Synthesis, Spectroscopic and Theoretical Studies of Ruthenafuran

Article pubs.acs.org/Organometallics

Synthesis, Spectroscopic and Theoretical Studies of Ruthenafuran and Osmafuran Prepared by Activation of Ynone in Alcohol Wai-Kuen Tsui,† Lai-Hon Chung,† Wai-Him Tsang, Chi-Fung Yeung, Chun-Hong Chiu, Hoi-Shing Lo, and Chun-Yuen Wong* Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, People’s Republic of China S Supporting Information *

ABSTRACT: Ruthenafuran and osmafuran monocationic complexes [Ru([14]aneS4)(C∧O)]+ or [M(bpy)2(C∧O)]+ (C∧O = anionic bidentate chelate [C(OR)CHC(Ph)O]−; [14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane; M = Ru, Os; bpy = 2,2′bipyridine) have been prepared from reactions between phenylynone HCC(CO)Ph and [Ru([14]aneS4)Cl 2 ] or [M(bpy)2Cl2] in alcoholic solvents ROH. The formation of metal− vinylidene intermediate, followed by nucleophilic attack by RO−, and carbonyl group coordination to the metal center are believed to be the key steps in the formation of these metallafurans. The nature of the anionic C∧O ligand was investigated by electrochemical, spectroscopic, and theoretical means.

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INTRODUCTION

RESULTS AND DISCUSSION Synthesis and Characterizations. Ruthenafuran and osmafuran monocationic complexes 1−3 have been prepared in high yield (50−80%) from reactions between phenyl-ynone HCC(CO)Ph and metal precursors [Ru([14]aneS4)Cl2] or [M(bpy)2Cl2] (M = Ru, Os) in alcoholic solvents (Scheme 1). These metallafuran complexes are air stable in both solution and solid forms. The alkoxy group attached to the Cα is determined by the alcoholic solvent used (cf. synthesis of 1 and 1′). The carbenoid character for the M−C bonds is indicated by the low-field 13C NMR signals (261−271 ppm for 1−2; 248 ppm for 3). The bonding within the five-membered metallacycle formed from the metal center M and C(OR)CHC(Ph)O moiety (denoted as C∧O) can be described by the mesomeric forms A and B, which is supported by X-ray crystallography (see discussion below). The molecular structures of 1(ClO4) and 2(ClO4)·CH2Cl2 have been determined by X-ray crystallography, and the perspective views of their cations are depicted in Figures 1 and 2. In each case, the C∧O moiety behaves as a bidentate chelate and coordinates to the Ru center through the C(1) and O(1) atoms to give an essentially planar five-membered metallacycle. The bite angles of the C∧O in 1 and 2 are 79.26(10) and 79.18(16)°, respectively. The C(1)−C(2) and C(2)−C(3) distances (1.396(4)−1.405(4) Å) are intermediate between carbon−carbon single and double bond, consistent with the mesomeric representations depicted in Scheme 1. Regarding the [Ru(C∧O)] metallacycle, the most pronounced structural difference between 1 and 2 is the Ru−C(1) bond

Activation of alkynes for functional and novel organic products by transition-metal complexes is one of the most important topics in organometallic chemistry.1 It is well documented that alkynes generally interact with d6-transition-metal centers through the formation of reactive yet sometimes isolable metal−vinylidene intermediates, which can further transform into other carbon-rich organometallic species including metal− acetylide, −acyl, −allenylidene, −alkoxycarbene, and −carbyne complexes, depending on the functionality of the alkynes and the reactants available in the reaction mixture.2,3 Our group has been scrutinizing the reactivity between a variety of organic substrates and structurally well-defined d6transition-metal complexes, and the spectroscopic properties of the derived organometallic complexes.4 As an extension of this research direction, we now present the reactivity of a specific type of alkyne, phenyl-ynone HCC(CO)Ph, toward [Ru([14]aneS4)Cl2] and [M(bpy)2Cl2] (M = Ru and Os; [14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane; bpy = 2,2′bipyridine) in alcoholic solvents ROH. Our results reveal that the resultant products are metallafuran monocationic complexes [Ru([14]aneS4)(C∧O)]+ and [M(bpy)2(C∧O)]+, where C∧O represents an anionic bidentate [C(−OR)CHC(−Ph) O]− chelate. It is worth mentioning that metallafuran and other members of metallacycles have received extensive attention in the field of organometallic and theoretical chemistry,5,6 and the reactivity reported in this work may represent a general synthetic approach for different metallafurans. Moreover, the electronic properties of the ruthenafurans and osmafuran have been probed by electrochemical, spectroscopic, and theoretical studies. © XXXX American Chemical Society

