Investigation of Monomeric versus Dimeric fac-Rhenium (I) Tricarbonyl

Article pubs.acs.org/Organometallics

Investigation of Monomeric versus Dimeric fac-Rhenium(I) Tricarbonyl Systems Containing the Noninnocent 8‑Oxyquinolate Ligand Helen C. Zhao,† Barbara Mello,† Bi-Li Fu,§ Hara Chowdhury,† David J. Szalda,‡,⊥ Ming-Kang Tsai,§ David C. Grills,‡ and Jonathan Rochford*,† †

Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States ‡ Chemistry Department, Brookhaven National Laboratory, Upton, New York 11793-5000, United States § Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan, Republic of China ⊥ Department of Natural Sciences, Baruch College, New York, New York 10010, United States S Supporting Information *

ABSTRACT: Synthesis and characterization of the dimeric [facRe(R-OQN)(CO) 3 ] 2 and monomeric fac-Re(R-OQN)(CO)3(CH3CN) complexes are reported where R = unsubstituted, 2-methyl, 5,7-dimethyl, or 5-fluoro and OQN = 8oxyquinolate. Facile solvolysis of the dimeric systems is observed in coordinating media quantitatively yielding the monomer complexes in situ. Due to poor synthetic yields of the dimeric precursors, a direct synthetic strategy for isolation of the acetonitrile monomer complexes with an improved yield was developed. The fac-Re(CH3CN)2(CO)3Cl complex was easily generated in situ as a convenient intermediate to give the desired products in quantitative yield via reaction with the appropriately substituted 8-hydroxyquinoline and tetramethylammonium hydroxide base. Key to the success of this reaction is the precipitation of the product with triflic acid, whose conjugate triflate base is here noncoordinating. Furthermore, isolation of the solvated single crystal [fac-Re(FOQN)(CO)3](μ-Cl)[facRe(FHOQN)(CO)3]·CH3C6H5 has allowed a unique opportunity to access a possible reaction intermediate, giving insight into the formation of the [fac-Re(R-OQN)(CO)3]2 dimeric systems. Spectroscopic features (UV−vis, FTIR, and 1H NMR) of both monomeric and dimeric structures are discussed in terms of the π-electron-donating ability of the oxyquinolate ligand. Interpretation of these electronic effects and the associated steric properties is aided by single-crystal X-ray diffraction, electrochemical, and DFT/TD-DFT computational studies.

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INTRODUCTION

significant covalent character present in the metal−ligand bond, which of course has a significant effect on the electronic and physical properties of the complex.7−20 Common examples, where the presence of metal−ligand π-bonding is a common trait, include the dioxolene ligand21−23 and its imino analogues,24 dithiolenes,25,26 nitrosyl ligands,27 and recent examples of N-heterocyclic carbene28−31 and phosphenium32,33 systems. The description of a ligand as being non-innocent however must be justified, as such a covalent interaction is, by default, also highly dependent upon the redox state of the contributing metal center and its remaining coordination sphere.34−36 Previously we reported on the non-innocent character of the 8-oxyquinolate (OQN) ligand at a d6 Ru(II) center.37 This study showed that the OQN π-orbitals overlap

Of growing interest in recent years to the inorganic community are the occurrences of transition metal complexes with redoxactive ligands. Indeed, redox-active organic frameworks are often exploited by naturally occurring enzymes and as such represent a major inspiration for the engineering of molecular catalyst systems today.1−4 For example, one of the most widely used redox-active ligands today is the 2,2-bipyridine (bpy) system, which typically displays a one-electron reduction of its π*-orbital in the presence of a suitable reductant or alternatively at an electrode interface with sufficient potential.5 A number of such redox-active ligands can be further categorized as non-innocent ligands, i.e., a ligand whose electronic coupling with the central metal d-orbitals is so effective that the resulting bonding/antibonding molecular orbitals formed cannot be unambiguously assigned to either metal or ligand entities.6 This is principally due to the © 2013 American Chemical Society

Received: December 25, 2012 Published: February 25, 2013 1832

dx.doi.org/10.1021/om301250v | Organometallics 2013, 32, 1832−1841

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Figure 1. Structural representations of the dimeric (1d−4d) and monomeric (1m−4m) complexes investigated in this study. d and m imply dimeric and monomeric structures, respectively. course of the reaction an orange color was first observed, which slowly turned a yellow-brown once reflux temperature was reached. Upon cooling to room temperature, a pale yellow precipitate was observed. The pale yellow powder was isolated by vacuum filtration and dried under vacuum overnight, giving analytically pure product consistently with 50−60% yield. 1d, [fac-Re(OQN)(CO)3]2. 1H NMR δ (CDCl3): 7.96 (dd, 2H, J = 1.2, 4.8 Hz), 7.77 (dd, 2H, J = 1.2, 8.4 Hz), 7.53 (t, 2H, J = 8.0 Hz), 7.42 (dd, 2H, J = 1.2, 8.0 Hz), 6.95 (dd, 2H, J = 1.2, 8.4 Hz), 6.86 (dd, 2H, J = 5.2, 8.4 Hz) ppm. UV−vis (CH2Cl2) λmax: 369 nm (ε = 8700 M−1 cm−1). FTIR (CH2Cl2) ν(CO): 1903(sh), 1908, 1933, 2021, 2037 cm−1. Anal. Calcd for C24H12N2O8Re2: C 34.78; H 1.46; N 3.38. Found: C 34.92; H 1.54; N 3.35. 2d, [fac-Re(MeOQN)(CO)3]2. UV−vis (CH2Cl2) λmax: 360 nm (ε = 8200 M−1 cm−1). FTIR (CH2Cl2) ν(CO): 1905 (br), 1930, 2021, 2036 cm−1. Anal. Calcd for C26H16N2O8Re2: C 36.45; H 1.88; N 3.27. Found: C 36.63; H 1.90; N 3.24. 3d, [fac-Re(Me2OQN)(CO)3]2. 1H NMR δ (CD2Cl2): 8.06−8.10 (m, 2H), 7.26−7.35 (m, 2H), 7.05 (dd, 1H, J = 3.6, 6.0 Hz) ppm. UV−vis (CH2Cl2) λmax: 371 nm (ε = 8300 M−1 cm−1). FTIR (CH2Cl2) ν(CO): 1893, 1906, 1929, 2018, 2034 cm−1. Anal. Calcd for C28H20N2O8Re2·0.5CH3C6H5: C 40.64; H 2.60; N 3.01. Found: C 40.86; H 2.63; N 2.98. 4d, [fac-Re(FOQN)(CO)3]2. 1H NMR δ(CD2Cl2): 8.06−8.10 (m, 2H), 7.26−7.35 (m, 2H), 7.05 (dd, 1H, J = 6.3, 3.6 Hz) ppm. UV−vis (CH2Cl2) λmax: 382 nm (ε = 9600 M−1 cm−1). FTIR (CH2Cl2) ν(CO): 1903, 1912, 1935, 2022, 2039 cm−1. Anal. Calcd for C24H10N2F2O8Re2: C 33.33; H 1.17; N 3.24. Found: C 33.36; H 1.19; N 3.15. General Synthesis of Monomeric fac-Re(R-OQN)(CO)3(CH3CN) Complexes 1m−4m. A 50 mL flask was charged with 100 mg (0.276 mmol) of rhenium pentacarbonyl chloride in 10 mL of neat acetonitrile. The system was degassed under vacuum followed by purging with argon (three cycles) to ensure an oxygen-free environment. Following four hours of reflux, complete conversion to the monomeric fac-Re(CH3CN)2(CO)3Cl intermediate complex was confirmed by FTIR spectroscopy, and the reaction mixture was cooled to room temperature. Subsequently, one equivalent (0.276 mmol) of the appropriately substituted 8-hydroxyquinoline ligand was added with one equivalent of tetramethylammonium hydroxide (0.2 mL of a 25 wt % solution in methanol). Reflux was resumed for a further three hours, and the reaction cooled to room temperature. An aqueous solution of triflic acid (5 mL, 0.1 M) was then added, and the acetonitrile carefully removed in vacuo, giving rise to an aqueous suspension with a dark orange precipitate. Analytically pure product was isolated by vacuum filtration followed by drying under vacuum overnight typically with quantitative yield (>90%). 1m, fac-Re(OQN)(CO)3(CH3CN). 1H NMR δ (CD3CN): 8.91 (dd, 1H, J = 1.2, 3.6 Hz), 8.41 (dd, 1H, J = 0.9, 6.0 Hz), 7.44−7.52 (m, 2H), 7.04 (dd, 1H, J = 0.9, 6.0 Hz), 6.91 (dd, 1H, J = 0.6, 6.0 Hz) ppm. UV−vis (CH3CN) λmax: 427 nm (ε = 5100 M−1 cm−1). FTIR

