Structure and Reactivity of a Manganese(VI) Nitrido Complex Bearing a Tetraamido Macrocyclic Ligand

Manganese complexes in +6 oxidation state are rare. Although a number of Mn(VI) nitrido complexes have been generated in solution via one-electron oxidation of the corresponding Mn(V) nitrido species, they are too unstable to isolate. Herein we report the isolation and the X-ray structure of a Mn(VI) nitrido complex, [Mn-VI(N)(TAML)](2-) (2), which was obtained by one-electron oxidation of [Mn-V(N)(TAML)](2-) (1). 2 undergoes N atom transfer to PPh3 and styrenes to give Ph3P = NH and aziridines, respectively. A Hammett study for various p-substituted styrenes gives a V-shaped plot; this is rationalized by the ability of 2 to function as either an electrophile or a nucleophile. 2 also undergoes hydride transfer reactions with NADH analogues, such as 10-methyl-9,10-dihydroacridine (AcrH(2)) and 1-benzyl-1,4-dihydronicotinamide (BNAH). A kinetic isotope effect of 7.3 was obtained when kinetic studies were carried out with AcrH(2) and AcrD2. The reaction of 2 with NADH analogues results in the formation of [Mn-V(N)(TAML-H+)](-) (3), which was characterized by ESI/MS, IR spectroscopy, and X-ray crystallography. These results indicate that this reaction occurs via an initial separated CPET (separated concerted proton-electron transfer) mechanism; that is, there is a concerted transfer of 1 e(-) + 1 H+ from AcrH(2) (or BNAH) to 2, in which the electron is transferred to the MnVI center, while the proton is transferred to a carbonyl oxygen of TAML rather than to the nitrido ligand.

Automated summary

This study presents the isolation and X-ray structure of a rare Mn(VI) nitrido complex, which exhibits N atom transfer reactions and catalytic abilities with NADH analogues.