Long-Range Intramolecular Electronic Communication in a Trinuclear

Article pubs.acs.org/IC

Long-Range Intramolecular Electronic Communication in a Trinuclear Ruthenium Tropolonate Complex Jun Yoshida,* Kyohei Kuwahara, Kota Suzuki, and Hidetaka Yuge Department of Chemistry, School of Science, Kitasato University 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan S Supporting Information *

ABSTRACT: Dinuclear and trinuclear ruthenium complexes, [Ru(trop)2(C2trop)Ru(dppe)Cp] [2b; trop = tropolonato, C2trop = ethynyltropolonato, dppe = 1,2-bis(diphenylphosphino)ethane] and [Ru(trop){(C2trop)Ru(dppe)Cp}2] (3), were synthesized, and their electronic and electrochemical properties were investigated in comparison with our previously reported complex [Ru(acac)2(C2trop)Ru(dppe)Cp] (2a). The electrondonating RuII(dppe)Cp unit and electron-accepting RuIIIO6 unit are connected by C2trop in these complexes. 2a incorporates acetylacetonate as an ancillary ligand, while 2b and 3 incorporate tropolonate as an ancillary ligand. Every complex, 2a, 2b, and 3, exhibits similar UV−vis−near-IR (NIR) absorption spectra, demonstrating the lack of explicit intramolecular electronic communication between the units at least in the neutral state. The weak NIR absorption in 2a further diminished upon electrochemical oxidation, indicating almost no electronic communication between the units. In contrast, 2b and 3 exhibit broad NIR absorptions upon oxidation. Additionally, 3 exhibits four stepwise redox couples in the electrochemical study, which are formally attributed to [RuII(trop)3]−/[RuIII(trop)3], two [RuII(dppe)Cp]/[RuIII(dppe)Cp]+, and [RuIII(trop)3]/[RuIV(trop)3]+ couples. Clear separation of the redox couples attributed to the two terminal [Ru(dppe)Cp] units demonstrates the thermodynamic stability of the intermediate oxidation states with respect to disproportionation. Further electrochemical studies using an electrolyte including perfluorinated weakly coordinating anions and density functional theory/ time-dependent density functional theory calculations confirmed the effect of ancillary ligands, acetylacetonate and tropolonate. In the case of 2a, electronic delocalization over the whole complex, especially over the [Ru(acac)2(trop)] unit, appears to be small. In contrast, the electronic communication between [Ru(dppe)Cp] and [Ru(trop)3] units in 3 seems to be enhanced upon oxidation, resulting in the long-range intramolecular electronic communication.

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INTRODUCTION The redox chemistry of tropolone (Htrop) and its derivatives has attracted wide attention from biological and chemical aspects. In the former view, Htrop and its derivatives have been mainly investigated in terms of the antioxidant properties such as the inhibition of various oxidases.1−8 In the latter sense, Htrop derivatives have attracted attention as a framework for organic redox systems,9−12 ever since Nozoe proposed tropoquinone (cyclohepta-3,6-diene-1,2,5-trione) as an oxidized form of 5-hydroxytropolone.9 The redox chemistry of metal tropolonate complexes has been also investigated,13−20 including the study of Htrop derivatives as redox-active ligands,21−26 while ruthenium tropolonate complexes have not been fully investigated. Even a basic cyclic voltammetry (CV) study of [Ru(trop)3] (1) had not been reported until our recent report.27 This is in contrast with the fact that ruthenium(III) complexes with similar bidentate ligands such as catecholate and acetylacetonate (acac) have been intensely investigated in terms of electrochemistry.28−41 Htrop can be regarded as a seven-membered-ring analogue of oxolene, which is a collective name for the three different redox states: catecholate (cat), semiquinonate (SQ), and quinone (Q).42−47 © XXXX American Chemical Society

Htrop and its derivatives are the old and new ligands in terms of the electrochemical and redox properties of the resulting metal complexes. We previously reported a dinuclear ruthenium complex (2a, Scheme 1) incorporating ethynyltropolonate (C2trop) as a bridge connecting an electron-donating Ru(dppe)Cp unit and an electron-accepting RuO6 unit.27 Our first aim was to regulate the ON/OFF of the electronic communication between the units using the proton response of ruthenium acetylide,48−50 while intramolecular electronic communication between the units was found to be quite small. During the course of modifying the electron delocalization efficiency, we found that the simple exchange of an ancillary acac ligand in 2a with tropolonate (trop) led to strongly enhanced intramolecular electronic communication, especially in the oxidized state. Here we present the largely different electrochemical properties between 2a and analogous dinuclear and trinuclear tropolonate complexes, [Ru(trop)2(C2trop)Ru(dppe)Cp] [2b; trop = tropolonate, C2trop = ethynyltropolonato, and dppe = Received: September 19, 2016

A

DOI: 10.1021/acs.inorgchem.6b02249 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

squares on F2. Crystallographic and experimental data are summarized in Table S1. Computational Methods. Restricted and unrestricted DFT calculations were carried out to optimize structures and to obtain the nature of the molecular orbitals (MOs) involved for 2a, 2a+, 2b, 2b+, 3, 3+, 32+, [Ru(acac)2(trop)], [Ru(acac)2(trop)]+, 1, and 1+. Calculations were performed using Gaussian 0953 with the CAMB3LYP functional.54 The 6-31G(d) basis set55−57 was employed for the C, H, O, and P atoms, while the LanL2DZ basis set was used for the Ru atom with associated effective core potentials.58−60 Each optimized structure was confirmed to be a minimum by frequency calculation. Solvent effects were included with the polarizable continuum model (PCM)61,62 using dichloromethane (DCM) as a solvent. DFT calculations were performed for both singlet and triplet states for the cases of 2a+, 2b+, and 3+. TD-DFT calculations were also performed to examine the electronic transitions of the compounds with the same functional and basis set. Solvent effects were included in the TD-DFT calculations of 2a, 2a+, 2b, and 2b+, while they were not taken into consideration for TD-DFT calculations of 3, 3+, and 32+ because of limited computer resources. The vibrational modes and MOs were visualized using GaussView, version 5.0.9.63 Materials. Tetrahydrofuran (THF) and DCM were distilled over sodium/benzophenone and CaH2, respectively, while other solvents employed were of reagent grade. 1,2-bis(diphenylphosphino)ethane, N-bromosuccinimide (NBS), dicyclopentadiene, triethylamine (TEA), and (trimethylsilyl)acetylene (Me3SiC2H) were purchased from Kanto Chemical (Tokyo, Japan) or TCI (Tokyo, Japan) and used without further purification. Tropolone (Htrop), [Ru(trop)3] (1), and [RuCl(dppe)Cp] were prepared following literature procedures.64−69 The preparations of [Ru(trop)2(Brtrop)] (1Br; Brtrop = 5bromotropolonate), [Ru(trop)(Brtrop)2] (1Br2), [Ru(Brtrop)3] (1Br3), and [Ru(Brtrop)2(Br2trop)] (1Br4; Br2trop = 3,5-dibromotropolonate) are described in the Supporting Information. [nBu4N][B(C6F5)4] was prepared according to the literature procedure and recrystallized from DCM/ether twice.70 [Ru(trop)2(Me3SiC2trop)] (1-Si). To a THF solution (30 mL) containing 1Br (300 mg, 0.552 mmol), CuI (10 mg), [PdCl2(PPh3)2] (15 mg), and TEA (0.3 mL) were successively added under a nitrogen atmosphere. To this solution was slowly added over 1 h a THF solution (4 mL) containing Me3SiC2H (0.10 mL). After additional stirring at ambient temperature for 30 min, the solvent was removed by a rotary evaporator. The residue was subjected to silica gel column chromatography with CHCl3/CH3CN = 20/1 as the eluent. 1-Si was obtained as a dark-red solid (226 mg, 0.403 mmol, 73% yield). 1 H NMR (600 MHz, CDCl3): δ −32.09(s, 2H), −18.80 (d, J = 9.0 Hz, 2H), −18.22 (d, J = 9.0 Hz, 2H), −11.02 (d, J = 10.2 Hz, 2H), 0.57 (s, 9H), 17.92 (d, J = 9.0 Hz, 2H), 19.45 (s, 2H), 19.96 (s, 2H). HRMS (ESI+). Calcd for C26H24O6RuSi ([M + H]+): m/z 562.0380 (100%), 561.0392 (58%). Found: m/z 562.0383, 561.0396. [Ru(trop)(Me3SiC2trop)2] (1-Si2). This compound was obtained by a procedure similar to that for 1-Si by using 1Br2 instead of 1Br. 1Si2 was obtained as a dark-red solid (198 mg, 0.301 mmol, 62% yield). 1 H NMR (600 MHz, CDCl3): δ −34.72 (s, 1H), −20.77 (d, J = 8.4 Hz, 2H), −14.15 (d, J = 10.8 Hz, 2H), −13.52 (d, J = 10.2 Hz, 2H), −0.57 (s, 18H), 18.91 (d, J = 9.0 Hz, 2H), 19.31 (d, J = 9.0 Hz, 2H), 20.63 (s, 2H). HRMS (ESI+). Calcd for C31H31O6Si2Ru ([M]+): m/z 657.0697 (100%), 656.0710 (60%). Found: m/z 657.0692, 656.0697. [Ru(trop)2(C2trop)Ru(dppe)Cp] (2b). 1-Si (0.150 g, 0.27 mmol), KF (0.038 g, 0.60 mmol), and [RuCl(dppe)Cp] (0.180 g, 0.30 mmol) were added to methanol (50 mL) under a nitrogen atmosphere, and the solution was then refluxed for 3 h. After cooling to room temperature, the solvent was removed by a rotary evaporator, and the residue was subjected to silica gel column chromatography with CHCl3/CH3CN = 20/1 as the eluent. 2b was obtained as a darkbrown solid (0.223 g, 0.21 mmol, 78% yield). 1 H NMR (600 MHz, CDCl3): δ −29.06 (s, 2H), −20.73 (s, 2H), −10.37 (d, J = 3.3 Hz, 2H), −8.07 (s, 2H), 1.95 (m, 2H), 2.49 (m, 2H), 4.91 (s, 5H), 7.21 (m, 16H), 7.75 (m, 4H), 15.07 (s, 2H), 16.34 (s, 2H), 24.15 (s, 2H). HRMS (ESI+). Calcd for C54H44O6P2Ru ([M + H]+): m/z 1054.0695 (100%), 1056.0705 (57%). Found: m/z

