Spectroscopic, Electrochemical, and Computational Aspects of the Charge Distribution in Ru(acac)₂(R-o-benzoquinonediimine) Complexes

Abstract

The syntheses and properties are reported for five Ru(acac)2(R-bqdi) species where acac is acetylacetonate, and R-bqdi is the non-innocent ligand ortho-benzoquinonediimine substituted with R = H (1), 4,5-dimethyl (2), 4-Cl (3), or 4-NO2 (4), and N,N''-dimethylsulfonyl (5). Their identities and purities were confirmed by NMR, mass spectra, IR and analytical data. The large degree of metal-to-ligand pi-back-donation was analyzed by spectroscopic (UV/visible, IR, Raman) and electrochemical data, supported by molecular orbital composition computations using density functional theory (DFT), with the polarizable continuum model (PCM) to mimic the presence of solvent, and prediction of electronic spectra using time-dependent DFT methods. Extended charge decomposition analysis (ECDA) and natural population analysis (NPA) both produced a detailed picture of the bonding between the non-innocent bqdi ligand and the metal center, allowing correlations to be drawn between the nature of the R substituents and the quantitative extent of pi-back-donation and sigma-forward donation. In conclusion, the issue of whether these species are best regarded as Ru(II)(quinonediimine) or coupled Ru(III)(semiquinonediiminate) species is discussed.

Bis(acetylacetonato)ruthenium Complexes of Noninnocent 1,2‐Dioxolene Ligands: Qualitatively Different Bonding in Relation to Monoimino and Diimino Analogues

“…Whereas RuA C H T U N G T R E N N U N G (acac) 2 complexes with the popular [10c] o-benzoquinone monoimine [14] and diimine [15] ligands have been described, there were also earlier reports of catecholate complexes with…”

Characterization of Structural and Electronic Transitions During Reduction and Oxidation of Ru(acac)3 Flow Battery Electrolytes by using X‐ray Absorption Spectroscopy

“…In previous metal–acetylacetonate studies, no oxidation potentials, structural changes during charge/discharge, or charge states were presented . The LANL2DZ basis set has been used for complexes similar to Ru(acac) 3 to effectively determine the charge of the metal versus the ligand for neutral species by using natural population analysis (NPA), and calculating molecular orbital energies . First, the predicted standard potentials were calculated by using the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) values of the neutral species in acetonitrile by using the polarizable continuum model (PCM).…”

“…[45] The LANL2DZ basis set has been used for complexes similar to Ru(acac) 3 to effectivelyd etermine the charge of the metal versus the ligand for neutral species by using natural population analysis (NPA), and calculating molecular orbital energies. [46] First, the predicted standard potentials were calculated by using the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) values of the neutral species in acetonitrile by using the polarizable continuum model (PCM). A linear correlation found by Cheng et al for 295 organic complexes [43] was used to convert the calculated HOMO and LUMO energies to the positive and negative standard potentials, respectively.T he optimized structures with different charges were compared to determine any significant changes in bond lengths and angles to compare with the XAS results.…”

4,4′-Dichloro-N,N′-(o-phenylene)dibenzenesulfonamide

“…Benzoquinonediimine compounds have been extensively studied as ligands in metal complex systems (Kalinina et al, 2008). As free ligands, they exist in the diamine form, however, they have the ability to bind to a metal in one of three oxidation states: as o-phenylenediamine, its one-electron oxidized o-semiquinonediiminate, or its doubly oxidized and strongly π-accepting o-benzoquinonediimine form.…”

“…Ruthenium complexes of o-benzoquinonediimines possess highly covalent bonds. The extent of electronic coupling between the metal and diimine ligand can be tuned by using substituented o-benzoquinones (Masui &Lever, 1993, andKalinina et al, 2008). We present here the synthesis and crystal structure of the title compound (I).…”