Electronically Strongly Coupled Divinylheterocyclic-Bridged Diruthenium Complexes

Abstract

Complexes [{Ru(CO)Cl(PiPr3 )2 }2 (μ-2,5-(CH-CH)2 -(c) C4 H2 E] (E=NR; R=C6 H4 -4-NMe2 (10 a), C6 H4 -4-OMe (10 b), C6 H4 -4-Me (10 c), C6 H5 (10 d), C6 H4 -4-CO2 Et (10 e), C6 H4 -4-NO2 (10 f), C6 H3 -3,5-(CF3 )2 (10 g), 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 10 a-g on the electrochemical and spectroscopic properties. The CVs display two consecutive one-electron redox events with ΔE°'=350-495 mV. A linear relationship between ΔE°' and the σp Hammett constant for 10 a-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.

Keywords: 5-membered heterocycles; class III Robin and Day; density functional calculations; ruthenium; spectroelectrochemistry.