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

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.