Scheme 1. Ruthenium Complexes Investigated, Including the Previously Reported Complex 2a and Newly Prepared Dinuclear (2b) and Trinuclear (3) Ruthenium Complexesa

a

Reagents and conditions for the syntheses of 2b and 3; (i) NBS, CHCl3; (ii) PdCl2(PPh3)2, CuI, Me3SiC2H, TEA, THF; (iii) [RuCl(dppe)Cp], KF, methanol.

1,2-bis(diphenylphosphino)ethane] and [Ru(trop){(C2trop)Ru(dppe)Cp}2] (3; Scheme 1). 2a, 2b, and 3 exhibit similar absorption spectra at the neutral state, whereas the absorption spectra change differently upon oxidation. The weak near-IR (NIR) absorption of 2a totally disappears upon electrochemical oxidation, while 2b and 3 exhibit strong and broad NIR absorption upon oxidation. Additionally, the redox couples attributed to two Ru(dppe)Cp units in 3 were found to be clearly separated in the cyclic voltammograms, indicating the thermodynamic stability of the intermediate oxidation states with respect to disproportionation. Further electrochemical studies using an electrolyte containing a perfluorinated weakly coordinating anion (WCA) and density functional theory (DFT)/time-dependent DFT (TD-DFT) calculations confirmed the influence of the acac and trop ancillary ligands on the electronic structure and the extent of electron delocalization through the complex framework.

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EXPERIMENTAL SECTION

Physical Measurements. 1H NMR spectra were recorded at 600 MHz with a Bruker AVANCE-II-600 or at 400 MHz with a Bruker AVANCE-III-400. All spectra are referenced to tetramethylsilane. Electrospray ionization mass spectrometry (ESI-MS) was performed with a Exactive Plus (Thermo Fisher Scientific); the mass range was m/z 20−2000 with a nominal resolution (at m/z 200) of 140000. Elemental analyses were carried out with a PerkinElmer 2400II. UV− vis−NIR spectra were recorded with a JASCO V-570 spectrometer. Electrochemical measurements were performed in a three-electrode cell using a 3-mm-diameter glassy carbon working electrode, a platinum auxiliary electrode, and a Ag/Ag+ reference electrode at room temperature with a BAS 610B system. The sample solution was bubbled with argon for 10 min prior to the measurement. A cyclic voltammogram was recorded at a scan rate of 0.1 V s−1 in 0.1 mol dm−3 nBu4N(ClO4)/CH2Cl2, while a differential pulse voltammogram was recorded with a pulse amplitude of 0.05 V, a pulse width of 0.05 s, a sampling width of 0.017 s, and a pulse period of 0.5 s. Spectroelectrochemical studies were performed using a 0.1 cm quartz cell with a platinum mesh as the working electrode. The crystal structure of 2b was determined by single-crystal X-ray diffraction. For collection of the diffraction data, a Bruker APEX II ULTRA diffractometer was used. The structure was solved by direct methods using the program SHELXT.51 The refinement and all further calculations were carried out using the program SHELXL.52 All nonH atoms were refined anisotropically, using weighted full-matrix least B


Article

Inorganic Chemistry 1054.0710, 1056.0713. Elem anal. Calcd for C54H43O6P2Ru2: C, 61.65; H, 4.12. Found: C, 61.65; H, 4.21. [Ru(trop){(C2trop)Ru(dppe)Cp}2] (3). This compound was obtained by a procedure similar to that for 2b by using 1-Si2 instead of 1-Si. 3 was obtained as a dark-brown solid (0.21 g, 0.13 mmol, 57% yield). 1 H NMR (600 MHz, CDCl3): δ −23.8 (s, 2H), −22.1 (s, 2H), −11.1 (s, 1H), −0.8 (s, 2H), 2.12 (m, 4H), 2.60 (m, 4H), 4.94 (s, 10H), 7.2−7.4 (m, 32H), 7.82 (m, 8H), 12.4 (s, 2H), 19.3 (s, 2H), 23.2 (s, 2H). HRMS (ESI+). Calcd for C87H71O6P4Ru3 ([M]+): m/z 1641.1417 (100%), 1640.1449 (94%). Found: m/z 1641.1454, 1640.1447. Elem anal. Calcd for C87H71O6P4Ru3: C, 63.73; H, 4.36. Found: C, 63.40; H, 4.45.

Figure 1. UV−vis−NIR spectra of 2a (solid line), 2b (dotted line), and 3 (bold line) measured in chloroform.

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RESULTS AND DISCUSSION Synthesis and Spectroscopic Characterization. The syntheses of the dinuclear (2b) and trinuclear (3) complexes were performed based on the postsynthetic modification71 of 1 and are outlined in Scheme 1. 1Br and 1Br2 were synthesized via the direct bromination of 1 with NBS.72−75 When 1 and 2 equiv of NBS were stirred in CHCl3 at 0 °C for 3.5 h, 1Br and 1Br2 were obtained in 24% and 29% yield, respectively. After examination of the reaction conditions, including the NBS/1 ratio, reaction time, and temperature, the reaction yields of 1Br and 1Br2 slightly increased to 44% and 49%, respectively. During the course of this investigation, we also obtained 1Br3 and 1Br4 as byproducts when 5 equiv of NBS was used. The results of the bromination reactions are summarized in Table S2. Sonogashira−Hagihara coupling of 1Br and 1Br2 with Me3SiC2H gave 1-Si and 1-Si2 in 73% and 62% yield, respectively. Further reaction of 1-Si and 1-Si2 with [RuCl(dppe)Cp] in the presence of KF76 gave 2b and 3 in 78% and 57% yield, respectively. The compounds obtained were characterized by 1H NMR, ESI-MS, and elemental analysis. In the 1H NMR measurements, the chemical shifts of acac and trop in newly synthesized ruthenium complexes were observed in the broad range from −35 to 25 ppm due to the paramagnetic ruthenium(III) of the RuO6 unit. Almost no paramagnetic effect was observed for dppe and Cp protons, confirming the diamagnetic property of the Ru(dppe)Cp unit. In high-resolution ESI-MS measurements, monosubstituted complexes [Ru(trop)2(L)] (L is a substituted trop) were observed as proton adducts, while the disubstituted complexes [Ru(trop)(L)2] were generally observed as cations (Figures S6−S9). Disubstitution of 1 appears to stabilize the cationic state, at least under the ESI-MS conditions used. The presence of 2 equiv of an alkyne unit in 3 was confirmed by UV−vis titration with p-toluenesulfonic acid based on the conversion of ruthenium acetylide to the vinylidene form upon the addition of an acid (Figures S10 and S11).48−50 2a, 2b, and 3 exhibit similar UV−vis−NIR spectra in chloroform with relatively strong absorptions around 460 and 590 nm and weak absorptions from 800 to 1000 nm (Figure 1). The absorption coefficients are on the order of 3 > 2b > 2a. The similar spectral shapes of 2a and 2b indicate that different ancillary ligands (acac and trop) slightly affect the electronic communication between the RuO6 and Ru(dppe)Cp units in the neutral state. Additionally, the similarity of the absorption spectra of 2b and 3 indicates no specific electronic communication between the two terminal Ru(dppe)Cp units in 3, at least in the neutral state. Crystal Structures. Single crystals of 2b were obtained by slowly evaporating the chloroform solution, whereas single crystals of 3 could not be obtained. The molecular structure of

