Thermal ring-opening polymerization (ROP) of strained, ring-tilted, phosphorus-bridged [1]ferrocenophanes: Synthesis of poly(ferrocenylphosphines) and poly(ferrocenylphosphine sulfides)

Article abstract of DOI:10.1021/om00012a017

A series of phosphorus(III)-bridged [1]ferrocenophanes Fe[η-C₅H₃R)(η-C₅H ₃R′)]PX (X = Ph, R = R′ = H (3); X = Cl, R = R′ = H (4); X = Ph, R = H, R′ = ⁿBu (5); X = Ph, R = R′ = SiMe₃ (6)) have been synthesized via the reaction of Fe[(η-C₅H₃RLi)(η-C₅H ₃R′Li)]·nTMEDA with PXCl2 (X = Cl, Ph). The reaction of 6 with an excess of elemental sulfur resulted in the quantitative formation of the phosphorus(V)-bridged species Fe[η-C₅H₃SiMe₃]₂P(S)Ph (7). The new compounds 4-7 were characterized by multinuclear NMR, by mass spectrometry and, in the cases of 4, 6, and 7, by single-crystal X-ray diffraction and elemental analysis. Ring-tilt angles (α) for 4 and 6 were found to be typical of phosphorus(III)-bridged [1]ferrocenophanes (4, 27.0(6)°; 6, 27.5(6)??) whereas in the case of the phosphorus(V)-bridged species 7 the tilt angle was slightly less (α = 25.3(3)°). The thermal ring-opening polymerization of 3, 5, and 6 at 120-250°C yielded the poly(ferrocenylphosphines) 8-10, respectively. These materials were characterized by multinuclear NMR and by elemental analysis. The molecular weight of the trimethylsilyl-substituted polymer 10 was determined by GPC in THF versus polystyrene standards to be M_w = 66 000, PDI = 1.98, whereas 8 and 9 failed to elute from the GPC column. The phosphorus(V)-bridged species 7 also underwent thermal ring-opening polymerization to yield the poly(ferrocenylphosphine sulfide) 13 which was analyzed by GPC (M_w = 22 000, PDI = 1.24); thermally-induced elimination of S(SiMe₃)₂ from the ring-opened polymer was identified as a side reaction. The macromolecular reactions of 8-10 with elemental sulfur yielded the poly(ferrocenylphosphine sulfides) 11-13. These were structurally characterized by multinuclear NMR and elemental analysis and their molecular distributions were analyzed by GPC (M_w = 18 000-65 000, PDI = 1.5-2.3).