extensively with the metal dπ-orbitals due to degenerative mixing, which imparts unique photophysical and electrochemical properties rendering the complex suitable toward photocurrent generation in a dye-sensitized solar cell. Consequently, it is anticipated that the electronic properties of the traditional d6 Re(I) tricarbonyl polypyridyl complexes can be similarly modulated by incorporation of the OQN ligand into the coordination sphere. Ultimately our goal is to investigate the impact of π-donating non-innocent ligand frameworks at the rhenium(I) tricarbonyl moiety toward the harvesting and storage of solar energy via photocatalytic CO2 conversion. By far the most selective CO2 reduction photocatalysts reported to date are the rhenium(I) polypyridyl systems [fac-ReI(N∧N)(CO)3L]n+ (N∧N = polypyridyl ligand, L = monodentate ligand), which produce CO under the typical photolysis conditions employed.38−48 This study reports on our first objective in meeting this goal with the targeted synthesis of monomeric rhenium(I) tricarbonyl oxyquinolate complexes. The structural and electronic properties of these systems are here investigated by FTIR, UV−vis, 1H NMR spectroscopy, single-crystal X-ray diffractometry, cyclic voltammetry, and density functional theory computational analysis.

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EXPERIMENTAL SECTION

Materials and Synthesis. Rhenium(I) pentacarbonyl chloride (98%), 8-hydroxyquinoline (99%), 2-methyl-8-hydroxyquinoline (98%), 5,7-dimethyl-8-hydroxyquinoline (98%), triflic acid (>99%), acetonitrile (spectrophotometric grade), dichloromethane (spectrophotometric grade), and m-xylene (reagent grade) were used as received from Sigma Aldrich. 5-Fluoro-8-quinolinol (99%) was purchased from TCI and used as received. fac-Re(CH3CN)2(CO)3Cl and [fac-Re(OQN)(CO)3]2 were both prepared according to the literature procedures.49,50 Additional analytical data for the previously published [fac-Re(OQN)(CO)3]2 complex are included below, as it is here more comprehensively characterized.50 Attempts to ionize either dimeric or monomeric systems by ESI-MS analysis were unsuccessful. The MeOQN complexes 2d and 2m showed very poor solubility and hence could not be qualitatively characterized by 1H NMR spectroscopy. Synthesis of Dimeric [fac-Re(R-OQN)(CO)3]2 Complexes 1d− 4d. A 50 mL flask was charged with 100 mg (0.276 mmol) of rhenium pentacarbonyl chloride and one equivalent (0.276 mmol) of the appropriately substituted 8-hydroxyquinoline ligand. A 5 mL amount of m-xylenes was then added to the flask along with a magnetic stir bar, and a reflux condenser was then attached. The system was degassed under vacuum followed by purging with argon three times to ensure an oxygen-free environment. Reflux was maintained for five hours to ensure maximum conversion to the dimeric complex. During the 1833


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Scheme 1. Reaction Scheme Depicting Synthesis of the [fac-Re(R-OQN)(CO)3]2 Complexes 1d−4d As Well As the Dimeric Side Product 5

(CH3CN) ν(CO): 1897, 1917, 2023 cm−1. Anal. Calcd for C24H12N2O8Re2: C 36.92; H 1.99; N 6.15. Found: C 36.98; H 2.01; N 6.12. 2m, fac-Re(MeOQN)(CO)3(CH3CN). UV−vis (CH3CN) λmax: 415 nm (ε = 4700 M−1 cm−1). FTIR (CH3CN) ν(CO): 1894, 1915, 2022 cm−1. Anal. Calcd for C15H11N2O4Re2: C 38.38; H 2.36; N 5.97. Found: C 38.58; H 2.38; N 5.95. 3m, fac-Re(Me2OQN)(CO)3(CH3CN). 1H NMR δ (CD3CN): 8.90 (dd, 1H, J = 1.2, 3.6 Hz), 8.48 (dd, 1H, J = 1.2, 6.3 Hz), 7.45 (d, 1H, J = 2.7, 6.3 Hz), 7.27 (s, 1H), 2.54 (s, 3H), 2.33 (s, 3H) ppm. UV−vis (CH3CN) λmax: 448 nm (ε = 4000 M−1 cm−1). FTIR (CH3CN) ν(CO): 1895, 1914, 2020 cm−1. Anal. Calcd for C16H13N2O4Re: C 39.75; H 2.71; N 5.79. Found: C 40.11; H 2.72; N 5.72. 4m, fac-Re(FOQN)(CO)3(CH3CN). 1H NMR δ (CD3CN): 8.97 (dd, 1H, J = 1.2, 3.6 Hz), 8.55 (dd, 1H, J = 0.9, 6.3 Hz), 7.58 (dd, 1H, J = 3.6, 4.2 Hz), 7.27 (dd, 1H, J = 1.5, 6.6 Hz), 6.79 (dd, 1H, J = 3.3, 6.6 Hz) ppm. UV−vis (CH3CN) λmax: 441 nm (ε = 2800 M−1 cm−1). FTIR (CH3CN) ν(CO): 1898, 1918, 2024 cm−1. Anal. Calcd for C14H8N2FO4Re2: C 35.52; H 1.70; N 5.92. Found: C 35.71; H 1.72; N 5.89. Physical Measurements. UV−vis absorption spectra were recorded on an Agilent 8453A diode array spectrophotometer in spectrophotometric grade dichloromethane or acetonitrile. FTIR spectra were recorded on a Thermo Nicolet 670 FTIR spectrophotometer in spectrophotometric grade dichloromethane or acetonitrile. 1 H NMR spectra were recorded on a Bruker UltraShield 400 MHz spectrometer. Deuterated solvents d-chloroform, d2-dichloromethane, and d3-acetonitrile were used as received from Cambridge Isotopes, and their residual solvent signals (δ = 7.26, 5.32, and 1.94 ppm, respectively) used as internal references for reporting the chemical shift (δ).51 Cyclic voltammetry was conducted on a CH Instruments 620D potentiostat for all complexes. Electrochemical analysis of the poorly soluble 2d and 2m complexes was possible by the more sensitive differential pulse voltammetry technique. A standard threeelectrode cell was used under an atmosphere of argon with a glassy carbon disc working electrode (3 mm diameter), a Pt wire counter electrode, and a nonaqueous reference electrode to minimize IR drop. The latter consisted of a Ag wire in a 0.1 M Bu4NPF6 acetonitrile electrolyte and was calibrated using ferrocene as a pseudoreference. The supporting electrolyte consisted of 0.1 M Bu4NPF6 in spectrophotometric grade solvent; noncoordinating 1,2-dichloroethane was used to study the dimeric complexes, and acetonitrile was used for the monomeric systems. The half-wave potential was determined from cyclic voltammetry as E1/2 = (Epa + Epc)/2, where Epa and Epc are the anodic and cathodic peak potentials, respectively. For quasi-reversible redox couples increased scan rates were used to accurately determine E1/2. Where E1/2 could not be calculated due to

