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Varying electronic structural forms of ruthenium complexes of non-innocent 9,10phenanthrenequinonoid ligands† Abhishek Mandal,a Tanaya Kundu,a Fabian Ehret,b Martina Bubrin,b Shaikh M. Mobin,c Wolfgang Kaim*b and Goutam Kumar Lahiri*a Bis(acetylacetonato)ruthenium complexes [Ru(acac)2(Q1–3)], 1–3, incorporating redox non-innocent 9,10-phenanthrenequinonoid ligands (Q1 = 9,10-phenanthrenequinone, 1; Q2 = 9,10-phenanthrenequinonediimine, 2; Q3 = 9,10-phenanthrenequinonemonoimine, 3) have been characterised electrochemically, spectroscopically and structurally. The four independent molecules in the unit cell of 2 are involved in intermolecular hydrogen bonding and π–π interactions, leading to a 2D network. The oxidation state-sensitive bond distances of the coordinated ligands Qn at 1.296(5)/1.289(5) Å (C–O), 1.315(3)/1.322 (4) Å (C–N), and 1.285(3)/1.328(3) Å (C–O/C–N) in 1, 2 and 3, respectively, and the well resolved 1H NMR resonances within the standard chemical shift range suggest DFT supported variable contributions from valence formulations [RuIII(acac)2(Q•−)] (spin-coupled) and [RuII(acac)2(Q0)], respectively. Complexes 1–3 exhibit one oxidation and two reduction steps with comproportionation constants Kc ∼ 107–1022 for the intermediates. The electrochemically generated persistent redox states 1n (n = 0, 1−, 2−) and 2n/3n (n = 1+, 0, 1−, 2−) have been analysed by UV-vis-NIR spectroelectrochemistry and by EPR for the paramagnetic intermediates in combination with DFT and TD-DFT calculations, revealing significant differ-
Received 2nd November 2013, Accepted 13th November 2013
ences in the oxidation state distribution at the {Ru–Q} interface for 1n–3n. In particular, the diminished propensity of the NH-containing systems for reduction results in the preference for RuII(Q0) relative to
DOI: 10.1039/c3dt53104j
RuIII(Q•−) (neutral compounds) and for RuII(Q•−) over the RuIII(Q2−) alternative in the case of the monoanionic complexes.
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Introduction The intricate mixing of the frontier orbitals of ruthenium and of biochemically relevant quinonoid moieties renders such systems with redox non-innocently behaving ligands (Scheme 1) as prototypical models to study electronic structures of strongly coupled coordination compounds.1–7 The results can be complex phenomena such as valence tautomerism1a,e,2j or redox induced electron transfer (RIET)1h,7d,8a,b at the metal–quinonoid ligand interface,
a Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. E-mail: [email protected] b Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany. E-mail: [email protected] c Discipline of Chemistry, School of Basic Sciences, Indian Institute of Technology Indore, Indore 452017, India † Electronic supplementary information (ESI) available: X-ray crystallographic files of 1–3 in CIF format, DFT dataset for 1n–3n (Tables S1–S5, S7–S18 and Fig. 3–5), mass spectra of 1–3 (Fig. S1), 1H NMR of 1–3 (Table S6, Fig. S2). CCDC 963958–963960 for 1–3. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt53104j
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Scheme 1
Oxidation state distribution in ruthenium-quinonoid complexes.
yielding an intermediate resonance situation8a instead of any specific configuration.8 As another result there are significant variations in the valence and spin distribution on even slight alterations of the molecular frameworks, involving the metal ion, the ancillary ligand and/or the quinone moiety, prompting continuous evaluation of new challenging molecular configurations. In this regard, the electronic structural features1–8 as well as potential applications in catalysis9 of ruthenium-obenzoquinone/o-benzoquinonemonoimine/o-benzoquinonediimine derivatives (Scheme 1) have been investigated in combination with ancillary ligands of different electronic properties,
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from neutral π-accepting to anionic σ/π-donating.1–8 However, reports on ruthenium complexes of 9,10-phenanthrenequinone and 9,10-phenanthrenequinonediimine derivatives are relatively limited.10 This has initiated the present approach of analysing the electronic structural aspects of three mononuclear ruthenium complexes 1–3 of 9,10-phenanthrenequinonoid ligands, having varying donor centres associated with the quinonoid moieties: O,O (1), N,N (2), and O,N (3).
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The neutral compounds 1, 2 and 3 exhibit ESI-MS(+) signals (m/z) at 507.91 (calc. 507.51), 506.11 (calc. 505.54) and 507.10 (calc. 506.52), respectively, in CH3CN (Fig. S1†). 1H NMR spectra of 1 and 2 exhibit the required symmetry while the unsymmetrical 3 shows twice as many 1H NMR resonance signals. The NH protons of Q2 and Q3 in 2 and 3 appear at 11.05 ppm and 14.04 ppm, respectively (see the Experimental section, Fig. S2, and Table S6†), which are exchangeable by D2O. Crystal structures
9,10-Phenanthrenequinone, one of the major constituents in diesel exhaust particles,11a can easily be transformed into the 9,10-phenanthrenesemiquinone radical state by biological reducing agents such as NADPH-cytochrome P450 reductase11b,c or nitric oxide synthase11d or thiol-based proteins.11e, f This in turn facilitates the formation of harmful hydroxyl radicals in the presence of intracellular iron catalysts.11g Herein we report the synthesis and structural characterisation of 1–3 as well as an investigation of the effects from the donor centres in 1n–3n, i.e. including the electrochemically accessible redox states (n = +1, 0, −1, −2). Special attention is given to a comparison with the reported analogous benzoquinonoid systems 4–6.2l,7b,8b
A comparison of the oxidation state-sensitive bond lengths from the single crystal X-ray structure (Fig. 1 and Tables 1, 2 and Table S3†) of 1, C1–O1, 1.296(5) Å (DFT: 1.277 Å) and C14– O2, 1.289(5) Å (DFT: 1.277 Å, Table 2), with the standard C–O bond lengths of coordinated o-benzoquinonoid ligands in different redox states (Q0: 1.22 Å, Q•−: 1.30 Å, Q2−: 1.34 Å)13 implies a valence state formulation according to [RuIII(acac)2(Q1•−)], where the unpaired spins on RuIII (t2g5, S = 1/2) and semiquinone radical ligands (Q1•−) are strongly coupled antiferromagnetically. The closed shell configuration of 1 is reflected by the well resolved 1H NMR resonances within the standard chemical shift range of δ, 0–10 ppm14 (Fig. S2, Table S6†), and by the absence of any EPR response, even at 4 K. The analogous [RuIII(acac)2(Q4•−)] (Q4•− = benzosemiquinone) (4) has been established to have an S = 1 ground state, exhibiting paramagnetically shifted 1H NMR resonances in a wide chemical shift range of δ, +6 to −10 ppm, and complex magnetic behaviour.7b The molecular structure and selected structural parameters of compound 2, crystallising with hexane solvent molecules, are shown in Fig. 2, Tables 1, 3 and Tables S1, S4,† respectively. The asymmetric unit consists of four independent molecules, three full molecules (molecules A–C) and one half molecule (molecule D) with slight differences in bond
Results and discussion Synthesis and characterisation Compound 1 has been synthesised from 9,10-phenanthrenequinone (Q10) and the precursor [RuII(acac)2(CH3CN)2]. Intramolecular electron-transfer between the ruthenium ion (RuII) and the quinonoid moiety (Q10) preferentially stabilises the {RuIIIQ1•−} configuration in 1 (see later) which is being further put into effect by the electron donating impact of acac−.12 Reaction of [Ru(acac)2(CH3CN)2] with 9,10-diaminophenanthrene (H2Q2) in the presence of NEt3 as a base, followed by chromatographic separation, leads to the isolation of [Ru(acac)2(Q2)] ( purple: 2) and [Ru(acac)2(Q3)] (blue: 3). The reproducible formation of 3 containing the phenanthrenequinonemonoimine ligand (Q3) is attributed to the partial hydrolysis of the imine bonds of Q2.
2474 | Dalton Trans., 2014, 43, 2473–2487
Fig. 1 ORTEP diagram of molecule 1 in the crystal. Ellipsoids are shown at the 50% probability level, and hydrogen atoms are omitted for clarity.
