Article pubs.acs.org/IC
Thiophene-Fused Nickel Dithiolenes: A Synthetic Scaffold for Highly Delocalized π‑Electron Systems Chad M. Amb,† Christopher L. Heth,† Sean J. Evenson,† Konstantin I. Pokhodnya,‡ and Seth C. Rasmussen*,† †
Department of Chemistry and Biochemistry, North Dakota State University, Department 2735, P.O. Box 6050, Fargo, North Dakota 58108, United States ‡ Center for Nanoscale Science and Engineering, North Dakota State University, Fargo, North Dakota 58102, United States S Supporting Information *
ABSTRACT: A series of thiophene-fused nickel dithiolene complexes have been prepared via synthetic methods which allow the addition of peripheral aryl groups to the fused thiophene of the dithiolene ligand, thus providing access to a range of structural and electronic modifications to the dithiolene core. X-ray structural studies of the anionic complexes show that the peripheral aryl rings lie in near-perfect coplanarity to the dithiolene core and can form π-stacked columns with N-methylpyridinium cations. Density functional theory calculations show significant delocalization of the frontier orbital electron density into the peripheral aryl rings. The complexes exhibit tunable, intense near-IR (NIR) absorption in the range of 1076−1160 nm with molar absorptivity as high as 25100 M−1 cm−1 in solution. The electronic tunability as well as the desirable solid-state packing arrangements of these systems suggests significant potential as NIR-absorbing materials for optoelectronic applications.
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INTRODUCTION The electronic and magnetic properties of metal dithiolene complexes have generated significant interest since their initial reports in 1962−1963,1−4 and as such they have been used in a wide variety of applications, including conducting and magnetic materials,5−11 dyes and photocatalysts,5,12,13 and nonlinearoptical materials.5,14,15 Metal dithiolene complexes are often ideal for the above-cited applications because the unique electronic structure and bulk packing of these complexes have resulted in extraordinary material properties such as superconductivity and ferromagnetism.5−8 In order to improve the desired properties in new materials, synthetic modification of the dithiolene ligand can be employed to alter the electronic structure of the complexes, as well as modify the solid-state packing arrangements.7 One approach to modifying the electronic properties and solid-state packing of metal dithiolene complexes has been the fusion of aromatic rings to the dithiolene core. Such ring fusion increases molecule planarity and enhances orbital overlap, thus maximizing electron delocalization into the organic ligands. Many fused-ring dithiolene systems have been studied, including the fusion of benzene,16−20 functionalized benzene,19−29 thiophene,10,11,30−36 pyridine,37 quinoxaline,31h,38 and other heterocyclic systems.39−41 The incorporation of such fused-ring systems allows synthetic modification of the resulting materials via substituents and heteroatoms on the fused-ring units, allowing a great deal of diversity in the resulting dithiolene systems and the potential to finely tune © XXXX American Chemical Society
