Heck Coupling of 10,10′-Dibromo-9,9′-bianthracene with Para-Substituted Styrenes—Evaluation of the Reaction as a Method for Synthesising Polyunsaturated Bianthracene Derivatives

Abstract

10,10′-dibromo-9,9′-bianthracene undergoes efficient Heck coupling with a series of para-substituted styrenes in the presence of a simple palladium-based catalytic system. The reaction proceeds with complete regio- and stereoselectivity. The disadvantage of this method is the minor competitive catalytic hydrodebromination.

1. Introduction

Anthracene is an important aromatic hydrocarbon consisting of three linearly connected benzene rings. Due to their system of conjugated π bonds, anthracene derivatives have interesting photochemical and photophysical properties [1,2]. These important properties make them suitable for use in advanced materials, such as organic light-emitting diodes (OLEDs) [3,4], organic field-effect transistors (OFETs) [5], and other types of materials [6,7]. Although the available results emphasise the importance of the bianthryl skeleton [8,9,10,11], bianthracenes have received relatively little attention. The vast majority of known bianthracene derivatives are aryl derivatives. Only a few 2-arylvinylic derivatives have been documented in the scientific literature (see Figure 1). The patent literature [12] identifies the compound in Figure 1 as an example of a material with electroluminescent properties. However, no data on its synthesis has been provided.

In 2015, Xue and Lu investigated the luminescent properties of a series of 9,9′-bianthracene derivatives that had been functionalised with phenothiazynyl groups. They obtained four compounds that differed in the length of the alkyl chains at the nitrogen atoms [13]. These compounds exhibit strong fluorescence both in solution and in the solid state. Additionally, the molecules exhibit distinct, reproducible and reversible mechanochromism. The compounds were synthesised via Heck coupling of 10,10′-dibromo-9,9′-bianthracene and vinyl derivatives of phenothiazine (Scheme 1).

Recently, Yu reported the synthesis of a p-vinylpyridine-functionalised 9,9′-bianthracene derivative using Heck coupling (see Scheme 2) [14].

These literature results encouraged us to develop procedures for the highly efficient and selective coupling of 10,10′-dibromo-9,9′-bianthracene with styrenes. This article describes our search for an effective catalytic procedure for synthesising a series of 10,10′-bis((E)-2-arylvinyl)-9,9′-bianthracenes via Heck coupling of 10,10′-dibromo-9,9′-bianthracene with various styrene derivatives. This procedure enables the selective synthesis of novel bianthracene structures. The resulting polyunsaturated products have potential applications in organic electronics.

2. Results and Discussion

We started our research by repeating the synthesis process outlined by Yu [14]. Unfortunately, we achieved an isolation efficiency of only 45%. Therefore, the first stage of our research was to determine the optimal catalytic conditions for the reaction, including the palladium catalyst, phosphine ligand, base, solvent, temperature and reaction time. We selected the Heck coupling of 10,10′-dibromo-9,9′-bianthracene with 4-methoxystyrene as the test reaction. We started the tests using the catalytic systems commonly employed in Heck coupling. A series of commercially available palladium complexes, such as [PdCl₂(PPh₃)₂], [Pd₂(dba)₃]/PPh₃, [Pd(PPh₃)₄], and [RuCl₂(IPr)(3-chloropyridine)] (PEPPSI-IPr), were tested. Additionally, palladium salts with Buchwald phosphine ligands, such as Pd(OAc)₂/XPhos, were applied. Treatment of 10,10′-dibromo-9,9′-bisanthracene with 4-methoxystyrene in the presence of the aforementioned palladium complexes and NEt₃ as a base at 80 °C in MeCN led to the formation of two coupling products, as shown in Scheme 3.

The initial reactions were performed at 80 °C for 24 h (

Table 1. Coupling of 10,10′-dibromo-9,9′-bianthracene (1) with 4-methoxystyrene (2a). Optimisation of the catalyst.

