C MAS NMR experiments were acquired using a radiofrequency field strength (1) of 62.5 kHz. Recycle delays were experimentally optimised to 10 s for f-CMK3/Cr(acac)3 and 0.5 s for u-CMK3/Cr(acac)3. Number of transients acquired were 2048 and 6144, respectively. Sample preparation: 50 mg of CMK-3 was mixed with 1 ml 0.5 wt/vl% Cr(acac)3 in EtOH to create a slurry. The solvent was allowed to evaporate overnight, affording a solid.