Tailor-made poly(vinylidene sulfide)s by Rh(I)-NHC catalyzed regioselective thiol-yne click polymerization

The [Rh(μ-Cl)(IPr)(η2-coe)]2/pyridine system efficiently catalyzes the polyhydrothiolation of a series of dialkynes with dithiols, producing sulfur-rich poly(vinylidene sulfide)s with a typical Mw in the range 20.000-124.000 and vinylidene content of 75-87%. A combination of flexible aliphatic dithiols, including 1,6-hexanedithiol and 2,2’-(ethylendioxy)diethanethiol, and the rigid aromatic dithiol 4,4’-thiobisbenzenethiol, with rigid aromatic dialkynes, 1,3-diethynylbenzene and 1,4-diethynylbenzene, and flexible dialkynes, including propargyl ether and 1,7-octadiyne, have been used to prepare poly(vinylidene sulfide)s. The copolymerization of flexible dithiols with rigid aromatic dialkynes or vice versa results in high molecular weight polymers, Mw up to 259.000, with low polydispersities. However, polyhidrothiolation of flexible dialkynes with flexible dithiols is much less efficient and usually results in the formation of oligomers. The interplay of the IPr and pyridine ligands on the RhCl(IPr)(py)(η2-coe) catalyst, which controls the regioselectivity of the alkyne insertion step towards the branched vinyl sulfide, is key in the preparation of these poly(vinylidene sulfide)s.