Entry	Catalyst/Additive	Mol %	Time [h]	Yield 3a [%]	Yield 4a B [%]
1	[PdCl2(PPh3)2]	5	24	42	7
2	[Pd(PPh3)4]	5	24	45	5
3	[Pd(PPh3)4]	5	48	52	4
4	[Pd2(dba)3]/PPh3	5/10	24	40	4
5	Pd(OAc)2	5	24	21	7
6	Pd(OAc)2/X-Phos	5/10	24	58	5
7	PEPPSI-IPr	5	24	38	10

Reaction conditions: [1]:[2a] = 1:2, NEt₃, MeCN, 80 °C, argon, molecular sieves.

) and afforded only moderate yields (38–58%) of the disubstituted product 3a. The accompanying product formed in lower yield was identified as the monosubstituted, protodebrominated compound 4a.

To minimise the protodebromination of the substrate, the reactions were carried out under strictly anhydrous conditions in the presence of dried molecular sieves to eliminate any residual moisture. However, we were unable to eliminate the debromination side reaction completely and still observed the formation of 4–10% of the monosubstituted product 4a. The best results were obtained when the reaction was catalysed with 5 mol% of Pd(OAc)₂ and two equivalents of the Buchwald phosphine ligand (XPhos), yielding product 3a with a yield of 58%. Other phosphine-based catalysts, such as Pd(PPh₃)₄ and PdCl₂(PPh₃)₂, also exhibited moderate to good activity. By contrast, the less active PEPPSI-IPr catalyst produced the desired product at only 38% yield, with a significant amount (10%) of by-product 4a. Our continuing research on finding conditions for highly efficient and selective reactions has led us to focus on investigating the effects of solvent, temperature, and base (

Table 2. Coupling of 10,10′-dibromo-9,9′-bianthracene (1) with 4-methoxystyrene (2a). Optimisation of the reaction conditions.

	Catalyst/Additive	Mol %	Base	Temp. [°C]	Yield 3a [%]	Yield 4a [%]
1	[PdCl2(PPh3)2]	5	NEt3	65	35 a	7 a
2	[Pd(PPh3)4]	5	NEt3	65	39 a	6 a
3	[PdCl2(PPh3)2]	5	NEt3	110	60 b	5 b
4	[Pd(PPh3)4]	5	EtNiPr2	110	64 b	4 b
5	[Pd(PPh3)4]	5	K3PO4	110	70 b	5 b
6	[PdCl2(PPh3)2]	5	K2CO3	140	55	6
7	[Pd(PPh3)4]	5	K3PO4	140	76	5
8	[Pd(PPh3)4]	5	K2CO3	140	80	5
9	[Pd(PPh3)4]	5	KOtBu	140	58	12
10	Pd(OAc)2/X-Phos	5/10	Cy2NMe	140	84	5
11	[Pd(t-Bu3P)2]	5	Cy2NMe	140	92	3
12	Pd(OAc)2/X-Phos	5/10	K2CO3	140	96 (86)	3
13	PdCl2/X-Phos	5/10	K2CO3	140	89	4
14	Pd(OAc)2/S-Phos	5/10	K2CO3	140	52	8
15	[Pd2(dba)3]/X-Phos	5/10	K2CO3	140	93 (82)	4
16	Pd(OAc)2/Ru-Phos	5/10	K2CO3	140	43	5
17	Pd(OAc)2/X-Phos	2.5/5	K2CO3	140	88	5
18	Pd(OAc)2/X-Phos	1/2	K2CO3	140	58	8
19	Pd(OAc)2/X-Phos	1/2	K2CO3	140	72 c	7 c
20	Pd(OAc)2/X-Phos/TBAB	5/10/5	K2CO3	100	86	4
21	Pd(OAc)2/X-Phos	5/10	Ag2CO3	140	62	9
22	Pd(OAc)2/X-Phos/Ag2CO3	5/10	K2CO3	140	84	5
23	Pd(OAc)2/X-Phos b	5/10	K2CO3	140	81 d	13 d
24	Pd(OAc)2/X-Phos	5/10	K2CO3	140	92 e	6 e

Reaction conditions: argon, molecular sieves, DMF, 24 h, yields based on ¹H NMR; isolated yields in parenthesis; (^a) THF was used as solvent; (^b) toluene was used as solvent; (^c) 48 h; (^d) 10 µL of H₂O was added; (^e) air.

