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 Benzylideneacetone and Benzonitrile

Abstract

The Ru(II) complex [(sulphos)Ru(NCMe) 3 ](OSO 2 CF 3 ) (1) has been immobilized on partially dehydroxylated high-surface-area silica via hydrogen-bonding interactions between the silanol groups of the support and the SO 3groups from both the sulphos ligand and the triflate counteranion (sulphos ) -O 3 S(C 6 H 4 )CH 2 C(CH 2 PPh 2 ) 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 ](OSO 2 CF 3 )/SiO 2 (1/SiO 2 ) has been characterized by DRIFT and CP MAS 31 P NMR studies. The supported hydrogen-bonded (SHB) complex 1/SiO 2 is an effective and selective catalyst for the hydrogenation of benzylideneacetone 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/n-octane or the homogeneous analogue [(triphos)Ru(NCMe) 3 ](OSO 2 CF 3 ) 2 in THF have been carried out (triphos ) MeC(CH 2 PPh 2 ) 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.

How To Turn the Catalytic Asymmetric Hydroboration Reaction of Vinylarenes into a Recyclable Process

“…Since both nuclei (F and P) were affected in the immobilisation process, we may suggest that the two ionic parts of the metal complex may interact with montmorillonite K-10 through weak forces such as electrostatic and/or hydrogenbonding interactions (Scheme 2). The fact that both the cation and anion counterparts from the complex seem to be adsorbed onto the solid implies a new concept which differs from the other supported hydrogen-bonded catalysts previously reported in the literature in which immobilisation mainly takes place in a monodentate way between the terminal silanols of different types of silica and the oxygen atom of sulfonate groups from phosphine ligands contained in the zwitterionic rhodium(i) complexes [24,25] or from triflate counteranions of cationic Ru II [26] and Rh I [25,27] complexes. Unfortunately, as the level of loading of the immobilised complexes was low, we could not confirm the presence of hydrogen bonding by IR spectroscopy.…”

Zwitterionic Relatives of Cationic Platinum Group Metal Complexes: Applications in Stoichiometric and Catalytic σ‐Bond Activation

“…[134] A comparative study documenting the performance of the ruthenium zwittercation 125 (Scheme 30), the related silicasupported complex 131 ( Figure 6), and the dicationic complex [(triphos)Ru(CH 3 CN) 3 ] 2+ (OTf À ) 2 (133) as pre-catalysts for the hydrogenation of unsaturated substrates has been published (Scheme 32). [130] Whilst 125, operating under aqueous biphasic conditions (water/n-octane), afforded higher conversions than were achieved with the supported catalyst 131 (suspended in n-octane) for the reduction of benzylideneacetone 134, this immobilized zwittercation catalyst exhibited high selectivity for the ketone product 135 over the alcohol 136. Contrary selectivity was achieved by use of the dicationic pre-catalyst 133 in THF, whereby rapid consumption of 134 was observed, resulting in the preferential formation of 136.…”

“…For all of these reactions employing 125 or 131, no appreciable ruthenium leaching was observed. [130] The synthesis and reactivity of rhodium and iridium coordination complexes of tris(pyrazolyl)methanesulfonate (tpms) have also appeared (Figure 7). Unlike more common k 2/3 -tris(pyrazolyl)borate (Tp) PGM species, for which resonance delocalization of the borate anionic charge onto the nitrogen donors leading to non-zwitterionic complexes is prevalent, analogous complexes of tpms that feature only MÀ N linkages can be viewed as being formally zwitterionic.…”

“…[128] The subsequent crystallographic characterization of 124, [129] 125, [130] and the iridium analogue of 122 [131] suggests that in this class of zwitterions, the sulfonate anion is spatially separated from the formally cationic PGM fragment. Although sulfonated phosphine ligands for use in preparing water-soluble transition metal complexes with applications in aqueous biphasic catalysis had been described previously, [132] the unique solubility profile of these zwitterionic sulphos complexes provided an entry point for the development of non-aqueous (alcohol/hydrocarbon) biphasic methods; 122 and 123 are not soluble in pure water, hydrocarbons, or diethyl ether, but do dissolve in light alcohols, such as methanol or ethanol, or in 1:1 (v/v) alcohol-water mixtures.…”

Immobilization of Optically Active Rhodium-Diphosphine Complexes on Porous Silica via Hydrogen Bonding

“…[4] We have recently introduced an alternative, facile and clean method for preparing silica-tethered polyphosphine metal catalysts, denoted supported hydrogen-bonded (SHB) catalysts, for use in both solid-gas and solid-liquid reactions in hydrocarbon solvents. [5,6] The procedure involves a hydrogen bonding interaction between the silanol groups of silica and sulphonate groups from the phosphine ligands and, possibly, also from triflate counter-anions [OTf = O 3 SCF 3 ]. Some of these SHB catalysts, namely (sulphos)Rh(cod)/SiO 2 (I) and…”