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Table 1 2(3)
Paper
Selected crystallographic parameters of 1, 3.5(2)·2C6H14 and
Formula Mr Radiation Crystal system Space group a/Å b/Å c/Å α (°) β (°) γ (°) V/Å3 Z μ/mm−1 T/K ρcalcd/g cm−3 F(000) θ Range (°) Data/restraints/ parameters R1, wR2 [I > 2σ(I)] R1, wR2 (all data) GOF on F 2 Largest diff. peak per hole/e Å−3
1
3.5(2)·2C6H14
2(3)
C24H22O6Ru 507.50 CuKα Triclinic ˉ P1 7.4141(2) 8.9708(4) 16.1229(7) 79.577(4) 84.280(3) 84.316(3) 1045.79(7) 2 6.406 150(2) 1.612 516 5.03 to 65.07 3561/0/284
C96H112N7O14Ru3.50 1941.67 MoKα Monoclinic C2/c 25.1917(4) 20.7180(4) 36.2929(5) 90 105.970(2) 90 18 211.0(5) 8 0.637 150(2) 1.416 8024 3.02 to 25.00 16 028/0/1048
C48H46N2O10Ru2 1013.01 MoKα Monoclinic P21/c 16.7929(2) 14.6472(10) 19.3765(2) 90 112.836(10) 90 4392.45(8) 4 0.749 150(2) 1.532 2064 2.98 to 25.00 7715/0/567
0.0446, 0.1262 0.0468, 0.1297 1.062 1.978 and −1.002
0.0320, 0.0817
0.0245, 0.0598
0.0409, 0.0859
0.0287, 0.0616
1.032 0.816 and −0.507
1.032 0.327 and −0.385
Table 2 Experimental (X-ray) and DFT calculated selected bond distances (Å) of 1n
DFT X-ray
Ru(1)–O(1) Ru(1)–O(2) Ru(1)–O(3) Ru(1)–O(4) Ru(1)–O(5) Ru(1)–O(6) C(1)–O(1) C(14)–O(2) C(1)–C(2) C(1)–C(14) C(2)–C(3) C(2)–C(7) C(3)–C(4) C(4)–C(5) C(5)–C(6) C(6)–C(7) C(7)–C(8) C(8)–C(9) C(8)–C(13) C(9)–C(10) C(10)–C(11) C(11)–C(12) C(12)–C(13) C(13)–C(14)
1
1+ (S = 1/2)
1 (S = 0)
1− (S = 1/2)
12− (S = 0)
2.003(3) 1.997(3) 2.031(3) 2.013(3) 2.019(3) 1.993(3) 1.296(5) 1.289(5) 1.437(5) 1.436(5) 1.405(5) 1.412(5) 1.370(6) 1.402(6) 1.382(6) 1.402(6) 1.474(6) 1.403(5) 1.410(6) 1.388(6) 1.394(7) 1.358(6) 1.407(5) 1.435(5)
2.105 2.104 2.024 1.995 1.995 2.023 1.256 1.256 1.442 1.499 1.409 1.425 1.387 1.399 1.396 1.401 1.483 1.401 1.425 1.396 1.399 1.387 1.409 1.442
2.047 2.045 2.052 2.053 2.050 2.047 1.277 1.277 1.449 1.449 1.408 1.424 1.386 1.402 1.390 1.408 1.476 1.408 1.424 1.390 1.402 1.386 1.408 1.449
2.054 2.054 2.075 2.089 2.087 2.073 1.308 1.308 1.444 1.414 1.415 1.430 1.382 1.408 1.386 1.413 1.461 1.413 1.430 1.386 1.408 1.382 1.415 1.444
2.105 2.104 2.088 2.115 2.114 2.088 1.314 1.314 1.436 1.421 1.425 1.444 1.378 1.418 1.385 1.417 1.444 1.417 1.444 1.385 1.418 1.378 1.425 1.436
parameters. The average C–N bond lengths of 2 of 1.318(4) Å (DFT: 1.321 Å) indicate13 an oxidation state situation best approximated by [RuII(acac)2(Q20)] according to the proposed
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standard values for o-benzoquinonediimines (Q0: 1.31 Å, Q•−: 1.35 Å, Q2−: 1.38 Å).13 This formulation is justified by the broken symmetry analysis which predicts identical energies for the broken symmetry singlet state and the closed shell singlet form. The diamagnetic complex 2 displays well resolved 1H NMR signals (Fig. S2 and Table S6†). The {RuIIQ0} form of the corresponding o-benzoquinonediimine complex [RuII(acac)2(Q50)] (5) has been addressed by the Lever group, based on the C–N lengths of 1.320(3) Å of Q54b as well as via a detailed DFT analysis.2l The average RuII–N(Q2) bond lengths of 1.966(2) Å in 2 is appreciably shorter than the average Ru–O(acac) bond lengths of 2.051(2) Å in 1 due to strong dπ(RuII) → pπ*(Q20) back-bonding, as has been reported earlier for the RuII-acac complexes of o-benzoquinonediimines.2l,15 The 31% ruthenium contribution in the LUMO of 2 (Table S11†) also supports strong dπ(RuII) → pπ*(Q20) back-bonding.2l,9e,15 The packing diagram of 2 (Fig. 3 and Table 4) reveals the existence of intermolecular hydrogen bonding and π–π interactions involving Q2 ligands of different molecules. Molecule A is connected to molecule B via π–π interaction between the two aromatic rings of Q2 (interplanar distance of about 3.643 Å) and molecule A and molecule B are linked to molecule C and molecule D on either side via N–H⋯O(acac) hydrogen bonding interactions (Table 4), leading to the formation of a 1D layer chain. The 1D chain is further linked to the neighbouring layer by C–H⋯π interactions (see Fig. 3), resulting in a 2D network. The asymmetric unit in the single crystal of complex 3 consists of two independent molecules (molecules E and F) with slight differences in bond parameters (Fig. 4, Table 5 and Tables S2, S5†). Both the C–O bond lengths of 3 (molecule E/molecule F) 1.287(3) Å/1.285(3) Å (DFT: 1.272 Å) and the C–N bond lengths 1.332(3) Å/1.328(3) Å (DFT: 1.330 Å) suggest an intermediate description [RuII(acac)2(Q30)]/spin-paired [RuIII(acac)2(Q3•−)], while identical energies of the broken symmetry singlet and the closed shell singlet of 3 support the {RuIIQ30} form. Accordingly, 3 shows well resolved 1H NMR signals within the standard chemical shift range, δ = 0–15 ppm (Fig. S2 and Table S6†). The analogous o-benzoquinoneimine derivative was assigned as spin coupled [RuIII(acac)2(Q6•−)] (6), primarily based on the C–O/C–N bond lengths of the coordinated Q6n of 1.291(4) Å/1.340(4) Å, similar values as observed here for Q3n in 3.8b,13 Cyclic voltammetry Complex 1 exhibits a quasi-reversible one-electron oxidation (0.69 V), a reversible first (−0.39 V) and a quasi-reversible second one-electron reduction (−1.51 V) process (Fig. 5, Table 6) with appreciable differences relative to 4 (0.91 V (oxidation) and −0.14 V (reduction)7b). The large comproportionation constants (RTlnKc = nF(ΔEo))16 of ∼1018 between successive redox processes reveal the thermodynamic stability of the intermediate redox states 1 and 1−. A similar behaviour was noted for compounds 2 and 3, with the expected decrease of potential values due to the shift from more (O) to less (N) electronegative atoms. Accordingly, the monocations 2+ and 3+ become more stable and could be
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Fig. 2 ORTEP diagram of 2 in the crystal (hexane solvent), showing four molecules (A–D) in the asymmetric unit. The inset shows the molecule A separately. Ellipsoids are shown at the 50% probability level; hydrogen atoms and the solvent of crystallisation are omitted for clarity.
studied by EPR and UV-vis-NIR spectroelectrochemistry. The shift effects are somewhat less pronounced for the 9,10-phenanthrenequinone systems as compared to the o-benzoquinone analogues, and similarly, the Kc values for 1n–3n are attenuated in relation to those of 4n–6n, both an effect of the more extended π system with less participation of the heteroatoms. Although the cyclic and differential pulse voltammograms exhibit variable intensity patterns, the reversibility of spectroelectrochemical experiments (cf. below) supports consecutive one-electron transfer processes. EPR spectroscopy While the diamagnetic precursors are EPR silent, the monoanions 1−–3− and two of the monocations (2+, 3+) could be characterised EPR spectroscopically in frozen solution at 4 K
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(anions) or 110 K (cations), after electrolytic generation intra muros. The cation 1+ was too unstable as also observed by UVvis spectroelectrochemistry (vide infra). Spectra are shown in Fig. 6, and the g values are listed in Table 7. Table 8 contains the calculated Mulliken spin densities; both Tables 7 and 8 provide the corresponding available data for the o-benzoquinone analogues. The cations 2+ and 3+ exhibit typical EPR spectra for ruthenium(III) species with g1, g2 > 2 and g3 around 2.0. The large average g (〈g〉) and g anisotropy (Δg) values are in agreement with about 80% calculated contribution from the heavy metal to the spin density and the remainder located at the acac− co-ligands (Table 8). In agreement with the DFT-calculated bond length changes (Tables 3 and 5) these results point to an oxidation state formulation [(acac)2RuIII(Q0)]+. As a
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Table 3 Experimental (X-ray) and DFT calculated selected bond distances (Å) of 2n
Table 4 Hydrogen bonding parameters in 2 [Å and (°)]
D–H⋯A
d(D–H)
d(H⋯A)
d(D⋯A)
107) neutral and anionic intermediate forms display high degrees of covalency2l,7b,8a,b with two oxidation state descriptions contributing to a comparable extent to the observed ground state structures. The present evaluation of bonding and electron transfer behaviour of Ru(acac)2 complexes of a series of N/O donor varied ortho-quinonoid ligands with minimal (4–6) and extended π conjugated systems (1–3) has thus shown that the increased ligand/metal covalency on stepwise exchange of O by NH can be modified by the higher degree of delocalisation in the phenanthrenequinonoid examples. The smaller frontier orbital gap and the diminished donor–metal interaction in the larger compounds described here lead to different bonding situations with the dioxolene complex (4) at one (ionic and
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Fig. 9 UV-VIS-NIR spectroelectrochemistry for 2n in CH3CN–0.1 mol dm3 [NBu4][PF6].
spin-uncoupled) end7b and the phenanthrenequinonediimine system 2 at the other (covalent) end. Although long recognised as a remarkably covalent chelate arrangement,2,18 the ruthenium/quinonoid ligand combination can thus still provide varied results which are not simply predictable and which justify the continued research in that area.
Experimental Materials The metal precursor Ru(acac)2(CH3CN)2 was prepared according to a literature reported procedure.19 The ligands 9,10-phenanthrenequinone and 9,10-diaminophenanthrene were purchased from Alfa Aesar and Sigma Aldrich, respectively. All other chemicals and reagents were of reagent grade and used
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without further purification. For spectroscopic and electrochemical studies HPLC-grade solvents were used.
