Preparation of Fe₄S₄ iron-sulphur protein analogues with hydrophobic macrocyclic tetrathiol ligand anchored to a 38-membered cyclophane type skeleton

The preparation of Fe₄S₄ cubane type active site analogues for iron-sulphur proteins in which the active core is surrounded by an intramolecular hydrophobic domain formed by a 38-membered ring consisting of a cyclophane skeleton is described. An efficient synthesis of the macrocyclic tetrathiol ligands, bis[N,N-bis(4-mercaptobenzoyl)-N, N′-octamethylene- 4,4′-diaminodiphenylmethane] (3a), bis- N,N′-bis {4-(mercaptomethyl)benzoyl}-N, N′-octamethylene -4,4′-diaminodiphenylmethane](3b) and bis[N,N′-bis(3-mercapto-3-methylbutanoyl0)-N, N′-octamethyleneN,N′- octamethylene-4,4′-diaminodiphenylmethane] (3c) is achieved. Reaction of the cyclic tetrathiol ligand 3 with [Fe₄S₄(SBu^t)₄]^2-(1c) afforded [Fe₄S₄{cycl- (XN-p-C₆a-H₄-p-CH₂-C₆ H₄-XN[CH₂]₈)₂}]^2- [X = p- SC₆H₄CO(2a), p-SCH₂C₆H₄CO(2b), SC(CH₃)_2- CH₂CO(2c)]. Thus the new clusters embedded in the cyclophane environment are obtained in good yields (70-90%) as black powders with melting points >300°C. They dissolve in DMF, DMSO and propylene carbonate, but are hardly soluble in most common organic solvents and water.