irreversible behavior, anodic (Epa) or cathodic (Epc) peaks are reported. Collection and Reduction of X-Ray Data. Crystals of [facRe(Me2OQN)(CO)3]2·0.5CH3C6H5 (3d·0.5CH3C6H5) and [fac-Re(FOQN)(CO) 3 ](μ-Cl)[fac-Re(FHOQN)(CO) 3 ]·CH 3 C 6 H 5 (5·CH3C6H5) were grown from toluene solutions at room temperature by slow evaporation of solvent. Similarly, crystals of facRe(Me2OQN)(CO)3(CH3CN) (3m) were grown by slow evaporation of CH3CN solvent at room temperature. A crystal of each of 5·CH3C6H5, 3d·0.5CH3C6H5, and 3m were mounted on the end of individual glass fibers. A Bruker Kappa Apex II diffractometer was used for the collection of diffraction data. Diffraction data for 5·CH3C6H5, 3d·0.5CH3C6H5, and 3m each indicated monoclinic symmetry and systematic absences consistent with space group P2(1)/c. Determination and Refinement of the Structure. The structures of 3d·0.5CH3C6H5, 3m, and 5·CH3C6H5 were solved52 by direct methods. In the least-squares refinement,52 anisotropic temperature parameters were used for all the non-hydrogen atoms. Hydrogen atoms were placed at calculated positions and allowed to “ride” on the atom to which they were attached except for the hydrogen atoms on the toluene of solvation in 3d·0.5CH3C6H5, which were not included. The isotropic thermal parameters for the hydrogen atoms were determined from the atom to which they were attached. The data were corrected using the multiscan method (SADABS).53 Crystal data and information about the data collection are provided in Table SI-7. Computational Details. All calculations were carried out using density functional theory (DFT) with the B3LYP functional as implemented in the Gaussian 09 program package.54 The LANL08 basis set55 was used for Re, and 6-31G(d,p) was used for other elements.56,57 The optimization calculations were carried out using the polarizable continuum model (PCM) with the dielectric constant of CH3CN and CH2Cl2 for the monomeric and dimeric complexes, respectively.58 A vibrational frequency analysis coupling with the PCM model was carried out in order to confirm the minimum-energy geometry in solution, followed by time-dependent density functional theory (TD-DFT).59

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RESULTS AND DISCUSSION Synthesis. The dimeric [fac-Re(R-OQN)(CO)3]2 complexes 1d−4d were successfully synthesized by modification of a previously published procedure for the unsubstituted [facRe(OQN)(CO)3]2 system.4 It was discovered that dimer formation is highly sensitive to reaction temperature, requiring high boiling point solvents for effective elimination of HCl to occur (Scheme 1). The optimum solvent for isolation of pure 1834


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problematic dimer synthesis and investigate the possibility of a more direct high-yielding synthesis for the acetonitrilecoordinated monomers. It was found that reflux of the isolable intermediate fac-Re(CH3CN)2(CO)3Cl in acetonitrile solvent with stoichiometric equivalents of R-HOQN and Me4NOH base gave the desired product in quantitative yield. Key to the success of this reaction is precipitation of the solid orange product using 0.1 M aqueous triflic acid whose conjugate triflate base is non-coordinating with respect to the rhenium centers of 1m−4m (Scheme 2). This procedure was equally successful when conducted in a one-pot procedure beginning with a Re(CO)5Cl reflux in neat acetonitrile followed by direct addition of the R-HOQN ligand and Me4NOH base. X-ray Crystallography. An ORTEP drawing of the chloride-bridged dimeric structure 5·CH3C6H5 is presented in Figure 2. The molecule consists of two Re(I) metal centers bridged by a chloride anion with a single interstitial proton disordered between two oxygen atoms, O17 and O27, of the FOQN ligands. The O17−H17 bond length was determined as 0.820 Å with a O27---H17 hydrogen bond length of 1.636 Ǻ . Detailed structural parameters for this proton are provided in Table SI-13. Each Re(I) center of 5·CH3C6H5 displays the anticipated octahedral geometry, albeit slightly distorted, with a facial arrangement of three CO ligands at each center. For the most part both Re(I) centers appear to be geometrically and electronically equivalent, in that corresponding bond lengths and angles are very similar, if not within experimental error of each other (Table 1). For example, the Re1−Cl [2.5371(11) Å]

dimeric [fac-Re(R-OQN)(CO)3]2 complexes was found to be m-xylene. With a reflux temperature of 139 °C in m-xylene sufficient energy is available to drive elimination of HCl from the monomeric fac-Re(R-HOQN)(CO)3Cl intermediates, resulting in precipitation of the pure dimeric [fac-Re(ROQN)(CO)3]2 complexes. In contrast, for example, attempted synthesis of the dimeric [fac-Re(FOQN)(CO)3]2 complex 4d in the lower boiling point toluene solvent (bp = 110 °C) resulted in an additional crystalline side product, 5·CH3C6H5, having the formula [fac-Re(FOQN)(CO)3](μ-Cl)[fac-Re(FHOQN)(CO)3]·CH3C6H5 (Scheme1; Figure 2). It is quite

Table 1. Selected Bond Lengths and Angles for 5·CH3C6H5. Figure 2. Crystal structure of the chloride-bridged dimer 5·CH3C6H5. The toluene solvent molecule and ligand protons have been omitted for clarity. The hydrogen atom H17 is disordered. (It is bound to O17 and hydrogen bonding with O27 50% of the time, bound to O27 and hydrogen bonding with O17 the other 50% of the time.)