2b was determined by single-crystal X-ray diffraction performed at 90 K. The bond lengths for the trop and C2trop ligands in 2b are comparable to those of 1 and 2a that we previously reported. The atoms in the trop and C2trop ligands are numbered as shown in Scheme 2. The C1−C2 bond lengths of Scheme 2. Numbering of the O and C Atoms in the C2trop Bridge

the two trop and C2trop ligands range from 1.452 to 1.475 Å, close to the sp2−sp2 single-bond linkage (1.47 Å), while other C−C bond lengths in the ligands range from 1.369 to 1.411 Å (Table 1), near the standard aromatic bond length of 1.39 Å in benzene. Conjugation appears to occur around the periphery of the tropolonato ring, as shown in Scheme 3. The slightly longer C3−C4 and C4−C5 bond lengths of C2trop ligands in both 2a and 2b are attributed to the extended π conjugation of Htrop with an ethynyl group. The Ru−O lengths in 2b (2.009−2.036 Å) are comparable to those in [Ru(acac)3],77 while the coordination geometry around Ru1 in 2b deviates considerably from the ideal octahedral arrangement. The O−Ru−O angles of the two trop ligands and the C2trop ligand in 2b are 79.60°, 79.99°, and 80.21°, respectively. This distortion reflects the tendency of trop to form a five-membered coordination ring, as reported for [Fe(trop)3].78 Electrochemical and Spectroelectrochemical Studies. The electrochemical properties of 2a, 2b, and 3 were studied by CV recorded for a CH2Cl2 solution containing each compound (1.0 mM) and [nBu4N](ClO4) (0.1 M) as the supporting electrolyte (Figures 2 and S12−S15). The redox potentials of these complexes are summarized in Table 2 with those of related compounds. 2b shows two reversible couples and one irreversible redox couple in the sweep from −1.5 to +0.5 V (vs Fc/Fc+), similar to 2a. Because 1 exhibits two reversible redox waves around −1.25 and +0.16 V (vs Fc/Fc+) attributed to RuII/RuIII and RuIII/RuIV couples and [Ru(dppe)Cp(C2Ph)] exhibits an irreversible oxidation around −0.06 V (vs Fc/Fc+),27 the two reversible redox couples at E1/2 = −1.35 and −0.13 V (vs Fc/Fc+) and the irreversible redox with an oxidation peak at 0.27 V in 2b are formally attributed to [RuII(trop)3]−/ [Ru III (trop) 3 ], [Ru II (dppe)Cp]/[Ru III (dppe)Cp] + , and [RuIII(trop)3]/[RuIV(trop)3]+ couples, respectively. 3 exhibits four pseudoreversible redox processes in the sweep from −1.6 to +0.5 V (vs Fc/Fc+), which are each assigned to one-electron redox from differential pulse voltammetry analysis (Figure C


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Inorganic Chemistry

Table 1. Average Bond Lengths (Å) in the acac, trop, and C2trop Ligands Calculated or Measured by X-ray Diffraction 2a

2a+ (triplet)

2a+ (singlet)

2b

2b+ (triplet)

2b+ (singlet)

3

3+ (triplet)

3+ (singlet)

32+ (quartet)

method

X-ray

calcd

calcd

calcd

X-ray

calcd

calcd

calcd

calcd

calcd

calcd

calcd

Ru2−C9 C8−C9 C4−C8 C3−C4 C4−C5 C2−C3 C5−C6 C1−C2 C6−C7 C1−C7 C1−O1 C7−O2 Ru1−O (C2trop) Ru−O (acac,trop)

1.993 1.214 1.435 1.398 1.421 1.376 1.380 1.404 1.404 1.452 1.313 1.313 2.015 2.011

2.017 1.226 1.426 1.407 1.407 1.383 1.383 1.405 1.405 1.452 1.299 1.299 2.038 2.033

1.927 1.245 1.399 1.419 1.419 1.371 1.371 1.416 1.416 1.470 1.279 1.279 2.064 2.017

1.907 1.256 1.362 1.447 1.447 1.353 1.353 1.437 1.437 1.450 1.275 1.275 2.009 2.036

1.996 1.212 1.435 1.413 1.413 1.377 1.377 1.397 1.397 1.460 1.305 1.305 2.014 2.022

2.008 1.228 1.420 1.410 1.410 1.380 1.380 1.406 1.406 1.446 1.302 1.302 2.023 2.052

1.928 1.246 1.397 1.420 1.420 1.370 1.370 1.416 1.417 1.470 1.277 1.277 2.066 2.024

1.933 1.248 1.374 1.438 1.438 1.359 1.359 1.426 1.427 1.429 1.294 1.294 1.982 2.030

1.964 1.255 1.414 1.431 1.431 1.389 1.389 1.420 1.420 1.455 1.320 1.320 2.032 2.058

1.937 1.261 1.402 1.437 1.437 1.384 1.384 1.423 1.423 1.446 1.320 1.320 2.021 2.033

1.934 1.262 1.401 1.437 1.437 1.384 1.384 1.424 1.424 1.449 1.319 1.319 2.019 2.042

1.920 1.264 1.402 1.435 1.435 1.385 1.385 1.422 1.422 1.455 1.315 1.315 2.026 2.017

Table 2. Redox Potentials (V vs Fc/Fc+) of 1, 2a, 2b, and 3a

Scheme 3. Plausible Resonance Structures of the C2tropRu(dppe)Cp Unit before and after the One-Electron Oxidation of 2b or 3

compound

electrolyte

[Ru(dppe) Cp(C2Ph)]

[nBu4N] (ClO4) [nBu4N] (ClO4) [nBu4N] [B(C6F5)4] [nBu4N] (ClO4) [nBu4N] [B(C6F5)4] [nBu4N] (ClO4) [nBu4N] [B(C6F5)4] [nBu4N] (ClO4)

1 2a 2a 2b 2b 3 3

(E1/2)1

(E1/2)2

(E1/2)3

(E1/2)4

−1.25

0.16

−1.36

−0.10

0.28b

−1.47c

−0.17

0.39

−1.35

−0.13

0.27b

−1.33

−0.20

0.24

−1.44

−0.25

0.00

0.26

−1.40

−0.35

−0.05

0.26

−0.06

a

Measurements were done for a DCM solution containing each complex (1.0 mM) and [nBu4N[(ClO4) (0.1 M) or [nBu4N][B(C6F5)4] by using ferrocene as an external standard. bIrreversible redox couple. The potential of the oxidation peak is listed in the table. c Irreversible redox couple. The potential of the reduction peak is listed in the table.

nm based on the optimized structure by DFT. The details of DFT calculations will be described in the following section. Cyclic voltammograms of 2a, 2b, and 3 were also measured by using [nBu4N][B(C6F5)4] as the electrolyte. [B(C6F5)4]− is one of the WCAs70,79−83 whose characteristic ion-pairing properties have been found to be effective in elucidating the difference between through-bond and through-space interactions. The reversibility of the redox processes in 2a, 2b, and 3 is highly improved with [nBu4N][B(C6F5)4] compared to the cases with [nBu4N](ClO4) (Figure 2), whereas only the redox process around −1.4 V (vs Fc+/Fc) in 2a is irreversible with [nBu4N][B(C6F5)4]. The difference implies the totally different electronic distributions between 2a and 2b in the reduced forms despite their similar molecular structure, while we here focus on the oxidation processes. The differences between E1/2 values, ΔE1/2 (V), are listed in Table 3. In all cases, the ΔE1/2 (V) values in the [nBu4N][B(C6F5)4]/CH2Cl2 medium are larger than those in [Bu4N](ClO4)/CH2Cl2. In particular, ΔE1/2, (E1/2)2 − (E1/2)3, explicitly increases for 2a compared to 2b and 3. The significantly higher ΔE1/2 in 2a and dependence

Figure 2. Cyclic voltammograms of (a) 2a, (b) 2b, and (c) 3. Measurements were conducted in a 0.1 mol dm−3 [Bu4N](ClO4)/ CH2Cl2 solution containing a 1 mmol dm−3 ruthenium complex (a-1, b-1, and c-1) or in a 0.1 mol dm−3 [Bu4N][B(C6F5)4]/CH2Cl2 solution containing 1 mmol dm−3 ruthenium complex (a-2, b-2, and c-2). The scan rate is 100 mV s−1.

