Abstract
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
.