Synthesis, structure and properties of TTF-carboxylate bridged paddlewheel dirhodium complexes, Rh2(ButCO2)3(TTFCO2) and Rh2(ButCO2)2(TTFCO2)2

Reaction of tetrathiafulvalene carboxylic acid (TTFCO2H) with paddlewheel dirhodium complex Rh2(ButCO2)4 yielded TTFCO2-bridged complexes Rh2(ButCO2)3(TTFCO2) (1) and cis- and trans-Rh2(ButCO2)2(TTFCO2)2 (cis- and trans-2). Their triethylamine adducts [1(NEt3)2] and cis-[2(NEt3)2] were purified and isolated with chromatographic separation, and characterized with single crystal X-ray analysis. Trans-[2(NEt3)2] is not completely separated from a mixture of cis- and trans-[2(NEt3)2], but its single crystals were obtained from a solution of the mixture. A three-step quasi-reversible oxidation process was observed for 1 in MeCN. The first two steps correspond to the oxidation of the TTFCO2 moiety and the last one is the oxidation of the Rh2 core. The oxidation of cis-2 is observed as a two-step process with very similar E1/2 values to those of the first two processes for 1. Both 1+ and cis-22+ in MeCN at room temperature show isotropic ESR spectra with a g value of 2.008 and aH = 0.135 mT for two equivalent H atoms and aH = 0.068 mT for one H atom. The redox and ESR data of cis-2 suggest that the intramolecular interaction between the TTF moieties is very small.