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Time-stacked in situ31P NMR spectra during catalysis (T = 25 °C, 1,4-dioxane). (A) t = 0 min; (B) t = 60 min; (C) t = 90 min. Chemical shifts (δ): anti-2·[O], 56.4 ppm; ‘unknown’ peaks at 87.3 and 94.4 ppm.