Highly Enantioselective and Helix-Sense-Controlled Synthesis of Stereoregular Helical Polycarbenes Using Chiral Palladium(II) Catalysts

Living polymerization of diazoacetate monomers bearing an R- or S-methylbenzyl ester (1r or 1s) substituent by a chiral allylPdCl/L R catalyst gives polycarbenes with well-defined molecular weights and low polydispersity. Remarkably, these polymers exhibited unexpectedly high stereoregularity, as revealed by NMR studies. Moreover, the polymerization showed high enantioselectivity on the polymerization of the two enantiomers. The polymerization rate of the two enantiomers can be up to 130 times difference, albeit the chiral center is remote from the polymerization site. Interestingly, the isolated polymers showed high optical activity because the backbone formed a predominant one-handed helix, confirmed by circular dichroism spectra and direct atomic force microscope observation as well.