Screw sense differentiating polymerization of achiral isocyanides

Screw Sense Selective Polymerization of Achiral Isocyanides Catalyzed by Optically Active Nickel(II) Complexes

Poly(isocyanidcs), ( R N = C < ) n, can be prepared from isocyanidcs, R N += C " , by the catalytic action of nickel(II) compounds. The main chain of these polymers is a rigid helix. This helical conformation results from a restricted rotation around the single bonds that connect the main-chain carbon atoms. Polymerization of achiral isocyanides generally gives a racemic mixture of leftand righ...

Intermediate Species in the Polymerization of Isocyanides

Helix-sense selective polymerization of carbodiimides: building permanently optically active polymers from achiral monomers.

The helix-sense selective polymerization of achiral monomers by homochiral catalysts was investigated. Polymerization of chiral carbodiimides (N-(R)-2,6-(dimethylheptyl)-N'-phenylcarbodiimide) by achiral catalysts yields polymers that undergo mutorotation at elevated temperatures, thus illustrating that these chains are formed under kinetic rather than thermodynamic control. Building on this ob...

Controlling the sign and magnitude of screw-sense preference from the C-terminus of an achiral helical foldamer.

The global screw-sense preference of an achiral helical oligomer may be controlled by a single chiral monomer located at one terminus. Remarkably, maximal control is induced in oligomers of the achiral quaternary amino acid Aib by a single C-terminal alaninamide residue, probably because the Ala side chain, though small, is compatible with a 310 helical conformation. The presence or absence of ...

Isoselective ring-opening polymerization of rac-lactide initiated by achiral heteroscorpionate zwitterionic zinc complexes.

A highly isotactic stereoblock PLA has been obtained using the achiral heteroscorpionate zwitterionic zinc complexes as catalysts, for the first time, via a chain-end control mechanism.