S16). The redox couples at −1.44 and +0.26 V (vs Fc/Fc+) in 3 are attributed to the RuII/RuIII and RuIII/RuIV couples of the central [Ru(trop)3] moiety by comparison with 1 and 2b (Table 2). The remaining two redox couples at −0.25 and +0.00 V (vs Fc/Fc+) are therefore formally attributed to the two [Ru(dppe)Cp] units. A clear separation of the two redox processes attributed to the terminal [Ru(dppe)Cp] units in 3 indicates that the two units electronically influence one another despite the long distance. The distance between the two Ru ions of the terminal [Ru(dppe)Cp] units is approximately 1.7 D


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Inorganic Chemistry

Table 3. ΔE1/2 Values (V) for 2a, 2b, and 3 in [Bu4N](ClO4)/CH2Cl2 and the [nBu4N][B(C6F5)4] Medium and the Increase of ΔE1/2 Values upon a Change of the Electrolyte electrolyte

(E1/2)2 − (E1/2)3

[ Bu4N](ClO4) [nBu4N][B(C6F5)4] [nBu4N](ClO4) [nBu4N][B(C6F5)4] [nBu4N](ClO4) [nBu4N][B(C6F5)4]

0.38 0.56 0.40 0.44 0.25 0.30

compound 2a 2a 2b 2b 3 3 a

n

difference of the ΔE1/2 valuesa 0.18 0.04 0.05

log Kcb

(E1/2)3 − (E1/2)4

difference of the ΔE1/2 values

log Kcb

6.4 9.5 6.8 7.4 4.2 5.1

0.26 0.31

0.05

4.4 5.2

Comparison of the ΔE1/2 values between two electrolytes. bThe values calculated for T = 298 K.

Scheme 4. log Kc Values and Ru−Ru Distances in the Reported Dinuclear Ruthenium Complexes Measured in DCM with [Bu4N](PF6) as the Electrolyte85,86

on the electrolytes indicate that there is a substantial Coulombic/through-space interaction.79 In contrast, the slight dependence of 2a and 3 on the electrolytes indicates the dominant contribution of resonance/delocalization over the complex. The use of WCAs clearly exhibited the different roles of ancillary ligands. The equilibrium constants (Kc) for the 3−/3/ 3+ and 3/3+/32+ comproportionation reactions were then deduced to compare the extent of electronic communication with related dinuclear ruthenium complexes.84 The reaction for the case of 3/3+/32+ is defined as follows: Ru ter−Rucen−Ru ter(3) ⇌ Ru ter +−Rucen−Ru ter(3+) ⇌ Ru ter +−Rucen−Ru ter +(32 +) ⎛ F ⎞ Kc = exp⎜ |E (1) − E1/2(2)|⎟ ⎝ RT 1/2 ⎠

Figure 3. UV−vis−NIR spectral changes of 3 (1 mM in CH2Cl2 with 0.1 M nBu4NClO4) upon the application of −0.22 V vs Fc/Fc+ from 0 to 40 min. (1)

(vs Fc/Fc+). The broad absorption is attributed to electrochemically generated 3+ according to the redox potentials (Table 2). The equilibrium between 3 and 3+ was confirmed by the gradual disappearance of the NIR absorption with further application of −1.0 V (vs Fc/Fc+; Figure S17). When 0.03 and 0.33 V (vs Fc/Fc+; each potential responds to the formation of 32+ and 33+) are applied to a newly prepared [Bu4N](ClO4)/ CH2Cl2 solution containing 3, different NIR absorptions are observed in the region from 800 to 1500 nm in each case (Figures S18 and S19). Spectroelectrochemical studies of 2a and 2b were similarly performed for CH2Cl2 solutions containing each compound and the electrolyte. When 0 and 0.29 V are applied to 2b (vs Fc/Fc+), at which 2b+ and 2b2+ are ideally formed, NIR absorptions appear from 1000 to 2000 nm and from 800 to 1500 nm, respectively (Figures S20 and S21). In contrast, when 0.0 V (vs Fc/Fc+) is applied to 2a, at which 2a+ is ideally formed, the weak NIR absorption from 800 to 1000 nm almost completely disappears and no new NIR

Here, E1/2(1) and E1/2(2) are the reversible half-wave potentials corresponding to the Ruter−Rucen−Ruter/Ruter+−Rucen−Ruter (3/3+) and Ruter+−Rucen−Ruter/Ruter+−Rucen−Ruter+ (3+/32+) redox couples, respectively. On the basis of the E1/2(1) values in Table 2, log Kc values of the 3−/3/3+ and 3/3+/32+ comproportionation reactions at 298 K were calculated to be 5.1 and 5.2, respectively. log Kc values of several reported dinuclear mixed-valence ruthenium complexes with a bis(βdiketonate)-type bridge are shown in Scheme 4.28,85,86 Compared to these complexes, electronic communication in 3 is deduced to be fairly large despite the long distance between ruthenium termini and the presence of a Ru(trop)3 moiety between the [Ru(dppe)Cp] units. We then performed spectroelectrochemical measurements of a [Bu4N](ClO4)/CH2Cl2 solution containing each ruthenium complex. For the case of 3, broad absorption gradually appears in the NIR region from 1000 to 2500 nm with isosbestic points at 824 and 904 nm (Figure 3) upon the application of −0.22 V E


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Inorganic Chemistry

Figure 4. Schematic representation of 2a, 2b, and 3 upon electrochemical oxidation. The circle and square units each correspond to RuO6 and Ru(dppe)Cp moieties bridged by C2trop, represented by the rectangle. The drawing in black and white schematically indicates whether the part is oxidized or not, respectively.

DFT and TD-DFT Calculations. To obtain missing structural information on the ruthenium complexes and investigate their electronic states in detail, the restricted or unrestricted DFT and TD-DFT calculations were performed for 2a, 2a+, 2b, 2b+, 3, 3+, and 32+. For the cases of 2a+, 2b+, and 3+, two spin states (singlet and triplet) were calculated. For the cases of 2a+ and 2b+, triplet states were calculated to be more stable compared to singlet states by 0.176 and 0.155 kcal mol−1, respectively. In the case of 3+, the singlet state was found to be more stable than the triplet state, while the difference is only 0.056 kcal mol−1. Because the energy differences are subtle and two spin states may coexist antiferromagnetically in the cationic compounds, we here do not conclude the most stable spin states for the cationic complexes and discuss both spin states. The bond lengths in the optimized structures of 2a and 2b are comparable to those of the crystal structures measured at 90 K. Additionally, 2a and 2b exhibit similar bond-length changes upon oxidation; a slight alternate expansion and contraction of the bond lengths is observed for C2trop. In triplet 2b+, the Ru2−C9,C8−C4, C2−C3, C5−C6, C1−O1, and C7−O2 bonds (Scheme 2) become shorter compared to 2b, while the C9C8, C3−C4, C4−C5, C1−C2, and C6−C7 bonds become longer. A similar trend was also observed for singlet 2b+. The C1−C7 length is almost the same between 2b and 2b+. A similar behavior is also observed for C2trop of 2a upon oxidation (for both singlet and triplet states; Table 1). The Ru−acetylide bond of Ru2−C9 in 2a and 2b is supposed to adopt partial vinylidene character upon oxidation to 2a+ and 2b+,87,88 which then triggers reconfiguration of the electron density over the whole complex. 3 shows behavior similar to that for 2b upon oxidation to 3+, while the bond-length changes are modest compared to those observed for oxidation from 2b and 2b+. The bond lengths of Ru2−C9, C8−C4, and C9C8 in 32+ approach the values of 2b+, while no explicit difference is observed for other C−C bonds in C2trop and Ru−O lengths in 3, 3+, and 32+. The effect of a positive charge on the molecular structure may be weak in 3 because of large π-electron delocalization over the whole complex. π conjugation over the C2trop and trop ligands is also supported by the frontier MOs of 2a, 2a+, 2b, 2b+, 3, 3+, and 32+ shown in Figures S23−S32. The spin-density plots for the complexes in the neutral and oxidized states also demonstrate the roles of the C2trop bridge and ancillary trop ligands (Figure 5). Although the spin density

absorptions appear (Figure S22). The results of the spectroelectrochemical study are summarized in Figure 4. The lack of NIR absorption for 2a upon oxidation demonstrates that an ancillary tropolonato ligand is critical for the appearance of broad NIR absorption in the oxidized forms of 2b and 3. In other words, the intramolecular electronic communication in 2b and 3 is quite sensitive to the electronic state of the tris(chelate)ruthenium unit. To clarify the difference between the acac (2a) and trop (2b and 3) types, we here compare the redox potentials of [Ru(trop)3] with those of [Ru(acac)2(trop)], [Ru(acac)3], and their derivatives. E1/2 values in these complexes are summarized in Table 4. The Table 4. Redox Potentials (V) of [Ru(acac)3] and Its Selected Derivatives (vs Fc/Fc+) Based on the Reported Articles28,85,86 and References Cited Thereina compound [Ru(acac)3] [Ru(phpa)2(acac)] [Ru(phpa)2(acacI)] [Ru(phpa)2(acacC2H)] [Ru(acac)2(mhmk)] [Ru(acac)2(trop)] [Ru(acac)2(Brtrop)] (1Br) [Ru(trop)3] (1)

solvent

(E1/2)1

(E1/2)2

ΔE1/2 = (E1/2)2 − (E1/2)1

CH2Cl2 acetonitrile acetonitrile acetonitrile acetonitrile acetonitrile CH2Cl2 acetonitrile

