Catalytic N 2 Reduction to Silylamines and Thermodynamics of N 2 Binding at Square Planar Fe

• Published in: Journal of the American Chemical Society 2017-07, Vol.139 (27), p.9291-9301
• Main Authors: Prokopchuk, Demyan E, Wiedner, Eric S, Walter, Eric D, Popescu, Codrina V, Piro, Nicholas A, Kassel, W Scott, Bullock, R Morris, Mock, Michael T
• Format: Article
• Language: English
• Subjects: dinitrogen; Environmental Molecular Sciences Laboratory; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; iron; Mossbauer; square planer; thermodynamics
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.7b04552

The geometric constraints imposed by a tetradentate P N ligand play an essential role in stabilizing square planar Fe complexes with changes in metal oxidation state. The square pyramidal Fe (N )(P N ) complex catalyzes the conversion of N to N(SiR ) (R = Me, Et) at room temperature, representing the highest turnover number of any Fe-based N silylation catalyst to date (up to 65 equiv N(SiMe ) per Fe center). Elevated N pressures (>1 atm) have a dramatic effect on catalysis, increasing N solubility and the thermodynamic N binding affinity at Fe (N )(P N ). A combination of high-pressure electrochemistry and variable-temperature UV-vis spectroscopy were used to obtain thermodynamic measurements of N binding. In addition, X-ray crystallography, Fe Mössbauer spectroscopy, and EPR spectroscopy were used to fully characterize these new compounds. Analysis of Fe , Fe , and Fe complexes reveals that the free energy of N binding across three oxidation states spans more than 37 kcal mol .