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Physical measurements UV-vis-NIR studies in CH3CN–0.1 mol dm3 Bu4NPF6 at 298 K were performed using an optically transparent thin layer electrochemical (OTTLE) cell20 which was mounted in the sample compartments of a J&M TIDAS spectrophotometer. 1H NMR spectra were recorded on a Bruker Avance III 400 spectrometer. The EPR measurements were made in a two-electrode capillary tube21 with an X-band Bruker system ESP300 equipped with a Bruker ER035M gaussmeter and a HP 5350B microwave counter. Cyclic voltammetric, differential pulse voltammetric and coulometric measurements were carried out using a PAR model 273A electrochemistry system. Platinum wire working and auxiliary electrodes and an aqueous saturated calomel reference electrode (SCE) were used in a three-electrode configuration. The supporting electrolyte was [Et4N][ClO4] and the solute concentration was ∼10−3 mol dm3. The half-wave potential Eo298 was set equal to 0.5(Epa + Epc), where Epa and Epc are anodic and cathodic cyclic voltammetric peak potentials, respectively. Elemental analysis was carried out with a PerkinElmer 240C elemental analyser. Electrospray mass spectra were recorded on a Micromass Q-ToF mass spectrometer. Crystallography
Fig. 10 UV-VIS-NIR spectroelectrochemistry for 3n in CH3CN–0.1 mol dm3 [NBu4][PF6].
Table 9 UV-VIS-NIR spectroelectrochemical data of 1n, 2n and 3n in CH3CN–0.1 mol dm3 [Bu4N][PF6]
Compound
λ/nm (ε/dm3 mol−1 cm−1)
1 1− 12− 2 2+ 2−
609 (13 550), 356 (11 220), 264 (35 940) 901 (4600), 445 (4960, sh), 363 (9800), 267 (35 940) 585 (8900), 495 (9960), 370 (11 750), 273 (33 610) 544 (16 160), 357 (12 670), 268 (33 680) 630 (sh), 534 (11 730), 425 (5690), 259 (29 250) 781 (10 830), 462 (12 590), 413 (11 160), 377 (10 230), 273 (32 860) 520 (11 770), 442 (7460, sh), 361 (9870), 268 (38 170) 576 (18 470), 352 (10 600), 259 (32 580) 593 (13 440), 253 (30 170) 836 (8550), 623 (3460, sh), 426 (9000), 365 (9860), 269 (33 490) 512 (9410), 382 (4760), 329 (8640), 254 (40 860)
22− 3 3+ 3− 32−
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Single crystals of 1 were grown by slow evaporation of its 3 : 2 dichloromethane–acetonitrile solution, while 2 and 3 were grown by slow evaporation of 1 : 1 dichloromethane–hexane solution. X-Ray crystal data were collected on a CCD Agilent Technologies (Oxford Diffraction) SUPER NOVA diffractometer. Data collection was evaluated by using the CrysAlisPro CCD software. The data were collected by standard phi–omega scan techniques, and were scaled and reduced using the CrysAlisPro RED software. The structures were solved by direct methods using SHELXS-97 and refined by full matrix least-squares with SHELXL-97, refining on F2.22 All non-hydrogen atoms were refined anisotropically. The remaining hydrogen atoms were placed in geometrically constrained positions and refined with isotropic temperature factors, generally 1.2Ueq of their parent atoms. Hydrogen atoms were included in the refinement process as per the riding model. Hydrogen atoms of the disordered solvent hexane molecules in 2 could not be located; however these have been considered for the empirical formula in Table 1. CCDC numbers for 1, 2 and 3 are 963958, 963959 and 963960, respectively. Computational details Full geometry optimisations were carried out by using the density functional theory method at the (R)B3LYP level for 1, 12−, 2, 22−, 3, 32− and the (U)B3LYP level for 1+, 1−, 2+, 2−, 3+ and 3−.23 Except for ruthenium all other elements were assigned the 6-31G* basis set. The LANL2DZ basis set with effective core potential was employed for the ruthenium atom.24 The vibrational frequency calculations were performed
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Table 10 Experimental and TD-DFT (B3LYP/CPCM/CH3CN) calculated electronic transitions for 1n (n = 0, 1−, 2−)
λ/nm expt. (DFT)
ε/dm3 mol−1 cm−1 ( f a)
Transitions
Character
n = 0 (S = 0) 609 (715) 356 (325)
13 550 (0.31) 11 220 (0.09)
264 (251)
35 940 (0.44)
HOMO−1 → LUMO(0.69) HOMO−2 → LUMO+2(0.57) HOMO → LUMO+6(0.22) HOMO−4 → LUMO+1(0.52) HOMO−3 → LUMO+2(0.32) HOMO−5 → LUMO+1(0.22)
Ru(dπ)/Q1(π) → Q1(π*)/Ru(dπ) Ru(dπ) → Q1(π*) Ru(dπ) → Ru(dπ)/Q1(π*) acac(π)/Q1(π) → Q1(π*) acac(π) → Q1(π*) Q1(π)/acac(π) → Q1(π*)
HOMO(β) → LUMO(β)(0.97) SOMO → LUMO+3(α)(0.80) HOMO(β) → LUMO+4(β)(0.42) SOMO → LUMO+3(α)(0.38) HOMO−3(β) → LUMO+1(β)(0.29) HOMO−1(β) → LUMO+1(β)(0.27) HOMO−4(α) → LUMO+1(α)(0.49) HOMO−3(β) → LUMO+1(β)(0.45) HOMO−4(α) → LUMO(α)(0.38) HOMO−2(α) → LUMO+4(α)(0.37)
Ru(dπ)/Q1(π) → Q1(π*)/Ru(dπ) Q1(π) → Q1(π*) Ru(dπ)/Q1(π) → Q1(π*) Q1(π) → Q1(π*)/acac(π*) acac(π) → Q1(π*) Ru(dπ)/Q1(π) → Q1(π*) acac(π) → acac(π*) acac(π) → Q1(π*) acac(π) → Q1(π*) Ru(dπ) → Q1(π*)
HOMO → LUMO(0.61) HOMO → LUMO+1(0.35) HOMO−2 → LUMO+1(0.63) HOMO → LUMO+5(0.40) HOMO−2 → LUMO+2(0.21) HOMO−4 → LUMO(0.54) HOMO−4 → LUMO+1(0.38)
Q1(π)/Ru(dπ) → Q1(π*) Q1(π)/Ru(dπ) → acac(π*) Ru(dπ) → acac(π*) Q1(π)/Ru(dπ) → Ru(dπ)/acac(π*) Ru(dπ) → acac(π*) Q1(π)/acac(π) → Q1(π*) Q1(π)/acac(π) → acac(π*)
n = 1− (S = 1/2) 901 (948) 445 (493)
4600 (0.21) 4960 (0.02)
363 (371)
9800 (0.05)
267 (258)
35 940 (0.32)
n = 2− (S = 0) 585 (615)
8900 (0.02)
495 (476) 370 (366)
9960 (0.11) 11 750 (0.07)
273 (267)
33 610 (0.50)
a
Oscillator strength.
Table 11 Experimental and TD-DFT (B3LYP/CPCM/CH3CN) calculated electronic transitions for 2n (n = 1+, 0, 1−, 2−)
λ/nm expt. (DFT)
ε/dm3 mol−1 cm−1( f a)
Transitions
Character
n = 0 (S = 0) 544 (542) 357 (353)
16 160 (0.36) 12 670 (0.25)
268 (261)
33 680 (0.32)
HOMO−1 → LUMO(0.68) HOMO → LUMO+4(0.58) HOMO−2 → LUMO+2(0.21) HOMO−4 → LUMO+1(0.54) HOMO−3 → LUMO+4(0.30) HOMO−12 → LUMO(0.26)
Ru(dπ) → Q2(π*) Ru(dπ)/acac(π) → acac(π*) Ru(dπ)/acac(π) → Q2(π*) acac(π)/Ru(dπ) → Q2(π*) Ru(dπ)/acac(π) → acac(π*) Q2(π) → Q2(π*)/Ru(dπ)
n = 1+ (S = 1/2) 630 (603) 534 (561)
sh (0.04) 11 730 (0.13)
425 (442) 259 (253)
5690 (0.07) 29 250 (0.22)
HOMO−2(β) → LUMO(β)(0.89) HOMO−4(β) → LUMO(β)(0.78) HOMO−1(β) → LUMO(β)(0.55) HOMO−3(α) → LUMO(α)(0.85) HOMO−3(β) → LUMO+4(β)(0.53) HOMO−2(β) → LUMO+5(β)(0.52)
acac(π)/Ru(dπ) → Ru(dπ) Ru(dπ)/acac(π) → Ru(dπ) acac(π)/Ru(dπ) → Ru(dπ) acac(π) → Q2(π*) Q2(π) → acac(π*)/Ru(dπ) acac(π)/Ru(dπ) → acac(π*)
n = 1− (S = 1/2) 781 (697) 462 (466)
10 830 (0.22) 12 590 (0.004)
413 (419) 377 (371)
11 160 (0.006) 10 230 (0.07)
273 (267)
32 860 (0.17)
HOMO−1(β) → LUMO(β)(0.94) HOMO−1(α) → LUMO+2(α)(0.66) HOMO(β) → LUMO+3(β)(0.45) HOMO−1(α) → LUMO(α)(0.83) HOMO−3(α) → LUMO+1(α)(0.54) HOMO(β) → LUMO+4(β)(0.37) HOMO−1(α) → LUMO+3(α)(0.31) HOMO−2(β) → LUMO+6(β)(0.62) HOMO−7(α) → LUMO(α)(0.21)
Ru(dπ)/Q2(π) → Q2(π*)/Ru(dπ) Ru(dπ) → acac(π*)/Q2(π*) Ru(dπ) → acac(π*) Ru(dπ) → Q2(π*) Ru(dπ) → acac(π*) Ru(dπ) → Q2(π*) Ru(dπ) → Q2(π*)/acac(π*) Ru(dπ) → Ru(dπ)/Q2(π*) acac(π) → Q2(π*)
n = 2− (S = 0) 520 (483) 442 (446)
11 770 (0.03) 7460 (0.03)
361 (359)
9870 (0.11)
268 (285)
38 170 (0.23)
HOMO → LUMO+5(0.68) HOMO−1 → LUMO+3(0.53) HOMO−3 → LUMO+1(0.29) HOMO → LUMO+7(0.43) HOMO−1 → LUMO+3(0.23) HOMO−4 → LUMO+1(0.54)
Q2(π) → Ru(dπ)/acac(π*) Ru(dπ) → Q2(π*) Ru(dπ)/Q2(π) → acac(π*) Q2(π)/Ru(dπ) → Q2(π*) Ru(dπ) → Q2(π*) Q2(π) → acac(π*)
a
Oscillator strength.
