Alternating right- and left-handed helical loops in a self-assembled polymer: direct observation of ring-opening polymerization of a macrocyclic gold complex.

Reaction of the ligand NN'-bis(pyridin-3-yl)-1,3-benzenedicarboxamide (1) with the diphosphanedigold(I) complex [(mu-PP)(AuO2CCF3)2] occurred by displacement of the trifluoroacetate ligands by the pyridyl groups of 1, and crystallization gave the macrocyclic complex [Au2(mu-PP)(mu-1)](CF3CO2)2 (2b), when PP = trans-[Ph2PCH=CHPPh2] but the polymer [(Au2(mu-PP)(mu-1)]x](CF3CO2)2x (3), when PP= Ph2PCH2CH2PPh2. The polymer 3 contains a series of helical turns connected by linear chain sections. and the helices have alternating right- and left-handed conformations. The polymer 3 dissolves to give an equilibrium mixture of the macrocyclic ring complex [Au2(mu-PP)(mu-1)](CF3CO2)2 (2a), and ring-opened oligomers, thus giving insight into the mechanism of the ring-opening polymerization reaction.