Formation of a Mn-O-Ce species from a Mn-hydroxo complex and ceric ammonium nitrate.

The addition of 1.0 equiv. ceric ammonium nitrate (CAN) to the Mn-hydroxo complex [Mn(OH)(PaPyQ)] (1) yields a new species (2) that contains a Mn-O-Ce core. The Mn oxidation state in 2 is supported by H NMR data, which reveal hyperfine-shifted protons from the PaPyQ ligand, and a solution magnetic moment of 4.87, consistent with an = 2 Mn ion. Analysis of Mn K-edge EXAFS data for 2 shows a Ce ion 3.8 Å from the Mn center, supportive of the Mn-O-Ce core. Complex 2 reacts with excess ferrocene to generate only 1.0 equiv. of the ferrocenium ion. Because 1 is unreactive with ferrocene, we attribute this stoichiometry to the presence of one Ce ion in 2. Complex 2 can oxidize PPh and tri--butylphenol, with enhanced reactivity relative to 1. We find no evidence that CAN oxidizes the Mn center in 1, even when using excess CAN at low temperatures. This result stands in contrast to the reactivity of similar systems, where excess CAN converted a Mn-hydroxo complex to a complex with a Mn-O-Ce core (Karmalkar . , 2019, , 16124-16129). We discuss the basis for these different reactivities.