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Table 12
Dalton Transactions Experimental and TD-DFT (B3LYP/CPCM/CH3CN) calculated electronic transitions for 3n (n = 1+, 0, 1−, 2−)
λ/nm expt. (DFT)
ε/dm3 mol−1 cm−1( f a)
Transitions
Character
n = 0 (S = 0) 576 (594) 352 (342)
18 470 (0.34) 10 600 (0.06)
259 (252)
32 580 (0.31)
HOMO−1 → LUMO(0.64) HOMO → LUMO+3(0.34) HOMO → LUMO+2(0.31) HOMO−4 → LUMO+1(0.43) HOMO−3 → LUMO+3(0.37) HOMO−3 → LUMO+2(0.22)
Ru(dπ)/acac(π) → Q3(π*)/Ru(dπ) Ru(dπ)/acac(π) → acac(π*) Ru(dπ)/acac(π) → Q3(π*) acac(π)/Q3(π) → Q3(π*) acac(π) → acac(π*) acac(π) → Q3(π*)
n = 1+ (S = 1/2) 593 (618)
13 440 (0.05)
253 (250)
30 170 (0.32)
HOMO−2(β) → LUMO(β)(0.57) HOMO−3(β) → LUMO(β)(0.51) HOMO−3(β) → LUMO+4(β)(0.42) HOMO−2(α) → LUMO+3(α)(0.36)
Q3(π)/acac(π) → Ru(dπ) Q3(π)/acac(π) → Ru(dπ) Q3(π)/acac(π) → Q3(π*)/acac(π*) Q3(π) → acac(π*)/Q3(π*)
HOMO−1(β) → LUMO(β)(0.82) HOMO(β) → LUMO(β)(0.51) SOMO → LUMO(α)(0.97) HOMO−3(β) → LUMO(β)(0.60) HOMO(β) → LUMO+1(β)(0.38) HOMO−2(α) → LUMO+2(α)(0.45) HOMO−1(β) → LUMO+6(β)(0.36) HOMO(β) → LUMO+6(β)(0.33) HOMO−4(α) → LUMO(α)(0.51) HOMO−3(β) → LUMO+3(β)(0.23)
Ru(dπ)/Q3(π) → Q3(π*)/Ru(dπ) Ru(dπ)/Q3(π) → Q3(π*)/Ru(dπ) Q3(π)/Ru(dπ) → Q3(π*) acac(π) → Q3(π*)/Ru(dπ) Ru(dπ)/Q3(π) → Q3(π*) Ru(dπ) → Q3(π*)/acac(π*) Ru(dπ)/Q3(π) → Q3(π*)/Ru(dπ) Ru(dπ)/Q3(π) → Q3(π*)/Ru(dπ) acac(π) → Q3(π*) acac(π) → acac(π*)
HOMO → LUMO+3(0.62) HOMO−3 → LUMO+1(0.46) HOMO−2 → LUMO+2(0.26) HOMO → LUMO+8(0.61) HOMO−4 → LUMO(0.46) HOMO−1 → LUMO+8(0.37)
Q3(π)/Ru(dπ) → Q3(π*) Ru(dπ)/Q3(π) → acac(π*) Ru(dπ)/Q3(π) → acac(π*) Q3(π)/Ru(dπ) → Q3(π*) Q3(π) → Q3(π*) Ru(dπ) → Q3(π*)
n = 1− (S = 1/2) 836 (759)
8550 (0.22)
623 (569) 426 (417)
3460 (0.01) 9000 (0.006)
365 (376)
9860 (0.07)
269 (263)
33 490 (0.16)
n = 2− (S = 0) 512 (569) 382 (393) 329 (339) 254 (276) a
9410 (0.07) 4760 (0.07) 8640 (0.07) 40 860 (0.21)
Oscillator strength.
to ensure that the optimised geometries represent the local minima and there are only positive eigenvalues. All calculations were performed with the Gaussian09 program package.25 Vertical electronic excitations based on (R)B3LYP/ (U)B3LYP optimized geometries were computed for 1n, 2n and 3n (n = +1, 0, −1, −2) using the time-dependent density functional theory (TD-DFT) formalism26 in acetonitrile using the conductor-like polarizable continuum model (CPCM).27 Chemissian 1.728 was used to calculate the fractional contributions of various groups to each molecular orbital. All calculated structures were visualized using ChemCraft.29 Preparation of complexes Synthesis of [Ru(acac)2(Q1)] (1). Ru(acac)2(CH3CN)2 (100 mg, 0.26 mmol) was taken in 30 cm3 ethanol and the ligand 9,10phenanthrenequinone (54 mg, 0.26 mmol) was added to it. The mixture was refluxed and stirred under a dinitrogen atmosphere for 4 h. The initial light orange colour of the reaction mixture gradually changed to bluish-green. The solvent was then removed under reduced pressure. The dried product was then purified by using a silica gel column having a mesh size of 60–120 which led to the elution of 1 by a 1 : 1 dichloromethane–hexane mixture. Evaporation of the solvent under reduced pressure yielded the pure complex in the solid state. Yield: 112 mg (84%). ESI-MS(+) (m/z, CH3CN): 507.91 (Calcd 507.51). 1H NMR (CDCl3): δ ( ppm): 8.63 (2H, d, J = 8.2 Hz),
2484 | Dalton Trans., 2014, 43, 2473–2487
8.54 (2H, d, J = 7.96 Hz), 7.86 (2H, dd, J = 7.6 Hz), 6.99 (2H, dd, J = 6.79 Hz), 5.22 (2H, s), 2.67 (6H, s), 2.09 (6H, s). Anal. Calcd for C24H22O6Ru: C, 56.80; H, 4.37. Found: C, 56.55; H, 4.17. Synthesis of [Ru(acac)2Q2] (2) and [Ru(acac)2Q3] (3). A mixture of Ru(acac)2(CH3CN)2 (100 mg, 0.26 mmol), 9,10-diaminophenanthrene (54 mg, 0.26 mmol) and a few drops of NEt3 in 30 cm3 ethanol was heated to reflux under a dinitrogen atmosphere for a period of 5 h. The initial light orange colour of the reaction mixture gradually changed to deep blue. The solvent was then removed under reduced pressure and it was then subjected to chromatographic purification on a neutral alumina column which led to the initial elution of a deep blue product corresponding to 3 by 1 : 3 dichloromethane–hexane followed by a purple product (2) by 3 : 1 dichloromethane– hexane. Evaporation of the solvent under reduced pressure resulted in the pure complexes 2 and 3 in the solid state. 2: yield: 35% (46 mg). ESI-MS (+) (m/z, CH3CN): 506.11 (Calcd 505.54). 1H NMR (CDCl3): δ ( ppm): 11.55 (2H, s), 8.53 (2H, d, J = 9.04 Hz), 8.40 (2H, d, J = 9.28 Hz), 7.59 (4H, m), 5.47 (2H, s), 2.39 (6H, s), 1.77 (6H, s). Anal. Calcd for C24H24N2O4Ru: C, 57.02; H, 4.79; N, 5.54. Found: C, 57.21; H, 4.61; N, 5.67. 3: yield: 48% (64 mg). ESI-MS(+) (m/z, CH3CN): 507.10 (Calcd 506.52). 1H NMR (CDCl3): δ ( ppm): 14.04 (1H, s), 9.05 (1H, d, J = 8.02 Hz), 8.68 (1H, d, J = 7.88 Hz), 8.38 (2H, dd, J = 8.24 Hz), 7.85 (1H, dd, J = 7.66 Hz), 7.58 (3H, m), 5.65 (1H, s),
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5.46 (1H, s), 2.59 (3H, s), 2.34 (3H, s), 2.01 (3H, s), 1.97 (3H, s). Anal. Calcd for C24H23NO5Ru: C, 56.91; H, 4.58; N, 2.77. Found: C, 56.99; H, 4.69; N, 2.97.
Acknowledgements Financial support received from the Department of Science and Technology and the Council of Scientific and Industrial Research (fellowship to A.M.), New Delhi (India), the DAAD, FCI and DFG (Germany) is gratefully acknowledged.
