we report our studies concerning the hydrogenation of quinoline and some analogous substrates, using the dihydride ruthenium complexes RuH 2 (CO) 2 (P n Bu 3 ) 2 , RuH 2 (CO) 2 (PPh 3 ) 2 and RuH 2 -(PPh 3 ) 4 . We have tried better conditions to perform the selective reduction of quinoline to 1,2,3,4-THQ (1,2,3,4-tetrahydroquinoline).…”

“…The catalytic activity of the dihydride ruthenium complexes, RuH 2 (CO) 2 (P n Bu 3 ) 2 , RuH 2 (CO) 2 (PPh 3 ) 2 and RuH 2 (PPh 3 ) 4 , in the hydrogenation of nitrogen containing heterocycles has been tested by analyzing the influence of reaction parameters such as temperature, hydrogen pressure, catalyst concentration, on the rate and regioselectivity of the reaction.…”

“…The complexes RuH 2 (CO) 2 (P n Bu 3 ) 2 , RuH 2 (CO) 2 (PPh 3 ) 2 have been chosen in consideration of their good catalytic activity in the hydrogenation of ketones, a,b-unsaturated ketones, alkenes, alkynes, and unsaturated nitrogen containing compounds [3,4], while the specie RuH 2 (PPh 3 ) 4 provides an excellent catalytic activity toward the hydrogenation of nitrogen containing compounds [3].…”

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AbstractThe catalytic activity of the dihydride ruthenium complexes, RuH 2 (CO) 2 (P n Bu 3 ) 2 , RuH 2 (CO) 2 (PPh 3 ) 2 and RuH 2 (PPh 3 ) 4 , in the hydrogenation of nitrogen containing heterocycles has been tested by analyzing the influence of reaction parameters such as temperature, hydrogen pressure, catalyst concentration, on the rate and regioselectivity of the reaction.RuH 2 (PPh 3 ) 4 shows a better catalytic activity with an 86.7% conversion of quinoline after 24 h at 100°C under a hydrogen pressure of 25 bar, while RuH 2 (CO) 2 (PPh 3 ) 2 and RuH 2 (CO) 2 (P n Bu 3 ) 2 in the same conditions give a conversion of 37.1% and 35.6%, respectively. These results are confirmed by the reaction rate of the hydrogenation of quinoline, since the K c in the presence of RuH 2 (PPh 3 ) 4 (1.46 · 10 À5 s À1 ) is higher than others (6.37 · 10 À6 s À1 for RuH 2 (CO) 2 (PPh 3 ) 2 and 6.36 · 10 À6 s À1 for RuH 2 (CO) 2 (P n Bu 3 ) 2 ).

Noteworthy is the selectivity of these catalytic systems in the hydrogenation of quinoline: in all tests the three catalysts lead to 1,2,3,4-tetrahydroquinoline as the major product, furthermore this compound is the only formed in the presence of RuH 2 (CO) 2 (PPh 3 ) 2 .

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