Synthesis, Properties, and Complex Formation of Antimony- and

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Synthesis, Properties, and Complex Formation of Antimony- and Bismuth-Bridged Bipyridyls Joji Ohshita,*,† Kosuke Yamaji,† Yousuke Ooyama,† Yohei Adachi,† Masashi Nakamura,‡ and Seiji Watase‡ †

Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan Osaka Research Institute of Industrial Science and Technology, Morinomiya Center, 1-6-50 Morinomiya, Joto-ku, Osaka 536-8553, Japan

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‡

S Supporting Information *

ABSTRACT: Antimony- and bismuth-bridged bipyridyls (dipyridinostibole and dipyridinobismole; DPySb and DPyBi) were prepared by the reactions of dilithiobipyridyl with dibromophenylstibine and diiodophenylbismuthine. Xray diffraction studies of the crystal structures revealed a high planarity of the heterole ring. Cyclic voltammograms obtained in acetonitrile indicated enhanced electron affinity in comparison to a bridge-free bipyridyl. These compounds showed weak fluorescence at room temperature and visible phosphorescence at 77 K with emission maxima and lifetimes of λmax = 453 nm and τ = 1.03 ms for DPySb and λmax = 454 nm and τ = 0.26 ms for DPyBi, respectively. Solid-state phosphorescence was also observed from these dipyridinoheteroles at 77 K. Their copper complexes were prepared by interaction with Cu2I2(PPh3)3, which produced red phosphorescence in the solid state at room temperature.

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INTRODUCTION The development of π-conjugated systems and the tuning of their electronic states to realize the desired properties and functionalities are of current importance in areas of organic optoelectronic materials. Bridging biaryl by a heavy element to form a fused heterole system is an efficient method to manipulate the electronic states of biaryls.1 In these systems, the improved planarity of the biaryls through the heteroatom bridge introduction enhances the conjugation. It is also often reported that the bonding interaction between the heteroatom σ* orbital and biaryl π* orbital (σ*−π* interaction) lowers the LUMO energy levels to decrease the HOMO−LUMO energy gaps.2 Examples include bithiophenes bridged by silicon, germanium, tin, and phosphorus units, namely dithienosilole,3a−h -germole,3i−n -stannole,3o−q and -phosphole,3r−t all of which have been extensively studied as basic units of conjugated functional materials, such as luminescent, semiconducting, and sensing materials.3 In regard to this, we recently prepared dithienobismole (DTBi) with bismuth as the bridging element (Chart 1).4 Bismuth is the heaviest abundant element without notable environmental or biological toxicity. In addition, heavy-atom effects that facilitate intersystem crossing were anticipated to provide phosphorescence to DTBi. As expected, DTBi derivatives exhibited stable phosphorescence in the solid state even in air at room temperature, in contrast to other dithienoheteroles that showed no phosphorescence except for 4-dithienophosphor© XXXX American Chemical Society

Chart 1. Bridged Biaryls

yl-2,2′-bipyridine-metal complexes. We also prepared antimony analogues (DTSb in Chart 1),5 but they are unstable toward UV irradiation and no detailed studies of their photoluminescence properties have been carried out. It was also demonstrated that the vacant orbitals of bismuth and antimony interact with the bithiophene π* orbital, lowering the LUMO energy levels in DTSb and DTBi. More recently, we prepared dipyridinosilole and -germole (DPyS and DPyG in Chart 1), which also exhibit solid-state phosphorescence, although only at low temperature.6 We also Received: December 30, 2018

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DOI: 10.1021/acs.organomet.8b00945 Organometallics XXXX, XXX, XXX−XXX

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Organometallics found that the σ*−π* interaction operates even with electrondeficient bipyridyl units to lower the LUMO energy levels, further enhancing the electron deficiency.6,7 The utility of diphenyldipyridinogermole (DPyG with R = Ph) as a ligand was also explored, and its interaction with Cu2I2(PPh3)3 generated an interesting polymeric copper complex (DPyGCu) in good yield,8 which is phosphorescent as a solid in air at room temperature. In contrast to a similar bridge-free bipyridyl-copper complex (BPy-Cu)9 that is insoluble in organic solvents, DPyG-Cu is soluble in common organic solvents, such as THF, chloroform, and toluene, and can be processed to DPyG-Cu-doped phosphorescent poly(methyl methacrylate) (PMMA) self-standing films. In this work, we prepared dipyridinostibole and -bismole (DPySb and DPyBi) as new heavy-element-bridged chromophores that are useful as building units of new π-conjugated optoelectronic materials. It seemed also interesting to us how the bridging antimony and bismuth vacant orbitals electronically interact with the bipyridyl π* orbital. Compounds DPySb and DPyBi were examined with respect to their optical and electrochemical properties. DFT calculations were carried out to understand the electronic states, and their crystal structures were determined by X-ray diffraction studies. The formation of complexes with Cu2I2(PPh3)3 and MeI is also described.

