Hydrogen Oxidation by Bioinspired Models of [FeFe]-Hydrogenase.

Synthetic azadithiolate-bridged diiron clusters serve as structural analogues of the active site of [FeFe]-hydrogenases. Recently, an o-alkyl substitution of aniline-based azadithiolate bridge allowed these synthetic models to both oxidize H₂ and reduce H⁺, i.e., bidirectional catalysis. Hydrogen oxidation by synthetic analogues of hydrogenases is rare, and even rarer is the ability of diiron hexacarbonyls to oxidize H₂. A series of synthetic azadithiolate-bridged biomimetic diiron hexacarbonyl complexes are synthesized where the substitution in the para position of the ortho-methyl aniline in the azadithiolate bridge is systematically varied between electron-withdrawing and electron-donating groups to understand factors that control H₂ oxidation by diiron hexacarbonyl analogues of [FeFe]-hydrogenases. The results show that the substituents in the para position of the ortho-ethyl aniline affect the electronic structure of the azadithiolate bridge as well as that of the diiron cluster. The electron-withdrawing -NO₂ substituent results in faster H₂ oxidation relative to that of a -OCH₃ substituent.