Re1 Cl Re1 C111 Re1 C122 Re1 C133 Re1 O17 Re1 N11 C17 O17 C110 F110 O17 H17a N11 Re1 O17 Re1 Cl Re2

possible that the single crystal of 5·CH3C6H5 represents a synthetic intermediate en route to complete conversion toward 4d via elimination of a second equivalent of HCl. A simple control experiment using the lower boiling point, noncoordinating dichloromethane solvent shows evidence for monomeric fac-Re(FHOQN)(CO)3Cl as the major product (Figure SI-1); the latter product is quantitatively converted to 4d upon reflux in m-xylene. A major goal of this study, however, was to isolate the monomeric solvent adducts where the facrhenium(I) tricarbonyl moiety is stabilized by the anionic oxyquinolate ligand opening upon the sixth coordination site for a neutral solvent molecule, in this case acetonitrile. Although dissolution of the dimeric [fac-Re(R-OQN)(CO)3]2 systems 1d−4d in coordinating acetonitrile solvent results in quantitative conversion to the desired solvated complexes 1m− 4m, an effort was made to bypass the moderate-yielding and

2.5371(11) 1.898(5) 1.898(5) 1.919(5) 2.171(3) 2.178(4) 1.361(5) 1.360(5) 0.820 75.72(12) 121.58(4)

Re2 Cl Re2 C222 Re2 C233 Re2 C211 Re2 O27 Re2 N21 C27 O27 C210 F210 O27 H27a N21 Re2 O27

2.5315(11) 1.896(5) 1.900(5) 1.919(5) 2.164(3) 2.169(4) 1.366(5) 1.362(6) 0.820 76.15(13)

a

The hydrogen atom is disordered over two positions, H17 and H27. Its position was calculated with a fixed distance of 0.820 Å.

and Re2−Cl [2.5315(11) Å] bond lengths as well as the Re1− O17 [2.171(3) Å] and Re2−O27 [2.164(3) Ǻ ] bond lengths suggest equal charge at both Re1 and Re2 metal centers. Furthermore, C17−O17 [1.361(5) Å] and C27−O27 [1.366(5) Å] bond lengths and bite angles of 75.72(12)° and 76.15(13)° observed between atoms N11−Re1−O17 and N21−Re2−O27 suggest isoelectronic 5-fluoro-8-oxyquinolate

Scheme 2. Synthesis of the fac-Re(R-OQN)(CO)3(CH3CN) Monomeric Complexes 1m−4m

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Figure 3. ORTEP diagrams of the dimeric 3d·0.5CH3C6H5 and monomeric 3m complexes. The toluene solvent molecule and ligand protons are omitted from the structure of 3d·0.5CH3C6H5 for clarity.

Table 2. Selected Bond Lengths (Å) for 3d·0.5CH3C6H5 and 3m. 3d·0.5CH3C6H5 Re1 C1 Re1 C2 Re1 C3 Re1 N11 Re1 O27 Re1 O17 C1 O1 C2 O2 C3 O3 C17 O17

1.897(12) 1.930(11) 1.911(10) 2.195(7) 2.216(5) 2.158(5) 1.165(11) 1.117(11) 1.139(11) 1.357(9)

3m Re2 C5 Re2 C4 Re2 C6 Re2 N21 Re2 O17 Re2 O27 C4 O4 C5 O5 C6 O6 C27 027

1.891(10) 1.925(10) 1.901(10) 2.168(6) 2.227(5) 2.165(5) 1.130(11) 1.163(10) 1.145(10) 1.374(9)

Re1 C121 Re1 C123 Re1 C122 Re1 N13 Re1 N11 Re1 O17 C121 O121 C122 O122 C123 O123 C17 O17

1.899(3) 1.903(3) 1.914(3) 2.150(2) 2.175(2) 2.1132(18) 1.156(3) 1.149(3) 1.155(3) 1.328(3)

Figure 4. Overlay of 1H NMR spectra for the dimeric 3d and monomeric 3m complexes recorded in CDCl3 and CD3CN, respectively.

made possible by single-crystal X-ray diffraction analysis of the 5,7-dimethylquinolate derivatives from this series, i.e., complexes 3d·0.5CH3C6H5 and 3m (Figure 3; Table 2). The immediate striking feature of 3d·0.5CH3C6H5 is how both Me 2OQN ligands are oriented in a syn configuration presumably due to a favorable π-stacking interaction. A similar configuration was observed previously by Czerwieniec et al. for the unsubstituted OQN dimer; however, 3d·0.5CH3C6H5

ligands at both rhenium centers. The relative orientation of each octahedral unit in the dimer, however, precludes a center of symmetry. This is satisfactorily explained with the bridging chloride adopting a bent geometry [Re1−Cl−Re2 = 121.58(4)°] and an angle of 61.54(6)° between each of the F-OQN ligand planes. Comparison of structural and electronic properties for the dimeric 1d−4d and monomeric 1m−4m structures was also 1836


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appears to show enhanced π-stacking with the angle between both ligand planes being 21.1(2)° compared to 29.5(2)° for the less hindered OQN system.50 3d·0.5CH3C6H5 is clearly asymmetrical and belongs to the C1 point group with both ligand planes not only nonparallel but also in a staggered conformation (Figure SI-2). The dihedral angle of 18.2(2)° observed between the Re1−O27−Re2 and O27−Re2−O17 planes is also representative of the asymmetry in this structure. While the CO bonds of 3d·0.5CH3C6H5 at each Re center (C1−O1 vs C4−O4; C2−O2 vs C6−O6; C3−O3 vs C5−O5) appear to be nonequivalent, in solution phase the CO stretching vibrational modes are conveniently interpreted by assigning a pseudo-C2v point group as discussed in detail below with respect to observed FTIR spectra. Upon solvolysis and formation of the fac-Re(Me2OQN)(CO)3(CH3CN) monomer 3m, the bridging role of the oxyanion is no longer required, which results in a shorter Re1−O17 bond length [2.1132(18) Å] relative to the 3d·0.5CH3C6H5 dimer [Re1−O17, 2.158(5) Å; Re2−O27, 2.165(5) Ǻ ]. The greater Re1−O17 bond order observed in 3m indicates an enhanced π-donating capacity of the oxyanion to the rhenium d(π) manifold, which correlates with our computational analysis discussed below and reinforces the non-innocent nature of the oxyquinolate ligand with the Re(I) tricarbonyl system. Surprisingly this effect is less obvious upon comparison of the CO bond lengths in 3d·0.5CH3C6H5 and 3m. The rhenium centers of 3d·0.5CH3C6H5 and 3m are isoelectronic, in that each metal center is formally exposed to a single anionic charge (two bridging anions in the dimer), which causes little deviation in Re→CO back-donation for both systems. For example, within experimental error, trans to the oxyanion of Me2OQN in 3m the C123−O123 bond length of 1.155(3) Å is not dissimilar to the corresponding C5−O5 [1.163(10) Å] and C3−O3 [1.139(11) Ǻ ] bonds in the 3d·0.5CH3C6H5 dimer. The classical trans effect is here complicated by the fact that all six CO π*-orbitals contribute degenerately to the HOMO orbitals of 1d−4d (Figures 9, SI-5, SI-7, SI-9).

