New Chiral Catalyst, t-Butyllithium Complexed with Axially Chiral Diamine, for Asymmetric Polymerizations of Triphenylmethyl Methacrylate and Its 2-Pyridyl Derivative

Abstract

ABSTRACT:Asymmetric polymerizations of achiral methacrylates such as bulky triphenylmethyl and diphenyl-2-pyridylmethyl esters were investigated in toluene at -78°C. t-Butyllithium complexed with a tetramethylethylenediamine derivative having an axially chiral 6,6'-dimethylbiphenyl-2,2'-diyl substituent (1) at -78°C was found to be a versatile chiral initiator for the above polymerizations. The produced poly(ester)s were easily soluble in THF, because of the limited molecular weights. The polymers of helical conformation showed large optical rotations, whose signs depended on the chirality of the used 1.KEY WORDS Asymmetric Polymerization / Helix / Triphenylmethyl Methacrylate / Diphenyl-2-pyridylmethyl Methacrylate / Axially Chiral Biphenyl / Tetramethylethylenediamine Derivatives / Butyllithium / PTrMA D2PyMAIn past years, much attention has been focused on optically active polymers obtained from bulky methacrylates such as triphenylmethyl methacrylate (TrMA) 1 -3 and diphenyl-2-pyridylmethyl ester (D2PyMA). 4 · 5 The optical activity of these polymers is attributed to the helical conformation stabilized by the isotactic sequence of bulky ester groups. 6 The conformation prevailing in one screw sense is formed through asymmetric polymerizations with chiral anionic initiators. 1 -5 The molecular weights of the polymers are critical for their solubility. Especially organic solventsoluble parts have been found by Okamoto et al. to be useful materials as chiral solid phases of high performance liquid chromatography for the optical resolution of various racemic substances. 5 • 7 We have already reported that chiral complexes of organolithiums with tetramethylethylenediamine (TMEDA) derivatives (1 and 2) having biaryl substituents also serve as excellent catalysts for the asymmetric polymerization of TrMA. 8 • 9 It is considered that the high stereoselectivities of these catalysts are ascribed to complementary effects between the chirality-recognizing ability of biaryl units and the flexibility of the TMEDA side-arm for