both the electronic structures and solid-state arrangements. In addition, fused benzene analogues containing additional disulfide pairs have also allowed the generation of extended one- and two-dimensional dithiolene-based coordination polymers.25,26 With the goal of producing potential magnetic and conducting/semiconducting materials, thiophene-fused metal dithiolenes are of particular interest. Because the molecular packing in the crystal is determined by the total balance of many weak intermolecular forces (hydrogen bonding, van der Waals, π−π interactions, and S···S/M···S interactions),7,8 additional thiophene content would be expected to increase such intermolecular interactions and provide more significant overlap of frontier orbitals, which could result in enhanced electrical conductivity or higher magnetic transition temperatures. In addition, such complexes could provide potential precursors to metal-dithiolene-containing conjugated polymers.9−11,34,42 In order to maintain a linear structure and to maximize conjugation along the molecular backbone, the known metal 2,3-thiophenedithiolene10,11,30−32 scaffold (Figure 1) was chosen as the initial core, from which the addition of aryl groups to the exterior thiophene α positions would produce complexes with more extended π systems. Initial success in the production of a thiophene-extended nickel thiophenedithiolene Received: June 24, 2016
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DOI: 10.1021/acs.inorgchem.6b01513 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
measurements were performed using powder samples (15−20 mg) loaded in gel-cap holders. The magnetization temperature dependence was obtained by cooling in zero field, and then data were collected upon warming in a 5 kOe external magnetic field using a Quantum Design Physical Properties Measurement System with ACMS options for measurement of the magnetization and alternating-current susceptibility as a function of the applied field and temperature, as previously described.45 The data were corrected for diamagnetic contributions using Pascal constants and a possible nickel(I) temperature-independent paramagnetism of 2.5 × 10−4 emu mol−1. 5-Bromothieno[2,3-d]-1,3-dithiol-2-one (2). Solid 1-bromo2,5-pyrrolidinedione (NBS; 1.73 g, 9.60 mmol) was slowly added to 1 (1.41 g, 8.00 mmol) in N,N-dimethylformamide (DMF; 200 mL). The mixture was stirred for 6 h and then poured onto 400 g of ice. After the ice melted, the solid residue was recovered by filtration and washed well with H2O. The solid was dissolved in CHCl3, dried with MgSO4, and evaporated to give a solid, which was recrystallized from hexane to give 1.97 g (96%) of white needles. Mp: 138.8−140.2 °C. 1 H NMR: δ 7.08 (s, 1H). 13C NMR: δ 192.8, 127.0, 124.2, 123.6, 113.1. General Procedure for the Synthesis of Acetate-Protected Ligands 5a−5c. The corresponding dibromides 4a−4c (5.0 mmol) were charged in a 250 mL, three-neck, round-bottomed flask, and 80 mL of Et2O was added. The resulting solution was cooled to −78 °C, and some material precipitated. tert-Butyllithium (tBuLi; 3.2 mL, 1.7 M in pentane) was then added dropwise, and the suspension was stirred for 30 min to 1 h, resulting in a clear solution. Sulfur (0.16 g, 5.0 mmol) was then added, and the mixture was stirred for 1 h at −78 °C, during which time a precipitate formed. The mixture was then warmed to room temperature, causing the solid to dissolve. The resulting homogeneous solution was then transferred via cannula to a cooled (−78 °C) solution of tBuLi (5.0 mL, 2.5 M in hexanes) in 150 mL of Et2O. This combined mixture was stirred for 2 h. Sulfur powder (0.40 g, 12.5 mmol) was then added, and the solution was stirred for 1 h and warmed to room temperature. The mixture was again cooled to −78 °C, and acetyl chloride (10 mL, 0.14 mol) was added. This solution was warmed to room temperature, poured into saturated aqueous NaHCO3 (150 mL), and extracted with Et2O (3 × 150 mL). The combined organic layers were then dried over MgSO4 and concentrated. The residue was then purified as detailed below. S,S′-2,2′-Bithiophene-4,5-diyl Diethanethioate (5a). Compound 5a was purified via silica gel chromatography (2% EtOAc in hexanes) and then recrystallized from hexanes to give a yellow solid (32% yield). Mp: 63.9−64.9 °C. 1H NMR: δ 7.28 (dd, J = 1.2 and 5.2 Hz, 1H), 7.24 (s, 1H), 7.21 (dd, J = 1.2 and 3.6 Hz, 1H), 7.03 (dd, J = 3.6 and 5.2 Hz, 1H), 2.43 (s, 3H), 2.42 (s, 3H). 