).

Changing the solvent from acetonitrile to toluene and increasing the temperature to 110 °C resulted in a noticeable improvement in the yield of product 3a. For Pd–phosphine complex-based catalytic systems, the yield increased from 40 to 52% in MeCN to 60–70% in toluene (Table 2, entries 3–5) with a comparable amount of monosubstituted product 4a, which remained at a moderate level of 4–5%. A further significant increase in the yield of the desired product 3a was achieved by using the high-boiling solvent DMF and increasing the temperature to 140 °C. Under these conditions, the use of [Pd(PPh₃)₄] in combination with mild inorganic bases (K₂CO₃, K₃PO₄) yielded 3a in 76–80% yield. In contrast, the use of the strong base KOtBu resulted in a decrease in the yield and selectivity of the process (entry 9). The desired product 3a was accompanied by an increased amount of by-product 4a (12%). Further significant improvement in both yield and selectivity was observed when Buchwald phosphine XPhos was applied. The Pd(OAc)₂/XPhos system in the presence of K₂CO₃ provided the disubstituted product 3a in up to 96% yield (isolated yield = 86%), with only 3% of the by-product 4a. Similarly, high efficiency was observed for the [Pd₂(dba)₃]/XPhos system (93%). By contrast, other Buchwald ligands such as SPhos and RuPhos were less effective, resulting in significantly lower yields (43–52%) of 3a. Excellent results were obtained using bicoordinate [Pd(PtBu₃)₂] in the presence of Cy₂NMe as a base. The reaction produced 3a in 92% yield, along with 3% of 4a. Finally, we investigated the possibility of reducing the catalyst loading (entries 17–19). Halving the concentration of Pd(OAc)₂/XPhos to 2.5 and 5 mol% resulted in only a slight decrease in yield to 88%. Reducing the catalyst load further to 1 mol% resulted in a significant decrease in catalytic activity, down to 58% (entry 18). The prolongation of the reaction time to 48 h furnished only a partial compensation for the reduction in catalyst concentration. A yield of 72% was obtained (entry 19). To reduce the amount of the protodebrominated product (4a), TBAB (tetrabutylammonium bromide) was added to the reaction mixture (Table 2, entry 20), and the temperature of the reaction was lowered to 100 °C. As a result of the reaction, a slight reduction in the yield of product 3a (86%) and the formation of 4% of monosubstituted product 4a were observed. In contrast, the use of Ag₂CO₃ at 140 °C (entry 21) led to a significant decrease in the yield of 3a to 62%, and an increased formation of 4a (9%). Moreover, the combined use of K₂CO₃ together with 1 equiv. of Ag₂CO₃ (entry 22) resulted in the formation of 3a with moderate yield (84%) accompanied by a reduced amount of 4a (5%). To understand the effect of moisture, the reaction was performed with extra water added (10 µL). Under these conditions an increase in the yield of by-product 4a (13%) was observed, while the yield of 3a remained high (81%) (entry 23). Unexpectedly, performing the reaction in aerobic conditions (entry 24) did not affect the reaction performance. The process afforded a high yield of 3a (92%) with only a slightly increased amount of 4a (6%). Finally, the study of the course of the reaction over a period of 24 h with monitoring of the composition of the reaction system was done by an ¹H NMR spectroscopy (Figures S1 and S2, Supplementary data). Performed experiment showed slow gradual formation of the hydrodebromination product 4a during the reaction course.

Having determined the optimal conditions, Heck cross-coupling of 10,10′-dibromo-9,9′-bianthracene (1) with a series of vinylarenes (2a–2f) was investigated (Scheme 4). The cross-coupling of 1 with styrenes (2a–2d) led to the highly efficient and selective formation of compounds 3a–3d (Figure 2). However, all attempts to synthesise cross-coupling product using vinylanthracene or vinylnaphthalene failed. Only unreacted substrates and hydrodebrominated bianthracenes were observed in the post-reaction mixtures.

