Enhancing Reactivity via Structural Distortion
| Autor: | Julie A. Kovacs, Durrell K. Rittenberg, Reza Loloee, Jason Shearer, Jeffrey J. Ellison, David M. Barnhart, Scott Lovell, Dirk Schweitzer, Steven C. Shoner |
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| Rok vydání: | 2002 |
| Předmět: |
Models
Molecular Azides Inorganic chemistry Molecular Conformation Crystallography X-Ray Ferric Compounds Catalysis Article Inorganic Chemistry Metal Structure-Activity Relationship chemistry.chemical_compound Nitrile hydratase Electrochemistry Molecule Reactivity (chemistry) Physical and Theoretical Chemistry Methylene Hydro-Lyases Alkyl chemistry.chemical_classification Molecular Structure Chemistry Ligand Temperature Crystallography visual_art visual_art.visual_art_medium Azide Algorithms |
| Zdroj: | Inorganic Chemistry. 41:3128-3136 |
| ISSN: | 1520-510X 0020-1669 |
| Popis: | To examine how small structural changes influence the reactivity and magnetic properties of biologically relevant metal complexes, the reactivity and magnetic properties of two structurally related five-coordinate Fe(III) thiolate compounds are compared. (Et,Pr)-ligated [Fe(III)(S(2)(Me2)N(3)(Et,Pr))]PF(6) (3) is synthesized via the abstraction of a sulfur from alkyl persulfide ligated [Fe(III)(S(2)(Me2)N(3)(Et,Pr))-S(pers)]PF(6) (2) using PEt(3). (Et,Pr)-3 is structurally related to (Pr,Pr)-ligated [Fe(III)(S(2)(Me2)N(3)(Pr,Pr))]PF(6) (1), a nitrile hydratase model compound previously reported by our group, except it contains one fewer methylene unit in its ligand backbone. Removal of this methylene distorts the geometry, opens a S-Fe-N angle by approximately 10 degrees, alters the magnetic properties by stabilizing the S = 1/2 state relative to the S = 3/2 state, and increases reactivity. Reactivity differences between 3 and 1 were assessed by comparing the thermodynamics and kinetics of azide binding. Azide binds reversibly to both (Et,Pr)-3 and (Pr,Pr)-1 in MeOH solutions. The ambient temperature K(eq) describing the equilibrium between five-coordinate 1 or 3 and azide-bound 1-N(3) or 3-N(3) in MeOH is approximately 10 times larger for the (Et,Pr) system. In CH(2)Cl(2), azide binds approximately 3 times faster to 3 relative to 1, and in MeOH, azide dissociates 1 order of magnitude slower from 3-N(3) relative to 1-N(3). The increased on rates are most likely a consequence of the decreased structural rearrangement required to convert 3 to an approximately octahedral structure, or they reflect differences in the LUMO (vs SOMO) orbital population (i.e., spin-state differences). Dissociation rates from both 3-N(3) and 1-N(3) are much faster than one would expect for low-spin Fe(III). Most likely this is due to the labilizing effect of the thiolate sulfur that is trans to azide in these structures. |
| Databáze: | OpenAIRE |
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