Development of Highly Enantioselective Polymeric Catalysts Using Rigid and Sterically Regular Chiral Polybinaphthols

Rigid and Sterically Regular Chiral 1,1′-Binaphthyl Polymers in Asymmetric Catalysis

“…[12,13] This polymer again showed very low chemoselectivity as well as enantioselectivity. Besides the addition product 7, a side-product, benzyl alcohol, was also generated from the reduction of benzaldehyde.…”

“…In order to improve the catalytic properties of the polymer catalyst, a soluble polymer (R)-8 was prepared by linking the binaphthyl units at the 6,6'-position with phenylene spacers containing flexible hexyloxyl groups through a Suzuki coupling polymerization. [12,13] This polymer was used to catalyze the reaction of benzaldehyde with diethylzinc. Although improvements were seen, both the chemoselectivity and enantioselectivity were still low.…”

“…A polymer (R)-9 with a molecular weight of either MW 6700 (PDI 1.5) or MW 24,300 (PDI 2.5) (measured by gel permeation chromatography relative to polystyrene standards) was then prepared. [12,13] This polymer possesses two features that are different from polymers (R)-4 and (R)-8: 1) The phenylene spacers in (R)-9 are linked at the 3,3'-positions of the binaphthyl units rather than the 6,6'-positions. This is expected to provide better steric control at the catalytic sites.…”

“…[12,13] However, with the addition of [Ti(OiPr) 4 ], (S)-8 can catalyze the reaction with both high chemoselectivity (100 %) and high enantioselectivity (86 % ee). [23] The catalytic properties of the polybinaphthyltitanium complex (S)-16, generated from the reaction of (S)-8 with [Ti(OiPr) 4 ], are very similar to those of the titanium complex derived from the monomer 1,1'-bi-2-naphthol.…”

Asymmetric Catalysis with Helical Polymers

“…These polymers were recovered readily by precipitation with methanol and used again without loss of activity and selectivity. [30] A similar approach was followed by Takata and co-workers by using a poly(binaphthyl salen metal complex). [31,32] Salen manganese complexes 33-35 were shown to be capable of oxidizing alkenes, albeit with low enantioselectivity (Scheme 13 a).…”