Polystyrene and polymethacrylate resin-supported Jacobsen’s alkene epoxidation catalyst

Abstract

Polystyrene and polymethacrylate-based resin supported Jacobsen's chiral Mn salen complexes have been prepared. The resins are of defined molecular structure and morphology, and the complexes have been attached primarily in a pendant fashion. The loadings of Mn() are in the range ~0.08-0.35 mmol g Ϫ1 to maximise the likelihood of site-isolation. The polymer-supported complexes have been used as enantioselective catalysts in the epoxidation of 1,2-dihydronaphthalene, indene, 1-phenylcyclohex-1-ene and 1-phenyl-3,4-dihydronaphthalene using m-chloroperbenzoic acid as the oxidant and 4-methylmorpholine N-oxide as the co-oxidant. Though the activities of the polymer catalysts are reduced relative to the soluble homogeneous analogue, the catalysts are sufficiently active to be useful. The corresponding reduction in enantioselectivity is more significant, and is both substrate and polymer resin dependent. However, in the case of 1-phenylcyclohex-1-ene and a macroporous polymethacrylate-based resin the enantioselectivity is equivalent to that of the soluble complex (91-92% ee). This is the first report of a polymersupported analogue of Jacobsen's catalyst being as selective as the homogeneous species. The catalysis data is discussed in detail in the context of the design of the polymer-supported system, and the existing data already available in the literature.Attempts have also been made to recycle the polymer catalysts with and without re-loading of Mn. In fact the level of leaching of Mn is very low, but the catalysts show a very rapid fall off in both activity and selectivity in the first and second cycles. Overall therefore it seems that the intrinsic stability of the chiral Mn() salen complex itself is too low to allow viable recycling, and the development of other more stable supported chiral metal salen complexes for use in other enantioselective reactions seems a better future option.

Hydroxyl Functionalized Methacrylic Terpolymers as Supports for Mn(III) Salen Catalysts and Their Application in Asymmetric Epoxidation

“…A slightly less enantiomeric excess of (1S,2R)-epoxyindene (69% ee) was obtained when the catalyst 6.1 (S,S) was applied for epoxidation. The obtained results are clearly better than those described by Sherrington and co workers [31] observed polystyrene and polymethacrylatebased resin supported chiral Mn salen complexes (33% ee (1R,2S)-indene oxide). However they are not such good as ones found by Kureshy et al [32] for the catalysts obtained by immobilization of chiral Mn(III) salen complex on mesoporous materials such as MCM-41 (80% ee) and SBA-15 (81% ee).…”

Engineering Polymer‐Enhanced Bimetallic Cooperative Interactions in the Hydrolytic Kinetic Resolution of Epoxides

“…Chlorobenzene was distilled over calcium dihydride and stored in a Schelenk flask under argon. (4-Vinylphenyl)methanol (1a), [17] 2-(4-vinylbenzyloxy)ethanol (1b), [18] 2-[2-(4-vinylbenzyloxy)ethoxy]ethanol (1c), [19] 2-{2-[2-(4-vinylbenzyloxy)ethoxy]ethoxy}etha-nol (1d), [20] (1R,2R)-1,2-diaminocyclohexane mono(hydrogen chloride) (3), [15,16] 3-tert-butyl-5-(chloromethyl)-2-hydroxybenzaldehyde, [21] and polyA C H T U N G T R E N N U N G (styrene)-supported Co-A C H T U N G T R E N N U N G (salen) complex Co(7) (cobalt loading: 1.37 mmol/ g, degree of polymerization: x = 24) [12a] were prepared according to published procedures. NMR spectra were acquired with a [a] Catalyst loadings based on cobalt.…”

Polyglycerol‐Supported Chromium‐Salen as a High‐Loading Dendritic Catalyst for Stereoselective Diels–Alder Reactions

“…[5d, 22,23] The first arene moiety of the salen ligand was generated by attachment of 3-tert-butyl-5-(chloromethyl)-2-hydroxybenzaldehyde 6 [25] to the PG 3.…”