Received: January 6, 2015

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DOI: 10.1021/acs.organomet.5b00009 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Scheme 1. Synthetic Routes for Cationic Complexes 1−3

Figure 2. Perspective view of cation 2 as represented by 30% probability ellipsoids; hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru(1)−C(1) 1.954(5), C(1)− C(2) 1.396(7), C(1)−O(2) 1.335(6), C(2)−C(3) 1.398(6), C(3)− O(1) 1.282(5), O(1)−Ru(1) 2.100(3), and C(1)−Ru(1)−O(1) 79.18(16).

Scheme 2. Plausible Mechanism for the Formation of Metallafurans in This Work

which subsequently undergoes 1,2-hydrogen shift to give a metal−vinylidene species.2 The electrophilic Cα of the vinylidene is then attacked by the nucleophile RO− originated from the alcoholic solvent ROH,2a,b,4a,b,7 leading to a C∧O moiety, which has suitable geometry to coordinate to M via both C and O atoms. Electrochemical, Spectroscopic, and Theoretical Studies. Electrochemical data for all the complexes (as perchlorate salt) are summarized in Table 1, and the cyclic voltammograms for 1, 2, and 3 are depicted in Figure 3. Each complex shows one reversible oxidation couple, with E1/2 values spanning from −0.03 to 0.50 V vs Cp2Fe+/0; the ease of oxidation is in the order 3 > 2 > 1 ≈ 1′, which parallels the calculated energies for their HOMOs (−5.4, −5.7, and −5.9 eV for 3, 2, and 1

Figure 1. Perspective view of cation 1 as represented by 30% probability ellipsoids; hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru(1)−C(1) 2.000(3), C(1)− C(2) 1.396(4), C(1)−O(2) 1.342(4), C(2)−C(3) 1.405(4), C(3)− O(1) 1.277(4), O(1)−Ru(1) 2.097(2), and C(1)−Ru(1)−O(1) 79.26(10).

distance (2.000(3) and 1.954(5) Å, respectively). Interestingly, these Ru−C bond distances are significantly longer than that in the Ru−methoxycarbene complex [Ru([14]aneS4)(C(OMe)(−CHCAr2))Cl]+ (1.9167(14) Å).4m By comparison of Ru−C bond distances between 1 and 2, we found that the [M(C∧O)] moiety in 1 is very close to the mesomeric form A, whereas that in 2 is better described as an intermediate between mesomeric forms A and B as depicted in Scheme 1. Concerning the preparation of metallafurans, there are several approaches documented in the literature. Examples include direct C−H activation of functionalized ketones by metal centers6l,o,q,r,t and activation of alkynes for metallafurans.6a,c,e,f,j,p,s,u,x,z Interestingly, the formation of metallafurans in this work involve not only the substrate phenylynone HCC(CO)Ph but also the alcoholic solvent ROH. A plausible mechanism for the formation of these metallafurans is depicted in Scheme 2: interaction between the metal center and phenyl-ynone first gives a metal−phenyl-ynone π-intermediate,

Table 1. Electrochemical Dataa E1/2b/V vs Cp2Fe+/0 1 1′ 2 3

oxidation

1st reduction

2nd reduction

0.50 0.48 0.26 −0.03

−2.33 −2.34 −1.93 −1.81

−2.15 −2.11

a

Supporting electrolyte: 0.1 M [Bu4N]PF6 in CH3CN. bE1/2 = (Epc + Epa)/2 at 298 K.

