Depolymerization of Poly(phosphinoboranes): From Polymers to Lewis Base Stabilized Monomers

We report on depolymerization reactions of poly(phosphinoboranes). The cleavage of the polymers [H2PBH2]n (2 a), [tBuHPBH2]n (2 c), [PhHPBH2]n (2 e) and the oligomer [Ph2PBH2]n (2 b), with strong Lewis bases (LBs), in particular with NHCs, leads to the corresponding monomeric phosphanylboranes R1R2PBH2LB. It is observed that the depolymerization depends on the strength and stability of the LBs as well as on the substitution pattern of the poly(phosphinoboranes). The solid state structures of the monomeric phosphinoboranes H2PBH2NHCMe (NHC=N‐heterocyclic carbene) (4 a), H2PBH2NHCdipp (5 a) and tBuHPBH2NHCMe (4 c) were determined. DFT calculations support the experimentally observed reaction behavior. Back to the monomers! A recycling strategy for high molecular weight poly(phosphinoboranes) by depolymerization with strong Lewis bases was discovered. N‐heterocyclic carbenes proved to be a valuable tool for these cleavage reactions.