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Solution and Refinement, University of Goettingen, Goettingen, Germany, 1997. 23 C. Lee, W. Yang and R. G. Parr, Phys. Rev. B: Condens. Matter, 1988, 37, 785. 24 (a) D. Andrae, U. Haeussermann, M. Dolg, H. Stoll and H. Preuss, Theor. Chim. Acta, 1990, 77, 123; (b) P. Fuentealba, H. Preuss, H. Stoll and L. V. Szentpaly, Chem. Phys. Lett., 1989, 89, 418. 25 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, J. E. Peralta Jr., F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
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R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox, Gaussian 09 (Revision A.02), Gaussian, Inc., Wallingford, CT, 2009. (a) R. Bauernschmitt and R. Ahlrichs, Chem. Phys. Lett., 1996, 256, 454; (b) R. E. Stratmann, G. E. Scuseria and M. J. Frisch, J. Chem. Phys., 1998, 109, 8218; (c) M. E. Casida, C. Jamorski, K. C. Casida and D. R. Salahub, J. Chem. Phys., 1998, 108, 4439. (a) V. Barone and M. Cossi, J. Phys. Chem. A, 1998, 102, 1995; (b) M. Cossi and V. Barone, J. Chem. Phys., 2001, 115, 4708; (c) M. Cossi, N. Rega, G. Scalmani and V. Barone, J. Comput. Chem., 2003, 24, 669. S. Leonid, Chemissian 1.7, 2005–2010. Available at http:// www.chemissian.com D. A. Zhurko and G. A. Zhurko, ChemCraft 1.5, Plimus, San Diego, CA. Available at http://www.chemcraftprog.com
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Varying electronic structural forms of ruthenium complexes of non-innocent 9,10phenanthrenequinonoid ligands† Abhishek Mandal,a Tanaya Kundu,a Fabian Ehret,b Martina Bubrin,b Shaikh M. Mobin,c Wolfgang Kaim*b and Goutam Kumar Lahiri*a Bis(acetylacetonato)ruthenium complexes [Ru(acac)2(Q1–3)], 1–3, incorporating redox non-innocent 9,10-phenanthrenequinonoid ligands (Q1 = 9,10-phenanthrenequinone, 1; Q2 = 9,10-phenanthrenequinonediimine, 2; Q3 = 9,10-phenanthrenequinonemonoimine, 3) have been characterised electrochemically, spectroscopically and structurally. The four independent molecules in the unit cell of 2 are involved in intermolecular hydrogen bonding and π–π interactions, leading to a 2D network. The oxidation state-sensitive bond distances of the coordinated ligands Qn at 1.296(5)/1.289(5) Å (C–O), 1.315(3)/1.322 (4) Å (C–N), and 1.285(3)/1.328(3) Å (C–O/C–N) in 1, 2 and 3, respectively, and the well resolved 1H NMR resonances within the standard chemical shift range suggest DFT supported variable contributions from valence formulations [RuIII(acac)2(Q•−)] (spin-coupled) and [RuII(acac)2(Q0)], respectively. Complexes 1–3 exhibit one oxidation and two reduction steps with comproportionation constants Kc ∼ 107–1022 for the intermediates. The electrochemically generated persistent redox states 1n (n = 0, 1−, 2−) and 2n/3n (n = 1+, 0, 1−, 2−) have been analysed by UV-vis-NIR spectroelectrochemistry and by EPR for the paramagnetic intermediates in combination with DFT and TD-DFT calculations, revealing significant differ-
Received 2nd November 2013, Accepted 13th November 2013
ences in the oxidation state distribution at the {Ru–Q} interface for 1n–3n. In particular, the diminished propensity of the NH-containing systems for reduction results in the preference for RuII(Q0) relative to
DOI: 10.1039/c3dt53104j
RuIII(Q•−) (neutral compounds) and for RuII(Q•−) over the RuIII(Q2−) alternative in the case of the monoanionic complexes.
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Introduction The intricate mixing of the frontier orbitals of ruthenium and of biochemically relevant quinonoid moieties renders such systems with redox non-innocently behaving ligands (Scheme 1) as prototypical models to study electronic structures of strongly coupled coordination compounds.1–7 The results can be complex phenomena such as valence tautomerism1a,e,2j or redox induced electron transfer (RIET)1h,7d,8a,b at the metal–quinonoid ligand interface,
a Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. E-mail: [email protected] b Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany. E-mail: [email protected] c Discipline of Chemistry, School of Basic Sciences, Indian Institute of Technology Indore, Indore 452017, India † Electronic supplementary information (ESI) available: X-ray crystallographic files of 1–3 in CIF format, DFT dataset for 1n–3n (Tables S1–S5, S7–S18 and Fig. 3–5), mass spectra of 1–3 (Fig. S1), 1H NMR of 1–3 (Table S6, Fig. S2). CCDC 963958–963960 for 1–3. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt53104j
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Scheme 1
Oxidation state distribution in ruthenium-quinonoid complexes.
yielding an intermediate resonance situation8a instead of any specific configuration.8 As another result there are significant variations in the valence and spin distribution on even slight alterations of the molecular frameworks, involving the metal ion, the ancillary ligand and/or the quinone moiety, prompting continuous evaluation of new challenging molecular configurations. In this regard, the electronic structural features1–8 as well as potential applications in catalysis9 of ruthenium-obenzoquinone/o-benzoquinonemonoimine/o-benzoquinonediimine derivatives (Scheme 1) have been investigated in combination with ancillary ligands of different electronic properties,
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from neutral π-accepting to anionic σ/π-donating.1–8 However, reports on ruthenium complexes of 9,10-phenanthrenequinone and 9,10-phenanthrenequinonediimine derivatives are relatively limited.10 This has initiated the present approach of analysing the electronic structural aspects of three mononuclear ruthenium complexes 1–3 of 9,10-phenanthrenequinonoid ligands, having varying donor centres associated with the quinonoid moieties: O,O (1), N,N (2), and O,N (3).
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The neutral compounds 1, 2 and 3 exhibit ESI-MS(+) signals (m/z) at 507.91 (calc. 507.51), 506.11 (calc. 505.54) and 507.10 (calc. 506.52), respectively, in CH3CN (Fig. S1†). 1H NMR spectra of 1 and 2 exhibit the required symmetry while the unsymmetrical 3 shows twice as many 1H NMR resonance signals. The NH protons of Q2 and Q3 in 2 and 3 appear at 11.05 ppm and 14.04 ppm, respectively (see the Experimental section, Fig. S2, and Table S6†), which are exchangeable by D2O. Crystal structures
9,10-Phenanthrenequinone, one of the major constituents in diesel exhaust particles,11a can easily be transformed into the 9,10-phenanthrenesemiquinone radical state by biological reducing agents such as NADPH-cytochrome P450 reductase11b,c or nitric oxide synthase11d or thiol-based proteins.11e, f This in turn facilitates the formation of harmful hydroxyl radicals in the presence of intracellular iron catalysts.11g Herein we report the synthesis and structural characterisation of 1–3 as well as an investigation of the effects from the donor centres in 1n–3n, i.e. including the electrochemically accessible redox states (n = +1, 0, −1, −2). Special attention is given to a comparison with the reported analogous benzoquinonoid systems 4–6.2l,7b,8b
A comparison of the oxidation state-sensitive bond lengths from the single crystal X-ray structure (Fig. 1 and Tables 1, 2 and Table S3†) of 1, C1–O1, 1.296(5) Å (DFT: 1.277 Å) and C14– O2, 1.289(5) Å (DFT: 1.277 Å, Table 2), with the standard C–O bond lengths of coordinated o-benzoquinonoid ligands in different redox states (Q0: 1.22 Å, Q•−: 1.30 Å, Q2−: 1.34 Å)13 implies a valence state formulation according to [RuIII(acac)2(Q1•−)], where the unpaired spins on RuIII (t2g5, S = 1/2) and semiquinone radical ligands (Q1•−) are strongly coupled antiferromagnetically. The closed shell configuration of 1 is reflected by the well resolved 1H NMR resonances within the standard chemical shift range of δ, 0–10 ppm14 (Fig. S2, Table S6†), and by the absence of any EPR response, even at 4 K. The analogous [RuIII(acac)2(Q4•−)] (Q4•− = benzosemiquinone) (4) has been established to have an S = 1 ground state, exhibiting paramagnetically shifted 1H NMR resonances in a wide chemical shift range of δ, +6 to −10 ppm, and complex magnetic behaviour.7b The molecular structure and selected structural parameters of compound 2, crystallising with hexane solvent molecules, are shown in Fig. 2, Tables 1, 3 and Tables S1, S4,† respectively. The asymmetric unit consists of four independent molecules, three full molecules (molecules A–C) and one half molecule (molecule D) with slight differences in bond
Results and discussion Synthesis and characterisation Compound 1 has been synthesised from 9,10-phenanthrenequinone (Q10) and the precursor [RuII(acac)2(CH3CN)2]. Intramolecular electron-transfer between the ruthenium ion (RuII) and the quinonoid moiety (Q10) preferentially stabilises the {RuIIIQ1•−} configuration in 1 (see later) which is being further put into effect by the electron donating impact of acac−.12 Reaction of [Ru(acac)2(CH3CN)2] with 9,10-diaminophenanthrene (H2Q2) in the presence of NEt3 as a base, followed by chromatographic separation, leads to the isolation of [Ru(acac)2(Q2)] ( purple: 2) and [Ru(acac)2(Q3)] (blue: 3). The reproducible formation of 3 containing the phenanthrenequinonemonoimine ligand (Q3) is attributed to the partial hydrolysis of the imine bonds of Q2.
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Fig. 1 ORTEP diagram of molecule 1 in the crystal. Ellipsoids are shown at the 50% probability level, and hydrogen atoms are omitted for clarity.