13C NMR: δ 192.6, 192.5, 142.4, 135.9, 131.8, 128.5, 128.23, 128.19, 126.1, 125.1, 30.3, 29.9. S,S′-3′-Hexyloxy-2,2′-bithiophene-4,5-diyl Diethanethioate (5b). Compound 5b was purified via silica gel chromatography (hexanes) to give a yellow oil (24% yield). Recrystallization from hexanes gave a low-melting yellow solid. Mp: 33.6−34.8 °C. 1H NMR (500 MHz): δ 6.40 (s, 1H), 7.31 (d, J = 5.5 Hz, 1H), 6.83 (d, J = 5.5 Hz, 1H), 4.11 (t, J = 6.5 Hz, 2H), 2.41 (s, 3H), 2.40 (s, 3H), 1.85 (p, J = 6.5 Hz, 2H), 1.50 (p, J = 6.5 hz, 2H), 1.35 (m, 4H), 0.91 (t, J = 7.0 Hz, 3H). 13C NMR (500 MHz): δ 193.8, 193.1, 154.3, 141.0, 131.3, 126.8, 123.4, 117.2, 114.2, 72.3, 31.7, 30.4, 29.8(3), 29.7(6), 25.9, 23.0, 14.3. S,S′-2-Phenylthiophene-4,5-diyl Diethanethioate (5c). Compound 5c was purified by silica gel chromatography (2.5% EtOAc in hexanes) and then recrystallized from hexanes to give an off-white solid (51% yield). Mp: 71.4−71.9 °C. 1H NMR: δ 7.58 (m, 2H), 7.40 (m, 2H), 7.39(8) (s, 1H), 7.33 (m, 1H), 2.44 (s, 3H), 2.43 (s, 3H). 13 C NMR: δ 192.9, 192.8, 149.4, 133.3, 132.2, 129.3, 128.9, 128.8, 128.5, 126.2, 30.4, 30.0. S,S′-5′-Bromo-2,2′-bithiophene-4,5-diyl Diethanethioate (5d). Solid NBS (0.28 g, 1.8 mmol) was added to a solution of 2a (0.50 g, 1.6 mmol) in degassed acetonitrile (MeCN; 50 mL). The mixture was stirred overnight in the dark, poured into saturated aqueous NaHCO3 (200 mL), and extracted with Et2O (3 × 150 mL). The combined organic layers were then dried over MgSO4, concentrated, and recrystallized from hexanes to give a yellow solid (78% yield). Mp:
Figure 1. Parent and aryl-extended nickel 2,3-thiophenedithiolene complexes.
complex (Figure 1) was previously reported,35 and this current report now presents a general approach to the production of such aryl-extended nickel thiophenedithiolene complexes as a potential new class of molecular materials. Such materials could be viewed as hybrid systems that combine the characteristics of metal dithiolenes and the well-studied oligothiophenes43 because they exhibit the planar, delocalized structures of the oligothiophenes while retaining the near-IR (NIR) absorption and magnetic properties common for metal dithiolenes, as well as the semiconducting properties of both classes of materials. Although three previous reports have produced alkyl-capped metal 2,3-thiophenedithiolenes31m,32,33 (where alkyl = methyl or tert-butyl), our previous communication35b and the current report represent the only known examples of aryl-extended metal 2,3-thiophenedithiolenes (Figure 1) to date. The synthetic methods reported herein bypass the common aryl1,3-dithiole-2-thione precursors, which are not always amenable to the production of more reactive targets and allow the generation of aryldithiolenes directly from o-dihaloaromatics. In addition, the applied methods allow the relatively simple incorporation of a variety of external aryl groups, thus providing access to a range of structural and electronic modifications to the dithiolene core in order to tune the properties of the resulting electronic materials. Full characterization of this new family of aryl-extended nickel thiophenedithiolene complexes is also reported, including their optical, electronic, magnetic, and solid-state properties.
