Phosphorus-Boron-Based Polymers Obtained by Dehydrocoupling of Ferrocenylphosphine-Borane Adducts

Dehydrocoupling of the ferrocenylphosphine–borane adducts [FcPH2(BH3)] (1) [Fc = Fe(C5H5)(C5H4)] and [FcCH2PH2(BH3)] (2) with [{Rh(μ‐Cl)(cod)}2] (cod = 1,5‐cyclooctadiene) as catalyst gave the corresponding phosphorus–boron‐based polymers [FcPH(BH2)]n (3) and [FcCH2PH(BH2)]n (4) as low‐ (heating in toluene, 3low and 4low) or high‐molecular‐weight (heating without solvent, 3high or 4high) poly(ferrocenylphosphinoborane)s depending on the reaction conditions. Dehydrocoupling of a racemic mixture of [2‐N,N‐dimethyl(N‐borane)aminomethyl‐1‐ferrocenyl]phosphine–borane (6) resulted in several products, as both BH3 moieties are apparently involved in polymer formation. Quaternization of the amino group in planar‐chiral [Fe(C5H5){C5H3(CH2NMe2)PH2}] (5) with MeI and treatment of the corresponding ammonium salt [Fe(C5H5){C5H3(CH2NMe3)PH2}]I (8) with BH3(THF) gave [Fe(C5H5){C5H3(CH2NMe3)PH2(BH3)}]I (9), which proved to be a suitable precursor for selective dehydrocoupling to yield an ionic polymer, namely, {[Fe(C5H5){C5H3(CH2NMe3)PH(BH2)}]I}n. The ferrocenylphosphine–borane adducts 1, 2, and 6 were characterized by 31P, 11B, 1H, and 13C NMR spectroscopy, and the polymers were characterized by multinuclear NMR and IR spectroscopy, gel permeation chromatography (GPC), and thermal analysis [differential thermal analysis (DTA)/thermogravimetry (TG)]. The ionic precursor 9 and the resulting polymer are highly insoluble and were characterized by solid‐state 31P NMR spectroscopy, IR spectroscopy, and thermal analysis. Molecular structures of 1, 6, 8, and 9 were determined by X‐ray crystallography. A new class of phosphine–borane adducts with ferrocenyl substituents, including the depicted ionic monomer containing a planar‐chiral ferrocene moiety, was prepared and employed in transition‐metal‐catalyzed dehydrocoupling {with [{Rh(μ‐Cl)(1,5‐cod)}2] (cod = 1,5‐cyclooctadiene) as catalyst} to give the first ferrocenyl‐substituted poly(phosphinoboranes).