Aza- and Oxadithiolates Are Probable Proton Relays in Functional Models for the [FeFe]-Hydrogenases

The dithiolate cofactor for the [FeFe]-hydrogenase models, Fe2(xdt)(CO)2(dppv)2 (where xdt = 1,3-propanedithiolate (pdt), azadithiolate (adt), (SCH2)2NH, and oxadithiolate (odt), (SCH2)2O; dppv = cis-1,2-bis(diphenylphosphino)ethylene) have been probed for their functionality as proton relays enabli...

Full description

Saved in:
Bibliographic Details
Published in:Journal of the American Chemical Society 2008-12, Vol.130 (50), p.16834-16835
Main Authors: Barton, Bryan E, Olsen, Matthew T, Rauchfuss, Thomas B
Format: Article
Language:English
Subjects:
Aza Compounds - chemistry
Calcitriol - analogs & derivatives
Calcitriol - chemistry
Catalytic Domain
Hydrogenase - chemistry
Hydrogenase - metabolism
Iron-Sulfur Proteins - chemistry
Iron-Sulfur Proteins - metabolism
Models, Biological
Molecular Structure
Protons
Sulfhydryl Compounds - chemistry
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The dithiolate cofactor for the [FeFe]-hydrogenase models, Fe2(xdt)(CO)2(dppv)2 (where xdt = 1,3-propanedithiolate (pdt), azadithiolate (adt), (SCH2)2NH, and oxadithiolate (odt), (SCH2)2O; dppv = cis-1,2-bis(diphenylphosphino)ethylene) have been probed for their functionality as proton relays enabling formation and deprotonation of terminal hydrides. Compared to the propanedithiolate derivative, the azadithiolate and oxaditiholate show enhanced rates of proton transfer between solution and the terminal site on one Fe center. The results are consistent with the heteroatom of the dithiolate serving a gating role for both protonation and deprotonation. The pK a of the transiently formed ammonium (pK CD2 Cl2 5.7−8.2) or oxonium (pK CD2 Cl2 −4.7−1.6) regulates the proton transfer. As a consequence, only the azadithiolate is capable of yielding the terminal hydride from weak acids. The aza- and oxadithiolates manifested the advantages of proton relays: the odt derivative proved to be a faster catalyst for hydrogen evolution than the pdt derivative as indicated from cyclic voltammetry plots of i c/i p vs [H+]. The adt derivative was capable of proton reduction from the weak acid [HPMe2Ph]BF4 (pK CD2 Cl2 = 5.7). The proton relay function does not apply to the isomeric bridged-hydrides [Fe2(xdt)(μ-H)(CO)2(dppv)2]+, where the hydride is too distant and too basic to interact to be affected by the heteroatomic relay site. None of these μ-H species can be deprotonated.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja8057666