Host-guest complexes of cucurbit[8]uril and [(η5-C5H4R)Mo(CO)3CH3] (R = H, CO2CH3) for controlled release of carbon monoxide

Gomes, Ana C.; Monteiro, Rodrigo P.; Calhau, Isabel B.; D. Lopes, André; Gonçalves, Isabel S.; Pillinger, Martyn

http://hdl.handle.net/10400.1/26194

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The monosubstituted cyclopentadienyl half-sandwich molybdenum(II) tricarbonyl complex [(eta 5-C5H4CO2CH3) Mo(CO)3CH3] (1) and its 1:1 inclusion compound with cucurbit[8]uril (1@CB8) have been prepared and characterised by elemental and thermogravimetric analyses, powder X-ray diffraction, diffuse reflectance UV-vis, solid-state 13C{1H} MAS NMR, FT-IR, and Raman spectroscopies. The CO-releasing behaviours of 1, 1@CB8 and, for comparison, [(eta 5-C5H5)Mo(CO)3CH3] (2) and its 1:1 inclusion complex with CB8, were assessed using a deoxymyoglobin-carbonmonoxymyglobin assay. For assays performed in the dark at 37 degrees C, complex 1 undergoes thermally assisted spontaneous CO release, with ca. 0.5 equivalents of CO being released after 6 h. The half-life (t1/2) of 325 min identifies 1 as a slow releaser when compared to complex 2 bearing the unsubstituted cyclopentadienyl ligand (t1/2 = 25 min). CO release from 1 was promoted by exposure to UV light (t1/2 = 85 min), establishing the complex as a photochemically activated CO-releasing molecule (photoCORM). For 1@CB8, t1/2 for photo-assisted CO release increased to ca. 7 h, and for 2@CB8 the dark-release t1/2 increased to 165 min, showing that molecular acceptors like cucurbiturils can be used effectively as second-sphere ligands to modulate the CO release profile of CORMs.