Ring-opening metathesis polymerization for the preparation of surface-grafted polymer supports

A series of norbornene-based, L-valine- and L-phenylalanine-containing chiral monomers have been prepared. Starting from norborn-2-ene-5-carboxylic acid chloride and norborn-2-ene-5,6-dicarboxylic anhydride, N-(norborn2-ene-5-carboxyl)-L-valine (I), N-(norborn-2-ene-5-carboxyl)-Lphenylalanine (II), N-(norborn-2-ene-5-carboxyl)-L-phenylalanine ethyl ester (III), the N,N-(norborn-2-ene-5,6-dicarbimid) (NBDCI)-protected amino acid derivatives NBDCI-L-valine (IV), NBDCI-L-phenylalanine (V), NBDCI-L-valine-tert-butylamide (VI), NBDCI-L-valine-anilide (VII), NBDCI-L-valine-m-nitroanilide (VIII), and NBDCI-L-valine-p-chloroanilide (IX) have been synthesized. Compounds I-M were polymerized via ring-opening metathesis polymerization (ROMP) using initiators based on both molybdenum (Mo(N-2,6-Me2-C(6)H(3))(CHCMe(2)Ph)(OCMe(CF(3))(2))(2)) (1) and ruthenium (Cl(2)Ru(CHPh-p-F)(PCy(3))(2), CY = cyclohexyl) (2). The polymers were characterized in terms of cis/trans structure as well as optical rotation. Bromomethylated, beaded polymer supports based on poly(styrene-divinylbenzene) (PS-DVB) were prepared either via direct bromomethylation or via transhalogenation of chloromethyl-PS-DVB and subsequently surface-derivatized with norborn-2-ene groups by reaction with sodium norborn-2-ene-5-ylmethanolate. Norborn-2-ene-derivatized silica-based supports were prepared by silanization employing norborn-2-ene-5-yltrichlorosilane. Surface grafting of the norbornene-modified supports with monomers III, VI, and VII was accomplished using ROMP. Both Schrock-type and Grubbs-type initiators were found suitable for that purpose. A poly-III surface-grafted, porous 5 mu m silica was found suitable for chiral HPLC separations.