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Table 1 2(3)
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Selected crystallographic parameters of 1, 3.5(2)·2C6H14 and
Formula Mr Radiation Crystal system Space group a/Å b/Å c/Å α (°) β (°) γ (°) V/Å3 Z μ/mm−1 T/K ρcalcd/g cm−3 F(000) θ Range (°) Data/restraints/ parameters R1, wR2 [I > 2σ(I)] R1, wR2 (all data) GOF on F 2 Largest diff. peak per hole/e Å−3
1
3.5(2)·2C6H14
2(3)
C24H22O6Ru 507.50 CuKα Triclinic ˉ P1 7.4141(2) 8.9708(4) 16.1229(7) 79.577(4) 84.280(3) 84.316(3) 1045.79(7) 2 6.406 150(2) 1.612 516 5.03 to 65.07 3561/0/284
C96H112N7O14Ru3.50 1941.67 MoKα Monoclinic C2/c 25.1917(4) 20.7180(4) 36.2929(5) 90 105.970(2) 90 18 211.0(5) 8 0.637 150(2) 1.416 8024 3.02 to 25.00 16 028/0/1048
C48H46N2O10Ru2 1013.01 MoKα Monoclinic P21/c 16.7929(2) 14.6472(10) 19.3765(2) 90 112.836(10) 90 4392.45(8) 4 0.749 150(2) 1.532 2064 2.98 to 25.00 7715/0/567
0.0446, 0.1262 0.0468, 0.1297 1.062 1.978 and −1.002
0.0320, 0.0817
0.0245, 0.0598
0.0409, 0.0859
0.0287, 0.0616
1.032 0.816 and −0.507
1.032 0.327 and −0.385
Table 2 Experimental (X-ray) and DFT calculated selected bond distances (Å) of 1n
DFT X-ray
Ru(1)–O(1) Ru(1)–O(2) Ru(1)–O(3) Ru(1)–O(4) Ru(1)–O(5) Ru(1)–O(6) C(1)–O(1) C(14)–O(2) C(1)–C(2) C(1)–C(14) C(2)–C(3) C(2)–C(7) C(3)–C(4) C(4)–C(5) C(5)–C(6) C(6)–C(7) C(7)–C(8) C(8)–C(9) C(8)–C(13) C(9)–C(10) C(10)–C(11) C(11)–C(12) C(12)–C(13) C(13)–C(14)
1
1+ (S = 1/2)
1 (S = 0)
1− (S = 1/2)
12− (S = 0)
2.003(3) 1.997(3) 2.031(3) 2.013(3) 2.019(3) 1.993(3) 1.296(5) 1.289(5) 1.437(5) 1.436(5) 1.405(5) 1.412(5) 1.370(6) 1.402(6) 1.382(6) 1.402(6) 1.474(6) 1.403(5) 1.410(6) 1.388(6) 1.394(7) 1.358(6) 1.407(5) 1.435(5)
2.105 2.104 2.024 1.995 1.995 2.023 1.256 1.256 1.442 1.499 1.409 1.425 1.387 1.399 1.396 1.401 1.483 1.401 1.425 1.396 1.399 1.387 1.409 1.442
2.047 2.045 2.052 2.053 2.050 2.047 1.277 1.277 1.449 1.449 1.408 1.424 1.386 1.402 1.390 1.408 1.476 1.408 1.424 1.390 1.402 1.386 1.408 1.449
2.054 2.054 2.075 2.089 2.087 2.073 1.308 1.308 1.444 1.414 1.415 1.430 1.382 1.408 1.386 1.413 1.461 1.413 1.430 1.386 1.408 1.382 1.415 1.444
2.105 2.104 2.088 2.115 2.114 2.088 1.314 1.314 1.436 1.421 1.425 1.444 1.378 1.418 1.385 1.417 1.444 1.417 1.444 1.385 1.418 1.378 1.425 1.436
parameters. The average C–N bond lengths of 2 of 1.318(4) Å (DFT: 1.321 Å) indicate13 an oxidation state situation best approximated by [RuII(acac)2(Q20)] according to the proposed
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standard values for o-benzoquinonediimines (Q0: 1.31 Å, Q•−: 1.35 Å, Q2−: 1.38 Å).13 This formulation is justified by the broken symmetry analysis which predicts identical energies for the broken symmetry singlet state and the closed shell singlet form. The diamagnetic complex 2 displays well resolved 1H NMR signals (Fig. S2 and Table S6†). The {RuIIQ0} form of the corresponding o-benzoquinonediimine complex [RuII(acac)2(Q50)] (5) has been addressed by the Lever group, based on the C–N lengths of 1.320(3) Å of Q54b as well as via a detailed DFT analysis.2l The average RuII–N(Q2) bond lengths of 1.966(2) Å in 2 is appreciably shorter than the average Ru–O(acac) bond lengths of 2.051(2) Å in 1 due to strong dπ(RuII) → pπ*(Q20) back-bonding, as has been reported earlier for the RuII-acac complexes of o-benzoquinonediimines.2l,15 The 31% ruthenium contribution in the LUMO of 2 (Table S11†) also supports strong dπ(RuII) → pπ*(Q20) back-bonding.2l,9e,15 The packing diagram of 2 (Fig. 3 and Table 4) reveals the existence of intermolecular hydrogen bonding and π–π interactions involving Q2 ligands of different molecules. Molecule A is connected to molecule B via π–π interaction between the two aromatic rings of Q2 (interplanar distance of about 3.643 Å) and molecule A and molecule B are linked to molecule C and molecule D on either side via N–H⋯O(acac) hydrogen bonding interactions (Table 4), leading to the formation of a 1D layer chain. The 1D chain is further linked to the neighbouring layer by C–H⋯π interactions (see Fig. 3), resulting in a 2D network. The asymmetric unit in the single crystal of complex 3 consists of two independent molecules (molecules E and F) with slight differences in bond parameters (Fig. 4, Table 5 and Tables S2, S5†). Both the C–O bond lengths of 3 (molecule E/molecule F) 1.287(3) Å/1.285(3) Å (DFT: 1.272 Å) and the C–N bond lengths 1.332(3) Å/1.328(3) Å (DFT: 1.330 Å) suggest an intermediate description [RuII(acac)2(Q30)]/spin-paired [RuIII(acac)2(Q3•−)], while identical energies of the broken symmetry singlet and the closed shell singlet of 3 support the {RuIIQ30} form. Accordingly, 3 shows well resolved 1H NMR signals within the standard chemical shift range, δ = 0–15 ppm (Fig. S2 and Table S6†). The analogous o-benzoquinoneimine derivative was assigned as spin coupled [RuIII(acac)2(Q6•−)] (6), primarily based on the C–O/C–N bond lengths of the coordinated Q6n of 1.291(4) Å/1.340(4) Å, similar values as observed here for Q3n in 3.8b,13 Cyclic voltammetry Complex 1 exhibits a quasi-reversible one-electron oxidation (0.69 V), a reversible first (−0.39 V) and a quasi-reversible second one-electron reduction (−1.51 V) process (Fig. 5, Table 6) with appreciable differences relative to 4 (0.91 V (oxidation) and −0.14 V (reduction)7b). The large comproportionation constants (RTlnKc = nF(ΔEo))16 of ∼1018 between successive redox processes reveal the thermodynamic stability of the intermediate redox states 1 and 1−. A similar behaviour was noted for compounds 2 and 3, with the expected decrease of potential values due to the shift from more (O) to less (N) electronegative atoms. Accordingly, the monocations 2+ and 3+ become more stable and could be
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Fig. 2 ORTEP diagram of 2 in the crystal (hexane solvent), showing four molecules (A–D) in the asymmetric unit. The inset shows the molecule A separately. Ellipsoids are shown at the 50% probability level; hydrogen atoms and the solvent of crystallisation are omitted for clarity.
studied by EPR and UV-vis-NIR spectroelectrochemistry. The shift effects are somewhat less pronounced for the 9,10-phenanthrenequinone systems as compared to the o-benzoquinone analogues, and similarly, the Kc values for 1n–3n are attenuated in relation to those of 4n–6n, both an effect of the more extended π system with less participation of the heteroatoms. Although the cyclic and differential pulse voltammograms exhibit variable intensity patterns, the reversibility of spectroelectrochemical experiments (cf. below) supports consecutive one-electron transfer processes. EPR spectroscopy While the diamagnetic precursors are EPR silent, the monoanions 1−–3− and two of the monocations (2+, 3+) could be characterised EPR spectroscopically in frozen solution at 4 K
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(anions) or 110 K (cations), after electrolytic generation intra muros. The cation 1+ was too unstable as also observed by UVvis spectroelectrochemistry (vide infra). Spectra are shown in Fig. 6, and the g values are listed in Table 7. Table 8 contains the calculated Mulliken spin densities; both Tables 7 and 8 provide the corresponding available data for the o-benzoquinone analogues. The cations 2+ and 3+ exhibit typical EPR spectra for ruthenium(III) species with g1, g2 > 2 and g3 around 2.0. The large average g (〈g〉) and g anisotropy (Δg) values are in agreement with about 80% calculated contribution from the heavy metal to the spin density and the remainder located at the acac− co-ligands (Table 8). In agreement with the DFT-calculated bond length changes (Tables 3 and 5) these results point to an oxidation state formulation [(acac)2RuIII(Q0)]+. As a
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Table 3 Experimental (X-ray) and DFT calculated selected bond distances (Å) of 2n
Table 4 Hydrogen bonding parameters in 2 [Å and (°)]
D–H⋯A
d(D–H)
d(H⋯A)
d(D⋯A)
107) neutral and anionic intermediate forms display high degrees of covalency2l,7b,8a,b with two oxidation state descriptions contributing to a comparable extent to the observed ground state structures. The present evaluation of bonding and electron transfer behaviour of Ru(acac)2 complexes of a series of N/O donor varied ortho-quinonoid ligands with minimal (4–6) and extended π conjugated systems (1–3) has thus shown that the increased ligand/metal covalency on stepwise exchange of O by NH can be modified by the higher degree of delocalisation in the phenanthrenequinonoid examples. The smaller frontier orbital gap and the diminished donor–metal interaction in the larger compounds described here lead to different bonding situations with the dioxolene complex (4) at one (ionic and
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Fig. 9 UV-VIS-NIR spectroelectrochemistry for 2n in CH3CN–0.1 mol dm3 [NBu4][PF6].
spin-uncoupled) end7b and the phenanthrenequinonediimine system 2 at the other (covalent) end. Although long recognised as a remarkably covalent chelate arrangement,2,18 the ruthenium/quinonoid ligand combination can thus still provide varied results which are not simply predictable and which justify the continued research in that area.
