Synthesis of side-chain regioregular and main-chain alternating poly(bichalcogenophene)s and an ABC-type periodic poly(terchalcogenophene)

Three unsymmetrical diiodobichalcogenophenes SSeI₂, STeI₂, and SeTeI₂ and a diiodoterchalcogenophene SSeTeI₂ were prepared. Grignard metathesis of SSeI₂, STeI₂, SeTeI₂, and SSeTeI₂ occurred regioselectively at the lighter chalcogenophene site because of its relatively lower electron density and less steric bulk. Nickel-catalyzed Kumada catalyst-transfer polycondensation of these Mg species provided a new class of side-chain regioregular and main-chain AB-type alternating poly(bichalcogenophene)s - PSSe, PSTe, and PSeTe - through a chain-growth mechanism. The ring-walking of the Ni catalyst from the lighter to the heavier chalcogenophene facilitated subsequent oxidative addition, thereby suppressing the possibility of chain-transfer or chain-termination. More significantly, the Ni catalyst could walk over the distance of three rings (ca. 1 nm) - from a thiophene unit via a selenophene unit to a tellurophene unit - to form PSSeTe, the first ABC-type regioregular and periodic poly(terchalcogenophene) comprising three different types of 3-hexylchalcogenophenes.