Arene-ruthenium(II)-phosphine complexes: Green catalysts for hydration of nitriles under mild conditions

Three new arene-ruthenium(II) complexes were prepared by treating [{RuCl(mu-Cl)(eta(6)-arene)}(2)] (eta(6)-arene = p-cymene) dimer with tri(2-furyl)phosphine (PFu(3)) and 1,3,5-triaza-7-phosphaadamantane (PTA), respectively to obtain [RuCl2(eta(6)-arene)PFu(3)] [Ru] -1, (RuCl(eta(6)-arene)(PFu(3))(PTA)]BF4 [Ru] -2 and HtuCl(eta(6)-arene)(PFu(3))(2)]BF4 [Ru] -3. All the complexes were structurally identified using analytical and spectroscopic methods including single-crystal X-ray studies. The effectiveness of resulting complexes as potential homogeneous catalysts for selective hydration of different nitriles into corresponding amides in aqueous medium and air atmosphere was explored. There was a remarkable difference in catalytic activity of the catalysts depending on the nature and number of phosphorus-donor ligands and sites available for catalysis. Experimental studies performed using structural analogues of efficient catalyst concluded a structural-activity relationship for the higher catalytic activity of [Ru] -1, being able to convert huge variety of aromatic, heteroaromatic and aliphatic nitriles. The use of eco-friendly water as a solvent, open atmosphere and avoidance of any organic solvent during the catalytic reactions prove the reported process to be truly green and sustainable.