Three Bis‐BODIPY Analogous Diruthenium Redox Series: Characterization and Electronic Structure Analysis

Abstract

The dianion derived from (2Z,6Z)‐3,7‐diphenyl‐N2,N6‐di(pyridin‐2‐yl)pyrrolo[2,3‐f]indole‐2,6(1H,5H)‐diimine (H2BL), a modified BODIPY ligand precursor, is shown to be capable of bridging two metal complex fragments RuL2, L=2,4‐pentanedionato (acac−), 2,2’‐bipyridine (bpy) or 2‐phenylazopyridine (pap) in [Ru(acac)2Ru(μ‐BL)Ru(acac)2] (1/2), [Ru(bpy)2Ru(μ‐BL)Ru(bpy)2](ClO4)2 ([3](ClO4)2) and [Ru(pap)2Ru(μ‐BL)Ru(pap)2](ClO4)2 ([4](ClO4)2). The compounds, including a diastereoisomeric pair 1 (meso) and 2 (rac) were spectroscopically and structurally characterized. Reversible electron transfers as revealed by cyclic and differential pulse voltammetry allowed for an EPR and UV‐vis‐NIR spectroelectrochemical investigation of several neighboring charge states. Together with susceptibility measurements and TD‐DFT calculations the assignment of oxidation states reveals that 1, 2 are diruthenium(III) species which can be oxidized or reduced by one electron whereas 32+ and 42+ contain ruthenium(II) and get reduced or oxidized mainly at the dianionic bridge (32+) or are reduced at the ancillary ligands pap (42+).

Bidirectional noninnocence of hinge-like deprotonated bis-lawsone on selective ruthenium platform: a function of varying ancillary ligands

“…The electron-accepting (π-acidic) ancillary ligands bpy and pap stabilised the metal ion in the +2 oxidation state in 1 2+ and 3 , respectively, while the electron-rich (σ-donating) acac preferentially stablised the metal ion in the +3 oxidation state in 2 under aerial reaction conditions due to the low Ru( iii )/Ru( ii ) oxidation potential of −0.28 V versus SCE (shown later). Dimeric 1 2+ and 2 in principle can exist in diastereomeric rac (ΔΔ/ΛΛ) and meso (ΔΛ) forms; 5 f ,14 however, the TLC (thin layer chromatography) experiment, single crystal X-ray structure and 1 H NMR suggested the selective formation of the rac form.…”

Donor–acceptor bridge 2,5-bis(2-oxido-phenyl)thiazolo-[5,4-d]thiazole derived diruthenium and diosmium systems. Structural and competitive electronic events as a function of metal ion, bridge and ancillary ligand

“…Similar to [ 1 ](ClO 4 ) 2 /[ 2 ](ClO 4 ) 2 , the analogous Os-bpy/Os-pap derivatives [ 3 ](PF 6 ) 2 /[ 4 ](ClO 4 ) 2 displayed two successive closely spaced reversible/irreversible oxidations (O2–O1: 70/120 mV) and two/four reversible reduction waves (R1, R2/R1–R4), respectively, and the potentials were positively shifted on moving from bpy to pap due to the stronger π-acceptance of pap. 22…”

“…The corresponding ruthenium-papbased [2](ClO 4 ) 2 displayed two closely spaced irreversible oxidations (O1/O2: 110 mV) and three reversible to quasireversible reductions (R1-R3), where the potential separation between R2/R3 (0.80 V) was greater than that of R1/R2 (0.57 V). The positively shifted redox potentials of [2](ClO 4 ) 2 (Ru-pap) with regard to that of [1](ClO 4 ) 2 (Ru-bpy) reflected the stronger π-accepting feature of pap compared to bpy, 22 and that in turn extended the irreversibility of the O1/O2 steps for the former. Similar to [1](ClO 4 ) 2 /[2](ClO 4 ) 2 , the analogous Os-bpy/Os-pap derivatives [3](PF 6 ) 2 /[4](ClO 4 ) 2 displayed two successive closely spaced reversible/irreversible oxidations (O2-O1: 70/120 mV) and two/four reversible reduction waves (R1, R2/R1-R4), respectively, and the potentials were positively shifted on moving from bpy to pap due to the stronger π-acceptance of pap.…”

“…Similar to [1](ClO 4 ) 2 /[2](ClO 4 ) 2 , the analogous Os-bpy/Os-pap derivatives [3](PF 6 ) 2 /[4](ClO 4 ) 2 displayed two successive closely spaced reversible/irreversible oxidations (O2-O1: 70/120 mV) and two/four reversible reduction waves (R1, R2/R1-R4), respectively, and the potentials were positively shifted on moving from bpy to pap due to the stronger π-acceptance of pap. 22 Although the impact of the better π-donor feature of Os with respect to Ru 23 was reflected in the lower oxidation potential of [3](PF 6 ) 2 (Os-bpy) as compared to [1](ClO 4 ) 2 (Ru-bpy), the same effect was remarkably missing when moving from the corresponding pap-derived [2](ClO 4 ) 2 (Ru-pap) to [4](ClO 4 ) 2 (Os-pap) (Fig. 5 and Table 6).…”

Structural and Electronic Diversity as a Function of Metal Ions and Co‐ligands in Deprotonated Epindolidione Bridged Diruthenium and Diosmium Set‐up

“…In relation to L 2À bridged analogous ruthenium derivatives [(bpy) 2 Ru II (μ-L 2À ) Ru II (bpy) 2 ](ClO 4 ) 2 [5](ClO 4 ) 2 and [(pap) 2 Ru II (μ-L 2À )Ru II (pap) 2 ](ClO 4 ) 2 [6](ClO 4 ) 2 , [13] oxidation and reduction potentials of the osmium derivatives [3](ClO 4 ) 2 /[4](ClO 4 ) 2 shifted to the less positive and more negative directions, respectively, due to the better π-donor feature of Os as compared to Ru. [34] The presence of multiple redox-active constituents i. e. metal (Ru, Os), bridge (L 2À ) [34] and ancillary ligand (acac, bpy, pap) [33,35] in 1/2, [3](ClO 4 ) 2 , [4](ClO 4 ) 2 introduced a competitive scenario in electron transfer steps i. e. metal or ligand or mixed metal/ligand along the redox chain in Figure 8, which was therefore evaluated by collective consideration of DFT calculated MOs and Mulliken spin density plots (MSD) at the paramagnetic states (Figures 9-12, Tables 5 and 6 and Tables S5-S30, Supporting Information).…”