−1.28 −1.16 −1.35 −1.205 −1.211 −1.34 −1.27 −1.19

0.54 0.60 0.49 0.578 0.614 0.37 0.49 0.46

1.82 1.76 1.84 1.78 1.83 1.71 1.76 1.65

CH2Cl2

−1.25

0.16

1.41

a

phpa = 2,2,6,6,-tetramethyl-3,5-heptanedionate ion, acacI = 3-iodo2,4-pentanedionate ion, acacC2H = 3-ethynyl-2,4-pentanedionate ion, and Hmhmk = 2-imino-4-hydroxypent-3-ene.

redox potentials in [Ru(acac)2(trop)], [Ru(acac)3], and their derivatives, of course, strongly depend on the ligand type, while the differences between the two redox couples, ΔE = E1/2(RuII/ RuIII) − E1/2(RuII/RuIII), are roughly the same in the range from 1.71 to 1.82 V irrespective of the ligand type. This means that one-electron oxidation and reduction take place at the orbital strongly localized on a Ru ion. In contrast, [Ru(trop)3] shows a smaller ΔE value (1.41 V), meaning that the d orbitals of the Ru ion are more strongly coupled with the ligand orbitals. F


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Inorganic Chemistry

Figure 5. Total spin-density surface plots for optimized structures of 2a, 2a+, 2b, 2b+, 3, 3+, 32+, [Ru(acac)2(trop)], [Ru(acac)2(trop)]+, [Ru(trop)3], and [Ru(trop)3]+ (isocontour values: ± 0.002 e bohr−3).

densities on two acetylatetonate ligands slightly increase from 0.0431 to 0.1278. In [Ru(trop)3], the electron densities increase in all trop ligands from (0.0572, 0.0747, and 0.0566) to (0.2761, 0.1987, 0.2759). The comparison of [Ru(acac)2(trop)] and [Ru(trop)3] demonstrates the electron delocalization over tropolonato ligands at the oxidized state. TD-DFT calculations were also performed for 2a, 2a+, 2b, 2b+, 3, 3+, and 32+, while calculation of the charge transfer in a fairly large system is often accompanied by difficulties.89−92 Although our rough calculation is still not realizing the actual system accurately, the calculation exhibited a roughly similar tendency with the experimental results. The UV−vis−NIR spectra calculated are shown in Figures S43−S52. At the neutral state, 2a, 2b, and 3 do not show explicit NIR absorptions, while oxidized species have the transition at the NIR region (Table S5). Only 3+ (triplet) exhibited the excitation around 2000 nm with an oscillator strength larger than 0.1, as found in the experimental study. The NIR transition in 3+ is a mixture of several transitions: 364β > 374β, 365β > 375β, 367β > 375β, 372β > 374β, 372β > 375β, 373β > 374β, 373β > 375β, 372β < 374β, and 373β < 374β (Figure S31). Although we still cannot reproduce the non-NIR-absorption in 2a+, the TD-DFT study supports the charge transfer between π orbitals delocalized over the complex. On the basis of the DFT and TD-DFT calculations and reported noninnocent behavior of related complexes [Ru(dppe)CpC2R] (R = aromatic moieties),93−96 the whole Ru(dppe)Cp(C2trop) unit rather than only the Ru ion appears to be oxidized. Possible resonance structures are shown in Scheme 3. The resonance structures are supposed to contribute

reflects not only the single orbital MO but also other components such as the dipole moment, the plots confirm the spin-density distribution over the complex, especially on the C2trop and trop ligands. The sum of the spin densities on C2trop explicitly increases from 0.1111 in 2b to 0.5710 in 2b+ (Table S3). Additionally, the spin densities on Ru1 and Ru2 and over the two trop ligands increase from 0.7868, 0.0069, 0.0457, and 0.465 in 2b to 0.8268, 0.3746, 0.0902, and 0.0901 in 2b+, respectively. Similarly, the sum of the spin densities over the two C2trop and ancillary trop ligands in 3 increases monotonically upon oxidation: 0.0269, 0.0861, and 0.0797 for 3, 0.0849, 0.3925, 0.3670 for 3+, and 0.0837, 0.5511, 0.5485 for 32+. While the spin densities over C2trop in 2a also increase upon oxidation (0.0715 for 2a and 0.3423 for 2a+) similarly to 2b and 3, a difference between 2a and 2b is observed in the spin distribution over the ancillary ligands. The spin densities over the two acetylacetonate ligands in 2a slightly increase from (0.0301 and 0.0510) to (0.0383 and 0.0612) upon oxidation, whereas the spin densities of the two trop ligands in 2b increase from (0.0457 and 0.0465) to (0.0902 and 0.0901). Natural population analysis also indicates the increase of positive charge over C2trop upon oxidation for both 2a and 2b, supporting the electron delocalization over C2trop (Figures S33−S38). To elucidate the role of ancillary ligands on the electronic structure, we performed DFT calculations of [Ru(acac)2(trop)] and [Ru(trop)3], which correspond to the core structures of 2a, 2b, and 3. [Ru(acac)2(trop)] and [Ru(trop)3] exhibit similar spin densities at the neutral states (Table S4). Upon oxidation, the electron densities over one trop ligand explicitly increase in [Ru(acac)2(trop)] from 0.0761 to 0.4950, while the spin G


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Inorganic Chemistry to the π-electron delocalization and stabilization of the cation form. In 3, the oxidation of one Ru(C2trop) unit further affects another unit through the central Ru(trop)3 unit. As a result, the redox couples of two Ru(dppe)Cp moieties of 3 are clearly separated in the electrochemical study. Additionally, slightly poor electron delocalization over the [Ru(acac)2(trop)] moiety explains the difference in the absorption spectra between 2a and 2b in their oxidized state. The largely different effects between [Ru(acac)2(trop)] and [Ru(trop)3] upon electron and/or spin delocalization are of interest and are used in terms of modulating the electronic state of ruthenium(III) complexes. The electronic state and redox chemistry of [Ru(acac)2(L′)]type (L′ is a chelate ligand) complexes have been actively investigated.29,31−41 One reason may be the presence of [Ru(acac) 2 (acetonitrile) 2 ], a useful precursor for [Ru(acac)2(L′)].97 For the case of ruthenium tropolonate complexes, the use of the [Ru(trop)3] unit rather than the [Ru(acac)2(trop)] unit has introduced fruitful results in terms of redox chemistry and electrochemistry.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the Kitasato University Research Grant for Young Researchers and Futaba Denshi Foundation. The computations were performed using the Research Center for Computational Science, Okazaki, Japan.

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(1) Sánchez-Ferrer, A.; Laveda, F.; García-Carmona, F. Partial Purification of Soluble Potato Polyphenol Oxidase by Partitioning in an Aqueous Two-Phase System. J. Agric. Food Chem. 1993, 41, 1219− 1224. (2) Espin, J. C.; Wichers, H. J. Slow-Binding Inhibition of Mushroom (Agaricus Bisporus) Tyrosinase Isoforms by Tropolone. J. Agric. Food Chem. 1999, 47, 2638−2644. (3) Pérez-Gilabert, M.; García Carmona, F. Characterization of Catecholase and Cresolase Activities of Eggplant Polyphenol Oxidase. J. Agric. Food Chem. 2000, 48, 695−700. (4) Gandia-Herrero, F.; Jiménez, M.; Cabanes, J.; Garcia-Carmona, F.; Escribano, J. Tyrosinase Inhibitory Activity of Cucumber Compounds: Enzymes Responsible for Browning in Cucumber. J. Agric. Food Chem. 2003, 51, 7764−7769. (5) Nunez-Delicado, E.; Serrano-Megias, M.; Perez-Lopez, A. J.; Lopez-Nicolas, J. M. Polyphenol Oxidase from Dominga Table Grape. J. Agric. Food Chem. 2005, 53, 6087−6093. (6) Kanade, S. R.; Paul, B.; Rao, A. G. A.; Gowda, L. R. The Conformational State of Polyphenol Oxidase from Field Bean (Dolichos Lablab) upon SDS and Acid-pH Activation. Biochem. J. 2006, 395, 551−562. (7) Asenstorfer, R. E.; Appelbee, M. J.; Mares, D. J. Impact of Protein on Darkening in Yellow Alkaline Noodles. J. Agric. Food Chem. 2010, 58, 4500−4507. (8) Manikandan, B.; Ramar, M. Detection of Natural and Induced Phenoloxidase Activities in Human Serum. Hum. Immunol. 2012, 73, 1005−1010. (9) Nozoe, T. Substitution Products of Tropolone and Allied Compounds. Nature 1951, 167, 1055−1057. (10) Ito, S.; Shoji, Y.; Takeshita, H.; Hirama, M.; Takahashi, K. Syntheses of Cyclohepta-3,6-Diene-1,2,5-Trione, p-Tropoquinone. Tetrahedron Lett. 1975, 16, 1075−1078. (11) Iyoda, M.; Sato, K.; Oda, M. Novel Diphenoquinone-Type Redox Systems Containing Seven-Membered Quinonoid Structure. Tetrahedron Lett. 1987, 28, 625−628. (12) Mori, A.; Goto, Y.; Takeshita, H. Synthesis and Electrochemical Properties of 3-(3,6-Dioxo-1,4-Cyclohexadienyl)methyl-p-Tropoquione. Analysis of a Four-Electron Redox System by Cyclic Voltammmetry. Bull. Chem. Soc. Jpn. 1987, 60, 2497−2501. (13) El-Hendawy, A. M. Ruthenium(II) and Ruthenium(III) Complexes Derived from O,O-Donor Ligands. Transition Met. Chem. 1992, 17, 250−255. (14) Roy, B. K.; Mallick, T. K.; Das, P. K.; Ghosh, B. K. Heteroleptic Tris-Complexes of Osmium (III/IV) 8-Quinolinolates: Synthesis, Characterization and Link-up of Oxidation Levels. Transition Met. Chem. 1993, 18, 89−92. (15) El-Hendawy, A. M.; Al-Kubaisi, A. H.; Al-madfa, H. A. Ruthenium (II) and (III) Bipyridine Complexes and Their Catalytic Oxidation Properties for Organic Compounds. Polyhedron 1997, 16, 3039−3045. (16) Franz, K. J.; Lippard, S. J. NO Disproportionation Reactivity of Fe Tropocoronand Complexes. J. Am. Chem. Soc. 1999, 121, 10504− 10512. (17) El-hendawy, A. M.; Alqaradawi, S. Y.; Al-madfa, H. A. Ruthenium (III) Mono (2, 2′-bipyridine) Complexes Containing O, O-Donor Ligands and Their Oxidation Properties for Organic Compounds. Transition Met. Chem. 2000, 25, 572−578.