B


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Organometallics

Figure 3. Cyclic voltammograms for 1, 2, and 3 as perchlorate salt (supporting electrolyte: 0.1 M [Bu4N]PF6 in CH3CN; 298 K; scan rate =100 mV s−1).

respectively). As the HOMOs for the complexes are dominated by the metal centers (61.5−66.2%; see Table 2 and Figure 4), the oxidation waves are assigned as Ru(II/III) or Os(II/III) couples. Table 2. Selected Molecular Orbital Compositions (%) for Cations 1, 2, and 3 from DFT/COSMO Calculations 1

2

3

MO

Ru/Os

C∧O

[14]aneS4/2×bpy

HOMO − 2 HOMO − 1 HOMO LUMO LUMO + 1 LUMO + 2 HOMO − 3 HOMO − 2 HOMO − 1 HOMO LUMO LUMO + 1 LUMO + 2 LUMO + 3 LUMO + 4 LUMO + 5 HOMO − 2 HOMO − 1 HOMO LUMO LUMO + 1 LUMO + 2 LUMO + 3 LUMO + 4 LUMO + 5 LUMO + 6

51.4 51.1 61.5 5.4 2.2 28.6 12.8 62.8 60.6 65.1 2.2 6.5 5.3 6.0 8.1 4.4 54.5 55.5 66.2 2.7 10.1 8.1 4.8 3.3 2.9 7.9

10.0 31.1 10.5 82.2 93.6 8.8 75.7 19.3 16.6 19.3 2.2 1.3 83.2 2.7 2.5 1.7 23.2 12.0 14.5 5.3 1.7 70.6 6.6 7.0 1.5 1.8

38.6 17.8 28.0 12.4 4.2 62.6 11.5 17.9 22.8 15.6 95.6 92.2 11.5 91.3 89.4 93.9 22.3 32.5 19.3 92.0 88.2 21.3 88.6 89.7 95.6 90.3

Figure 4. HOMO and LUMO surfaces for cations 1, 2, and 3 (hydrogen atoms are omitted for clarity; surface isovalue = 0.04 au).

of reduction is in the order 3 > 2 > 1 ≈ 1′, which again parallels the calculated energies for their LUMOs (−2.4, −2.3, and −1.9 eV for 3, 2, and 1, respectively). The UV−visible absorption data for all the complexes (as perchlorate salt) are summarized in Table 3, and their spectra Table 3. UV−Vis Absorption Data (Solvent = CH3CN; 298 K) λmax/nm (εmax/dm3 mol−1 cm−1) 1 1′ 2 3

244 (20000), 284 (11200), 388 (11110) 244 (18520), 284 (10580), 387 (10310) 244 (33740), 291 (54680), 351 (sh, 8520), 395 (12810), 469 (11230), 550 (sh, 5740) 244 (33710), 293 (54160), 353 (sh, 10530), 398 (18080), 479 (10120), 568 (7960), 750 (sh, 2610)

recorded in CH3CN are depicted in Figure 5. Complexes 1 and 1′ each features an absorption band with λmax ≈ 390 nm and εmax ≈ 1 × 104 dm3 mol−1 cm−1. The absorption profiles for complexes 2 and 3 are more complicated than those in 1 and 1′: apart from a dominant absorption band at λmax ≈ 400 nm (εmax ≈ 1−2 × 104 dm3 mol−1 cm−1), each of those also exhibits a slightly less intense broad absorption profile covering the whole visible region, which tails up to 700 nm for 2 and 800 nm for 3. As the structural difference between the 1/1′ and 2/3 series is the auxiliary ligand ([14]aneS4 vs (bpy)2), the broad absorption profiles in the visible region for 2 and 3 are likely attributed to the dπ(RuII/OsII) → π*(bpy) metal-to-ligand charge transfer (MLCT) transition, given that Ru(II) and Os(II)-bipyridine complexes are well-known to exhibit dπ(RuII/ OsII) → π*(bpy) MLCT transition in the visible region.

Complexes 1 and 1′ each exhibits one reversible reduction couple within the solvent window (E1/2 = −2.33 and −2.34 V, respectively), whereas two reversible reduction couples are recorded for 2 and 3. Because the LUMO for 1 is dominated by the C∧O ligand (82.2%), the reduction couples for 1 and 1′ are assigned as ligand-centered C∧O reduction. However, the LUMOs calculated for 2 and 3 are dominated by the bpy ligand (95.6 and 92.0%, respectively); thus, their first reduction couples are assigned as ligand-centered bpy reduction. The ease C


