Nature has extensively developed hydrogen chemistry via hydrogenase enzymes, whose active sites utilize abundant base metals, iron and nickel, in H2 production or oxidation. The mono-iron hydrogenase has a unique ability for H2 heterolysis and hydride transfer to an organic substrate. In our work, a small molecule mimic [Fe(CO)2(IMes)(NS)]a (Fe-NH-S-1  ; IMes, 1,3-bis(2,4,6-trimethylphenyl) imidazol-2-ylidene; NS, 2-Aminobenzenethiol) was found to possess related catalytic activity in the H2 reduction of quinone. Here we report a DFT computational study that explores the mechanism of this reaction. The protonation on the amine of the model (i.e. Fe-N2H-S-1+  ) activates the catalyst and facilitates H2 heterolysis: reducing activation energy from 37.5 to 16.8 kcal/mol. The hydride and proton from H2 cleavage are accommodated by the iron and the thiolate on the NS ligand, respectively, forming FeH-NH2-SH-1+  . An interesting observation is that the mimic must lose a proton to form FeH-NH2-S-1  ,before it can reduce the quinone by hydride transfer with a contaminant proton transfer through a 6-membered ring, concerted transition state. The protonation of the catalyst is subtle since one proton can activate it, but excess protons might render the catalyst inactive as FeH-NH2-SH-1+  . The non-innocence of the NS ligand is expected to be involved in the hydride transfer because both protons that extinguish the non-innocence, are removed before or along with the hydride transfer. The catalyst Fe-N2H-S-1+  is regenerated after the production of hydroquinone by protonation .

Computational study of quinone reduction with hydrogen catalyzed by a mono-Fe hydrogenase biomimetic

248th National Meeting (2014)

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