Metal‐Templated, Tight Loop Conformation of a Cys‐X‐Cys Biomimetic Assembles a Dimanganese Complex

Abstract

With the goal of generating anionic analogues to MN2S2⋅Mn(CO)3Br we introduced metallodithiolate ligands, MN2S22− prepared from the Cys‐X‐Cys biomimetic, ema4− ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=NiII, [VIV≡O]2+ and FeIII) to Mn(CO)5Br. An unexpected, remarkably stable dimanganese product, (H2N2(CH2C=O(μ‐S))2)[Mn(CO)3]2 resulted from loss of M originally residing in the N2S24− pocket, replaced by protonation at the amido nitrogens, generating H2ema2−. Accordingly, the ema ligand has switched its coordination mode from an N2S24− cavity holding a single metal, to a binucleating H2ema2− with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH2‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn2 product. By computational studies we compared the conformations of “linear” ema4− to ema4− frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H2ema2− that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state.