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Organometallics

be described as mainly dπ(RuII) → π*(C∧O) MLCT in character, admixed with some Ru → [14]aneS4 charge transfer. The electronic difference density plots for 1 corresponding to transitions I and II clearly show that electronic charge is depleted from the dπ(Ru) and accumulated at the π*(C∧O) and [14]aneS4 (Figure 7, generated by taking the difference between the excited state electron density and ground state electron density). However, the broad absorption profiles in the visible region for 2 and 3 are dominated by dπ(RuII/OsII) → π*(bpy) MLCT transitions (transitions III, IV, and V for 2, and VII, VIII, and IX for 3), and their dπ(RuII/OsII) → π*(C∧O) MLCT transitions are mixed with some dπ(RuII/OsII) → π*(bpy) MLCT transitions (transition VI for 2, X for 3). Figure 5. UV−vis absorption spectra of 1, 2, and 3 as perchlorate salt in CH3CN at 298 K.

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CONCLUSIONS

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EXPERIMENTAL SECTION

In this work, a general synthetic methodology toward ruthenafuran and osmafuran has been developed. Three families of metallafurans, [Ru([14]aneS4)(C∧O)]+, [Ru(bpy)2(C∧O)]+, and [Os(bpy)2(C∧O)]+, have been prepared by reacting metal precursors [Ru([14]aneS4)Cl2], [Ru(bpy)2Cl2], or [Os(bpy)2Cl2], with phenyl-ynone HC C(CO)Ph in alcoholic solvents ROH. The formation of metal−vinylidene intermediate, followed by nucleophilic attack by RO− and carbonyl group coordination to the metal center, are believed to be the key steps in the formation of these metallafurans. The nature of the anionic C∧O ligand was investigated by electrochemical, spectroscopic, and theoretical means. The findings that (1) the C∧O-centered reduction for the [Ru([14]aneS4)(C∧O)]+ series are more negative than the bpy-centered reduction for [Ru(bpy)2(C∧O)]+ and [Os(bpy)2(C∧O)]+ and that (2) the dπ(RuII) → π*(C∧O) MLCT transition energy for the [Ru([14]aneS4)(C∧O)]+ series are higher than that for the dπ(RuII/OsII) → π*(bpy) MLCT transition for [Ru(bpy) 2 (C ∧ O)] + and [Os(bpy)2(C∧O)]+ suggest that the π*(C∧O) is higher lying than the π*(bpy). Applications of this synthetic methodology for the design of new organometallic emitters are currently under investigation.

Time-dependent DFT (TD-DFT) calculations on cations 1, 2, and 3 produce absorption spectra (Figure 6) highly

General Procedures. All reactions were performed under an argon atmosphere using standard Schlenk techniques unless otherwise stated. All reagents were used as received, and solvents for reactions were purified by a PureSolv MD5 solvent purification system. [Ru([14]aneS4)Cl2],8 [M(bpy)2Cl2] (M = Ru, Os),9 and phenylynones10 were prepared in accordance with literature methods. 1H, 13 C{1H}, DEPT-135, 1H−1H COSY, and 1H−13C HSQC NMR spectra were recorded on a Bruker 400 DRX FT-NMR spectrometer. Peak positions were calibrated with solvent residue peaks as internal standard. Labeling scheme for H and C atoms in NMR assignment is shown in Chart 1. Electrospray mass spectrometry was performed on a PE-SCIEX API 3000 triple quadrupole mass spectrometer. Elemental analyses were done on an Elementar Vario Micro Cube carbon− hydrogen−nitrogen elemental microanalyzer. UV−visible spectra were recorded on a Shimadzu UV-1700 spectrophotometer. Cyclic voltammetry was performed with a CH Instrument model 600C series electrochemical analyzer/workstation. All of the electrochemical measurements were performed in CH3CN solution with [n-Bu4N]PF6 (0.1 M) as supporting electrolyte at room temperature. The glassycarbon working electrode was polished with 0.05 μm alumina on a microcloth, sonicated for 5 min in deionized water, and rinsed with CH3CN before use. An Ag/AgNO3 (0.1 M in CH3CN) electrode was used as reference electrode, with a platinum wire as the counter electrode. All solutions were degassed with argon before experiments.