Figure 6. Theoretical IR spectra (DFT) and experimental FTIR spectra of dimeric 4d (blue) and monomeric 4m (red) complexes recorded in CH2Cl2 and CH3CN, respectively.

Figure 7. UV−vis absorption spectra of dimer 3d and monomer 3m, recorded in CH2Cl2 and CH3CN, respectively, with predicted TDDFT transitions (see Table 4).

Figure 5. Cartesian axis (a) and structural representations from an aerial perspective along the z-axis for monomer (b) and dimer (c) complexes. Peripheral ligand structure and dimer axial ligands are removed to clearly display complex symmetries. 1

H NMR Spectra. Apart from the 2-methylquinolate complexes 2d and 2m, which have limited solubility, each complex was characterized satisfactorily by 1H NMR spectroscopy. Spectra for the dimeric 1d−4d systems were recorded in either CD2Cl2 or CDCl3, whereas spectra for the monomeric 1m−4m systems were recorded in coordinating CD3CN solvent. It is noteworthy that dissolution of the dimeric complexes 1d, 3d, and 4d in neat CD3CN results in quantitative conversion to their monomeric analogues. In contrast, upon dissolution of the monomer systems 1m, 3m, and 4m in noncoordinating CDCl3 the complexes mostly revert back to their dimeric structures (Figure SI-3). Figure 4 shows

Figure 8. UV−vis absorption spectra of monomeric complexes 1m− 4m recorded in CH3CN.

an overlay of typical 1H NMR spectra observed for the dimeric 3d and monomeric 3m complexes in CDCl3 and CD3CN, 1837


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in order of decreasing frequency (Table SI-1). While the assumption of a Cs point group may not be entirely accurate, as evident in the crystal structure of 3m, with bond lengths of 2.150(2) and 2.175(2) Å for Re1−N11(Me2OQN) and Re1− N13(CH3CN), respectively, it does hold true in the observed and calculated IR spectra for each complex in the monomeric series 1m−4m (Tables 3 and SI-2). In noncoordinating dichloromethane the dimeric form of these complexes is preserved with three facial CO ligands at each rhenium center, giving rise to multiple ν(CO) absorption bands in a similar range to their monomeric counterparts. FTIR spectra are consistent with pseudo-C2v symmetry (Figure 5c) where multiple ν(CO) absorption bands observed for these dimers are a result of symmetric and asymmetric combinations of both fac-Re(CO)3 moieties as elucidated by DFT analysis (Table SI3). For example, the set of carbonyl stretching vibrations observed at 2039 and 2022 cm−1 for 4d consists of symmetric and antisymmetric coupling of the A(1)′ stretching band of each fac-Re(CO)3 center, while the overlapping 1903−1935 cm−1 absorptions are a result of coupling between the A(2)′ and A″ vibrational stretching modes (Figure 6, Tables 3 and SI3). Thus, both experimental and calculated IR spectra of the dimeric complexes allude to the presence of equivalent electronic environments at both rhenium centers in the dimer series. While it is difficult to directly compare ν(CO) absorption frequencies of dimer versus monomer systems, due to the different origin of their vibrational stretching modes, the influence of ligand substituents in the independent monomer and dimer series certainly warrants discussion. In the monomer series a minimal shift is observed in the highfrequency A(1)′ mode between the unsubstituted 1m (2023 cm−1) and fluorinated 4m (2024 cm−1) systems, where the πdonating ability of the fluorine substituent may be counteracting its inductive withdrawing influence. In contrast, the Me2OQN ligand, which possesses only an inductive donating property, results in a shift to slightly lower frequency for the same A(1)′ mode of 3m at 2020 cm−1 ascribed to enhanced Re→CO π-back-donation. A similar trend is also observed for the A(2)′ and A″ modes for these systems. Complex 2m, with a single methyl substituent ortho to the pyridyl N atom of the MeOQN ligand, falls intermediate between 1m and 3m, with an A(1)′ mode observed at 2022 cm−1. In the dimer series we will focus on the symmetric/antisymmetric combination of A(1)′ modes observed in the high-frequency region (2010− 2040 cm−1), as the lower frequency absorptions (1890−1940 cm−1) are unresolved for all complexes. Indeed, a similar trend is observed to that for the monomer series, with the Me2OQN ligand in 3d imparting a shift to lower frequency (2018 and

Figure 9. Selection of molecular orbitals for 3d and 3m.

respectively. Only a single set of peaks is observed for 3d in CDCl3, implying that, at least on the NMR time scale, both Re(I) centers are electronically equivalent. This result is in contrast to the solid-state structure of 3d·0.5CH 3 C 6 H 5 observed by X-ray diffraction, however, and agrees well with the pseudo-C2v symmetry observed in the FTIR spectra discussed below. The most notable observation in comparing 1 H NMR spectra for 3d and 3m complexes is the contrasting chemical shifts of Ha, Hb, and Hc protons on the pyridyl component of the Me2OQN ligand (Figure 4). Indeed, a closer look at the crystal structure shows that the pyridyl components of both Me2OQN ligands in the dimeric 3d system are arranged in a staggered π−π stacking conformation (Figure SI-2). A similar upfield shift has been previously reported by Thummel and Meyer et al. for a series of π−π-stacked Cu(I) biquinoline systems.60 Infrared and Electronic Absorption Spectroscopy. Using FTIR spectroscopy, characteristic CO ligand vibrational stretching modes are observed in the range 1800−2100 cm−1 for the monomeric and dimeric systems, which are highly dependent upon complex symmetry. This is most convenient in that the monomeric and dimeric complexes can be clearly distinguished by their characteristic IR absorption profiles. The monomeric fac-Re(R-OQN)(CO)3(CH3CN) class of complexes 1m−4m is best described by a pseudo-Cs point group symmetry with the oxyanion of the R-OQN ligand being electronically distinct from the isoelectronic N atoms of the acetonitrile and R-OQN ligands. Thus, only the identity operation (E) and a single reflection (σyz) symmetry operation are present for the monomeric systems (Figure 5b). Using the tabular method to generate a reducible representation the Cs point group symmetry is easily correlated with observed FTIR spectra assigning the vibrational modes as A(1)′, A(2)′, and A″

Table 3. UV−vis and FTIR Absorption Data for Dimeric 1d−4da and Monomeric 1m−4mb Complexes. complex

UV−vis

FTIR

IR calculated

λmax (nm); (ε × 103 M−1 cm−1)