For products 3a–3c, single crystals suitable for X-ray studies were obtained. The crystal structures are shown in Figure 3. Moreover, Figure 4 shows an overlay of the structures.

In the solid state, the molecular geometry is largely invariant across the series, irrespective of the nature of the substituent. Any observed geometric differences therefore arise primarily from intermolecular interactions rather than from intrinsic molecular structural variations. To quantify these effects, the dihedral angles between the phenyl substituent and the anthracene core were compared. The highest degree of asymmetry is observed for derivative 3a, with dihedral angles of 66.2° and 89.4°. In compound 3b, the corresponding angles are more similar, measuring 85.1° and 70.8°. Derivative 3c exhibits the highest symmetry, with nearly identical angles of 81.9° and 82.7°.

The crystal structures of all three derivatives are based on dimeric structural motifs stabilised by C–H···π interactions between adjacent anthracene units (Figures S4–S6). The distance between the hydrogen atom at the ring edge and the anthracene π-plane ranges from 2.58 to 2.99 Å, depending on the derivative, with the shortest contact observed for 3b. Additional stabilisation of the dimers arises from edge-to-face interactions between phenyl rings and in the case of 3a, from C–H···O hydrogen bonding (C–H···O = 2.66 Å). Both the phenyl rings and anthracene moieties engage in a network of successive edge-to-face interactions that collectively stabilise the three-dimensional crystal lattice. Furthermore, in the crystal structures of 3a and 3c, face-to-face π···π interactions between parallel anthracene fragments also contribute to lattice stabilisation.

All three crystal structures incorporate solvent molecules trapped within the host framework (Figures S4–S6). In derivative 3b, approximately 32% of the unit-cell volume is accessible to solvent molecules, with cyclohexane located in cavities and tetrahydrofuran (THF) occupying intermolecular channels. For 3c, solvent-accessible voids account for 24% of the unit-cell volume; the crystal contains one cyclohexane molecule encapsulated within an intermolecular cavity and one THF molecule per asymmetric unit residing in channels. In contrast, the crystal structure of 3a provides only 8.6% of the unit-cell volume for solvent inclusion, accommodating a single cyclohexane molecule confined within a structural void between host molecules.

3. Materials and Methods

3.1. General Methods and Chemicals

Commercially available reagents were used during the research. 10,10′-dibromo-9,9′-bis-anthracene (98%) was purchased from Ambeed, Inc. (Buffalo Grove, IL, USA), 4-methoxystyrene (98%) was purchased from Angene International Limited (Hong Kong, China), diethyl ether and anhydrous N,N-dimethylformamide were purchased from Honeywell International Inc. (Morristown, NJ, USA), 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl (X-Phos) (97%) was purchased from Ark Pharm (Arlington Heights, IL, USA), dichloromethane and hexane (95%) were purchased from chemsolve^® (WITKO, Poland) toluene was purchased from Stanlab (Lublin, Poland), deuterated chloroform (99.6% isotopic purity) was purchased from TCI Chemicals (Tokyo, Japan), argon (99.999% purity) was purchased from Linde Gas (Pullach, Germany). Molecular sieves, silica gel, celite, 4-methylstyrene, 4-chlorostyrene, 4-tert-butylstyrene), potassium carbonate were purchased from Sigma-Aldrich (now Merck, Darmstadt, Germany). Styrenes were dried over CaH₂ and distilled under vacuum prior to use. The syntheses of the compounds were carried out in an inert gas atmosphere (argon) using a vacuum-gas line and standard Schlenk techniques. ¹H NMR and ¹³C NMR spectroscopic spectra were recorded using a Bruker Biospin (Karlsruhe, Germany) Avance 600 MHz spectrometer at frequencies of 600 MHz and 151.2 MHz, respectively, at T = 298 K. Samples for measurements were prepared in 5 mm diameter NMR tubes. Deuterated chloroform CDCl₃ was used as a solvent.

