Synthesis of tetranuclear iron–sulphur protein analogues with tetrathiol ligands attached to macrocycles which provide intramolecular hydrophobic domains

Abstract

A new type of active-site analogue for 4Fe–4S iron-sulphur proteins is introduced, where the active site core is surrounded by an intramolecular hydrophobic domain formed by a 36-membered ring consisting of a methylene backbone. An efficient synthesis of the macrocyclic ligands 1,10,19,28-tetra(4-mercaptobenzoyl)-1,10,19,28-tetra-azacyclohexatriacontane, 1,10,19,28-[4-(mercaptomethyl)benzoyl]-1,10,19,28-tetra-azacyclohexatriacontane and 1,10,19,28-tetra-(3-mercapto-3-methylbutanoyl)-1,10,19,28-tetra-azacyclohexatriacontane is described. Their reaction with [Fe₄S₄(SBu^t)₄]^2– afforded novel clusters in good yields (70–90%) as black powders with m.p. >300 °C. They dissolve in dimethylformamide, dimethyl sulphoxide, and propylene carbonate. Complex formation with Fe₄S₄ clusters was mainly demonstrated by u.v.–visible and n.m.r. studies and the properties of the new clusters are discussed.