Light- or oxidation-triggered CO release from [MnI(CO)3(κ3-L)] complexes: reaction intermediates and a new synthetic route to [Mn III/IV2(μ-O)2(L)2] compounds

Abstract

The reaction products and intermediates of the three CO-releasing manganese(I) coordination compounds [Mn(tpm)(CO)₃]⁺, [Mn(bpza)(CO)₃] and [Mn(tpa)(CO)₃]⁺ were analysed by combining IR-spectroscopy, electrochemical measurements and single-crystal XRD. The intermediate formation of manganese(I) biscarbonyl compounds and the rather facile oxidation of these species were identified as key reaction steps that accompany CO liberation. For the use of [Mn^I(CO)₃] complexes as light-triggered CO sources, the results indicate that in this case photo- and redox-chemistry seem to be strongly coupled which could be important and potentially even useful in the pharmacological context. Additionally, one has to be aware of the fact that [Mn^II(κ³-L)(solv)₃]²⁺ complexes, the primary reaction products after CO substitution, are able to bind to proteins, which was demonstrated using bovine serum albumin as a model. And finally it could be shown that the CO-release reactions can be used as a new synthetic route to prepare multinuclear μ-oxido-bridged manganese complexes: the mixed-valence compound [Mn^III/IV₂(μ-O)₂(tpa)₂]³⁺ could be prepared in a single step from [Mn(tpa)(CO)₃]⁺via photo- or electrochemically induced CO substitution.