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CONCLUSION The electronic state of dinuclear and trinuclear ruthenium tropolonate complexes, 2b and 3, has been investigated in comparison with [Ru(acac)2(C2trop)Ru(dppe)Cp] (2a). In the electrochemical study, 3 exhibited two clearly separated redox couples, although the distance between the two terminal Ru(dppe)Cp moieties is fairly long (ca. 1.7 nm). Additionally, 2b and 3 exhibited broad NIR absorptions upon oxidation, while 2a did not exhibit absorption in the NIR region upon oxidation. The only difference between 2a and 2b is the ancillary ligand, acac or trop. A comparison of the electrochemical data for ruthenium complexes and DFT calculations indicates electron and spin delocalization over the Ru(trop)3 unit in 2b+ and 3+ as well as delocalization over the Ru(dppe)Cp(C2trop) unit. The long-range intramolecular electronic communication in 3 upon one-electron oxidation can be explained by oxidation of the whole Ru(dppe)Cp(C2trop) unit, followed by electronic communication over the complex via a partially oxidized Ru(trop)3 unit. Although the study on ruthenium tropolonate complexes is still highly limited, Ru(trop)3 is of interest and is used as a building block for long-range charge-transfer and/or multistep redox systems.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02249. Detailed description for bromination reactions of [Ru(trop)3], ESI-MS measurements, UV−vis titration experiments, electrochemical and spectroelectrochemical measurements, single-crystal X-ray diffraction, and DFT/TDDFT calculations (PDF) X-ray crystallographic data for 2b in CIF format (CIF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: 81-42-778-7980. Fax: 81-42-778-9953. ORCID

Jun Yoshida: 0000-0002-2618-152X H


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Alternatives in Diastereoisomeric Complexes. Inorg. Chem. 2008, 47, 5204−5211. (35) Kundu, T.; Mobin, S. M.; Lahiri, G. K. Paramagnetic Ruthenium-Biimidazole Derivatives [(acac)2RuIII(LHn)]m, n/m = 2/ +, 1/0, 0/-. Synthesis, Structures, Solution Properties and Anion Receptor Features in Solution State. Dalton Trans. 2010, 39, 4232− 4242. (36) Das, A.; Scherer, T.; Maji, S.; Mondal, T. K.; Mobin, S. M.; Urbanos, F. A.; Jiménez-Aparicio, R.; Kaim, W.; Lahiri, G. K. Reductive Approach to Mixed Valency (n = 1-) in the Pyrazine Ligand-Bridged [(acac)2Ru(μ-L2‑)Ru(acac)2]n (L2‑ = 2,5-PyrazineDicarboxylate) through Experiment and Theory. Inorg. Chem. 2011, 50, 7040−7049. (37) Roy, S.; Sarkar, B.; Imrich, H.-G.; Fiedler, J.; Záliš, S.; JimenezAparicio, R.; Urbanos, F. A.; Mobin, S. M.; Lahiri, G. K.; Kaim, W. Charged, but Found “not Guilty”: Innocence of the Suspect Bridging Ligands [RO(O)CNNC(O)OR]2‑ = L2‑ in [(acac)2Ru(μ-L)Ru(acac)2]n, n = + , 0, -, 2-. Inorg. Chem. 2012, 51, 9273−9281. (38) Mondal, P.; Ehret, F.; Bubrin, M.; Das, A.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. A Diruthenium Complex of A “nindigo” ligand. Inorg. Chem. 2013, 52, 8467−8475. (39) Yoshida, J.; Sugawara, K.; Yuge, H.; Okabayashi, J. Bis(acetylacetonato)bis(pyrazolato)Ruthenate(III) as a Redox-Active Scorpionate Ligand. Dalton Trans. 2014, 43, 16066−16073. (40) Ehret, F.; Bubrin, M.; Zalis, S.; Priego, J. L.; Jimenez-Aparicio, R.; Kaim, W. Metal-Induced Thiophene Ring Opening and C-C Bond Formation to Produce Unique Hexa-1,3,5-Trienediyl-Coupled NonInnocent Ligand Chelates. Chem. - Eur. J. 2015, 21, 15163−15166. (41) Mondal, P.; Das, A.; Lahiri, G. K. The Electron-Rich {Ru(acac)2} Directed Varying Configuration of the Deprotonated Indigo and Evidence for Its Bidirectional Noninnocence. Inorg. Chem. 2016, 55, 1208−1218. (42) Haga, M.; Dodsworth, E. S.; Lever, A. B. P. Catechol-Quinone Redox Series Involving Bis(bipyridine)ruthenium(II) and Tetrakis(pyridine)rutbenium(II). Inorg. Chem. 1986, 25, 447−453. (43) Lever, A. B. P.; Auburn, P. R.; Dodsworth, E. S.; Haga, M.; Liu, W.; Melnik, M.; Nevin, W. A. Bis(Dioxolene)(Bipyridine)ruthenium Redox Series. J. Am. Chem. Soc. 1988, 110, 8076−8084. (44) Boyer, J. L.; Rochford, J.; Tsai, M.-K.; Muckerman, J. T.; Fujita, E. Ruthenium Complexes with Non-Innocent Ligands: Electron Distribution and Implications for Catalysis. Coord. Chem. Rev. 2010, 254, 309−330. (45) Kaim, W. Manifestations of Noninnocent Ligand Behavior. Inorg. Chem. 2011, 50, 9752−9765. (46) Brown, S. N. Metrical Oxidation States of 2-Amidophenoxide and Catecholate Ligands: Structural Signatures of Metal-Ligand π Bonding in Potentially Noninnocent Ligands. Inorg. Chem. 2012, 51, 1251−1260. (47) Broere, D. L. J.; Plessius, R.; van der Vlugt, J. I. New Avenues for Ligand-Mediated Processes − Expanding Metal Reactivity by the Use of Redox-Active Catechol, o-Aminophenol and o-Phenylenediamine Ligands. Chem. Soc. Rev. 2015, 44, 6886−6915. (48) Bruce, M. I.; Humphrey, M. G.; Snow, M. R.; Tiekink, E. R. T. Cyclopentadienyl-Ruthenium and -Osmium Chemistry: XXVII. X-Ray Structures of Ru(CCPh)(dppe)(η-C5H5) and of [Ru(L)(PPh3)2(ηC5H5)]X (L = C(OMe)Et, X = PF6; L = CCMePh, X = I). J. Organomet. Chem. 1986, 314, 213−225. (49) Consiglio, G.; Morandini, F.; Ciani, G. F.; Sironi, A. Stereochemical Studies on the Interconversion of Alkylidenecarbene, Carbene, and Alkyl Ligands in Chiral Cyclopentadienyl Ruthenium Complexes. Organometallics 1986, 5, 1976−1983. (50) Bruce, M. I. Organometallic Chemistry of Vinylidene and Related Unsaturated Carbenes. Chem. Rev. 1991, 91, 197−257. (51) Sheldrick, G. M. SHELXT - Integrated Space-Group and Crystal-Structure Determination. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3−8. (52) Sheldrick, G. M. Crystal Structure Refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8.

