Synthesis, structure and polymerization behaviour of borane adducts of a phosphorus-bridged [1]ferrocenophane, [(η-C5H4)2FePPh]

Abstract

Phosphorus(III)-bridged [1]ferrocenophanes cannot be polymerized via transition-metal catalyzed ring-opening polymerization, presumably due to the phosphorus lone pair ligating the catalyst. We have investigated a potential solution to this problem, which involves protection of the phosphorus lone pair through the formation of borane adducts. The adducts [(η-C₅H₄)₂FeP(Ph)BX₃] (2, X=H; 3, X=Cl) were synthesized in high yield from the reactions of appropriate boranes with P-phenylphospha[1]ferrocenophane, 1, and fully characterized by NMR, UV–Vis, MS, elemental analysis, and X-ray crystallography. Ring-opening polymerizations of 2 and 3 have been attempted both thermally and using transition-metal catalysts, resulting in insoluble polymeric products, [(η-C₅H₄)₂FeP(Ph)BX₃]_n (5, X=H; 6, X=Cl), which have been characterized by solid-state NMR and by pyrolysis-MS. Well-defined borane adducts of poly(ferrocenylphenylphosphine), [(η-C₅H₄)₂FeP(Ph)BX₃]_n (5b, X=H; 6b, X=Cl) were synthesized and characterized to provide comparative data for the insoluble products 5a, 6a and 6c. The data support the conclusion that both 2 and 3 may be ring-opened thermally to provide polymeric products consistent with the corresponding adducts of poly(ferrocenylphenylphosphine) 4. In contrast, transition-metal catalyzed ROP proceeds inefficiently, leading predominantly to products of unknown structure.