Ferrocenyl thiocarboxylates: Synthesis, solid-state structure and electrochemical investigations

Abstract

The synthesis and characterization of four ferrocenyl thiocarboxylate complexes are reported. Thus, treatment of [Fe(η5-C5H5)(η5-C5H4S−)] (1) with one equivalent of the acid chlorides 2-ClC(O)-cC4H3X(2a, X = O; 2b, X = NMe) gave [Fe(η5-C5H5)(η5-C5H4SC(O)-2-cC4H3X)] (3a, X = O; 3b, X = NMe (b)). When 1,1′-[Fe(η5-C5H4S−)2] (4) was reacted with 2-ClC(O)-cC4H3X in a 1:2 molar ratio then the respective ferrocenyl-1,1'-bis(thiocarboxylates) 1,1′-[Fe(η5-C5H4SC(O)-2-cC4H3X)2] (5a, X = O; 5b, X = NMe (b)) were produced. The solid state structures of 5a and 5b were determined by X-ray crystal structure analysis. The Crystal structure of 5a indicated the presence of oxygen…oxygen contacts, the inter-oxygen distance is 0.13 Å less than the sum of van der Waals radii. Investigation of Cambridge Structural Data base for 2-substtiuted furan molecules indicated the presence of short O…O contacts in 49 examples. Geometrical analysis of the O…O contacts indicated that the geometrical arrangement of these contacts is very similar to the well-defined C-X…X-C contacts (X = Cl, Br or I). Cyclic voltammetric studies of 3a, b and 5a, b showed reversible events at 158 and 243 mV for 3a, b and at 187 and 284 mV for 5a, b, using [NnBu4][B(C6F5)4] as the supporting electrolyte. It was found that the furyl-functionalized systems resulted in a significant higher Fc/Fc+ redox potential (E0′) as observed for the more electron-rich pyrrolyl derivatives. The Fc/Fc+ redox potential (E0′) for 5a, b is significantly higher than the one for 3a, b, due to the presence of two electron withdrawing thioester groups attached to the ferrocene in 5a, b.