Eight-Membered-Ring-Forming Chain-Growth Cyclopolymerization of 2,2'-Diisocyano-1,1'-binaphthalenes for the Synthesis of Helical Poly([1,4]diazocine-2,3-diyl)s

25 October 2024, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Novel helical macromolecules, poly([1,4]diazocine-2,3-diyl)s (PDACs), are synthesized by cyclopolymerization of 2,2'-diisocyano-1,1'-binaphthalenes in the presence of organonickel or organopalladium complexes as initiators, with the former being more efficient. The polymerization proceeds in a living fashion similar to the polymerization of monoisocyanides, but involves the formation of an eight-membered [1,4]diazocine ring, resulting in the exclusive formation of an array of [1,4]diazocine rings connected at their 2,3-positions without forming a monoiminomethylene unit. The structure of PDAC was identified by 13C-labeling experiments, mass spectrum, and X-ray crystallographic analysis of the isolated living 2-([1,4]diazocinyl)palladium complex. The conformation of the main PDAC chain obtained from (R)-2,2'-diisocyano-1,1'-binaphthalene is deduced from DFT calculations, which reveal that the two C=N bonds in the diazocine ring form a dihedral angle of –73(+-5), while the two inter-unit C=N bonds exhibit a nearly anti (+167(+-4)) orientation, resulting in the formation of a left-handed helical main chain. The enantiopure monomer polymerized significantly faster than the racemic monomer, forming stereoisomeric PDACs, the NMR spectra of which differ.

Keywords

Polyisocyanide
Helical polymer
Coordination polymerization
Isonitrile
Axial chirality

Supplementary materials

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Supporting Information
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General procedure of experiments and spectral information of new compounds.
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