Experimental Materials The metal precursor Ru(acac)2(CH3CN)2 was prepared according to a literature reported procedure.19 The ligands 9,10-phenanthrenequinone and 9,10-diaminophenanthrene were purchased from Alfa Aesar and Sigma Aldrich, respectively. All other chemicals and reagents were of reagent grade and used
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without further purification. For spectroscopic and electrochemical studies HPLC-grade solvents were used.
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Physical measurements UV-vis-NIR studies in CH3CN–0.1 mol dm3 Bu4NPF6 at 298 K were performed using an optically transparent thin layer electrochemical (OTTLE) cell20 which was mounted in the sample compartments of a J&M TIDAS spectrophotometer. 1H NMR spectra were recorded on a Bruker Avance III 400 spectrometer. The EPR measurements were made in a two-electrode capillary tube21 with an X-band Bruker system ESP300 equipped with a Bruker ER035M gaussmeter and a HP 5350B microwave counter. Cyclic voltammetric, differential pulse voltammetric and coulometric measurements were carried out using a PAR model 273A electrochemistry system. Platinum wire working and auxiliary electrodes and an aqueous saturated calomel reference electrode (SCE) were used in a three-electrode configuration. The supporting electrolyte was [Et4N][ClO4] and the solute concentration was ∼10−3 mol dm3. The half-wave potential Eo298 was set equal to 0.5(Epa + Epc), where Epa and Epc are anodic and cathodic cyclic voltammetric peak potentials, respectively. Elemental analysis was carried out with a PerkinElmer 240C elemental analyser. Electrospray mass spectra were recorded on a Micromass Q-ToF mass spectrometer. Crystallography
Fig. 10 UV-VIS-NIR spectroelectrochemistry for 3n in CH3CN–0.1 mol dm3 [NBu4][PF6].
Table 9 UV-VIS-NIR spectroelectrochemical data of 1n, 2n and 3n in CH3CN–0.1 mol dm3 [Bu4N][PF6]
Compound
λ/nm (ε/dm3 mol−1 cm−1)
1 1− 12− 2 2+ 2−
609 (13 550), 356 (11 220), 264 (35 940) 901 (4600), 445 (4960, sh), 363 (9800), 267 (35 940) 585 (8900), 495 (9960), 370 (11 750), 273 (33 610) 544 (16 160), 357 (12 670), 268 (33 680) 630 (sh), 534 (11 730), 425 (5690), 259 (29 250) 781 (10 830), 462 (12 590), 413 (11 160), 377 (10 230), 273 (32 860) 520 (11 770), 442 (7460, sh), 361 (9870), 268 (38 170) 576 (18 470), 352 (10 600), 259 (32 580) 593 (13 440), 253 (30 170) 836 (8550), 623 (3460, sh), 426 (9000), 365 (9860), 269 (33 490) 512 (9410), 382 (4760), 329 (8640), 254 (40 860)
22− 3 3+ 3− 32−
2482 | Dalton Trans., 2014, 43, 2473–2487
Single crystals of 1 were grown by slow evaporation of its 3 : 2 dichloromethane–acetonitrile solution, while 2 and 3 were grown by slow evaporation of 1 : 1 dichloromethane–hexane solution. X-Ray crystal data were collected on a CCD Agilent Technologies (Oxford Diffraction) SUPER NOVA diffractometer. Data collection was evaluated by using the CrysAlisPro CCD software. The data were collected by standard phi–omega scan techniques, and were scaled and reduced using the CrysAlisPro RED software. The structures were solved by direct methods using SHELXS-97 and refined by full matrix least-squares with SHELXL-97, refining on F2.22 All non-hydrogen atoms were refined anisotropically. The remaining hydrogen atoms were placed in geometrically constrained positions and refined with isotropic temperature factors, generally 1.2Ueq of their parent atoms. Hydrogen atoms were included in the refinement process as per the riding model. Hydrogen atoms of the disordered solvent hexane molecules in 2 could not be located; however these have been considered for the empirical formula in Table 1. CCDC numbers for 1, 2 and 3 are 963958, 963959 and 963960, respectively. Computational details Full geometry optimisations were carried out by using the density functional theory method at the (R)B3LYP level for 1, 12−, 2, 22−, 3, 32− and the (U)B3LYP level for 1+, 1−, 2+, 2−, 3+ and 3−.23 Except for ruthenium all other elements were assigned the 6-31G* basis set. The LANL2DZ basis set with effective core potential was employed for the ruthenium atom.24 The vibrational frequency calculations were performed
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Table 10 Experimental and TD-DFT (B3LYP/CPCM/CH3CN) calculated electronic transitions for 1n (n = 0, 1−, 2−)
λ/nm expt. (DFT)
ε/dm3 mol−1 cm−1 ( f a)
Transitions
Character
n = 0 (S = 0) 609 (715) 356 (325)
13 550 (0.31) 11 220 (0.09)
264 (251)
35 940 (0.44)
HOMO−1 → LUMO(0.69) HOMO−2 → LUMO+2(0.57) HOMO → LUMO+6(0.22) HOMO−4 → LUMO+1(0.52) HOMO−3 → LUMO+2(0.32) HOMO−5 → LUMO+1(0.22)
Ru(dπ)/Q1(π) → Q1(π*)/Ru(dπ) Ru(dπ) → Q1(π*) Ru(dπ) → Ru(dπ)/Q1(π*) acac(π)/Q1(π) → Q1(π*) acac(π) → Q1(π*) Q1(π)/acac(π) → Q1(π*)
HOMO(β) → LUMO(β)(0.97) SOMO → LUMO+3(α)(0.80) HOMO(β) → LUMO+4(β)(0.42) SOMO → LUMO+3(α)(0.38) HOMO−3(β) → LUMO+1(β)(0.29) HOMO−1(β) → LUMO+1(β)(0.27) HOMO−4(α) → LUMO+1(α)(0.49) HOMO−3(β) → LUMO+1(β)(0.45) HOMO−4(α) → LUMO(α)(0.38) HOMO−2(α) → LUMO+4(α)(0.37)
Ru(dπ)/Q1(π) → Q1(π*)/Ru(dπ) Q1(π) → Q1(π*) Ru(dπ)/Q1(π) → Q1(π*) Q1(π) → Q1(π*)/acac(π*) acac(π) → Q1(π*) Ru(dπ)/Q1(π) → Q1(π*) acac(π) → acac(π*) acac(π) → Q1(π*) acac(π) → Q1(π*) Ru(dπ) → Q1(π*)
HOMO → LUMO(0.61) HOMO → LUMO+1(0.35) HOMO−2 → LUMO+1(0.63) HOMO → LUMO+5(0.40) HOMO−2 → LUMO+2(0.21) HOMO−4 → LUMO(0.54) HOMO−4 → LUMO+1(0.38)
Q1(π)/Ru(dπ) → Q1(π*) Q1(π)/Ru(dπ) → acac(π*) Ru(dπ) → acac(π*) Q1(π)/Ru(dπ) → Ru(dπ)/acac(π*) Ru(dπ) → acac(π*) Q1(π)/acac(π) → Q1(π*) Q1(π)/acac(π) → acac(π*)
n = 1− (S = 1/2) 901 (948) 445 (493)
4600 (0.21) 4960 (0.02)
363 (371)
9800 (0.05)
267 (258)
35 940 (0.32)
n = 2− (S = 0) 585 (615)
8900 (0.02)
495 (476) 370 (366)
9960 (0.11) 11 750 (0.07)
273 (267)
33 610 (0.50)
a
Oscillator strength.
Table 11 Experimental and TD-DFT (B3LYP/CPCM/CH3CN) calculated electronic transitions for 2n (n = 1+, 0, 1−, 2−)
λ/nm expt. (DFT)
ε/dm3 mol−1 cm−1( f a)
Transitions
Character
n = 0 (S = 0) 544 (542) 357 (353)
16 160 (0.36) 12 670 (0.25)
268 (261)
33 680 (0.32)
HOMO−1 → LUMO(0.68) HOMO → LUMO+4(0.58) HOMO−2 → LUMO+2(0.21) HOMO−4 → LUMO+1(0.54) HOMO−3 → LUMO+4(0.30) HOMO−12 → LUMO(0.26)
Ru(dπ) → Q2(π*) Ru(dπ)/acac(π) → acac(π*) Ru(dπ)/acac(π) → Q2(π*) acac(π)/Ru(dπ) → Q2(π*) Ru(dπ)/acac(π) → acac(π*) Q2(π) → Q2(π*)/Ru(dπ)
n = 1+ (S = 1/2) 630 (603) 534 (561)
sh (0.04) 11 730 (0.13)
425 (442) 259 (253)
5690 (0.07) 29 250 (0.22)
HOMO−2(β) → LUMO(β)(0.89) HOMO−4(β) → LUMO(β)(0.78) HOMO−1(β) → LUMO(β)(0.55) HOMO−3(α) → LUMO(α)(0.85) HOMO−3(β) → LUMO+4(β)(0.53) HOMO−2(β) → LUMO+5(β)(0.52)
acac(π)/Ru(dπ) → Ru(dπ) Ru(dπ)/acac(π) → Ru(dπ) acac(π)/Ru(dπ) → Ru(dπ) acac(π) → Q2(π*) Q2(π) → acac(π*)/Ru(dπ) acac(π)/Ru(dπ) → acac(π*)
n = 1− (S = 1/2) 781 (697) 462 (466)
10 830 (0.22) 12 590 (0.004)
413 (419) 377 (371)
11 160 (0.006) 10 230 (0.07)
273 (267)
32 860 (0.17)
HOMO−1(β) → LUMO(β)(0.94) HOMO−1(α) → LUMO+2(α)(0.66) HOMO(β) → LUMO+3(β)(0.45) HOMO−1(α) → LUMO(α)(0.83) HOMO−3(α) → LUMO+1(α)(0.54) HOMO(β) → LUMO+4(β)(0.37) HOMO−1(α) → LUMO+3(α)(0.31) HOMO−2(β) → LUMO+6(β)(0.62) HOMO−7(α) → LUMO(α)(0.21)
Ru(dπ)/Q2(π) → Q2(π*)/Ru(dπ) Ru(dπ) → acac(π*)/Q2(π*) Ru(dπ) → acac(π*) Ru(dπ) → Q2(π*) Ru(dπ) → acac(π*) Ru(dπ) → Q2(π*) Ru(dπ) → Q2(π*)/acac(π*) Ru(dπ) → Ru(dπ)/Q2(π*) acac(π) → Q2(π*)
n = 2− (S = 0) 520 (483) 442 (446)
11 770 (0.03) 7460 (0.03)
361 (359)
9870 (0.11)
268 (285)
38 170 (0.23)
HOMO → LUMO+5(0.68) HOMO−1 → LUMO+3(0.53) HOMO−3 → LUMO+1(0.29) HOMO → LUMO+7(0.43) HOMO−1 → LUMO+3(0.23) HOMO−4 → LUMO+1(0.54)
Q2(π) → Ru(dπ)/acac(π*) Ru(dπ) → Q2(π*) Ru(dπ)/Q2(π) → acac(π*) Q2(π)/Ru(dπ) → Q2(π*) Ru(dπ) → Q2(π*) Q2(π) → acac(π*)
a
Oscillator strength.
