Preparation, characterization, and performance of the supported hydrogen-bonded ruthenium catalyst [(sulphos)Ru(NCMe)(3)](OSO2CF3)/SiO2. Comparisons with analogous homogeneous and aqueous-biphase catalytic systems in the hydrogenation of benzylidenea

摘要

The Ru(II) complex [(sulphos)Ru(NCMe)(3)](OSO2CF3) (1) has been immobilized on partially dehydroxylated high-surface-area silica via hydrogen-bonding interactions between the silanol groups of the support and the SO3- groups from both the sulphos ligand and the triflate counteranion (sulphos = -O3S(C6H4)CH2C(CH2PPh2)(3)). Compound 1 has been authenticated in the solid state by a single-crystal X-ray analysis and in solution by NMR spectroscopy, while its silica-grafted form [(sulphos)Ru(NCMe)(3)](OSO2CF3)/SiO2 (1/SiO2) has been characterized by DRIFT and CP MAS P-31 NMR studies. The supported hydrogen-bonded (SHB) complex 1/SiO2 is an effective and selective catalyst for the hydrogenation of benzylidene-acetone to benzylacetone and of benzonitrile to benzylidenebenzylamine in n-octane. No appreciable ruthenium leaching into the hydrocarbon phase was observed in either case. Analogous hydrogenation reactions catalyzed by either the aqueous-biphase catalyst 1 in water-octane or the homogeneous-analogue [(triphos)Ru(NCMe)(3)](OSO2CF3)(2) in THF have been carried out (triphos = MeC(CH2PPh2)(3)). The silica-supported catalyst is slightly less active but much more selective and recyclable than the soluble congeners. In an attempt to rationalize the selectivity exhibited by the SHB catalyst, various model studies have been performed in different phase variation systems. Incorporation of the results obtained led to the conclusion that, in contrast to fluid solution reactions, no heterolytic splitting of H-2 at ruthenium occurs in the heterogeneous phase. [References: 64]