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EXPERIMENTAL SECTION
Unless otherwise specified, all reactions were carried out under a nitrogen atmosphere with reagent-grade materials. Tetrahydrofuran (THF) and diethyl ether (Et2O) were distilled from sodium/ benzophenone prior to use. Methanol (MeOH) was degassed by freeze−pump−thaw cycles and then backfilled with nitrogen gas. Thieno[2,3-d]-1,3-dithinol-2-one (1),31c 5-aryl-2,3-dibromothiophenes 4a−4c,44 and Bu4N[NiTDT]31b were synthesized by literature procedures. Chromatographic separations were performed using standard column methods with silica gel (230−400 mesh). 1H and 13 C NMR spectra were measured on a 400 MHz Varian spectrometer in CDCl3 unless otherwise stated. All NMR data were referenced to residual solvent peaks, and the peak multiplicities were reported as follows: s = singlet, d = doublet, t = triplet, p = pentet, dd = doublet of doublets, and m = multiplet. High-resolution mass spectrometry (HRMS) was obtained using electrospray ionization and quantitative time-of-flight, and elemental analysis was performed by Atlantic Microlab, Inc. Electrochemical measurements were performed on a Bioanalytical Systems BAS 100B/W instrument in various solvents using a platinum disk working electrode, a platinum wire counter electrode, and a silver wire quasi-reference electrode calibrated to the ferrocene/ferrocenium redox couple. UV−vis−NIR spectroscopy measurements were taken on a dual-beam-scanning Cary 500 UV− vis−NIR spectrophotometer in matched 1 cm quartz cuvettes. Pressed pellets for conductivity measurements were prepared by using a cylindrical 1.1-cm-diameter dye and applying 15000 lb. of pressure with a hydraulic press for 5 min. Conductivity values were measured using a four-point probe with 0.1375 cm probe spacing. Magnetic B
DOI: 10.1021/acs.inorgchem.6b01513 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry 87.1−89.1 °C. 1H NMR: δ 7.17 (s, 1H), 6.99 (d, J = 4.0 Hz, 1H), 6.95 (d, J = 4.0 Hz, 1H), 2.44 (s, 3H), 2.42 (s, 3H). 13C NMR: δ 192.5(2), 192.5(0), 141.3, 137.5, 131.9, 131.2, 128.9, 128.8, 125.4, 113.1, 30.5, 30.1. HRMS. Calcd for C12H9BrNaO2S4 m/z 414.8561. Found: m/z 414.8566 ([M + Na]+). S,S′-5′-Acetyl-2,2′-bithiophene-4,5-diyl Diethanethioate (5e). A 100 mL Schlenk flask was charged with AlCl3 (0.64 g, 4.8 mmol), and dry CH2Cl2 (50 mL) was added. Compound 2a (0.50 g, 1.6 mmol) was then added as a solid, followed by acetyl chloride (0.45 mL, 6.4 mmol), and the mixture was stirred for 2 h at room temperature. This was then poured into 100 mL of saturated aqueous NaHCO3 and extracted with Et2O (3 × 150 mL), and the combined organic fractions were dried over MgSO4. The solvent was removed, and the solid residue was recrystallized from a hexanes/EtOAc mixture to give a yellow crystalline material (75% yield). Mp: 138.8−140.2 °C. 1H NMR: δ 7.59 (d, J = 4.0 Hz, 1H), 7.35, (s, 1H), 7.20 (d, J = 4.0 Hz, 1H), 2.55 (s, 3H), 2.45 (s, 3H), 2.43 (s, 3H). 