(18) Nishinaga, T.; Aono, T.; Isomura, E.; Watanabe, S.; Miyake, Y.; Miyazaki, A.; Enoki, T.; Miyasaka, H.; Otani, H.; Iyoda, M. Structural, Electronic and Magnetic Properties of Cu(II) Complexes of 2Substituted Tropones Bearing a Ferrocenyl Group at 5-Position. Dalton Trans. 2010, 39, 2293−2300. (19) Singh, K. S.; Svitlyk, V.; Mozharivskyj, Y. Mono and Dinuclear Arene Ruthenium(II) Triazoles by 1,3-Dipolar Cycloadditions to a Coordinated Azide in Ruthenium(II) Compounds. Dalton Trans. 2011, 40, 1020−1023. (20) Pittracher, M.; Frisch, U.; Kopacka, H.; Wurst, K.; Müller, T.; Oehninger, L.; Ott, I.; Wuttke, E.; Scheerer, S.; Winter, R. F.; Bildstein, B. π - Complexes of Tropolone and Its N - Derivatives: Ambidentate [O,O]/[N,O]/[N,N]-Cycloheptatrienyl Pentamethylcyclopentadienyl Ruthenium Sandwich Complexes. Organometallics 2014, 33, 1630− 1643. (21) Forbes, C. E.; Holm, R. H. Dithiotropolonates. II. The Synthesis and Properties of Dithiotropolone and Its Metal(II) Complexes. J. Am. Chem. Soc. 1970, 92, 2297−2303. (22) Roesky, P. W. The Co-ordination Chemistry of Aminotroponiminates. Chem. Soc. Rev. 2000, 29, 335−345. (23) Roesky, P. W. Cyclooctatetraene Complexes of Yttrium and the Lanthanides with Chiral and Achiral Aminotroponiminates. J. Organomet. Chem. 2001, 621, 277−283. (24) Nomura, M.; Imamura, F.; Ba Tuyet Nga, N.; Fujita-Takayama, C.; Sugiyama, T.; Kajitani, M. Synthesis and Electrochemistry of Organometallic Cobaltadithiaazulenes. Inorg. Chem. 2012, 51, 10695− 10703. (25) Lichtenberg, C.; Krummenacher, I. Aminotroponiminates as Tunable, Redox-Active Ligands: Reversible Single Electron Transfer and Reductive Dimerisation. Chem. Commun. 2016, 52, 10044−10047. (26) Lichtenberg, C. Aminotroponiminates: Alkali Metal Compounds Reveal Unprecedented Coordination Modes. Organometallics 2016, 35, 894−902. (27) Yoshida, J.; Kuwahara, K.; Yuge, H. A Mixed-Valence Dinuclear Ruthenium Complex Composed of Ru(II)-Acetylide and Ru(III)Tropolonato Units: Acetylide-Vinylidene Interconversion in Solution and Solid State. J. Organomet. Chem. 2014, 756, 19−26. (28) Kasahara, Y.; Hoshino, Y.; Kajitani, M.; Shimizu, K.; Sato, G. P. Synthesis of binuclear (β-diketonato)ruthenium(III) complexes through Introduction of an Ethynyl Group at a g-Position of of Tris(β-diketonato)ruthenium(III) and Electrochemistry of the Binuclear Complexes. Organometallics 1992, 11, 1968−1971. (29) Remenyi, C.; Kaupp, M. Where Is the Spin? Understanding Electronic Structure and G-Tensors for Ruthenium Complexes with Redox-Active Quinonoid Ligands. J. Am. Chem. Soc. 2005, 127, 11399−11413. (30) Hashimoto, T.; Hara, S.; Shiraishi, Y.; Yamauchi, M.; Natarajan, K.; Shimizu, K. Reactions of Ketones with Coordinated Nitriles on βDiketonato Ruthenium Complexes Leading to Formation of Compounds with New Carbon−carbon Bonds. Inorg. Chim. Acta 2005, 358, 2207−2216. (31) Ghumaan, S.; Sarkar, B.; Maji, S.; Puranik, V. G.; Kaim, W.; Lahiri, G. K.; Fiedler, J.; Urbanos, F. A.; Jimenez-Aparicio, R. ValenceState Analysis through Spectroelectrochemistry in a Series of Quinonoid-Bridged Diruthenium Complexes [(acac)2Ru(μ-L)Ru(acac)2]n (n = + 2, + 1, 0, −1, −2). Chem. - Eur. J. 2008, 14, 10816−10828. (32) Kalinina, D.; Dares, C.; Kaluarachchi, H.; Potvin, P. G.; Lever, A. B. P. Spectroscopic, Electrochemical, and Computational Aspects of the Charge Distribution in Ru(acac)2(R-o-Benzoquinonediimine) Complexes. Inorg. Chem. 2008, 47, 10110−10126. (33) Kumbhakar, D.; Sarkar, B.; Maji, S.; Mobin, S. M.; Fiedler, J.; Urbanos, F. a; Jiménez-Aparicio, R.; Kaim, W.; Lahiri, G. K. Intramolecular Valence and Spin Interaction in meso and rac Diastereomers of a p-Quinonoid-Bridged Diruthenium Complex. J. Am. Chem. Soc. 2008, 130, 17575−17583. (34) Maji, S.; Sarkar, B.; Mobin, S. M.; Fiedler, J.; Urbanos, F. A.; Jimenez-Aparicio, R.; Kaim, W.; Lahiri, G. K. Valence-State I


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Inorganic Chemistry

(70) LeSuer, R. J.; Geiger, W. E. Improved Electrochemistry in LowPolarity Media Using Tetrakis(pentafluorophenyl)borate Salts as Supporting Electrolytes. Angew. Chem., Int. Ed. 2000, 39, 248−250. (71) Ren, T. Peripheral Covalent Modification of Inorganic and Organometallic Compounds through C-C Bond Formation Reactions. Chem. Rev. 2008, 108, 4185−4207. (72) Nozoe, T.; Mukai, T.; Takase, K. On β-Monobromohinokitiol. Proc. Japan Acad. 1950, 26, 19−23. (73) Cook, J. W.; Gibb, A. R.; Raphael, R. A. Tropolone. Part III. Halogenated Derivatives of Tropolone. J. Chem. Soc. 1951, 2244− 2248. (74) Cook, J. W.; Loudon, J. D.; Steel, D. K. V. Tropolone. Part VII. Orientation in Tropolone. J. Chem. Soc. 1954, 530−535. (75) Endo, A.; Shimizu, K.; Sato, P. G. Preparation of Tris (3substituted acetylacetonato) Ruthenium(II) Complexes and Their Electrochemical Behavior in Acetonitrile. Chem. Lett. 1985, 14, 581− 584. (76) Bruce, M. I.; Hall, B. C.; Kelly, B. D.; Low, P. J.; Skelton, B. W.; White, A. H. An Efficient Synthesis of Polyynyl and Polyynediyl Complexes of ruthenium(II). J. Chem. Soc., Dalton Trans. 1999, 3719− 3728. (77) Chao, G. K.-J.; Sime, R. L.; Sime, R. J. The Crystal and Molecular Structure of Tris-acetylacetonatoruthenium(III). Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1973, 29, 2845− 2849. (78) Hamor, T. A.; Watkin, D. J. J. The Crystal Structure of Tris(Tropolonato) Iron (III) (″Ferric Tropolone″) J. Chem. Soc. D. J. Chem. Soc. D 1969, 0, 440−441. (79) Barrière, F.; Geiger, W. E. Use of Weakly Coordinating Anions to Develop an Integrated Approach to the Tuning of ΔE1/2 Values by Medium Effects. J. Am. Chem. Soc. 2006, 128, 3980−3989. (80) Diallo, A. K.; Daran, J. C.; Varret, F.; Ruiz, J.; Astruc, D. How Do Redox Groups Behave around a Rigid Molecular Platform? Hexa(ferrocenylethynyl)benzenes and Their “electrostatic” redox Chemistry. Angew. Chem., Int. Ed. 2009, 48, 3141−3145. (81) Diallo, A. K.; Absalon, C.; Ruiz, J.; Astruc, D. FerrocenylTerminated Redox Stars: Synthesis and Electrostatic Effects in MixedValence Stabilization. J. Am. Chem. Soc. 2011, 133, 629−641. (82) Guasch, J.; Grisanti, L.; Lloveras, V.; Vidal-Gancedo, J.; Souto, M.; Morales, D. C.; Vilaseca, M.; Sissa, C.; Painelli, A.; Ratera, I.; Rovira, C.; Veciana, J. Induced Self-Assembly of a TetrathiafulvaleneBased Open-Shell Dyad through Intramolecular Electron Transfer. Angew. Chem., Int. Ed. 2012, 51, 11024−11028. (83) Lawrence, E. J.; Oganesyan, V. S.; Wildgoose, G. G.; Ashley, A. E. Exploring the Fate of the Tris(pentafluorophenyl)borane Radical Anion in Weakly Coordinating Solvents. Dalton. Trans. 2013, 42, 782−789. (84) D’Alessandro, D. M.; Keene, F. R. Current Trends and Future Challenges in the Experimental, Theoretical and Computational Analysis of Intervalence Charge Transfer (IVCT) Transitions. Chem. Soc. Rev. 2006, 35, 424−440. (85) Hoshino, Y.; Higuchi, S.; Fiedler, J.; Su, C.-Y.; Knödler, A.; Schwederski, B.; Sarkar, B.; Hartmann, H.; Kaim, W. Long-Range Electronic Coupling in Various Oxidation States of a C4-Linked Tris(β-Diketonato)ruthenium Dimer. Angew. Chem., Int. Ed. 2003, 42, 674−677. (86) Koiwa, T.; Masuda, Y.; Shono, J.; Kawamoto, Y.; Hoshino, Y.; Hashimoto, T.; Natarajan, K.; Shimizu, K. Synthesis, Characterization, and Detailed Electrochemistry of Binuclear Ruthenium(III) Complexes Bridged by Bisacetylacetonate. Crystal and Molecular Structures of [{Ru(acac)2}2(tae)] (acac = 2,4-Pentanedionate Ion, tae = 1,1,2,2Tetraacetylethanate Dianion. Inorg. Chem. 2004, 43, 6215−6223. (87) Sato, M.; Shintate, H.; Kawata, Y.; Sekino, M.; Katada, M.; Kawata, S. Oxidized Ruthenium Ferrocenylacetylide Complexes, [(ηC5H5)L2RuCCFc]PF6 and [(η-C5Me5)L2CCFc]PF6 (L = Phosphines). Electron-Delocalized Heterobinuclear Mixed-Valence Complexes. Organometallics 1994, 13, 1956−1962. (88) Sato, M.; Kawata, Y.; Shintate, H.; Habata, Y.; Akabori, S.; Unoura, K. Novel Structural Rearrangements Induced by Metal-Metal

