Synthesis and solution stability of water-soluble κN,κO-bis(3,5-dimethylpyrazolyl)ethanol manganese(i) tricarbonyl bromide (CORM-ONN1).

The reaction of (OC)MnBr with bis(3,5-dimethyl-1-pyrazolyl)methane yields [{(Pz)CH}Mn(CO)Br] (1). The use of tridentate heteroscorpionates such as bis(3,5-dimethyl-1-pyrazolyl)acetic acid and 2,2-bis(3,5-dimethyl-1-pyrazolyl)ethanol leads to the formation of mononuclear [(OC)Mn{(Pz)CH-CO}] (2) and [(OC)Mn{(Pz)CH-CHOH}]Br (3, CORM-ONN1). Salt-like photoCORM 3 is soluble in aqueous media up to a concentration of 200 μM, non-toxic up to an approx. 65 μM solution and releases all carbonyl ligands upon irradiation. The molecular complexes 1 and 2 are insoluble in aqueous solutions. CORM-ONN1 (3) slowly degrades in methanol yielding iCORM 4, consisting of the complex cation [{(Pz)CH-CHOH}{(Pz)CH-CHO}Mn] and the [Mn(CO)] counter anion with the cations linked to a dimeric unit by intermolecular hydrogen bridges between the alcohol and alkoxide functionalities.