Chiral polymeric

Transition metal coupling polymerization has also been used to synthesize optically active polymers with stable main-chain chirality such as polymers 33, 34, 35, and 36 by using optically active monomers.29-31 These polymers are useful for chiral separation and asymmetric catalysis. For example, polymers 33 and 34 have been used as polymeric chiral catalysts for asymmetric catalysis. Due... 

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

Shamsi, S. A. (2001). Micellar electrokinetic chromatography-mass spectrometry using a polymerized chiral surfactant. Anal. Chem. 73, 5103-5108. 

The low thermal stability and the volatility of some of the low molecular weight stationary phases restricted their general use. Therefore, thermally stable and nonvolatile polymeric chiral stationary phases were developed by coupling the diamide phase, via the amino functionality, to a statistical copolymer of dimethylsiloxane and (2-carboxypropyl)methylsiloxane of appropriate viscosity131. The fluid polymeric phase, referred to as Chirasil-Val (Table 2), exhibits excellent properties for the enantiomer separation of a variety of compound classes over a broad temperature range141142. 

However, in this context CPSs are defined throughout this article as very stable phy-sisorbed (physically absorbed) and/or most often covalently bound chiral selector compounds to a nonchiral (most often silica) surface. To the same category belong the CSPs, which have as their bases beads of polymeric chiral selector material. The strong irreversible adsorption of chiral selector molecules (macromolecules or small molecules onto a plain or premodified surface) depends, of course, on the nature of the mobile phase and whether or not it has some solvation strength for the adsorbed chiral selector moiety. 

A third type of synthetic polymer-based chiral stationary phase, developed hy Blaschke. is produced when a chiral selecior is either incorporated within the polymer network or attached as pendant groups onto the polymer matrix. Both arc analogous to methods used lo produce polymeric chiral stationary phases for gc. 

Chromatographic separatum of enantiomersThe carbamate, ureido, and amide derivatives obtained without racemization from enantiomeric amines, alcohols, and carboxylic acids, respectively (equations T III), with this isocyanate are stable for months and are suitable for gas chromatographic separation using a polymeric chiral stationary phase (derived, for example, from L-valine-(S)-a-phenylethylamide). This methodology permits separation of chiral a- and /1-hydroxy acids and also N-mclhylnmino acids. 

Pfeiffer, J. and Schurig, V. (1999) Enantiomer Separation of Amino Acid Derivatives on a New Polymeric Chiral Resorc[4]arene Stationary Phase by Capillary Gas Chromatography, J. Chromatogr. A 840, 145-150. 

In research with Ziegler catalysts, Cossee (11) and Arlmann and Cossee (12) hypothesized that the insertion of propylene monomer takes place in a cis conformation into a titanium-carbon bond. Natta et al. (8) postulated that in the stereospecific polymerization, chiral centers on the surface are needed to produce isotactic polymers. These and other issues regarding the nature of the active sites have helped to increase the interest in investigations of homogeneous metallocene catalysis. 

S. Anderson, S. Allenmark, P. Moller, B. Persson, and D. Sanchez, Chromatographic separation of enantiomers on V,V -diallyl-L-tartardiamide-based network—Polymeric chiral stationary phases, J. Chromatogr. 741 (1996), 23. 

Not only polystyrene supports, also other polymer supports were used in the preparation of polymeric amino alcohol ligands for dialkylzinc alkylation. For example, a vinylferrocene derivative with A,N -disubstituted norephedrine was copolymerized with vinylferrocene [60]. This polymeric chiral ligand (53) was used in the ethylation of aldehydes with moderate activity. Brown has reported that chiral oxazaborolidines have catalytic activity in the addition of diethyl zinc to aldehydes [61]. Polymers bearing chiral oxazaborolidines 37 were also active in the reaction and result on moderate enantioselectivity (<58 % ee) [62]. Enantiopure a,a -diphenyl-L-prolinol coupled to a copolymer prepared from 2-hydroxyethylmethacrylate and octadecyl methacrylate... 

The soluble polymer-supported catalysts have also been used for asymmetrically catalyzed reactions Following a procedure for the preparation of insoluble polymeric chiral catalysts a soluble linear polystyrene-supported chiral rhodium catalyst has been prepared. This catalyst displays high enantiomeric selectivity compared to the low molecular weight catalyst. Thus, hydroformylation of styrene using this catalyst produces aldehydes in high yields. The branched chiral hy drotropaldehy de is formed in 95% selectivity. 

As for the use of monomeric and polymeric chiral surfactants as pseudo-stationary phases for enantiomer separations in MEKC, a review article has been available. 

Types of particulate packings include bonded, polymeric, chiral, and restricted access materials. 