13C NMR: δ 192.2, 192.0, 190.6, 144.0, 133.4, 131.9, 130.9, 130.2, 125.5, 30.5, 30.2, 27.0. HRMS. Calcd for C14H12NaO3S4: m/z 378.9561. Found: m/z 378.9545 ([M + Na]+). General Procedure for the Synthesis of Extended Nickel Thiophenedithiolenes 6a−6e. The desired acetate-protected ligand 5a−5e (0.32 mmol) was added to a solution of sodium metal (2.0 g) in 50 mL of degassed MeOH and stirred for 45 min. A nitrogensparged solution of Ni(H2O)6Cl2 (0.038 g, 0.16 mmol) in 3 mL of MeOH was then added dropwise. This mixture was stirred for 1 h, air was bubbled through the solution for 20 min, and then either tetrabutylammonium bromide (0.41 g, 1.27 mmol) or N-methylpyridinium iodide was added, forming a suspension. The precipitate was filtered, washed with H2O, MeOH, and Et2O, and further purified as described below. Tetrabutylammonium Bis(5-(2-thienyl)-2,3-thiophenedithiolato)nickelate(III), [Bu4N][6a]. The isolated green powder was recrystallized from MeCN to give a dark-green crystalline solid (52% yield). Mp: 227 °C (dec). HRMS. Calcd for C16H8NiS8: m/z 513.7740. Found: m/z 513.7732 ([M−]). Calcd for C16H36N: m/z 242.2842. Found: m/z 242.2849 ([M+]). Elem anal. Calcd for C32H44NNiS8: C, 50.71; H, 5.85; N, 1.84. Found: C, 50.98; H, 5.75; N, 1.90. Tetrabutylammonium Bis(5-(3-hexyloxy-2-thienyl)-2,3-thiophenedithiolato)nickelate(III), [Bu4N][6b]. [Bu4N][6b] was recrystallized from 25% MeOH in MeCN to give a dark-green material (53% yield). Mp: 143.3−144.5 °C. HRMS. Calcd for C28H32NiO2S8: m/z 713.9516. Found: m/z 713.9511 ([M−]). Calcd for C16H36N: m/z 242.2842. Found: m/z 242.2836 ([M+]). Elem anal. Calcd for C44H68NNiO2S8: C, 55.15; H, 7.15; N, 1.46. Found: C, 54.75; H, 7.01; N, 1.41. Tetrabutylammonium Bis(5-(5-bromo-2-thienyl)-2,3-thiophenedithiolato)nickelate(III), [Bu4N][6c]. [Bu4N][6c] was recrystallized from MeCN to give a black shiny solid (39% yield). Mp: >300 °C. HRMS. Calcd for C16H6Br2NiS8: m/z 669.5950. Found: m/z 669.5951 ([M−]). Calcd for C16H36N: m/z 242.2842. Found: m/z 242.2831 ([M+]). Elem anal. Calcd for C32H42Br2NNiS8: C, 41.97; H, 4.62; N, 1.53. Found: C, 42.03; H, 4.53; N, 1.48. Tetrabutylammonium Bis(5-( 5-acetyl-2-thi enyl)-2,3thiophenedithiolato)nickelate(III), [Bu4N][6d]. [Bu4N][6d] was prepared as above with the following modification: Following the addition of a Ni(H2O)6Cl2 solution and stirring for 1 h, a solution of acetic acid (6 mL, 95 mmol) in 20 mL of H2O was then added, and the mixture was stirred for an additional 10 min. Tetrabutylammonium bromide was then added, and the product was isolated as above. The product was recrystallized from MeCN to give a black shiny solid (65% yield). Mp: 209.2−211.4 °C. HRMS. Calcd for C20H12NiO2S8: m/z 597.7951. Found: m/z 597.7932 ([M−]). Calcd for C16H36N m/z 242.2842. Found: m/z 242.2831 ([M+]). Elem anal. Calcd for C36H48NNiO2S8: C, 51.35; H, 5.75; N, 1.66. Found: C, 51.34; H, 5.73; N, 1.77. Tetrabutylammonium Bis(5-(phenyl)-2,3-thiophenedithiolato)nickelate(III), [Bu4N][6e]. [Bu4N][6e] was recrystallized from MeCN to give a wine-colored solid (56% yield). Mp: 244.1−247.2 °C. Elem anal. Calcd for C36H48NNiS6: C, 57.97; H, 6.49; N, 1.88. Found: C, 57.88; H, 6.49; N, 1.86.