Figure 6. Calculated absorption spectra for cations 1, 2, and 3 from TD-DFT/COSMO calculations. Excitation energies and oscillator strength are shown by the blue vertical lines; spectra (in black) are convoluted with Gaussian function having a full-width-half-maximum of 3000 cm−1. See Figure 7 for the electronic difference density plots for the marked vertical transitions.

resembling their experimental spectra, and important vertical transitions are summarized in Table 4. For 1, the calculated lowest-energy dipole allowed transition band, composed of transitions I and II marked in Figure 6, mainly originates from the HOMO − 2 → LUMO transition, accompanied by some HOMO → LUMO + 2 character. With reference to the composition of the molecular orbitals, the transition band can D


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Organometallics Table 4. Important Vertical Transitions from TD-DFT/COSMO Calculationsa 1 2

3

a

λ/nm (marked transition)

oscillator strength

361.5 (I) 350.3 (II) 501.1 (III) 453.4 (IV) 431.4 (V) 366.5 356.4 (VI) 340.3 328.2 537.4 (VII) 473.6 (VIII) 450.9 (IX) 380.0 375.4(X) 366.1 364.7 354.9 339.5 337.8

0.164 0.054 0.055 0.068 0.089 0.072 0.230 0.058 0.073 0.095 0.061 0.073 0.065 0.177 0.097 0.076 0.187 0.089 0.056

major contribution 54% 35% 71% 69% 55% 60% 49% 58% 37% 82% 44% 44% 57% 39% 41% 47% 47% 49% 37%

H−2→L, 28% H→L+2 H→L+2, 28% H−2→L, 14% H−2→L+2, 11% H−1→L+2 H−1→L, 14% H−2→L+1 H−2→L+1, 12% H−1→L H−1→L+1, 24% H−2→L H→L+4, 20% H−2→L+2, 13% H−1→L+3 H−2→L+2, 18% H→L+5, 15% H→L+4 H−1→L+5, 16% H−2→L+3 H−2→L+4, 28% H−3→L H−1→L H−2→L+1, 15% H−1→L+2, 14% H−1→L+1, 10% H−2→L H−1→L+1, 24% H−2→L+1 H→L+6, 16% H−1→L+6 H→L+5, 38% H−2→L+2 H−1→L+4, 29% H−2→L+2 H−1→L+4, 24% H−2→L+3 H−2→L+3, 30% H−1→L+6 H−2→L+4, 32% H−2→L+5 H−2→L+5, 23% H−2→L+4, 19% H−1→L+6

Only excitations with oscillator strength >0.05 are listed.

Figure 7. Electronic difference density plots for 1, 2, and 3 at their excited states marked in Figure 6 (isodensity value = 0.003 au). [Ru([14]aneS4)(C∧O)](ClO4), 1(ClO4), and 1′(ClO4). A mixture of [Ru([14]aneS4)Cl2] (0.23 mmol) and phenyl-ynones (0.51 mmol) was refluxed in MeOH (for 1) or EtOH (for 1′) (30 mL) under argon for 17 h. Upon cooling to room temperature, a saturated aqueous NaClO4 solution (5 mL) was added, and the MeOH/EtOH was removed under vacuum. The yellow solids were collected by suction filtration and washed with water (5 mL × 2), EtOH (5 mL × 2), and finally Et2O (10 mL × 3). The solids were recrystallized by slow diffusion of Et2O into a CH3NO2 solution of 1(ClO4) and 1′(ClO4) to give bright orange crystals. Complex 1(ClO 4 ). Yield 0.116 g, 80%. Anal. Calcd for C20H29S4RuCl1O6: C, 38.12; H, 4.64, N, 0.00. Found: C, 38.01; H,

Chart 1. Labeling Scheme for H and C Atoms in the NMR Assignment

The E1/2 value of the ferrocenium/ferrocene couple (Cp2Fe+/0) measured in the same solution was used as an internal reference. E


