Synthesis, Structure, and Ring-Opening Polymerization (ROP) of a Phosphonium-Bridged [1]Ferrocenophane

The stable phosphonium-bridged [1]ferrocenophane [(η-C 5 H 4 ) 2 FePPhMe][OTf] ( 10b ) was synthesized by the reaction of the phosphorus-bridged [1]ferrocenophane (η-C 5 H 4 ) 2 FePPh ( 3a ) with methyl triflate (MeOTf). A single-crystal X-ray diffraction study of 10b revealed an angle of 24.4(5)° between the planes of the cyclopentadienyl rings, less than the respective angle (26.7°) for 3a . Compound 10b and a number of other tetracoordinate, phosphorus-bridged [1]ferrocenophanes, (η-C 5 H 4 ) 2 FeP(S)Ph ( 5a ), (η-C 5 H 4 ) 2 FeP[Fe(CO) 4 ]Ph ( 6 ), and [(η-C 5 H 4 ) 2 FePFpPh][PF 6 ] ( 7 ) (where Fp = (η-C 5 H 5 )Fe(CO) 2 ), were investigated with respect to their ring-opening polymerization (ROP) behavior. Only compound 10b was found to undergo ROP, which occurred both thermally and in the presence of a transition-metal catalyst (PtCl 2 ). The resultant ionomeric polymer {[(η-C 5 H 4 ) 2 FePPhMe][OTf]} n ( 11 ) was found to be soluble in dimethylformamide (DMF), dimethyl sulfoxide (DMSO), methanol, and acetone but displayed only limited stability in these solvents. The thermally ring-opened polymer was found to possess a glass transition temperature of 176 °C and was thermally stable to weight loss up to ca. 400 °C. Analysis by wide-angle X-ray scattering (WAXS) revealed that the polymer was amorphous. A study on the partial to full methylation of the polymer [(η-C 5 H 4 ) 2 FePPh] n ( 14 ) gave results that were consistent with those from the ROP of 10b . Dynamic light scattering studies on polymer 11 produced via thermal ROP and transition-metal-catalyzed ROP gave hydrodynamic radii in the range of 30−45 nm, which suggested that the compounds were polymeric rather than oligomeric in nature. On the basis of the glass transition temperatures for a series of samples of polymers 11 of known molecular weight with varying numbers of repeat units (from 20 to 100), the molecular weight ( M n ) of the transition-metal-catalyzed ROP product was greater than 46 000 (ca. 100 repeat units) and the molecular weight of the thermally produced polymer was even higher.