N-Substituted indole-3-thiolate [4Fe–4S] clusters with a unique and tunable combination of spectral and redox properties

A series of N-substituted indole-3-thiols, synthesized by sequential alkylation, thiouronium salt formation, and hydrolysis, are used to generate a novel family of [4Fe–4S] clusters. The redox transitions of the clusters deviate from those of other [4Fe–4S] cluster families, with half-wave potentials lying in a range midway between those of [4Fe–4S] clusters bound by aliphatic thiolate ligands and those bound by thiophenolate-based ligands. In UV–vis spectroscopy, the new cluster family shows absorption maxima that are among the most red-shifted reported thus far in [4Fe–4S] cluster chemistry. The indole-3-thiolate ligand thus leads to a highly specific and uncommon combination of [4Fe–4S] cluster properties, which can be fine-tuned by facile derivatization at the indole nitrogen atom.