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Organometallics 4.57, N, 0.06. 1H NMR (400 MHz, CD3CN): δ 1.70−3.63 (m, 20H, [14]aneS4), 4.06 (s, 3H, CH3), 6.87 (s, 1H, Hβ), 7.42−7.50 (m, 3H, Hb+Hc), 7.96−7.98 (m, 2H, Ha). 13C NMR (100.6 MHz, CD3CN): δ 24.93, 25.39, 31.60, 32.32, 32.80, 34.15, 35.18, 35.24, 39.21 (C on [14]aneS4), 58.92 (CH3), 107.91 (Cβ), 128.61 (Ca), 129.41 (Cb), 132.47 (Cc), 137.37 (quaternary carbon on Ph), 200.26 (Cγ), 261.73 (Ru−C). IR (KBr, cm−1): νCO = 1633. ESI-MS: m/z 533.2 [M]+. Complex 1′(ClO 4 ). Yield 0.116 g, 78%. Anal. Calcd for C21H31S4RuCl1O6: C, 39.12; H, 4.85; N, 0.00. Found: C, 39.02; H, 4.81; N, 0.05. 1H NMR (400 MHz, CD3CN): δ 1.44−1.48 (m, 3H, CH3), 1.70−3.63 (m, 20H, [14]aneS4), 4.30−4.37 (m, 2H, CH2), 6.83 (s, 1H, Hβ), 7.41−7.49 (m, 3H, Hb+Hc), 7.94−7.96 (m, 2H, Ha). 13C NMR (100.6 MHz, CD3CN): δ 15.27 (CH3), 24.93, 25.39, 31.63, 32.33, 32.38, 32.82, 34.14, 35.15, 35.25, 39.04 (C on [14]aneS4), 68.06 (CH2), 108.28 (Cβ), 128.57 (Ca), 129.38 (Cb), 132.38 (Cc), 137.40 (quaternary carbon on Ph), 199.98 (Cγ), 260.99 (Ru−C). IR (KBr, cm−1): νCO = 1634. ESI-MS: m/z 545.2 [M]+. [Ru(bpy)2(C∧O)](ClO4), 2(ClO4). A mixture of [Ru(bpy)2Cl2] (0.23 mmol) and phenyl-ynones (0.51 mmol) was refluxed in MeOH (30 mL) under argon for 17 h. Upon cooling to room temperature, a saturated aqueous NaClO4 solution (5 mL) was added, and MeOH was removed under vacuum. The deep red solids were collected by suction filtration and washed with water (5 mL × 2), EtOH (5 mL × 2), and finally with Et2O (10 mL × 3). The solids were recrystallized by slow diffusion of Et2O into CH2Cl2 solution of 2(ClO4) to give deep red crystals. Complex 2(ClO 4 ). Yield 0.099 g, 64%. Anal. Calcd for C30H25N4RuCl1O6: C, 53.45; H, 3.74; N, 8.31. Found: C, 53.42; H, 3.71; N, 8.28. 1H NMR (400 MHz, CD2Cl2): δ 3.78 (s, 3H, CH3), 6.89 (s, 1H, Hβ), 7.08−7.10 (m, 1H), 7.34−7.44 (m, 6H), 7.58−7.59 (m, 1H), 7.72 (m, 2H), 7.85−7.99 (m, 5H), 8.13−8.15 (m, 1H), 8.20−8.21 (m, 1H), 8.26−8.34 (m, 3H), 8.65−8.67 (m, 1H). 13C NMR (100.6 MHz, CD2Cl2): δ 59.05 (CH3), 106.41 (Cβ), 122.86, 123.08, 123.23, 123.61, 126.18, 126.75, 127.04, 127.27, 127.85, 128.86, 131.50, 134.36, 135.75, 136.42 (16 carbons, resolved by 13C−1H HSQC NMR experiment), 137.06 (quaternary carbon), 137.55, 149.40, 151.38, 151.74 (4 carbons), 155.17 (quaternary carbon), 155.89 (1 carbon), 157.67, 158.01, 158.16 (3 quaternary carbons), 199.32 (Cγ), 270.68 (Ru−C). IR (KBr, cm−1): νCO = 1632. ESI-MS: m/z 575.0 [M]+. [Os(bpy)2(C∧O)](ClO4), 3(ClO4). A mixture of [Os(bpy)2Cl2] (0.23 mmol) and phenyl-ynones (0.51 mmol) was refluxed in MeOH (30 mL) under argon for 17 h. Upon cooling to room temperature, a saturated NaClO4 solution (5 mL) was added, and MeOH was removed under vacuum. The deep brown solids were collected by suction filtration and washed with water (5 mL × 2), EtOH (5 mL × 2), and finally with Et2O (10 mL × 3). The product was purified by column chromatography (basic alumina, gradual elution with CH2Cl2/ acetone (from 9.5:0.5 to 6:4, v/v)) as a purple band. After the removal of the solvent, the solids were recrystallized by slow diffusion of Et2O into acetone solution of 3(ClO4) to give deep brown crystals. Complex 3(ClO4). Yield 0.089 g, 50%. Anal. Calcd for C30H25N4 OsCl1O6: C, 47.21; H, 3.30; N, 7.34. Found: C, 47.19; H, 3.24; N, 7.30. 1H NMR (400 MHz, CD2Cl2): δ 3.61 (s, 3H, CH3), 6.88 (s, 1H, Hβ), 6.95−6.97 (m, 1H), 7.26−7.28 (m, 2H), 7.34−7.38 (m, 3H), 7.44−7.50 (m, 2H), 7.66−7.68 (m, 2H), 7.77−7.78 (m, 1H), 7.85− 7.91 (m, 4H), 8.13−8.19 (m, 2H), 8.28−8.31 (m, 3H), 8.56−8.58 (m, 1H). 13C NMR (100.6 MHz, CD2Cl2): δ 58.80 (CH3), 110.40 (Cβ), 123.05, 123.11, 123.84, 123.98, 127.19, 127.23, 127.41, 127.87, 128.12, 128.55, 131.35, 132.81, 135.23, 135.40 (16 carbons, resolved by 13 C−1H HSQC NMR experiment), 135.94 (quaternary carbon), 137.14, 148.44, 150.46, 151.71, 155.97 (5 carbons), 156.90, 159.27, 160.88, 161.54 (4 quaternary carbons), 200.86(Cγ), 248.05 (Ru−C). IR (KBr, cm−1): νCO = 1632. ESI-MS: m/z 665.4 [M]+. X-ray Crystallography. X-ray diffraction data for 1(ClO4) and 2(ClO4)·CH2Cl2 were collected on an Oxford Diffraction Gemini S Ultra X-ray single crystal diffractometer with Cu (for 1) and Mo (for 2) Kα radiation (λ = 1.54178 and 0.71073 Å, respectively) at 193 K. The data were processed using CrysAlis.11 The structures were solved by the Patterson method and refined by full-matrix least-squares based

