Toward Diiron Dithiolato Biomimetics with Rotated Conformation of the [FeFe]-Hydrogenase Active Site: A DFT Case Study on Electron-Rich, Isocyanide-Based Scaffolds

The electron rich Fe2(pdt)(RNC)6 1 (pdt=CH2(CH2S−)2) has been used as starting point for a DFT multi-functional study to assess the feasibility of designing a stable inverted (or rotated) disposition of the two FeL3 pyramidal moieties in the dimetallic core, a key feature of [FeFe]-hydrogenase cofactor. The choice of 1 was motivated by the presence of a rotated form in solution, slightly less stable than the unrotated stereoisomer. Aimed to find an upgraded version of 1, featuring the rotated isomer as ground state, various combinations of factors have been tested, for their effect on the relative stability of rotated vs unrotated isomers. The general result is that combining coordination asymmetry, electron donor presence and isocyanides R substituents able to establish intramolecular interactions is effective in stabilizing the rotated isomer. Our DFT study may inspire the design of synthetic biomimetics, with improved resemblance to the natural system.