Stille type P–C coupling polycondensation towards phosphorus-crosslinked polythiophenes with P-regulated photocatalytic hydrogen evolution

Recently, exploring new type polymerization protocols has been a major driving force in advancing organic polymers into highly functional materials. Herein we report a new polycondensation protocol to implant the phosphorus (P) atom in the main backbone of crosslinked polythiophenes. The polycondensation harnesses a Stille phosphorus-carbon (P-C) coupling reaction between phosphorus halides and aryl stannanes that has not been reported previously. Mechanistic studies uncovered that the P-electrophile makes the reactivity of a catalytic Pd-center highly sensitive towards the chemical structures of aryl stannanes, which is distinct from the typical Stille carbon-carbon coupling reaction. The efficient P-C polycondensation afforded a series of P-crosslinked polythiophenes (PC-PTs). Leveraging on the direct P-crosslinking polymerization, solid-state 31P NMR studies revealed highly uniform crosslinking environments. Efficient post-polymerization P-chemistry was also applied to the PC-PTs, which readily yielded the polymers with various P-environments. As a proof of concept, new PC-PTs were applied as the photocatalysts for H2 evolution under visible light irradiation. PC-PTs with an ionic P(Me)-center exhibit a H2 evolution rate up to 2050 μmol h-1 g-1, which is much higher than those of PC-PTs with a P(O)-center (900 μmol h-1 g-1) and P(iii)-center (155 μmol h-1 g-1). For the first time, the studies reveal that regulating P-center environments can be an effective strategy for fine tuning the photocatalytic H2 evolution performance of organic polymers.