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

We report on depolymerization reactions of poly(phosphinoboranes). The cleavage of the polymers [H2 PBH2 ]n (2 a), [tBuHPBH2 ]n (2 c), [PhHPBH2 ]n (2 e) and the oligomer [Ph2 PBH2 ]n (2 b), with strong Lewis bases (LBs), in particular with NHCs, leads to the corresponding monomeric phosphanylboranes R1 R2 PBH2 LB. 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 H2 PBH2 NHCMe (NHC=N-heterocyclic carbene) (4 a), H2 PBH2 NHCdipp (5 a) and tBuHPBH2 NHCMe (4 c) were determined. DFT calculations support the experimentally observed reaction behavior.