N-Methylpyridinium Bis(5-(2-thienyl)-2,3-thiophenedithiolato)nickelate(III), [NMP][6a]. [NMP][6a] was recrystallized from MeCN (41% yield). Mp: >300 °C. HRMS. Calcd for C16H8NiS8: m/z 513.7740. Found: m/z 513.7743 ([M−]). Calcd for C6H8N: m/z 94.0651. Found: m/z 94.0651 ([M+]). Elem anal. Calcd for C24H16NNiS8: C, 43.35; H, 2.65; N, 2.30. Found: C, 43.48; H, 2.59; N, 2.43. N-Methylpyridinium Bis(5-(3-hexyloxy-2-thienyl)-2,3-thiophenedithiolato)nickelate(III), [NMP][6b]. [NMP][6b] was recrystallized from MeCN/MeOH to give a dark-green material (33% yield). Mp: >300 °C. HRMS. Calcd for C28H32NiO2S8: m/z 713.9516. Found: m/ z 713.9509 ([M−]). Elem anal. Calcd for C34H40NNiO2S8: C, 50.42; H, 4.98; N, 1.73. Found: C, 50.15; H, 4.81; N, 1.50. N-Methylpyridinium Bis((5-(5-bromothienyl)-2,3-thiophenedithiolato)nickelate(III), [NMP][6c]. [NMP][6c] was recrystallized from MeCN (36% yield). Mp: >300 °C. Elem anal. Calcd for C22H14Br2NNiS8: C, 34.43; H, 1.84; N, 1.83. Found: C, 34.59; H, 1.71; N, 1.88. N-Methylpyridinium Bis(5-(2′-(5-acetyl-2-thienyl)-2,3-thiophenedithiolato)nickelate(III), [NMP][6d]. [NMP][6d] was prepared with the modification described above for [Bu4N][3d]. It was recrystallized from 50% DMF in MeCN (57% yield). Mp: >300 °C. HRMS. Calcd for C20H12NiO2S8: m/z 597.7951. Found: m/z 597.7936 ([M−]). Calcd for C6H8N: m/z 94.0651. Found: m/z 94.0652 ([M+]). Elem anal. Calcd for C26H20NNiO2S8: C, 45.02; H, 2.91; N, 2.02. Found: C, 44.95; H, 2.74; N, 2.03. N-Methylpyridinium Bis(5-phenyl-2,3-thiophenedithiolato)nickelate(III), [NMP][6e]. The solid was recrystallized from 10% DMF in MeCN to give a wine-colored solid (50% yield). Mp: >300 °C. Elem anal. Calcd for C26H20NNiS6·C2H3N: C, 52.66; H, 3.63; N, 4.39. Found: C, 52.49; H, 3.56; N, 4.14. Calculations. All calculations were performed using the Gaussian03 software package. Optimized geometries were calculated using density functional theory (DFT) methods utilizing a SDD basis set (Dunning/Huzinaga full double-ζ up to argon, with Stuttgart/ Dresden effective core potentials for the remainder of the elements) and a B3LYP correlation functional. A single-point-energy calculation using methods matching the geometry optimization followed. Molecular orbital (MO) diagrams were generated using GaussView 3.09 from the checkpoint file generated during the single-point-energy calculation and an isovalue of 0.03. Time-dependent DFT (TDDFT) calculations, when performed, followed the single-point-energy calculation. The application of these methods to previously reported systems gave results consistent with those of other computational methods.5,19a X-ray Crystallography. X-ray-quality crystals of 2 and [NMP][6a] were grown by the slow evaporation of hexanes and MeCN solutions, respectively. X-ray-quality crystals of [NMP][6c] and [NMP][6e] were grown by the slow diffusion of Et2O vapor into DMF solutions. The X-ray intensity data of the crystals were measured at 273 K on a CCD-based X-ray diffractometer system equipped with a molybdenum-target X-ray tube (λ = 0.71073 Å) operated at 2000 W of power. The detector was placed at a distance of 5.047 cm from the crystal. Frames