Cyclodextrin and cucurbit[7]uril as protective encapsulation agents of the CO-releasing molecule [CpMo(CO)Me]

• Published in: Dalton transactions : an international journal of inorganic chemistry 2024-12, Vol.54 (1), p.166-18
• Main Authors: Monteiro, Rodrigo P, Calhau, Isabel B, Gomes, Ana C, Lopes, André D, Da Silva, José P, Gonçalves, Isabel S, Pillinger, Martyn
• Format: Article
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d4dt01863j

The CO releasing ability of the complex [CpMo(CO) 3 Me] ( 1 ) (Cp = η 5 -C 5 H 5 ) has been assessed using a deoxymyoglobin-carbonmonoxymyoglobin assay. In the dark, CO release was shown to be promoted by the reducing agent sodium dithionite in a concentration-dependent manner. At lower dithionite concentrations, where dithionite-induced CO release was minimised, irradiation at 365 nm with a low-power UV lamp resulted in a strongly enhanced release of CO (half-life ( t 1/2 ) = 6.3 min), thus establishing complex 1 as a photochemically activated CO-releasing molecule. To modify the CO release behaviour of the tricarbonyl complex, the possibility of obtaining inclusion complexes between 1 and β-cyclodextrin (CD) or cucurbit[7]uril (CB7) by liquid-liquid interfacial precipitation ( 1 @βCD(IP)), liquid antisolvent precipitation ( 1 @CB7), and mechanochemical ball-milling ( 1 @βCD(BM)) was evaluated. All these methods led to the isolation of a true inclusion compound (albeit mixed with nonincluded 1 for 1 @βCD(BM)), as evidenced by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), FT-IR and FT-Raman spectroscopies, and 13 C{ 1 H} magic angle spinning (MAS) NMR. PXRD showed that 1 @βCD(IP) was microcrystalline with a channel-type crystal packing structure. High resolution mass spectrometry studies revealed the formation of aqueous phase 1 : 1 complexes between 1 and CB7. For 1 @βCD(IP) and 1 @CB7, the protective effects of the hosts led to a decrease in the CO release rates with respect to nonincluded 1 . βCD had the strongest effect, with a ca. 10-fold increase in t 1/4 for dithionite-induced CO release, and a ca. 2-fold increase in t 1/2 for photoinduced CO release. For inclusion compounds between the complex [CpMo(CO) 3 Me] ( 1 ) and β-cyclodextrin or cucurbit[7]uril, the macrocyclic hosts modulate to different degrees the UV light-mediated CO release from encapsulated 1 .