Diiron hexacarbonyl complexes as potential CO-RMs: CO-releasing initiated by a substitution reaction with cysteamine and structural correlation to the bridging linkage

摘要

The CO-releasing behaviours of nine diiron carbonyl complexes (1-9) were examined via the substitution reaction of cysteamine (CysA), of which complex 4 was reported recently. These complexes fall into three categories, the diiron core bridged by two thiolates, a dithiolate and 1,8-naphthalene dithiolate. Our results reveal that the CO-releasing rates of these complexes are highly dependent on their structures. Complexes (2-4) bearing two monothiolates as their bridging linkage ("open" form) are more vulnerable to decomposition upon nucleophilic substitution reactions compared with complexes (6-9) that possess a dithiolate as their bridging linkage. When the bridging linkage lacks an electron-donating group(complex 1), the metal centre is less negatively charged as revealed by DFT calculation, and thus it exhibits fast substitution reaction with CysA to release CO. A linkage with conjugating nature (5) shows a similar effect because electron density on the metal centre decreases due to electron-density diverting from the metal centre into the naphthalene moiety. Kinetic analysis suggests that CO-releasing at the first stage of these complexes is a first-order reaction.