were collected with a scan width of 0.3° in ω and an exposure time of 10 s frame−1 and then integrated with the Bruker SAINT software package using an arrow-frame integration algorithm. The unit cell was determined and refined by least squares upon refinement of the XYZ centeroids of reflections above 20σ(I). The structure was refined using the Bruker SHELXTL (version 5.1) software package. The crystallographic data for 2, [NMP][6c], and [NMP][6e] are given in Table 1. Analogous data for [NMP][6a] were reported in a previous communication.35b
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RESULTS AND DISCUSSION Synthesis. Initial attempts to generate aryl-extended analogues of the NiTDT core involved functionalization of the 2,3-thiophenedithiolate precursor 1, as outlined in Scheme 1. While the initial intermediate 2 could be easily produced in high yield via standard bromination conditions, attempts to
C
DOI: 10.1021/acs.inorgchem.6b01513 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
cross-coupling of 2,3,5-tribromothiophene resulted in various 5aryl-2,3-dibromothiophene derivatives (4a−4c).44 These intermediates were developed with the intent of using metal− halogen exchange followed by a sulfur quench to give the desired 5-aryl-2,3-thiophenedithiolate ligands. However, initial attempts performed in THF resulted in the formation of multiple compounds with no clear major product. It was suspected that this was a result of undesired rearrangements stemming from the halogen dance reaction,46 leading to a complex mixture of inseparable products. Optimization then involved a move from THF to Et2O and reversal of the order of the addition during the second metal−halogen exchange. Thus, the bromothiophene intermediate was added to solutions of excess tBuLi, a technique known to suppress the halogen dance reaction.46 As shown in Scheme 2, these methods resulted in the successful isolation of thiophenedithiolate ligands as their acetate-protected thioesters (5a−5c). Two additional ligands (5d−5e) were then produced via regioselective electrophilic substitutions of 5a. The corresponding nickel dithiolate complexes 6a−6e were synthesized through deprotection of the acetyl groups by saponification in MeOH, followed by the addition of a solution of Ni(H2O)6Cl2 in MeOH (Scheme 3). Air was subsequently
Table 1. Crystallographic Data for Compounds 2, [NMP][6c], and [NMP][6e] 2 chemical formula fw temperature (K) space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalc (g cm−3) μ (cm−1) final R indices [I > 2σ(I)] R indices (all data)a a
[NMP][6c]
[NMP][6e]
C5HBrOS3
C22H14Br2NNiS8
C29H27N2NiOS6
253.15 293(2)
767.35 273(2)
670.60 273(2)
P212121 3.9500(8) 10.568(2) 18.064(4) 90.00 90.00 90.00 754.0(3) 4 2.230 6.199 R1 = 0.0455, wR2 = 0.0827 R1 = 0.1009, wR2 = 0.1032
P2(1)/c 16.9960(14) 11.3007(9) 14.3233(12) 90.00 95.2170(10) 90.00 2739.6(4) 4 1.860 4.250 R1 = 0.0562, wR2 = 0.1535 R1 = 0.1166, wR2 = 0.1932
Cc 17.799(3) 10.7709(15) 16.151(2) 90.00 105.043(3) 90.00 2990.2(7) 4 1.490 1.095 R1 = 0.0487, wR2 = 0.1291 R1 = 0.0863, wR2 = 0.1519
R1 = ∑(||Fo| − |Fc||)/∑|Fo|; wR2 = [∑(w(Fo2 − Fc2)2)/∑(Fo2)2]1/2.