(53) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö .; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision D.01; Gaussian Inc.: Wallingford, CT. 2009. (54) Yanai, T.; Tew, D. P.; Handy, N. C. A New Hybrid Exchange− correlation Functional Using the Coulomb-Attenuating Method (CAM-B3LYP). Chem. Phys. Lett. 2004, 393, 51−57. (55) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.; Pople, J. A. Self-Consistent Molecular Orbital Methods. XXIII. A Polarization-Type Basis Set for Second-Row Elements. J. Chem. Phys. 1982, 77, 3654. (56) Rassolov, V. A.; Pople, J. A.; Ratner, M. A.; Windus, T. L. 631G* Basis Set for Atoms K through Zn. J. Chem. Phys. 1998, 109, 1223−1229. (57) Rassolov, V. A.; Ratner, M. A.; Pople, J. A.; Redfern, P. C.; Curtiss, L. A. 6-31G* Basis Set for Third-Row Atoms. J. Comput. Chem. 2001, 22, 976−984. (58) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for the Transition Metal Atoms Sc to Hg. J. Chem. Phys. 1985, 82, 270−283. (59) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for K to Au Including the Outermost Core Orbitals. J. Chem. Phys. 1985, 82, 299−310. (60) Wadt, W. R.; Hay, P. J. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for Main Group Elements Na to Bi. J. Chem. Phys. 1985, 82, 284−298. (61) Barone, V.; Cossi, M.; Tomasi, J. A New Definition of Cavities for the Computation of Solvation Free Energies by the Polarizable Continuum Model. J. Chem. Phys. 1997, 107, 3210−3221. (62) Cossi, M.; Scalmani, G.; Rega, N.; Barone, V. New Developments in the Polarizable Continuum Model for Quantum Mechanical and Classical Calculations on Molecules in Solution. J. Chem. Phys. 2002, 117, 43−54. (63) Dennington, R.; Keith, T.; Millam, J. GaussView, version 5; Semichem Inc.: Shawnee Mission, KS, 2009. (64) Stevens, H. C.; Reich, D. A.; Brandt, D. R.; Fountain, K. R.; Gaughan, E. J. A New Tropolone Synthesis via Dichloroketene. J. Am. Chem. Soc. 1965, 87, 5257−5259. (65) Stevens, H. C.; Rinehart, J. K.; Lavanish, J. M.; Trenta, G. M. The Hydrolysis of 7,7-Dich1orobicyc1o[3.2.0]hept-2-En-6-On. J. Org. Chem. 1971, 36, 2780−2784. (66) Minns, R. A. Tropolone. Org. Synth. 1977, 57, 117. (67) Ashby, G. S.; Bruce, M. I.; Tomkins, I. B.; Wallis, R. C. Cyclopentadienyl-Ruthenium and -Osmium Chemistry. VII. Complexes Containing Nitriles, Tertiary Phosphines or Phosphites Formed by Addition or Displacement Reactions. Aust. J. Chem. 1979, 32, 1003−1016. (68) Endo, A.; Shimizu, K.; Satô, G. P.; Mukaida, M. A New Method for Synthesis of Ruthenium(III) and Ruthenium(II) Complexes of βDiketones From “Ruthenium Blue” Solution. Chem. Lett. 1984, 13, 437−440. (69) Bruce, M. I.; Hameister, C.; Swincer, A. G.; Wallis, R. C.; Ittel, S. D. Chloro(η5-cyclopentadienyl)bis(triphenyl-phosphine) Ruthenium(II): RuCl(PPh3)2(η5-C5H5). Inorganic Syntheses; John Wiley & Sons, Inc.: New York, 1990; pp 270−272. J


Article

Inorganic Chemistry Interactions in Ruthenium (II) Ruthenocenyl- and (Pentamethylruthenocenyl) Acetylide Complexes, RcCCRuL2(η5-C5R5) and RcCCRuL2(η5-C5R5) [Rc = Ruthenocenyl, Rc′ = Pentamethylruthenocenyl, L2 = 2PPh3 or Ph2PCH2CH2PPh2 (dppe), R = H or Me]. Organometallics 1997, 16, 1693−1701. (89) Dreuw, A.; Head-Gordon, M. Failure of Time-Dependent Density Functional Theory for Long-Range Charge-Transfer Excited States: The Zincbacteriochlorin - Bacteriochlorin and Bacteriochlorophyll - Spheroidene Complexes. J. Am. Chem. Soc. 2004, 126, 4007− 4016. (90) Zhao, Y.; Truhlar, D. G. Density Functional for Spectroscopy: No Long-Range Self-Interaction Error, Good Performance for Rydberg and Charge-Transfer States, and Better Performance on Average than B3LYP for Ground States. J. Phys. Chem. A 2006, 110, 13126−13130. (91) Rohrdanz, M. A.; Martins, K. M.; Herbert, J. M. A Long-rangecorrected Density Functional That Performs Well for both Groundstate Properties and Time-dependent Density Functional Theory Excitation Energies, Including Charge-transfer Excited States. J. Chem. Phys. 2009, 130, 054112. (92) Adamo, C.; Jacquemin, D. The Calculations of Excited-State Properties with Time-Dependent Density Functional Theory. Chem. Soc. Rev. 2013, 42, 845−856. (93) Powell, C.; Cifuentes, M.; Morrall, J.; Stranger, R.; Humphrey, M.; Samoc, M.; Luther-Davies, B.; Heath, G. Organometallic Complexes for Nonlinear Optics. 30. Electrochromic Linear and Nonlinear Optical Properties of Alkynylbis(diphosphine)ruthenium Complexes. J. Am. Chem. Soc. 2003, 125, 602−610. (94) Paul, F.; Ellis, B. G.; Bruce, M. I.; Toupet, L.; Roisnel, T.; Costuas, K.; Halet, J.-F.; Lapinte, C. Bonding and Substituent Effects in Electron-Rich Mononuclear Ruthenium σ-Arylacetylides of the Formula [(η2-dppe)(η5-C5Me5)Ru(CC)-1,4-(C6H4)X][PF6]n (n = 0, 1; X = NO2, CN, F, H, OMe, NH2). Organometallics 2006, 25, 649− 665. (95) Fox, M. A.; Roberts, R. L.; Khairul, W. M.; Hartl, F.; Low, P. J. Spectroscopic Properties and Electronic Structures of 17-Electron Half-Sandwich Ruthenium Acetylide Complexes, [Ru(CCAr)(L2)Cp′]+ (Ar = phenyl, p-tolyl, 1-naphthyl, 9-Anthryl; L2 = (PPh3)2, Cp′ = Cp; L2 = dppe; Cp’ = Cp*). J. Organomet. Chem. 2007, 692, 3277− 3290. (96) Fox, M. A.; Le Guennic, B.; Roberts, R. L.; Brue, D. A.; Yufit, D. S.; Howard, J. A. K.; Manca, G.; Halet, J.-F.; Hartl, F.; Low, P. J. Simultaneous Bridge-Localized and Mixed-Valence Character in Diruthenium Radical Cations Featuring Diethynylaromatic Bridging Ligands. J. Am. Chem. Soc. 2011, 133, 18433−18446. (97) Kasahara, Y.; Hoshino, Y.; Shimizu, K.; Satô, G. P. Reaction of Tris(β-diketonato)ruthenium(III) Complexes with Strong Acids in Acetonitrile. Formation of Bis(acetonitrile)bis(β-diketonato)ruthenium(III) Complexes. Chem. Lett. 1990, 19, 381−384.

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