on F2 with the programs SHELXS-97 and SHELXL-9712 within WinGX.13 All non-hydrogen atoms were refined anisotropically in the final stage of least-squares refinement. The positions of H atoms were calculated based on riding mode with thermal parameters equal to 1.2 times that of the associated C atoms. CCDC 1041815 (1(ClO4)) and 1041816 (2(ClO4)·CH2Cl2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam. ac.uk/data_request/cif. Computational Methodology. DFT calculations were performed on cations 1, 2, and 3 (spin-restricted Kohn−Sham solutions) using the ORCA software package (version 3.0.2).14 Their electronic ground states in gas-phase were optimized using the PBE0 functional15 accompanied by the zero-order regular approximation (ZORA)16 to account for relativistic effects. The def2-SVP basis sets were used for the H, C, N, and O atoms, while the def2-TZVP(-f) basis sets were used for the S, Ru, and Os atoms.17 The combination of the resolution of the identity and the “chain of spheres exchange” algorithms (RIJCOSX)18 was used to accelerate all DFT and TD-DFT calculations with the use of appropriate auxiliary basis sets. Tight SCF convergence criteria (1 × 10−8 Eh in energy, 1 × 10−7 Eh in the density charge, and 1 × 10−7 in the maximum element of the DIIS error vector) were used throughout. The first 80 vertical transitions for these complexes in CH3CN were computed at their respective gasphase-optimized ground-state geometries using the TD-DFT method with the aforementioned density functional and basis sets. The conductor-like screening model (COSMO)19 was used to account for solvent effects upon electronic transitions.

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ASSOCIATED CONTENT

S Supporting Information *

Theoretical calculation details (XYZ for 1, 2, and 3) and crystallographic data (CIF) for 1(ClO4) and 2(ClO4)·CH2Cl2. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Author Contributions †

W.-K.T. and L.-H.C. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work described in this paper was supported by grants from the Hong Kong Research Grants Council (project no. CityU 103911) and City University of Hong Kong (project no. 7004212). We are grateful to Dr. Shek-Man Yiu for X-ray diffraction data collection.

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