Reductive Nitrosylation and Proton-Assisted Bridge Splitting of a (μ-Oxo)dimanganese(III) Complex Derived from a Polypyridine Ligand with One Carboxamide Group

Aerobic oxidation of the Mn(II) complex [Mn(Papy3)(H2O)](ClO4) (1, PaPy3- is the anion of the designed ligand
N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide) in acetonitrile affords the (μ-oxo)dimanganese(III) complex [(Mn(PaPy3))2(μ-O)](ClO4)2 (3) in high yield. The unsupported single oxo bridge between the two
high-spin Mn(III) centers in 3 is readily cleaved upon addition of proton sources such as phenol, acetic acid, and
benzoic acid, and complexes of the type [Mn(PaPy3)(L)](ClO4) (5, L = PhO-; 6, L = AcO-; 7, L = BzO-) are
formed. The basicity of the bridge is evident by the fact that simple addition of methanol to a solution of 3 in
acetonitrile affords the methoxide complex [Mn(PaPy3)(OMe)](ClO4) (4). The structures of 3−5 and 7 have been
determined. Passage of NO through a solution of 3 in acetonitrile produces the {Mn−NO}6 nitrosyl [Mn(PaPy3)(NO)](ClO4) (2) via reductive nitrosylation. Complexes 4−7 also afford the {Mn−NO}6 nitrosyl 2 upon reaction with
NO. In the latter case, the anionic O-based ligands (such as MeO- and PhO-) act as built-in bases and promote
reductive nitrosylation of the Mn(III) complexes.