Self-Assembly of Hexameric Macrocycles from Pt-II/Ferrocene Dimetallic Subunits - Synthesis, Characterization, Chemical Reactivity, and Oxidation Behavior

New compounds Ia-h of the form [(Me2SO) ClPt(HR2DTO kappa-S,S Pt)] (HR2DTO = secondary dithiooxamide, with R = methyl, ethyl, n-propyl, n-butyl, n-decyl, isopropyl, (R)-1-phenylethyl, or (S)-2-hydroxypropyl; kappa-S, S Pt denotes the co-ordination of the DTO moiety to the Pt atom) have been prepared and used to synthesize platinum(II)/ferrocene dimetallic species IIa-h of formula [(dppf) Pt(HR2DTO kappa-S, S Pt)] Cl (dppf = 1,1'-diphosphinoferrocene). Complexes IIa-e, bearing unbranched groups on the dithiooxamide moiety (i.e., R = methyl, ethyl, n-propyl, n-butyl, or n-decyl groups), self-assemble upon standing to form unprecedented hexameric macrocycles IIIa-e. Compounds IIa-e, IIIa-e, as well as IIf-h, have been characterized by a combination of H-1, C-13, P-31 NMR spectroscopy and 2D-ROESY and diffusion-ordered NMR spectroscopy (DOSY) experiments; the latter experiments have been used to calculate the hydrodynamic radius of IIa-e and IIIa-e, assisted by the data provided by the Xray crystal structure of IIh. Compounds IIIa-e are characterized by the presence of six dppf bridging units occupying the inner rim of the macrocycles and exhibit interesting properties, for example, oxidation of IIIa-e occurs around +0.40 V versus saturated calomel electrode (SCE), whereas oxidation of the type II species occurs at potentials greater than +1.0 V. Oxidation of IIIa-e is explained through a delocalized orbital extending over the six dppf subunits. The reversibility of the self-assembly process is finally demonstrated by alternate addition of acids and bases to the type III compounds.