Compound 6x

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

The cyclic oligomers 6_x observed by ¹H NMR spectroscopy and ESI mass spectrometry during the synthesis of polymer 7_c bear resemblance to similar cyclics based on ferrocene. Significant effort has been committed to isolation of cyclic species 6_x, but unfortunately, due to the dynamic equilibrium involving monomer 5, cyclics 6_x and polymer 7, attempts to crystallise 6_x from the supernatant of the polymerisation (by altering the solvent composition, or the temperature) simply resulted in re-equilibration. The isolation and purification of the aforementioned ferrocene cyclic oligomers relies on column chromatography, and in addition to re-equilibration of 6_x in dilute solution, the highly air- and moisture-sensitive nature of nickelocene vs. ferrocene renders this type of purification unsuitable. 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.