ν(CO) (cm−1)

ν(CO) (cm−1)

1d, [fac-Re(OQN)(CO)3]2 1m, fac-Re(OQN)(CO)3(CH3CN) 2d, [fac-Re(MeOQN)(CO)3]2 2m, fac-Re(MeOQN)(CO)3(CH3CN) 3d, [fac-Re(Me2OQN)(CO)3]2 3m, fac-Re(Me2OQN)(CO)3(CH3CN) 4d, [fac-Re(FOQN)(CO)3]2 4m, fac-Re(FOQN)(CO)3(CH3CN) a

369 427 360 415 371 448 382 441

(8.7) (5.1) (8.2) (4.7) (8.3) (4.0) (9.6) (2.8)

1903 (sh), 1908, 1933, 2021, 2037 1897, 1917, 2023 1905 (br), 1930, 2021, 2036 1894, 1915, 2022 1893, 1906, 1929, 2018, 2034 1895, 1914, 2020 1903, 1912, 1935, 2022, 2039 1898, 1918, 2024

1959.5, 1925.2, 1954.0, 1952.1, 1953.3, 1949.8, 1961.1, 1953.5,

1959.6, 1972.0, 1954.1, 1970.2, 1953.8, 1969.5, 1961.1, 1973.1,

1970.9, 2078.8 1960.1, 2078.6 1967.6, 2076.7 1973.0, 2079.4

1984.8, 2080.4, 2094.7 1972.5, 2077.7, 2091.2 1980.3, 2077.4, 2091.4 1986.8, 2081.6, 2096.0

Recorded in CH2Cl2. bRecorded in CH3CN. 1838


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2034 cm−1) relative to 1d (2021 and 2037 cm−1). The highfrequency absorptions of 4d (2022 and 2039 cm−1) are shifted to only slightly higher frequency in comparison to 1d, again suggesting that its inductive withdrawing influence is offset by the π-donating ability of the fluorine substituent. Electronic communication between the two rhenium centers appears to be comparable across the series 1d−4d, with each complex displaying a difference between its symmetric/antisymmetric A(1)′ combinations within the very narrow range of Δν = 15− 17 cm−1. Contrasting spectra are also observed for the dimeric and monomeric systems via UV−vis absorption spectroscopy.50 The dimeric systems are pale yellow in the solid state and absorb only at the high-energy end of the visible region when dissolved in noncoordinating dichloromethane (Figure SI-4). The monomeric systems are a brownish-orange color in the solid state and accordingly show a substantial red shift of their UV−vis spectra in acetonitrile (∼60 nm) relative to the dimeric systems (Figures 7 and 8; Table 3). The visible transitions for complexes 1m−4m originate from the HOMO, which has significant contributions from both the rhenium d-orbital manifold and the lone-pair π-donating frontier orbital of the oxyanionic R-OQN ligands, as outlined in the computational analysis below. Computational and Electrochemical Studies. A theoretical investigation of the dimer 1d−4d and monomer 1m− 4m series has been conducted to ascertain their root difference in electronic properties. Close inspection of the electron density distribution for the HOMO orbitals of 1d−4d suggests an equal contribution from both Re(R-OQN) moieties of these dimeric systems. For example, in Figure 9 significant mixing of rhenium d(π)-orbitals with the Me2OQN ligand π-system is evident for the HOMO level of 3d, justifying the ligand’s description in these electronic states as being non-innocent in character. The lowest energy absorption for 1d−4d observed experimentally in the narrow range 369−382 nm in dichloromethane is assigned to a HOMO−LUMO electronic transition and is primarily (metal−ligand)-to-ligand charge-transfer (MLLCT) in character, as predicted by TD-DFT (Tables 4, SI-4, SI-

empty LUMO and LUMO+1 orbitals (Tables 4, SI-4, SI-5, SI6). In contrast, fewer electronic transitions are observed for the monomeric fac-Re(R-OQN)(CO)3(CH3CN) complexes 1m− 4m. Coordination of acetonitrile at the rhenium(I) center in lieu of a bridging R-OQN ligand increases the Re−O bond order significantly due to enhanced π-bonding as discussed earlier with respect to the X-ray diffraction data. Ultimately the oxyanion lone-pair of electrons is now available solely for πdonation to a single Re(I) center. This effectively destabilizes the HOMO orbital, narrowing the HOMO−LUMO band gap, giving rise to a lower energy visible transition for the monomer series occurring in the range 414−448 nm. This assessment is further corroborated by electrochemical analysis, where an impressive cathodic shift of 0.58 V is observed upon comparison of 3d and 3m (Figure 10) and similar shifts of

Figure 10. Cyclic voltammograms of 3d (top) and 3m (bottom) recorded at 50 mV s−1 and 1 mM concentration in 0.1 M Bu4PF6 supporting electrolyte with 1,2-dichloroethane and acetonitrile, respectively.

0.52 V for the unsubstituted and fluorinated analogues (Table 5), although it must be acknowledged that solvent polarity may also contribute albeit marginally to this observation. While oxidation and reduction of the dimer series is completely irreversible, the monomeric series shows quasi-reversible behavior upon one-electron oxidation with recovery of the cathodic peak at scan rates > 100 mV s−1 (Figure 11, SI-10;

Table 4. Character Table of Selected Electronic Transitions for 3d and 3m Calculated by TD-DFT

3d

3m

electronic transition (nm)

occupied orbitals

empty orbitals

contribution (%)

oscillator strength ( f)

349.24 355.72 379.99 389.97 404.81 410.88 307.77 319.16 326.23 468.90

H-3 H-3 H-1 H-1 H H H-3 H H-2 H

L+1 L L+1 L L+1 L L L+3 L L

78 85 97 94 94 98 94 77 85 98

0.075 0.019 0.030 0.021 0.055 0.053 0.049 0.037 0.027 0.080

Table 5. Electrochemical Data for Dimeric 1d−4da and Monomeric 1m−4mb Complexes. E1/2 (V vs Fc+/0) oxidation 1d, [fac-Re(OQN)(CO)3]2 1m, fac-Re(OQN)(CO)3(CH3CN) 2d, [fac-Re(MeOQN)(CO)3]2 2m, fac-Re(MeOQN)(CO)3(CH3CN) 3d, [fac-Re(Me2OQN)(CO)3]2 3m, fac-Re(Me2OQN)(CO)3(CH3CN) 4d, [fac-Re(FOQN)(CO)3]2 4m, fac-Re(FOQN)(CO)3(CH3CN)

5, SI-6). Significant Re−CO metal−ligand mixing is also observed in the HOMO−2 and HOMO−3 levels due to the strong π-back-donation as described by the Dewar−Chatt− Duncanson model.61 Multiple underlying transitions are observed at higher energy in the UV region of the spectra for 1d−4d due to a series of overlapping electronic transitions involving the filled HOMO, HOMO−1, and HOMO−3 and

+1.02c +0.50d +1.02c +0.53c +0.98c +0.40d +1.17c +0.55d

reduction −2.07c −2.19c −2.21c −2.17c −2.14c −2.22c −1.90c −2.07c

−2.19c −2.49c −2.46c −2.51c −2.51c −2.39c −2.30c

a Recorded in 1,2-dichloroethane with 0.1 M Bu4PF6 supporting electrolyte. bRecorded in acetonitrile with 0.1 M Bu4PF6 supporting electrolyte. cIrreversible. dQuasi-reversible.

