May 14, 2004

Considering A Single Site Mechanism for Iron-Mediated Nitrogen Fixation

Dr. Jonas Peters

The science community has had a longstanding fascination with the mechanism by which nitrogenase promotes biological nitrogen reduction. Whereas structural biologists/chemists have suggested Fe(N) species may be plausible intermediates during nitrogen fixation (see Rees et al., Science, 2002, 1696), biomimetic chemists have emphasized molybdenum as the redox rich site where nitrogen reduction occurs in the cofactor (see Yandulov & Schrock, Science, 2003, 76; G. J. Leigh Science, 2003, 55). Fueling the molybdenum hypothesis is the
conventional wisdom that a single iron center can not span the rich range of oxidation states necessary (at least four) to mediate N2
reduction, nor support certain key intermediates such as a terminal nitride (i.e., Fe≡N). This talk will question these basic chemical assumptions using fundamental concepts in transition metal coordination chemistry. Using a bottom-up approach that will begin with a consideration of the d-orbitals of tetrahedral ions, a single site mechanism for dinitrogen will be proposed that
emphasizes a remarkably redox rich, pseudotetradral iron site. Given
the importance of nitrogen reduction to sustaining life, understanding the mechanism by which it occurs is essential.
1. Elucidation of a Low Spin Cobalt(II) System in a Distorted Tetrahedral Geometry David M. Jenkins, Angel J. Di Bilio, Matthew J. Allen, Theodore A. Betley and Jonas C. Peters J. Am. Chem. Soc., 124, 15336-15350 (2002)
2. Solution and Solid-State Spin-Crossover Behavior in a Pseudotetrahedral d7 Ion David M. Jenkins and Jonas C. Peters, J. Am. Chem. Soc., 125, 11162-11163 (2003)
3. A Low-Spin d5 Iron Imide: Nitrene Capture by Low-Coordinate Iron(I) Provides the 4-Coordinate Fe(III) Complex [PhB(CH2PPh2)3]Fe>kN-p-tolyl Steven D. Brown, Theodore A. Betley and Jonas C. Peters J. Am. Chem. Soc., 125, 322-323 (2003)
4. Hydrogenolysis of [PhBP3]Fe>kN-p-tolyl: Probing the Reactivity of an Iron Imide with H2 Steven D. Brown and Jonas C. Peters J. Am. Chem. Soc., 126, 4538-4539 (2004)
5. The Strong-Field Tripodal Phosphine Donor, [PhB(CH2PiPr2)3]¡V,
Provides Access to Electronically and Coordinatively Unsaturated
Transition Metal Complexes Theodore A. Betley and Jonas C. Peters Inorg. Chem., 42, 5074-5084 (2003)
6. Dinitrogen Chemistry from Trigonally Coordinated Iron and
Cobalt PlatformsTheodore A. Betley and Jonas C. Peters J. Am. Chem. Soc., 125, 10782-10783 (2003)
7. A Tetrahedrally Coordinated L3Fe-Nx Platform that Accommodates Terminal Nitride (FeIV(N)) and Dinitrogen (FeI-N2) Ligands Theodore A. Betley and Jonas C. Peters published online ASAP