Synthesis and (spectro)electrochemistry of mixedvalent diferrocenyl–dihydrothiopyran derivatives

Abstract

Three novel diferrocenyl complexes were prepared and characterised. 2,2-Diferrocenyl-4,5-dimethyl- 3,6-dihydro-2H-thiopyran (1, sulphide) was accessible by the hetero-Diels–Alder reaction of diferrocenyl thioketone with 2,3-dimethyl-1,3-butadiene. Stepwise oxidation of 1 gave the respective oxides 2,2- diferrocenyl-4,5-dimethyl-3,6-dihydro-2H-thiopyran-1-oxide (2, sulfoxide) and 2,2-diferrocenyl-4,5- dimethyl-3,6-dihydro-2H-thiopyran-1,1-dioxide (3, sulfone), respectively. The molecular structures of 1 and 3 in the solid state were determined by single crystal X-ray crystallography. The oxidation of sulphide 1 to sulfone 3, plays only a minor role on the overall structure of the two compounds. Electrochemical (cyclic voltammetry (= CV), square wave voltammetry (= SWV)) and spectroelectrochemical (in situ UV-Vis/NIR spectroscopy) studies were carried out. The CV and SWV measurements showed that an increase of the sulphur atom oxidation from −2 in 1 to +2 in 3 causes an anodic shift of the ferrocenylbased oxidation potentials of about 100 mV. The electrochemical oxidation of 1–3 generates mixedvalent cations 1+–3+. These monooxidised species display low-energy electronic absorption bands between 1000 and 3000 nm assigned to IVCT (= Inter-Valence Charge Transfer) electronic transitions. Accordingly, the mixed-valent cations 1+–3+ are classified as weakly coupled class II systems according to Robin and Day.Authors (K. K. and G. M.) thank the National Science Centre (Poland) for financial support (Project Maestro-3; Dec-2012/06/ A/ST5/00219) and R. C. thanks the German Federal Ministry of Education and Research (BMBF) for support. The support from the German Academic Exchange Service (DAAD) in the framework of the exchange program “Ostpartnerschaften” is highly appreciated