Sulfoxantphos ligands, supported ionic

Recently, van Leeuwen and co-workers provided support for the similarity between the active catalytic species in ionic liquids and in organic solvents by spectroscopic investigations [80]. These authors compared the complex formation of [Rh(acac)(CO)2] in the presence of 4 equivalents of sulfoxantphos ligand dissolved in [BMIM][PF6] and... 

The first fixed-bed application of a supported ionic liquid-phase catalyst was hydroformylation of propylene, with the reactants concentrated in the gas phase (265). The catalyst was a rhodium-sulfoxantphos complex in two ionic liquids on a silica support. The supported ionic liquid phase catalysts were conveniently prepared by impregnation of a silica gel with Rh(acac)(CO) and ligands in a mixture of methanol and ionic liquids, [BMIMJPFg and [BMIM][h-C8Hi70S03], under an argon atmosphere. 

In 2005, Riisager and Wasserscheid [109] linked a Rh(Sulfoxantphos) complex via [BMIM] [n-CgHj yOSOg] on a partly dehydroxylated silica support. In the hydroformylation of propene, a large dependence on the nature of the support and especially the P/Rh ratio was found. Fast deactivation took place at a small excess of the ligand. The stability of the supported ionic liquid phase (SILP) catalyst was directly related to the degradation of the catalytically active complex. 

Reaction conditions aUcenerCOrEL = 1 1 1, T = 100 °C, 0.2 wt% Rh metal loading, silica 100 p = 10 bar for guanidinium and norbos-Cs, p = 5 bar for sulfoxantphos ionic liquid used for impregnation [BMIM][PF6] a) molar ligand to metal ratio b) ratio of ionic liquid volume to support pore volume c) mol aldehyde per mol rhodium per hour d) ratio between linear and branched aldehyde e) support loaded with ionic liquid only. 

Importantly, it was also realized in these initial studies that the catalysts deactivated in prolonged use with simultaneous decrease in catalytic activity and selectivity, independent of the type of ionic liquid, ionic liquid loading a, and the ligand/rhodium ratio of the system. However, additional studies demonstrated a suitable thermal pre-treatment of the silica support to be necessary to obtain stable SILP catalysts. This technique was applied to prepare Rh-sulfoxantphos catalysts with [BMIMjfn-CsHiyOSOs] and similar systems without ionic liquid. Both systems were compared in 60 h continuous propene hydroformylation reactions using similar conditions as previously reported (Table 5.6-4, entries 11 and 12, Fig. 5.6-8) [93]. 

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