Polymerization Studies of Diiodohexatriyne and Diiodooctatetrayne Cocrystals

The formation of
ordered polydiacetylenes (PDAs) from conjugated
triynes and longer polyynes has proven challenging due to the low
stability of the starting materials and the possibility of varying
regiochemistry for the polymerization. We report here the preparation
of host–guest cocrystals of diiodohexatriyne and diiodooctatetrayne,
each with a bis­(nitrile)­oxalamide host. Single-crystal X-ray diffraction
studies show that the halogen-bonding interactions between the host
and guest align the diiodopolyyne monomers with the proper parameters
for 1,4-topochemical polymerization. Using Raman spectroscopy, solid-state 13C MAS NMR, and single-crystal X-ray diffraction, we have
demonstrated the formation of a single highly ordered PDA, poly­(iodoethynyl­iododiacetylene)
(PIEDA), from the 1,4-polymerization of diiodohexatriyne. Diiodo­octatetrayne
also forms ordered cocrystals, but attempts to form polymer from these
crystals led to disordered species. This work represents the first
reported single-crystal-to-single-crystal 1,4-polymerization of a
conjugated triyne.