Coordination Sphere Flexibility of Active-Site Models for Fe-Only Hydrogenase: Studies in Intra- and Intermolecular Diatomic Ligand Exchange
- 17 March 2001
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 123 (14) , 3268-3278
- https://doi.org/10.1021/ja003147z
Abstract
A series of dinuclear complexes, (μ-SRS)Fe2(CO)6 (R = −CH2CH2−, −CH2CH2CH2−, −CH2−C6H4−CH2−; edt, pdt, and o-xyldt, respectively) has been examined for specific characteristics that might relate to structural similarity with the active site of Fe-only hydrogenases. Variable-temperature proton NMR studies display the fluxionality of the iron−dithiocyclohexane unit in (μ-pdt)Fe2(CO)6 while in the (μ-o-xyldt)Fe2(CO)6 compound, the bridge is fixed. Temperature-dependent 13C NMR spectral studies establish intramolecular CO site exchange localized on discrete Fe(CO)3 units in all complexes, which is influenced by steric effects of the μ-SRS unit. Kinetic studies of intermolecular CO/CN- ligand-exchange reactions establish associative or Ia mechanisms in sequential steps to form the dicyano dianion, (μ-SRS)[Fe(CO)2(CN)]2= with 100% selectivity. Theoretical calculations (DFT) of transition states in the intramolecular site-exchange processes lead to a rationale for the interesting cooperativity in the CN-/CO intermolecular ligand-exchange process. The hinge motion of the three light atom S-to-S bridge is related to a possible heterolytic H2 activation/production process in the enzyme.This publication has 54 references indexed in Scilit:
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