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(N)(TAML)] (), which was obtained by one-electron oxidation of [Mn(N)(TAML)] (). undergoes N atom transfer to PPh and styrenes to give PhP═NH and aziridines, respectively. A Hammett study for various -substituted styrenes gives a V-shaped plot; this is rationalized by the ability of to function as either an electrophile or a nucleophile. also undergoes hydride transfer reactions with NADH analogues, such as 10-methyl-9,10-dihydroacridine (AcrH) and 1-benzyl-1,4-dihydronicotinamide (BNAH). A kinetic isotope effect of 7.3 was obtained when kinetic studies were carried out with AcrH and AcrD. The reaction of with NADH analogues results in the formation of [Mn(N)(TAML-H)] (), 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 (or BNAH) to , in which the electron is transferred to the Mn center, while the proton is transferred to a carbonyl oxygen of TAML rather than to the nitrido ligand.