Electronically Strongly Coupled Divinylheterocyclic-Bridged Diruthenium Complexes

Complexes [{Ru(CO)Cl(PiPr(3))(2)}(2)(mu-2,5-(CH=CH)(2)-(C4H2E)-C-c] (E=NR; R=C6H4-4-NMe2 (10a), C6H4-4-OMe (10b), C6H4-4-Me (10c), C6H5 (10d), C6H4-4-CO2Et (10e), C6H4-4-NO2 (10 f), C6H3-3,5-(CF3)(2) (10g), CH3 (11); E=O (12), S (13)) are discussed. The solid state structures of four alkynes and two complexes are reported. (Spectro) electrochemical studies show a moderate influence of the nature of the heteroatom and the electron-donating or -withdrawing substituents R in 10a-g on the electrochemical and spectroscopic properties. The CVs display two consecutive one-electron redox events with Delta E degrees'=350-495 mV. A linear relationship between Delta E degrees' and the sigma(p) Hammett constant for 10a-f was found. IR, UV/Vis/NIR and EPR studies for 10(+)-13(+) confirm full charge delocalization over the {Ru} CH=CH-heterocycle-CH=CH{Ru} backbone, classifying them as Class III systems according to the Robin and Day classification. DFT-optimized structures of the neutral complexes agree well with the experimental ones and provide insight into the structural consequences of stepwise oxidations.