Recycling asymmetric hydrogenation catalysts by their immobilisation onto ion-exchange resinsElectronic supplementary information (ESI) available: Experimental section, 31P{1H} HP NMR spectra, typical EDS surface area spectrum and ESEM images. See http://www.rsc.org/suppdata/dt/b4/b406179a/

Abstract

New systems based on cationic chiral phosphine-rhodium complexes anchored to a commercial cation-exchange gel-type resin showed high efficiency and easy recycling in the asymmetric hydrogenation of prochiral olefins.

Recycling Asymmetric Hydrogenation Catalysts by Their Immobilization onto Ion‐Exchange Resins

“…[71] Recently, EDS analysis (energy dispersive X-ray spectrometery) coupled to ESEM microscopy (environmental scanning electron microscopy) was used to characterise asymmetric hydrogenation catalysts immobilised onto ionexchage resins. [48] Examples of typical ESEM images and EDS spectra are reported in Figures 2 and 3, respectively. [48,72] Use of the above tech-A C H T U N G T R E N N U N G niques proved to be particularly suited to investigate this kind of system, owing to the possibility to combine detailed analytical and morphological data at a nanometric level, without sample metallation and highvacuum conditions.…”

“…[48] Examples of typical ESEM images and EDS spectra are reported in Figures 2 and 3, respectively. [48,72] Use of the above tech-A C H T U N G T R E N N U N G niques proved to be particularly suited to investigate this kind of system, owing to the possibility to combine detailed analytical and morphological data at a nanometric level, without sample metallation and highvacuum conditions. [73] Metal loading estimates obtained by EDS analysis were comparable to those obtained through atomic emission spectroscopy.…”

“…[44] Because of the high solvation of lithium, swelling is also highest for Li + -derivatised resins (Scheme 2). [44,48] Mechanical instability and difficulty of preparation prevented the use of very low cross-linked resins.…”

“…Use of cation-exchange resins as insoluble supports for asymmetric hydrogenation catalysts is motivated by the fact that four-coordinate, cationic, rhodium(i) complexes are among the most used homogeneous catalysts for enantioselective alkene reduction. [53,[68][69][70] The preformed, molecular complexes of the formula [Rh(PP)-A C H T U N G T R E N N U N G (diolefin)]X were used for this purpose: PP is the bis-chelate chiral phosphine ligand Ph-bglup, [43][44][45][46] propraphos, [43][44][45][46] norphos, [47] DIOP [47,48] or TMBTP [48] depicted here; diolefin is…”

“…[46][47][48] Indeed, catalyst loadings in the range 0.3-1.4 % (Rh, w/w) were estimated by using various techniques, corresponding to a 17-99.9 % of the total amount of complex used in the immobilisation process. Selected examples are reported in Table 2.…”