Stepwise Construction of Mo-Fe-S Clusters Using a LEGO Strategy.

The rational synthesis of iron-sulfur clusters with excellent control of the core ligands has been a significant challenge in biomimetic chemistry. In this work, the rational construction of versatile Mo-Fe-S cubane clusters was realized using a LEGO strategy. (LEGO is a line of plastic construction toys consisting of various interlocking plastic bricks which can be assembled and connected in different ways to construct versatile objects. Herein we use "LEGO strategy" as an analogy for the stepwise synthetic methodology, and we use "brick" to represent a corner atom of the cubane structure.) Through careful synthetic control, the ⟨Fe⟩, ⟨S⟩, and ⟨Cl⟩ bricks were mounted piece-by-piece onto the basic ⟨MoS3⟩ frame to stepwise construct the incomplete cubane core ⟨MoFe2S3Cl⟩ and the complete cubane core ⟨MoFe3S3Cl⟩. The significantly elongated Fe-Cl bonds for the bridging chlorides in the ⟨MoFe2S3Cl⟩ and ⟨MoFe3S3Cl⟩ cores permit ligand metatheses to introduce 2p donors at the bridging sites, which used to be a challenge in traditional iron-sulfur chemistry. Therefore, in subsequent controlled reactions, the bridging ⟨Cl⟩ bricks of the ⟨MoFe2S3Cl⟩ and ⟨MoFe3S3Cl⟩ frames could be easily replaced by ⟨N⟩ , ⟨O⟩, or ⟨S⟩ bricks to generate the ⟨MoFe2S3N⟩, ⟨MoFe2S3O⟩, ⟨MoFe3S3N⟩, and ⟨MoFe3S4⟩ cluster cores, demonstrating more choices for the LEGO synthetic strategy. The series of Mo-Fe-S clusters and their derivatives, together with related synthetic strategies, offers a good platform and methodology for biomimetic chemistry in relation to nitrogenase, especially the FeMo cofactor.