Figure 1. ORTEP drawings (50% probability level) and packing structures of DPySb (a, b) and DPyBi (c, d). The DPySb crystal contains water. DPyBi has two independent molecules with essentially the same structural parameters, and only one of them is presented in the ORTEP drawing.

Table 1. Endocyclic Bond Angles (deg) of Bridged Bipyridylsa

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DPyS1b

RESULTS AND DISCUSSION Synthesis of Dipyridinophenylheteroles. DPySb and DPyBi were prepared, as shown in Scheme 1. The reaction of

C−E−C E−CC CC−C a

Scheme 1. Synthesis of Antimony- and Bismuth-Bridged Bipyridyls

b

90.69 109.66 114.95

DPySb > <
<
300 °C; 1H NMR (δ in CD2Cl2) 7.21−7.46 (m, 33H, m,p-Ph of DPyBi and Ph of PPh3), 7.68 (dd, 2H, J = 4.0, 1.3 Hz, o-Ph of DPyBi), 7.86 (d, 2H, J = 5.3 Hz, pyridine ring H), 8.83 (d, 2H, J = 5.3 Hz, pyridine ring H), 8.90 (d, 2H, J = 0.7 Hz, pyridine ring H). Anal. Calcd for (C52H41Cu2I2N2P2Bi)n: C, 46.41; H, 3.07; N, 2.08. Found: C, 47.39; H, 2.93; N, 1.91. The higher carbon content may be understood by inclusion of triphenylphosphine as additional ligands. The amount was estimated to be approximately 10 mol %. Anal. Calcd for [(C52H41Cu2I2N2P2Bi)0.9(C18H15P)0.1]n: C, 47.17; H, 3.13; N, 2.04. Attempted measurements of the 13C NMR spectra of DPyBi-Cu and DPyBi-Cu gave no signals, due to their low solubility. Preparation of DPySb-MeI. To a solution of 50.0 mg (0.142 mmol) of DPySb in 5 mL of dichloromethane was added 40.3 mg (0.341 mmol) of methyl iodide, and the reaction mixture was stirred at room temperature for 36 h. After evaporation of the solvent, the residue was purified by recrystallization from methanol to provide 23.2 mg (33% yield) of DPySb-MeI as a red solid: mp 273.3−274.0 °C; 1H NMR (δ in DMSO-d6) 4.33 (s, 3H, CH3), 7.19−7.22 (m, 3H, m,p-Ph), 7.37−7.39 (m, 2H, o-Ph), 8.36 (dd, 1H, J = 5.3, 0.9 Hz, pyridine ring H), 8.81 (d, 1H, J = 6.4 Hz, pyridine ring H), 8.87 (d, 1H, J = 5.3 Hz, pyridine ring H), 9.03 (d, 1H, J = 6.4 Hz, pyridine ring H), 9.27 (s, 1H, pyridine ring H), 9.33 (d, 1H, J = 0.9 Hz, pyridine ring H); 13C NMR (δ in DMSO-d6) 47.58, 120.89, 121.70, 128.51, 128.72, 135.19, 139.00, 145.23, 145.47, 148.67, 149.71, 150.13, 151.82, 156.42, 162.06; HRMS (ESI): m/z calcd for C17H14N2Sb 367.01897 [M+], found 367.01886. Preparation of DPySb-2MeI. To a solution of 50.0 mg (0.142 mmol) of DPySb in 5 mL of acetonitrile was added 40.3 mg (0.341 mmol) of methyl iodide, and the reaction mixture was heated to reflux for 6 h. After evaporation of the solvent, the residue was purified by recrystallization from methanol to provide 36.2 mg (40% yield) of DPySb-2MeI as a black solid: mp 253.3−254.1 °C; 1H NMR (δ in DMSO-d6) 4.43 (s, 6H, CH3), 7.20−7.24 (m, 3H, m,p-Ph), 7.43− 7.46 (m, 2H, o-Ph), 9.05 (d, 2H, J = 6.5 Hz, pyridine ring H), 9.24 (d, 2H, J = 6.5 Hz, pyridine ring H), 9.42 (s, 2H, pyridine ring H); 13C NMR (δ in DMSO-d6) 48.21, 123.93, 128.70, 128.79, 135.68, 139.13, 145.70, 150.50, 152.21, 158.13; HRMS (ESI): m/z calcd for C18H17N2Sb 191.02095 [M2+], found 191.02051.

analogues. We investigated how the element bridges affect the electronic states and found that the influence of the antimony bridge enhancing the electron affinity and the conjugation of viologens is comparable to that of Si and Ge bridges and smaller than that of the PO bridge. These results demonstrate that the properties and functionalities of bipyridyls can be modified by introducing different element bridges.