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Me2OQN derivative 3m in particular give just cause to expect unique excited-state properties for this system relative to its traditional bpy analogue. An investigation of these systems toward photocatalytic CO2 reduction is currently under way.

■

ASSOCIATED CONTENT

S Supporting Information *

Additional spectral, electrochemical, computational, X-ray diffraction, and Cartesian coordinate data. Complete ref 54. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected].

Figure 11. Scan rate dependence for the one-electron oxidation of 3m. The inset shows a reversible Faradaic response recorded at a scan rate of 1 V s−1.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS J.R. thanks UMass Boston for financial support. The authors would like to acknowledge Ken White and Noel Blackburn from the Office of Educational Programs at BNL for their support through the U.S. Department of Energy (DOE) Faculty and Student Team (FaST) program. D.C.G. is supported by the DOE, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, under contract #DE-AC02-98CH10886. B.L.F. and M.K.T. are supported by the National Science Council of Taiwan (Grants 99-2113-M-003-007-MY2 and 101-2113-M-003-003-MY2) and are grateful to the National Center for High-Performance Computing for computer time and facilities.

diffusion coefficient D ≈ 5.6 × 10−6 cm2 s−1). To clarify, oneelectron reduction of the monomer series remains irreversible even at enhanced scan rates. Again, the HOMO orbital of the monomer series consists of significant Re(I) d(π)−p(π) ROQN mixing, with the lowest energy HOMO−LUMO visible absorption assigned to an ML-LCT electronic transition (Table 4). The strong visible absorption observed for 1m−4m is encouraging with respect to our future goals of employing these complexes in a photocatalytic system for CO2 reduction and represents a significant shift relative to the 2,2-bipyridyl counterpart [fac-Re(bpy)(CO)3(CH3CN)]+ (λmax = 330 nm, ε = 3.4 × 103 M−1 cm−1).62 The Me2OQN complex 3m displays the lowest energy λmax at 448 nm (ε = 4.0 × 103 M−1 cm−1), no doubt due to the stronger donating character of this ligand, correlating to the most negative oxidation potential and reduced band gap (ΔEHOMO−LUMO = 2.62 V) of the series. The 5-fluoro derivative 4m (λmax = 441 nm, ε = 2.8 × 103 M−1 cm−1) is also red-shifted with respect to the unsubstituted complex 1m (λmax = 427 nm, ε = 5.1 × 103 M−1 cm−1); however this observation is best explained by the anodic shift in its reduction potential (Epc = −2.07 V) due to the more electron-deficient π*-LUMO of the FOQN ligand.

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REFERENCES

(1) Siegbahn, P. E. M.; Blomberg, M. R. A. Philos. Trans. R. Soc., A 2005, 363, 847−860. (2) Stubbe, J.; van der Donk, W. A. Chem. Rev. 1998, 98, 705−762. (3) Hohloch, S.; Braunstein, P.; Sarkar, B. Eur. J. Inorg. Chem. 2012, 546−553. (4) Bheemaraju, A.; Beattie, J. W.; Lord, R. L.; Martin, P. D.; Groysman, S. Chem. Commun. 2012, 48, 9595−9597. (5) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.; Vonzelewsky, A. Coord. Chem. Rev. 1988, 84, 85−277. (6) Jorgensen, C. K. Coord. Chem. Rev. 1966, 164−178. (7) Allgeier, A. M.; Mirkin, C. A. Angew. Chem., Int. Ed. 1998, 37, 895−908. (8) Wada, T.; Tsuge, K.; Tanaka, K. Chem. Lett. 2000, 910−911. (9) Chaudhuri, P.; Wieghardt, K. Prog. Inorg. Chem. 2001, 50, 151− 216. (10) Hino, T.; Wada, T.; Fujihara, T.; Tanaka, K. Chem. Lett. 2004, 33, 1596−1597. (11) Abakumov, G. A.; Poddel’sky, A. I.; Grunova, E. V.; Cherkasov, V. K.; Fukin, G. K.; Kurskii, Y. A.; Abakumova, L. G. Angew. Chem., Int. Ed. 2005, 44, 2767−2771. (12) Haneline, M. R.; Heyduk, A. F. J. Am. Chem. Soc. 2006, 128, 8410−8411. (13) Miyazato, Y.; Wada, T.; Tanaka, K. Bull. Chem. Soc. Jpn. 2006, 79, 745−747. (14) Bouwkamp, M. W.; Bowman, A. C.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc. 2006, 128, 13340−13341. (15) Miyazato, Y.; Wada, T.; Muckerman, J. T.; Fujita, E.; Tanaka, K. Angew. Chem., Int. Ed. 2007, 46, 5728−5730. (16) Blackmore, K. J.; Sly, M. B.; Haneline, M. R.; Ziller, J. W.; Heyduk, A. F. Inorg. Chem. 2008, 47, 10522−10532. (17) Muckerman, J. T.; Polyansky, D. E.; Wada, T.; Tanaka, K.; Fujita, E. Inorg. Chem. 2008, 47, 1787−1802.

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CONCLUSIONS An optimized one-pot synthesis for the 1m−4m series of monomeric fac-Re(R-OQN)(CO)3(CH3CN) complexes has been established, precluding the need for preparation of their 1d−4d dimeric [fac-Re(R-OQN)(CO)3]2 precursors. The characteristic CO ligand vibrational stretching modes of the fac-rhenium(I) tricarbonyl moieties have been assigned and used as a powerful tool in discerning between monomeric and dimeric systems. Strong changes observed in the spectral responses (UV−vis, FTIR, 1H NMR) and electrochemical redox potentials have been explained in terms of the greater πelectron-donating capacity of the R-OQN ligands in the monomeric systems relative to the oxyanion-bridged dimers. These electronic effects, and the associated structural properties, of both dimeric and monomeric systems have been correlated with the aid of single-crystal X-ray diffraction and DFT studies. The dramatic non-innocent ligand effect of the ROQN ligands on the absorption properties of the monomeric fac-rhenium(I) tricarbonyl complexes has been interpreted with a combination of TD-DFT and electrochemical analysis. The low energy and strong absorption of the electron-rich 1840


