Hydrogenation of single and multiple N–N or N–O bonds by Ru(II) catalysts in homogeneous phase

Abstract

The ruthenium(II) complexes RuH 2 (CO) 2 (P n Bu 3 ) 2 , RuH 2 (CO) 2 (PPh 3 ) 2 , and RuH 2 (PPh 3 ) 4 are catalytically active in the hydrogenation of organic substrates containing a N@N, N(O)@N or NO 2 group. The reduction of the first two groups leads to hydrazine as intermediate and amine as the final product, while reducing a NO 2 group the corresponding amine is selectively formed. A complete conversion was reached, depending on temperature, catalyst and substrate concentration. The catalysts are also active in the hydrogenolysis of an N-N group giving the corresponding amine with a 97.3% conversion using RuH 2 (PPh 3 ) 4 as catalyst. A firstorder reaction rate with respect to substrate, catalyst or hydrogen pressure was detected in all cases. Finally, the activation parameters and the kinetic constants of these reactions were calculated. In the hydrogenation of azobenzene, the rate determining step involves an associative or a dissociative step depending on the catalyst employed while in the hydrogenation of all other substrates an associative rate determining step is always involved. A catalytic cycle is suggested for the hydrogenation of azobenzene, taking into account the intermediate complexes identified in the reaction medium.

Nitrogen-nitrogen bond cleavage catalyzed by ruthenium complexes

“…However quite recent results in the literature indicate that hydrogenolysis of 6a can be only achieved using RuH 2 (PPh 3 ) 4 under high hydrogen pressures. 13 On the other hand pretty good results have been obtained in this work with commercially available Ru 3 (CO) 12 . A blank experiment (without catalyst) was also made with 6a, recovering only starting material contamined by 8a.…”

Chemoselective Hydrogenation of Nitroarenes Catalyzed by Molybdenum Sulphide Clusters

“…One of the most fundamental hydrogenation reactions in chemistry involves the use of nitroarenes as starting materials, since the resulting anilines are key building blocks and central intermediates for the chemical,p harmaceutical and agrochemical industries. [3][4][5] Despite the significant progress achieved duringl ast decades in both homogeneous [6][7][8][9][10][11][12][13][14] and heterogeneous catalysis, [15][16][17][18][19][20][21][22][23][24][25][26][27] the environmentally benign chemoselective hydrogenation of nitroarenes conducted atm ild conditions and using non-noble metal based catalysts remains an actuala nd important topic for both academia and industry.…”

Chemoselective Hydrogenation of Nitroarenes Using an Air-Stable Base-Metal Catalyst

“…The catalytic hydrogenation of azobenzene to hydrazobenzene was previously achieved using rare and expensive transition metals like Pd, 35 Pt, 36 and Ru. 37 …”