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EXPERIMENTAL SECTION

General Considerations. All reactions were carried out in dry argon. THF that was used as the reaction solvent was distilled from CaH2 and stored over activated molecular sieves until use. The starting compound 3,3′-dibromo-4,4′-bipyridyl was prepared as reported in the literature.13 NMR spectra were recorded on a Varian 400-MR spectrometer. ESI mass spectra were measured on a Thermo Fisher Scientific LTQ Orbitrap XL spectrometer at N-BARD Hiroshima University. UV−vis absorption and PL spectra were measured on Hitachi U-2910 and HORIBA FluoroMax-4 spectrophotometers, respectively. We examined combustion elemental analysis for DPySb and DPyBi. However, we obtained data with carbon values smaller than the theoretical values by approximately 3%. This may be due to the hardly combustible properties of these compounds, because of the heteroaromatic ring systems with heavy inorganic elements. Preparation of DPySb. To a solution of 0.942 g (3.00 mmol) of 3,3′-dibromobipyridyl in 150 mL of THF was added dropwise 2.17 mL (6.00 mmol) of a 2.6 M solution of n-butyllithium in hexane at −90 °C. After the reaction mixture was stirred at this temperature for 5 min, a suspension of 1.08 g (3.00 mmol) of dibromophenylstibine in 60 mL of THF was slowly added. The resulting mixture was further stirred at room temperature overnight and hydrolyzed with water. The organic layer was separated, and the aqueous layer was extracted with toluene. The organic layer and the extract were combined, washed with brine, and dried over anhydrous magnesium sulfate. After evaporation, the residue was subjected to silica gel column chromatography using ethyl acetate/methanol 10/1 as eluent to give a crude sample that was recrystallized from ethanol to provide 0.227 g (21% yield) of DPySb as a colorless solid: mp 74.8−75.6 °C; 1 H NMR (δ in CD2Cl2) 7.19 (m, 2H, m-Ph), 7.24 (m, 1H, p-Ph), 7.29 (m, 2H, o-Ph), 7.88 (dd, 2H, J = 5.2, 0.9 Hz, pyridine ring H), 8.74 (d, 2H, J = 5.2 Hz, pyridine ring H), 8.95 (d, 2H, J = 0.9 Hz, pyridine ring H); 13C NMR (δ in CDCl3) 118.97, 129.17, 129.28, 135.20, 135.84, 140.98, 150.18, 155.54, 155.71; HRMS (ESI) m/z calcd for C16H12N2Sb 353.00332 [M + H+], found 353.00403. Preparation of DPyBi. To a solution of 0.697 g (2.22 mmol) of 3,3′-dibromobipyridyl in 110 mL of THF was added dropwise 1.61 mL (4.44 mmol) of a 2.6 M solution of n-butyllithium in hexane at −90 °C. After the reaction mixture was stirred at this temperature for 5 min, a suspension of 1.20 g (2.22 mmol) of diiodophenylbismuthine in 60 mL of THF was slowly added. The resulting mixture was further stirred at room temperature overnight and hydrolyzed with water. The organic layer was separated, and the aqueous layer was extracted with ethyl acetate. The organic layer and the extract were combined, washed with brine, and dried over anhydrous magnesium sulfate. After evaporation, the residue was subjected to silica gel column chromatography using ethyl acetate/methanol 10/1 as eluent to give a crude sample that was recrystallized from ethanol to provide 0.080 g (8% yield) of DPyBi as a colorless solid: mp 187.8−188.6 °C; 1 H NMR (δ in CD2Cl2) 7.21 (m, 1H, p-Ph), 7.27 (m, 2H, m-Ph), 7.69 (dd, 2H, J = 8.0, 1.4 Hz, o-Ph), 7.86 (dd, 2H, J = 5.2, 0.8 Hz, pyridine ring H), 8.83 (d, 2H, J = 5.2 Hz, pyridine ring H), 8.90 (d, 2H, J = 0.8 Hz pyridine ring H); 13C NMR (δ in CDCl3) 121.44, 128.37, 130.94, 137.14, 149.28, 150.81, 157.63, 159.23, 163.73; HRMS (ESI): m/z calcd for C16H12N2Bi 441.07988 [M + H+], found 441.07962. Preparation of DPySb-Cu. A solution of 84.5 mg (0.239 mmol) of DPySb and 0.279 g (0.239 mmol) of Cu2I2(PPh3)3 in 20 mL of THF was stirred at room temperature for 12 h. The resulting

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00945. CVs of DPySb and DPyBi, details of theoretical calculations, fabrication and performance of an OLED based on DPySb-Cu, and NMR spectra of DPySb, DPyBi, DPySb-Cu, DPyBi-Cu, DPySb-MeI, and DPySb-2MeI (PDF) F

DOI: 10.1021/acs.organomet.8b00945 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

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Optimized geometries of DPySb, DPyBi, DPySb2Me2+, and BPy2Me2+ obtained by the DFT calculations (ZIP) Accession Codes

CCDC 1887958−1887961 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail for J.O.: [email protected]. ORCID

Joji Ohshita: 0000-0002-5401-514X Yohei Adachi: 0000-0001-8311-5046 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by JSPS KAKENHI Grant Number JP17H03105. REFERENCES

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DOI: 10.1021/acs.organomet.8b00945 Organometallics XXXX, XXX, XXX−XXX