Compound 7

| 1H NMR | ChemDraw

Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.

5 (90 mg, 0.393 mmol) was dissolved in d₅-pyridine (0.5 mL) to afford a dark blue solution (0.79 M, sample 7_b). The solution was stirred at room temperature for 24 h (at low concentrations, no colour change was observed, and at higher concentrations a colour change from blue to green was evident). ¹H NMR spectra were recorded after 24 h, 48 h and 7 days. ¹H NMR (48 h, 500 MHz, d₅-pyridine: δ [peak width at half height] = 266.8 [788 Hz] (6₂: br s, C₅H₄–CH₂–CH₂–), 197.3 [511 Hz] (6₃: br s, C₅H₄–CH₂–CH₂–), 185.2 [468 Hz] (6₄: br s, C₅H₄–CH₂–CH₂–), 181.6 (6₅: overlapping br s, C₅H₄–CH₂–CH₂–), 176.9 [435 Hz] (7: br s, C₅H₄–CH₂–CH₂–), 9.6 [140 Hz] (7: br s, C₅H₄–CH₂–CH₂–), –29.0 [212 Hz] (5: br s, C₅H₄–CH₂–CH₂–), –245.4 [704 Hz] (5: br s, α-C₅H₄), –250.0 [1207 Hz] (7: br s, C₅H₄), –270.9 [836 Hz] (5: br s, β-C₅H₄) ppm.

Polymeric material was isolated in the cases of 7_a, 7_b and 7_c (1.31, 0.79 and 0.44 M initial monomer concentration respectively) via precipitation of the polymerization solution (0.5 mL) into rapidly stirred hexanes (30 mL). The green solid was isolated, dissolved in a minimum volume of THF (0.5 mL), and quickly precipitated again into hexanes (30 mL). The precipitate was isolated and dried in vacuo to yield green polymeric material in yields of 62, 30 and 21% respectively for 7_a, 7_b and 7_c.

The supernatant solution of the first precipitation of 7_c revealed an increase in proportion of cyclic oligomers. ¹H NMR (500 MHz, d₅-pyridine/hexanes: δ [peak width at half height] = 266.9 [709 Hz] (6₂: br s, C₅H₄–CH₂–CH₂–), 197.1 [412 Hz] (6₃: br s, C₅H₄–CH₂–CH₂–), 184.8 [334 Hz] (6₄: br s, C₅H₄–CH₂–CH₂–), 181.3 [276 Hz] (6₅: br s, C₅H₄–CH₂–CH₂–), 180.0 (6₆: overlapping br s, C₅H₄–CH₂–CH₂–), 179.4 (6₇: overlapping br s, C₅H₄–CH₂–CH₂–), 178.9 (6₈: overlapping br s, C₅H₄–CH₂–CH₂–), 177.0 (7: overlapping br s, C₅H₄–CH₂–CH₂–),. ESI-MS (positive mode): m/z 228.0443 [5]⁺, 456.0895 [6₂]⁺, 684.1345 [6₃]⁺, 912.1796 [6₄]+.