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(18) Ringenberg, M. R.; Kokatam, S. L.; Heiden, Z. M.; Rauchfuss, T. B. J. Am. Chem. Soc. 2008, 130, 788−789. (19) Blackmore, K. J.; Lal, N.; Ziller, J. W.; Heyduk, A. F. J. Am. Chem. Soc. 2008, 130, 2728−2729. (20) Lyaskovskyy, V.; de Bruin, B. ACS Catal. 2012, 2, 270−279. (21) Pierpont, C. G.; Buchanan, R. M. Coord. Chem. Rev. 1981, 38, 45−87. (22) Pierpont, C. G. Coord. Chem. Rev. 2001, 219, 415−433. (23) Zanello, P.; Corsini, M. Coord. Chem. Rev. 2006, 250, 2000− 2022. (24) Deibel, N.; Schweinfurth, D.; Hohloch, S.; Fiedler, J.; Sarkar, B. Chem. Commun. 2012, 48, 2388−2390. (25) Sugimoto, H.; Tsukube, H. Chem. Soc. Rev. 2008, 37, 2609− 2619. (26) Fekl, U.; Sarkar, B.; Kaim, W.; Zimmer-De Iuliis, M.; Nguyen, N. Inorg. Chem. 2011, 50, 8685−8687. (27) McCleverty, J. A. Chem. Rev. 2004, 104, 403−418. (28) Siemeling, U.; Färber, C.; Leibold, M.; Bruhn, C.; Mücke, P.; Winter, R. F.; Sarkar, B.; von Hopffgarten, M.; Frenking, G. Eur. J. Inorg. Chem. 2009, 2009, 4607−4612. (29) Findlay, N. J.; Park, S. R.; Schoenebeck, F.; Cahard, E.; Zhou, S.z.; Berlouis, L. E. A.; Spicer, M. D.; Tuttle, T.; Murphy, J. A. J. Am. Chem. Soc. 2010, 132, 15462−15464. (30) Siemeling, U. Eur. J. Inorg. Chem. 2012, 3523−3536. (31) Deibel, N.; Schweinfurth, D.; Hohloch, S.; Sarkar, B. Inorg. Chim. Acta 2012, 380, 269−273. (32) Day, G. S.; Pan, B. F.; Kellenberger, D. L.; Foxman, B. M.; Thomas, C. M. Chem. Commun. 2011, 47, 3634−3636. (33) Pan, B. F.; Xu, Z. Q.; Bezpalko, M. W.; Foxman, B. M.; Thomas, C. M. Inorg. Chem. 2012, 51, 4170−4179. (34) Paretzki, A.; Das, H. S.; Weisser, F.; Scherer, T.; Bubrin, D.; Fiedler, J.; Nycz, J. E.; Sarkar, B. Eur. J. Inorg. Chem. 2011, 2413−2421. (35) Kaim, W. Inorg. Chem. 2011, 50, 9752−9765. (36) Kaim, W. Eur. J. Inorg. Chem. 2012, 343−348. (37) Zhao, H. C.; Harney, J. P.; Huang, Y.-T.; Yum, J.-H.; Nazeeruddin, M. K.; Grätzel, M.; Tsai, M.-K.; Rochford, J. Inorg. Chem. 2011, 51, 1−3. (38) Hawecker, J.; Lehn, J. M.; Ziessel, R. J. Chem. Soc., Chem. Commun. 1984, 328−330. (39) Hawecker, J.; Lehn, J. M.; Ziessel, R. Helv. Chim. Acta 1986, 69, 1990−2012. (40) Keene, F. R. Electrochemical and Electrocatalytic Reactions of Carbon Dioxide; Sullivan, B. P., Krist, K., , Guard, H. E., Eds.; Elsevier, 1993; pp 1−18. (41) Arakawa, H.; Areasta, M.; Armor, J. N.; Barteau, M. A.; Beckman, E. J.; Bell, A. T.; Bertcaw, J. E.; Creutz, C.; Dinjus, E.; Dixon, D. A.; Domen, K.; DuBois, D. L.; Eckert, J.; Fujita, E.; Gibson, D. H.; Goddart, W. A.; Goodman, D. W.; Keller, J.; Kubas, G. J.; Kung, H. H.; Lyons, J. E.; Manzer, L. E.; Marks, T. J.; Morokuma, K.; Nicholas, K. M.; Periana, R.; Que, L.; Rostrup-Nielsen, J. R.; Sachtler, W. M. H.; Schmidt, L. D.; Sen, A.; Somorjai, J. A.; Stair, P. C.; Stults, B. R.; Tumas, W. Chem. Rev. 2001, 101, 953−996. (42) Fujita, E.; Brunschwig, B. S. Catalysis, Heterogeneous Systems, Gas Phase Systems, Electron Transfer in Chemistry; Balzani, V., Ed.; WileyVCH, 2001; Vol. 4, pp 88−126. (43) Morris, A. J.; Meyer, G. J.; Fujita, E. Acc. Chem. Res. 2009, 42, 1983−1994. (44) Benson, E. E.; Kubiak, C. P.; Sathrum, A. J.; Smieja, J. M. Chem. Soc. Rev. 2009, 38, 89−99. (45) Doherty, M. D.; Grills, D. C.; Muckerman, J. T.; Polyansky, D. E.; Fujita, E. Coord. Chem. Rev. 2010, 254, 2472−2482. (46) Takeda, H.; Ishitani, O. Coord. Chem. Rev. 2010, 254, 346−354. (47) Mikkelsen, M.; Jorgensen, M.; Krebs, F. C. Energy Environ. Sci. 2010, 3, 43−81. (48) Grills, D. C.; Fujita, E. J. Phys. Chem. Lett. 2010, 1, 2709−2718. (49) Kunkely, H.; Vogler, A. Inorg. Chem. Commun. 1998, 1, 398− 401. (50) Czerwieniec, R.; Kapturkiewicz, A.; Anulewicz-Ostrowska, R.; Nowacki, J. J. Chem. Soc., Dalton. Trans. 2001, 2756−2761.

(51) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. Organometallics 2010, 29, 2176−2179. (52) Sheldrick, G. M. SHELXL, 5; Siemens Analytical Instruments Inc.: Madison, WI, 1994. (53) SADABS Version 2007/2; Sheldrick, Bruker AXS Inc.: 2007. (54) Frisch M. J.; et al. Gaussian 09, Revision A.1; Gaussian Inc.: Wallingford, CT, 2009. (55) Roy, L. E.; Hay, P. J.; Martin, R. L. J. Chem. Theory Comput. 2008, 4, 1029−1031. (56) Harihara, P.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213−222. (57) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.; Defrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654−3665. (58) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105, 2999−3093. (59) Scalmani, G.; Frisch, M. J.; Mennucci, B.; Tomasi, J.; Cammi, R.; Barone, V. J. Chem. Phys. 2006, 124, 94107. (60) Riesgo, E. C.; Hu, Y. Z.; Bouvier, F.; Thummel, R. P.; Scaltrito, D. V.; Meyer, G. J. Inorg. Chem. 2001, 40, 3413−3422. (61) Frenking, G.; Pidun, U. J. Chem. Soc., Dalton. Trans. 1997, 1653−1662. (62) Johnson, F. P. A.; George, M. W.; Hartl, F.; Turner, J. J. Organometallics 1996, 15, 3374−3387.

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Investigation of Monomeric versus Dimeric fac-Rhenium (I) Tricarbonyl

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