Vinyl Ruthenium-Modified Biphenyl and 2,2′-Bipyridines

Abstract

We report here on ruthenium alkenyl complexes 2 and 3 derived from 2,2'-bipyridine and their Re(CO)3X adducts 4a,b and 5. Detailed electrochemical studies on these complexes and spectroscopic characterization of their oxidized forms by IR, UV/vis/NIR, and electron paramagnetic resonance spectroscopies as well as quantum chemical studies reveal sizable (bridging) ligand contributions to the redox orbitals. Engagement of the free bipy functions of complexes 2 and 3 in binding to the electron-withdrawing fac-Re(CO)3X (X = Br, Cl) moiety enhances the metal-to-ligand charge-transfer character of the optical excitations, causes sizable anodic shifts of the redox potentials, and decreases the number of observable anodic redox waves by one when compared to complexes 2 and 3. Despite the decreasing electron density at the terminal or bridging alkenyl bipyridine ligand, the anodic redox processes still maintain appreciable ligand character as is seen by the shifts of the Ru(CO) and Re(CO)3 stretching frequencies on oxidation. Binding of the fac-Re(CO)3X moiety also attenuates the degree of ground-state delocalization in the mixed-valent states.

Electron‐Rich Diruthenium Complexes with π‐Extended Alkenyl Ligands and Their F4TCNQ Charge‐Transfer Salts**

“…This also holds true for complexes Ru 2 ‐7 and Ru 2 ‐8 , which exhibit substantially larger redox splittings Δ E 1/2 as a consequence of the smaller extension of the π‐conjugated linker and stronger electronic coupling in the one‐electron‐oxidized, mixed‐valent (MV) state (see below). This agrees with the general behaviour of previously reported divinylarylene‐bridged diruthenium complexes [19a–f,h,22] . The half‐wave potentials for the stepwise oxidations of the acac − complexes Ru 2 ‐4 , Ru 2 ‐8 and Ru 2 ‐10 are by roughly 200 or even 300 mV ( Ru 2 ‐10 ) ( E 1/2 0/+ ) or 150 to 225 mV ( E 1/2 +/2+ ) lower than those of their 16 VE chloro precursors Ru 2 ‐3 , Ru 2 ‐7 and Ru 2 ‐9 , which is due to their increased valence electron count [21b] …”

A “Pretender” Croconate-Bridged Macrocyclic Tetraruthenium Complex: Sizable Redox Potential Splittings despite Electronically Insulated Divinylphenylene Diruthenium Entities

“…The remaining two bands at 1935 and 1949 cm −1 correspond to the less intense symmetric and the intense antisymmetric combinations of Ru(CO) stretches of the one-electron oxidized divinylphenylene diruthenium moiety. The overall Ru(CO) band shifts and the increased energy difference between the two vibrational modes of the oxidized divinylphenylene diruthenium entity are in complete agreement with the oxidation-induced changes for other, related complexes of this type [49][50][51][52]83,84]. During the second oxidation, the band at 1917 cm −1 starts to fade, while the other two bands shift further blue, to 1941 and 1952 cm −1 .…”

Oxidized Styrylruthenium–Ferrocene Conjugates: From Valence Localization to Valence Tautomerism

“…The other metrical data are unremarkable compared to those of closely related structures of five‐, , , , and six‐coordinate[3a], alkenylruthenium complexes with the Ru(CO)(P i Pr 3 ) 2 (L) moiety and warrant no further discussion. Owing to the strong σ‐ trans influence of the alkenyl ligand, the Ru–O bond opposite the latter ligand is longer than that opposite the carbonyl ligand by ca.…”