Ruthenium Hydride Complexes with Zwitterionic Quinonoid Ligands – Isomer Separation, Structural Properties, Electrochemistry, and Catalysis

Abstract

Reactions of [Ru(PPh3)3(CO)(H)Cl] with the zwitterionic p‐benzoquinonemonoimine‐type ligands 4‐(n‐butylamino)‐6‐(n‐butylimino)‐3‐oxocyclohexa‐1,4‐dien‐1‐olate (Q1), 4‐(isopropylamino)‐6‐(isopropylimino)‐3‐oxocyclohexa‐1,4‐dien‐1‐olate (Q2), and 4‐(benzylamino)‐6‐(benzylimino)‐3‐oxocyclohexa‐1,4‐dien‐1‐olate (Q3) in the presence of a base led to the formation of mononuclear complexes [Ru(PPh3)2(CO)(H)(Q1–H)] (1a and 1b), [Ru(PPh3)2(CO)(H)(Q2–H)] (2a and 2b), and [Ru(PPh3)2(CO)(H)(Q3–H)] (3a and 3b), respectively. The positional isomers (a and b) that were formed in each case were separated by preparative TLC. The structural characterization of 2a and 3a·MeCN helped to identify the isomers, and established the distorted octahedral coordination geometry around the ruthenium center. The bond lengths in the complexes are consistent with localization of the double bonds in Q2–H and Q3–H in both their monodeprotonated and metal‐coordinated forms. The Ru–C–O(carbonyl) bond angle is almost linear. Cyclic voltammetry of the complexes showed one oxidation and one reduction process. These are predominantly centered on the quinonoid ligands, which shows their redox‐noninnocent character. Studies of transfer hydrogenation with 2a as a precatalyst showed that, in the presence of KOH, acetophenone could be converted to 1‐phenylethanol within 10 h in over 90 % yield.

Investigation of Monomeric versus Dimericfac-Rhenium(I) Tricarbonyl Systems Containing the Noninnocent 8-Oxyquinolate Ligand

“…5-Fluoro-8-quinolinol (99%) was purchased from TCI and used as received. fac-Re(CH 3 CN) 2 (CO) 3 Cl and [fac-Re(OQN)(CO) 3 ] 2 were both prepared according to the literature procedures. 49,50 Additional analytical data for the previously published [fac-Re(OQN)(CO) 3 ] 2 complex are included below, as it is here more comprehensively characterized.…”

“…Of growing interest in recent years to the inorganic community are the occurrences of transition metal complexes with redox-active ligands. Indeed, redox-active organic frameworks are often exploited by naturally occurring enzymes and as such represent a major inspiration for the engineering of molecular catalyst systems today. − For example, one of the most widely used redox-active ligands today is the 2,2-bipyridine (bpy) system, which typically displays a one-electron reduction of its π*-orbital in the presence of a suitable reductant or alternatively at an electrode interface with sufficient potential . A number of such redox-active ligands can be further categorized as non-innocent ligands, i.e., a ligand whose electronic coupling with the central metal d - orbitals is so effective that the resulting bonding/antibonding molecular orbitals formed cannot be unambiguously assigned to either metal or ligand entities .…”

Highly efficient blue and deep-blue emitting zwitterionic iridium(iii) complexes: synthesis, photophysics and electroluminescence

“…Zwitterionic compounds of various metal complexes have been described so far, with extensive use in catalysis due to the mutual combination of the desirable reactivity prole of related cationic complexes and the broad solubility and solvent tolerance of neutral species. 18,19 On the other hand, the advantage of using a luminescent doublecomplex or "so" salts based on oppositely charged ion-paired iridium complexes 20 for OLED applications has been recently proved by Thompson and coworkers. 21 In such materials charge mobility is indeed expected to be higher than that in the related neutral lattice, due to the higher dielectric constant in the sosalt lattice.…”

The isomer-sensitive electrochemical HER of ruthenium(ii)–hydrido complexes involving redox-active azoheteroaromatics

“…5 and Table 3) and the potentials were varied as a function of L1-L2, an isomeric identity. 27,32 A fairly large K c1 value (involving R1/R2 in Fig. 5 and Table 3) of 10 [16][17][18][19] implied appreciable stability of the intermediate Ru II -L •− electronic form in 1-2.…”