Scheme 3. Synthesis of Extended Nickel Thiophenedithiolenes 6a−6e
Scheme 1. Failed Synthesis of 5-(2-Thienyl)thieno[2,3-d]1,3-dithinol-2-one
generate the desired extended ligand precursor 3 via Stille cross-coupling were unsuccessful. This was likely due to oxidative addition into the sulfur−carbonyl bond rather than the halo−aryl bond, forming a stable chelate and deactivating the catalyst. The application of alternate methods, however, resulted in the successful preparation of a number of aryl-functionalized thiophenedithiolene-based ligands via a new and general synthetic approach. As shown in Scheme 2, regioselective
bubbled into the reaction to oxidize the complexes from dianionic to anionic species. The compounds could be purified by cross-metathesis with salts of organic cations [tetrabutylammonium (Bu4N) bromide or N-methylpyridinium (NMP) iodide], causing precipitation from MeOH, followed by further recrystallization, resulting in the isolation of crystalline products. Crystallography. The crystal structures have been determined for three of the five extended nickel dithiolene complexes 6a−6e. The N-methylpyridinium salt of the parent thiophene species [NMP][6a] was previously reported in a communication,35b and the structures of the two additional salts [NMP][6c] and [NMP][6e] are reported in this current broader study. After numerous attempts to grow single crystals of [NMP][6b] and [NMP][6d], X-ray-quality crystals could not be obtained. Ellipsoid plots of the complexes 6c and 6e are shown in Figure 2, and selected bond distances for the nickel thiophenedithiolene cores of 6a, 6c, and 6e are given in Table 2, along with the NiTDT anion for comparison. As can be seen from Table 2, the nickel thiophenedithiolene cores of the three aryl-extended structures are consistent with the previously reported structure of NiTDT.31e The two thiophenedithiolate ligands adopt the commonly observed trans configuration, and Ni−S bond lengths are observed ranging from 2.167 to 2.176 Å. In addition, the fused thiophene rings of the thiophenedithiolate ligands agree fairly well with
Scheme 2. Synthesis of Acetate-Protected Thiophenedithiolate Ligands
D
DOI: 10.1021/acs.inorgchem.6b01513 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
consistent with the reduced conjugation typical between phenyl and thiophene rings. The two different complex anions found in the asymmetric unit of [NMP][6a] reside in alternating layers of π-stacked anion−cation columns and two-dimensional anion−anion sheets, respectively.34b The edge-to-edge sheets are ordered via complementary close contacts mediated by sulfur atoms, with two C−H···S (2.966 Å) and one S···S (3.592 Å) interactions between each pair of anions. In the π-stacked columns, the face-to-face distance between anions and cations is ∼3.6 Å. The packing of the phenyl derivative [NMP][6e] also exhibits extended arrays as a result of S···S and π-stacking interactions, as shown in Figure 3.
Figure 2. Face and edge ellipsoid plots of extended nickel thiopheneditholenes 6e (A) and 6c (B) at the 50% probability level.
Table 2. Selected Bond Distances (Å) of Nickel Thiophenedithiolenes parameter
[BzPy][NiTDT]a
[NMP][6a]b
[NMP][6c]
[NMP][6e]
Ni−S1 Ni−S2 S1−C1 S2−C2 C1−C2 C1−S5 C2−C5 C5−C6 S5−C6 C6−C9
2.1628(9) 2.1633(8) 1.717(3) 1.733(3) 1.377(4) 1.733(3) 1.491(4) 1.374(5) 1.705(3)
2.167(2) 2.171(2) 1.714(6) 1.732(5) 1.382(6) 1.733(5) 1.486(9) 1.423(8) 1.745(5) 1.445(9)
2.175(2) 2.170(2) 1.708(6) 1.733(7) 1.396(8) 1.748(6) 1.445(9) 1.386(8) 1.746(6) 1.472(8)
2.174(3) 2.176(3) 1.732(9) 1.731(10) 1.442(12) 1.725(8) 1.439(13) 1.395(11) 1.739(8) 1.51(1)
a
Reference 31e. PzPy = N-benzylpyridinium. bReference 35b.
the structure of the parent thiophene,47 with the exception of a small amount of asymmetry, as was previously reported for other thiophenes fused along the b face of the heterocycle.48 As previously reported,34b the asymmetric unit of the thiophene-extended [NMP][6a] contains two complex anions, one nearly completely planar (
