Catalytic Reduction of Dinitrogen to Ammonia at a Single Molybdenum Center

Abstract

Dinitrogen (N₂) was reduced to ammonia at room temperature and 1 atmosphere with molybdenum catalysts that contain tetradentate [HIPTN₃N]^3– triamidoamine ligands {such as [HIPTN₃N]Mo(N₂), where [HIPTN₃N]^3– is [{3,5-(2,4,6-i-Pr₃C₆H₂)₂C₆H₃NCH₂CH₂}₃N]^3–} in heptane. Slow addition of the proton source [{2,6-lutidinium}{BAr′₄}, where Ar′ is 3,5-(CF₃)₂C₆H₃]and reductant (decamethyl chromocene) was critical for achieving high efficiency (∼66% in four turnovers). Numerous x-ray studies, along with isolation and characterization of six proposed intermediates in the catalytic reaction under noncatalytic conditions, suggest that N₂ was reduced at a sterically protected, single molybdenum center that cycled from Mo(III) through Mo(VI) states.