Synthesis and solution stability of water-soluble κ2N,κO-bis(3,5-dimethylpyrazolyl)ethanol manganese(i) tricarbonyl bromide (CORM-ONN1)

Abstract

The reaction of (OC)₅MnBr with bis(3,5-dimethyl-1-pyrazolyl)methane yields [{(Pz^Me2)₂CH₂}Mn(CO)₃Br] (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)₃Mn{(Pz^Me2)₂CH–CO₂}] (2) and [(OC)₃Mn{(Pz^Me2)₂CH–CH₂OH}]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^Me2)₂CH–CH₂OH}{(Pz^Me2)₂CH–CH₂O}Mn]⁺ and the [Mn(CO)₅]⁻ counter anion with the cations linked to a dimeric unit by intermolecular hydrogen bridges between the alcohol and alkoxide functionalities.