The enantioselective alkynylation of ketones catalyzed by Zn(salen) complexes has been reported [24]. Polymeric salen ligand 30 was prepared with a polycondensation reaction and subsequently used as a polymeric chiral ligand of Zn. The polymeric Zn(salen) complex (prepared by 30) was then used as a catalyst of asymmetric addihon of phenylacetylene to aldehyde in the presence of 2 equivalents of Et/Zri. Subsequent asymmetric alkynylahon of 31 gave 33 in 96% yield and 72% ee (Scheme 3.9) [25]. 

Scheme 3.12 illustrates the polymer-supported aUylboron reagents derived from chiral N-sulfonylamino alcohols and used for the asymmetric synthesis of homoal-lylic alcohols and amines (see Scheme 3.12) ]29]. All of these asymmetric allylbora-tions were performed using the polymeric chiral aUylboron reagent prepared from triallylborane and PS-supported N-sulfonylamino alcohols 38-41. High levels of enantioselectivity were obtained in the asymmetric allylboration of imines with the polymeric reagent derived from norephedrine.

In recent years, catalytic asymmetric Mukaiyama aldol reactions have emerged as one of the most important C—C bond-forming reactions [35]. Among the various types of chiral Lewis acid catalysts used for the Mukaiyama aldol reactions, chirally modified boron derived from N-sulfonyl-fS)-tryptophan was effective for the reaction between aldehyde and silyl enol ether [36, 37]. By using polymer-supported N-sulfonyl-fS)-tryptophan synthesized by polymerization of the chiral monomer, the polymeric version of Yamamoto s oxazaborohdinone catalyst was prepared by treatment with 3,5-bis(trifluoromethyl)phenyl boron dichloride ]38]. The polymeric chiral Lewis acid catalyst 55 worked well in the asymmetric aldol reaction of benzaldehyde with silyl enol ether derived from acetophenone to give [i-hydroxyketone with up to 95% ee, as shown in Scheme 3.16. In addition to the Mukaiyama aldol reaction, a Mannich-type reaction and an allylation reaction of imine 58 were also asymmetrically catalyzed by the same polymeric catalyst ]38]. 

A similar approach has been examined by using polymer-supported ALB 91 (Scheme 3.25). When this polymeric chiral ALB catalyst was used for the asymmetric Michael reaction, the corresponding chiral adduct was obtained in 91% yield with 96% ee [48]. 

A poly(bmaphthyl metallosalen complex) 128 (Scheme 3.36) was prepared and used as a catalyst for the asymmetric epoxidation of alkene [72]. Although enantioselectivities obtained by using the polymeric catalyst were low, this represented a new type of polymeric chiral complex based on the main-chain hehcity. 

Seebach introduced a novel concept for the immobilization of chiral ligands in PS. The ligand of choice was placed in the core of a styryl-substituted dendrimer 134, which was copolymerized with styrene under suspension polymerization conditions to give the polymeric chiral ligand 135 [74]. The corresponding polymeric (salen) Mn complexes were used to catalyze the enantioselective epoxidation of alkene (Scheme 3.38), with the polymeric complexes being recycled ten times... 

Sharpless asymmetric epoxidation was also conducted by using polymer-supported catalysts. Some very interesting phenomena were observed when methoxy PEG (MeO-PEG) -supported tartrate 147 was used as the polymeric chiral ligand (Scheme 3.43). In the epoxidation of 148 under Sharpless epoxidation conditions, 2S,3S -trans 149 with 93% ee was obtained using 147 (MW = 750), while (2R,3R)-trans 149 with 93% ee was obtained using 147 (MW = 2000) [80]. More recently, Janda studied the precise effects of the molecular weight of the PEG chain on the... 

An alternative approach is the use of a PS support bearing sulfonate pendant groups. For this, a quaternary ammonium salt of styrenesulfonic acid was copolymerized with a N-(p-styrenesulfonyl)-l,2-diphenylethylenediamine monomer. The polymeric chiral Ru complex was prepared from 177 and [RuCl2(p-cymene)]2 and applied to the asymmetric transfer hydrogenation of aromatic ketones in water (Scheme 3.55) [114]. The polymeric chiral complex was evenly suspended in water and the reaction proceeded smoothly to produce the alcohol in quantitative yield and with high enantioselectivity. For several of the aromatic ketones tested, higher... 

Among the many examples of asymmetric hydrogenation catalysts that have been developed, chiral complexes prepared from 1,2-dianiines and RuCb/diphosphines provide one example of the most powerful catalysts for this reaction. Polymer-supported fR -BINAP was treated with RuCh and fR,R -l,2-diphenylethylenedi-amrne to give the polymeric chiral complex 180 (Scheme 3.56) this serves as an excellent precatalyst for the asymmetric hydrogenation of aromatic ketones to give the chiral secondary alcohols in quantitative yields with 84—97% ee-values [115]. For example, the asymmetric hydrogenation of I -acetonaphthone with (R,RR)-180 occurred in quantitative conversion within 26 h with 98% ee. The enantioselectivity, turnover number (TON) and turnover frequency (TOF) in this reaction... 

Polymer-supported Ru precatalysts were prepared from the polymeric chiral... 

---