May 14, 2004
Considering A Single Site Mechanism
for Iron-Mediated Nitrogen Fixation
Dr. Jonas Peters
Abstract:
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.
Refs
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