Optically active poly(diphenyl‐2‐pyridylmethyl methacrylate): Asymmetric synthesis, stability of helix, and chiral recognition ability

Abstract

Abstract Dipheny‐2‐pyridylmethyl methacrylate (D2PyMA) was anionically polymerized with several organolithium complexes of chiral ligands such as (‐)‐sparteine (Sp), ( S,S )‐( + )‐ and ( R , R )‐(‐)‐2,3‐dimethoxy‐1,4‐bis(dimethylamino)butane [(+)‐ and (‐ )‐DDB], ( S )‐(‐)‐1 ‐ methyl‐2‐(piperi‐dinomethyl)pyrrolidine (MPP), ( S,S )‐( + )‐3,4‐dimethoxy‐ N ‐(2‐(dimethylamino)ethyl)pyrrolidine (DDEP), and ( S,S )‐(+ )‐ N ‐benzyl‐3,4‐dimethoxypyrrolidine (BDP) in toluene at low temperature. Sp complexes gave a polymer of low optical activity. DDB was a better chiral ligand, and its complex, particularly the complex with N,N' ‐diphenylethylenediamine monolithium amide (DPEDA‐Li), was effective in preparing a polymer of high optical rotation. A THF‐soluble portion of the polymer obtained with (‐)‐DDB‐DPEDA‐Li showed [α] 25/365 about ‐ 1400°, which was comparable to that of poly(triphenylmethyl methacrylate) (PTrMA) with pure one‐handed helical structure. However, in the polymerization with DDB‐DPEDA‐Li, optical rotation of the polymer depended greatly on polymerization conditions, such as monomer and initiator concentrations, reaction temperature, and polar additives. Fractionation by THF and/or gel permeation chromatography of the obtained polymers revealed that poly(diphenyl‐2‐pyridylmethyl methacrylate) (PD2PyMA) consisted of a mixture of (+)‐ and (‐)‐ polymers which probably were not enantiomeric to each other. DDEP‐DPEDA‐Li and DDEP‐fluorenyllithium complexes were also efficient chiral initiators that gave polymer of the same or higher optical rotation in comparison with DDB complexes. The optical rotation of PD2PyMA in CHCl 3 ‐2,2,2‐trifluoroethanol (90:10) slowly changed with time. Optically active PD2PyMA coated on macroporous silica gel resolved racemic compounds as a chiral stationary phase for high‐performance liquid chromatography (HPLC).