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Table 12
Dalton Transactions Experimental and TD-DFT (B3LYP/CPCM/CH3CN) calculated electronic transitions for 3n (n = 1+, 0, 1−, 2−)
λ/nm expt. (DFT)
ε/dm3 mol−1 cm−1( f a)
Transitions
Character
n = 0 (S = 0) 576 (594) 352 (342)
18 470 (0.34) 10 600 (0.06)
259 (252)
32 580 (0.31)
HOMO−1 → LUMO(0.64) HOMO → LUMO+3(0.34) HOMO → LUMO+2(0.31) HOMO−4 → LUMO+1(0.43) HOMO−3 → LUMO+3(0.37) HOMO−3 → LUMO+2(0.22)
Ru(dπ)/acac(π) → Q3(π*)/Ru(dπ) Ru(dπ)/acac(π) → acac(π*) Ru(dπ)/acac(π) → Q3(π*) acac(π)/Q3(π) → Q3(π*) acac(π) → acac(π*) acac(π) → Q3(π*)
n = 1+ (S = 1/2) 593 (618)
13 440 (0.05)
253 (250)
30 170 (0.32)
HOMO−2(β) → LUMO(β)(0.57) HOMO−3(β) → LUMO(β)(0.51) HOMO−3(β) → LUMO+4(β)(0.42) HOMO−2(α) → LUMO+3(α)(0.36)
Q3(π)/acac(π) → Ru(dπ) Q3(π)/acac(π) → Ru(dπ) Q3(π)/acac(π) → Q3(π*)/acac(π*) Q3(π) → acac(π*)/Q3(π*)
HOMO−1(β) → LUMO(β)(0.82) HOMO(β) → LUMO(β)(0.51) SOMO → LUMO(α)(0.97) HOMO−3(β) → LUMO(β)(0.60) HOMO(β) → LUMO+1(β)(0.38) HOMO−2(α) → LUMO+2(α)(0.45) HOMO−1(β) → LUMO+6(β)(0.36) HOMO(β) → LUMO+6(β)(0.33) HOMO−4(α) → LUMO(α)(0.51) HOMO−3(β) → LUMO+3(β)(0.23)
Ru(dπ)/Q3(π) → Q3(π*)/Ru(dπ) Ru(dπ)/Q3(π) → Q3(π*)/Ru(dπ) Q3(π)/Ru(dπ) → Q3(π*) acac(π) → Q3(π*)/Ru(dπ) Ru(dπ)/Q3(π) → Q3(π*) Ru(dπ) → Q3(π*)/acac(π*) Ru(dπ)/Q3(π) → Q3(π*)/Ru(dπ) Ru(dπ)/Q3(π) → Q3(π*)/Ru(dπ) acac(π) → Q3(π*) acac(π) → acac(π*)
HOMO → LUMO+3(0.62) HOMO−3 → LUMO+1(0.46) HOMO−2 → LUMO+2(0.26) HOMO → LUMO+8(0.61) HOMO−4 → LUMO(0.46) HOMO−1 → LUMO+8(0.37)
Q3(π)/Ru(dπ) → Q3(π*) Ru(dπ)/Q3(π) → acac(π*) Ru(dπ)/Q3(π) → acac(π*) Q3(π)/Ru(dπ) → Q3(π*) Q3(π) → Q3(π*) Ru(dπ) → Q3(π*)
n = 1− (S = 1/2) 836 (759)
8550 (0.22)
623 (569) 426 (417)
3460 (0.01) 9000 (0.006)
365 (376)
9860 (0.07)
269 (263)
33 490 (0.16)
n = 2− (S = 0) 512 (569) 382 (393) 329 (339) 254 (276) a
9410 (0.07) 4760 (0.07) 8640 (0.07) 40 860 (0.21)
Oscillator strength.
to ensure that the optimised geometries represent the local minima and there are only positive eigenvalues. All calculations were performed with the Gaussian09 program package.25 Vertical electronic excitations based on (R)B3LYP/ (U)B3LYP optimized geometries were computed for 1n, 2n and 3n (n = +1, 0, −1, −2) using the time-dependent density functional theory (TD-DFT) formalism26 in acetonitrile using the conductor-like polarizable continuum model (CPCM).27 Chemissian 1.728 was used to calculate the fractional contributions of various groups to each molecular orbital. All calculated structures were visualized using ChemCraft.29 Preparation of complexes Synthesis of [Ru(acac)2(Q1)] (1). Ru(acac)2(CH3CN)2 (100 mg, 0.26 mmol) was taken in 30 cm3 ethanol and the ligand 9,10phenanthrenequinone (54 mg, 0.26 mmol) was added to it. The mixture was refluxed and stirred under a dinitrogen atmosphere for 4 h. The initial light orange colour of the reaction mixture gradually changed to bluish-green. The solvent was then removed under reduced pressure. The dried product was then purified by using a silica gel column having a mesh size of 60–120 which led to the elution of 1 by a 1 : 1 dichloromethane–hexane mixture. Evaporation of the solvent under reduced pressure yielded the pure complex in the solid state. Yield: 112 mg (84%). ESI-MS(+) (m/z, CH3CN): 507.91 (Calcd 507.51). 1H NMR (CDCl3): δ ( ppm): 8.63 (2H, d, J = 8.2 Hz),
2484 | Dalton Trans., 2014, 43, 2473–2487
8.54 (2H, d, J = 7.96 Hz), 7.86 (2H, dd, J = 7.6 Hz), 6.99 (2H, dd, J = 6.79 Hz), 5.22 (2H, s), 2.67 (6H, s), 2.09 (6H, s). Anal. Calcd for C24H22O6Ru: C, 56.80; H, 4.37. Found: C, 56.55; H, 4.17. Synthesis of [Ru(acac)2Q2] (2) and [Ru(acac)2Q3] (3). A mixture of Ru(acac)2(CH3CN)2 (100 mg, 0.26 mmol), 9,10-diaminophenanthrene (54 mg, 0.26 mmol) and a few drops of NEt3 in 30 cm3 ethanol was heated to reflux under a dinitrogen atmosphere for a period of 5 h. The initial light orange colour of the reaction mixture gradually changed to deep blue. The solvent was then removed under reduced pressure and it was then subjected to chromatographic purification on a neutral alumina column which led to the initial elution of a deep blue product corresponding to 3 by 1 : 3 dichloromethane–hexane followed by a purple product (2) by 3 : 1 dichloromethane– hexane. Evaporation of the solvent under reduced pressure resulted in the pure complexes 2 and 3 in the solid state. 2: yield: 35% (46 mg). ESI-MS (+) (m/z, CH3CN): 506.11 (Calcd 505.54). 1H NMR (CDCl3): δ ( ppm): 11.55 (2H, s), 8.53 (2H, d, J = 9.04 Hz), 8.40 (2H, d, J = 9.28 Hz), 7.59 (4H, m), 5.47 (2H, s), 2.39 (6H, s), 1.77 (6H, s). Anal. Calcd for C24H24N2O4Ru: C, 57.02; H, 4.79; N, 5.54. Found: C, 57.21; H, 4.61; N, 5.67. 3: yield: 48% (64 mg). ESI-MS(+) (m/z, CH3CN): 507.10 (Calcd 506.52). 1H NMR (CDCl3): δ ( ppm): 14.04 (1H, s), 9.05 (1H, d, J = 8.02 Hz), 8.68 (1H, d, J = 7.88 Hz), 8.38 (2H, dd, J = 8.24 Hz), 7.85 (1H, dd, J = 7.66 Hz), 7.58 (3H, m), 5.65 (1H, s),
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5.46 (1H, s), 2.59 (3H, s), 2.34 (3H, s), 2.01 (3H, s), 1.97 (3H, s). Anal. Calcd for C24H23NO5Ru: C, 56.91; H, 4.58; N, 2.77. Found: C, 56.99; H, 4.69; N, 2.97.
Acknowledgements Financial support received from the Department of Science and Technology and the Council of Scientific and Industrial Research (fellowship to A.M.), New Delhi (India), the DAAD, FCI and DFG (Germany) is gratefully acknowledged.
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