HAA by the first {Mn(iii)OH} complex with all O-donor ligands

There is considerable interest in MnOH(x) moieties, particularly in the stepwise changes in those O–H bonds in tandem with Mn oxidation state changes. The reactivity of aquo-derived ligands, {MOH(x)}, is also heavily influenced by the electronic character of the other ligands. Despite the prevalence of oxygen coordination in biological systems, preparation of mononuclear Mn complexes of this type with all O-donors is rare. Herein, we report several Mn complexes with perfluoropinacolate (pin(F))(2−) including the first example of a crystallographically characterized mononuclear {Mn(iii)OH} with all O-donors, K(2)[Mn(OH)(pin(F))(2)], 3. Complex 3 is prepared via deprotonation of K[Mn(OH(2))(pin(F))(2)], 1, the pK(a) of which is estimated to be 18.3 ± 0.3. Cyclic voltammetry reveals quasi-reversible redox behavior for both 1 and 3 with an unusually large ΔE(p), assigned to the Mn(iii/ii) couple. Using the Bordwell method, the bond dissociation free energy (BDFE) of the O–H bond in {Mn(ii)–OH(2)} is estimated to be 67–70 kcal mol(−1). Complex 3 abstracts H-atoms from 1,2-diphenylhydrazine, 2,4,6-TTBP, and TEMPOH, the latter of which supports a PCET mechanism. Under basic conditions in air, the synthesis of 1 results in K(2)[Mn(OAc)(pin(F))(2)], 2, proposed to result from the oxidation of Et(2)O to EtOAc by a reactive Mn species, followed by ester hydrolysis. Complex 3 alone does not react with Et(2)O, but addition of O(2) at low temperature effects the formation of a new chromophore proposed to be a Mn(iv) species. The related complexes K(18C6)[Mn(iii)(pin(F))(2)], 4, and (Me(4)N)(2)[Mn(ii)(pin(F))(2)], 5, have also been prepared and their properties discussed in relation to complexes 1–3.