Scrutinizing the Noninnocence of Quinone Ligands in Ruthenium Complexes: Insights from Structural, Electronic, Energy, and Effective Oxidation State Analyses

Abstract

The most relevant manifestations of ligand noninnocence of quinone and bipyridine derivatives are thoroughly scrutinized and discussed through an extensive and systematic set of octahedral ruthenium complexes, [(en)2RuL](z), in four oxidation states (z = +3, +2, +1, and 0). The characteristic structural deformation of ligands upon coordination/noninnocence is put into context with the underlying electronic structure of the complexes and its change upon reduction. In addition, by means of decomposing the corresponding reductions into electron transfer and structural relaxation subprocesses, the energetic contribution of these structural deformations to the redox energetics is revealed. The change of molecular electron density upon metal- and ligand-centered reductions is also visualized and shown to provide novel insights into the corresponding redox processes. Moreover, the charge distribution of the π-subspace is straightforwardly examined and used as indicator of ligand noninnocence in the distinct oxidation states of the complexes. The aromatization/dearomatization processes of ligand backbones are also monitored using magnetic (NICS) and electronic (PDI) indicators of aromaticity, and the consequences to noninnocent behavior are discussed. Finally, the recently developed effective oxidation state (EOS) analysis is utilized, on the one hand, to test its applicability for complexes containing noninnocent ligands, and, on the other hand, to provide new insights into the magnitude of state mixings in the investigated complexes. The effect of ligand substitution, nature of donor atom, ligand frame modification on these manifestations, and measures is discussed in an intuitive and pedagogical manner.

Structure of Electronically Reduced N-Donor Bidentate Ligands and Their Heteroleptic Four-Coordinate Zinc Complexes: A Survey of Density Functional Theory Results

“…Within each family, the forms of DFT exchange and DFT correlation remain constant, allowing the effect of EXX on the properties under study to be estimated. Results for PBE (GGA functional, EXX=0%), 89 PBE0 (hybrid-GGA functional, EXX=25%), 90 TPSS (meta-GGA functional, EXX=0%), 91 TPSSh (hybrid-meta-GGA functional, EXX=10%) 92 and M11 (RSH functional, 42.8/100% of EXX at short/long range) 93 are in accordance to their EXX contribution compared to the results of the 11 functionals (see SI).…”

“…Indeed, based on the X-ray structure of neutral bpy 0 , 34 monoanionic bpy -1 35 and dianionic bpy -2 , 35,36 it has been shown that the intramolecular CC and CN bond lengths of the bpy ligand vary as a function of the overall ligand charge because of changes in the bonding and antibonding interactions of the bpy 0 p* orbital (lowest unoccupied molecular orbital, LUMO). 35 This structural signature, which has also been studied in other non-innocent ligands such as substituted bipyridine, [37][38][39] phenanthroline, 40 terpyridine, 38,39,41 pyridine-2,6-diimine 40 or quinones 42 is a good indicator of both the electronic population of the coordinated ligands and the electronic structure of the complexes. [43][44][45][46][47] If high resolution X-ray crystallographic structures can be obtained, accurate bond lengths and the way in which they change upon varying the oxidation level can allow the redox state of the ligands in their coordination complexes to be determined unambiguously.…”

From 0 to II in One‐Electron Steps: A Series of Ruthenium Complexes Supported by TropPPh2

“…[4] Generally, complexes with transition metals in the 5th and 6th row undergo reactions such as oxidative addition and reductive elimination in which the oxidation state changes by two units, while complexes with 4th row metals frequently show one-electron redox chemistry. [6] Without such ligands, mononuclear Ru I complexes are inherently unstable. Ruthenium complexes with redox active ligands have been reported to undergo one-electron reductions/oxidations, but these occur at the ligand while the oxidation state at the metal center remains + 2.…”

“…Ruthenium complexes with redox active ligands have been reported to undergo one-electron reductions/oxidations, but these occur at the ligand while the oxidation state at the metal center remains + 2. [6] Without such ligands, mononuclear Ru I complexes are inherently unstable. [7] For this reason, most of the Ru I species are reactive intermediates detected in situ, [7,8] or form binuclear/ multinuclear complexes containing metal-metal bonds.…”

“…Ru 0 (tropPPh 2 ) 2 (1) was prepared by heating a mixture of RuH 2 (PPh 3 ) 4 and tropPPh 2 [2] in DME at 80 8C for two days without stirring, during which 1 crystallized out of the solution Scheme 1. Synthesis of complexes 1-5. a) DME, 80 8C, 2 days; b) DCM, CO, or pyridine, r.t., < 5 min; c) [Cp 2 Fe][PF 6 ], THF, r.t., overnight; d) Cr(C 6 H 6 ) 2 , THF, r.t., 7 h; e) AgOTf, THF or DCM, r.t., 2 h; f) Cp* 2 Co, DME, r.t., 7 h; g) AgOTf, DCM, r.t., 11 h (one anion in 5 is PF 6 in 60 % yield (Scheme 1). An X-ray diffraction study of a single crystal of 1 (see the Supporting Information), [10] revealed that the ruthenium center is coordinated to two tropPPh 2 ligands in a butterfly coordination environment (Figure 1 a).…”