3.2. Methods

3.2.1. Representative Procedure of the Catalytic Test

In a typical catalytic test a 10 mL Schlenk flask equipped with a magnetic stirrer was charged with 0.1 g of previously dried 4 Å molecular sieves, 0.1 g of 10,10′-dibromo-9,9′-bianthracene (0.2 mmol), 0.08 g of K₂CO₃ (0.6 mmol), 2.2 mg of Pd(OAc)₂ (0.01 mmol), 9.5 mg (0.02 mmol) of XPhos, and 0.01 g of 1,3,5-trimethoxybenzene as an internal standard. The Schenk flask has been evacuated using Schlenk line techniques and filled with argon. Then, 0.06 mL of 4-methoxystyrene (2.2 equivalents) and 4 mL of dimethylformamide (DMF) were added under an inert atmosphere. The reaction mixture has been intensively stirred, and 0.1 mL sample was taken for NMR analysis. The Schlenk flask was placed in an oil bath and the reaction mixture was heated at 140 °C for 24 h. After this time, the mixture was cooled to room temperature, and the solvent was evaporated in vacuo. The resulting solid was dried under reduced pressure. To identify the components of the post-reaction mixture ¹H NMR analysis was performed.

3.2.2. Synthesis of 10,10′-bis((E)-4-Methoxystyryl)-9,9′-bianthracene (3a)

A 50 mL Schlenk flask equipped with a magnetic stirrer was charged with 0.2 g (0.4 mmol) of 10,10′-dibromo-9,9′-bianthracene, 1.2 mmol of K₂CO₃, 0.02 mmol of palladium acetate Pd(OAc)₂, 0.04 mmol of 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl (X-Phos) and 0.1 g of previously dried 4 Å molecular sieves. The flask was connected to a vacuum gas line, after which the contents were dried for one hour. Next, 0.9 mmol of 4-methoxystyrene and 5 mL of anhydrous dimethylformamide (DMF) were added under an inert gas atmosphere. The mixture was heated in a closed system at 140 °C, in an oxygen-free and anhydrous atmosphere for 24 h. After this time, the mixture was cooled to 22 °C and concentrated to 1 mL volume. The separated precipitate was filtered through a layer of celite and washed successively with 5 mL of hexane and 5 mL of diethyl ether. The crude product was purified by column chromatography on silica gel using hexane: methylene chloride mixture in a ratio of 10:1 as eluent. The isolated product was dried in vacuum for 2 h. Finally, 10,10′-bis((E)-4-methoxystyryl)-9,9′-bianthracene was obtained with an 83% of isolated yield (0.2 g). ¹H NMR (600 MHz, CDCl₃) δ 8.53 (m, J = 8.9 Hz, 4H, anthracene), 7.96 (d, J = 16.5 Hz, 2H, -CH=CH-), 7.73–7.69 (m, 4H, Ar), 7.44 (m, 4H, anthracene), 7.18–7.13 (m, 8H, anthracene), 7.08 (d, J = 16.5 Hz, 2H, -CH=CH-), 7.06–7.03 (m, 4H, Ar), 3.92 (s, 6H, OCH₃). ¹³C NMR (151 MHz, CDCl₃) δ 159.70, 137.17, 133.93, 133.00, 131.51, 130.26, 129.66, 127.89, 127.36, 126.44, 125.58, 125.24, 122.84, 114.33, 55.46; HRMS (ESI+): calc for [C₄₆H₃₄O₂]⁺: 618.2559; found: 618.2546.

3.2.3. Synthesis of 10,10′-bis((E)-4-Methylstyryl)-9,9′-bianthracene (3b)

A 50 mL Schlenk flask equipped with a magnetic stirrer was charged with 0.2 g (0.4 mmol) of 10,10′-dibromo-9,9′-bianthracene, 1.2 mmol of K₂CO₃, 0.02 mmol of palladium acetate Pd(OAc)₂, 0.04 mmol of X-Phos and 0.1 g of previously dried 4 Å molecular sieves. Then, the Schlenk flask was connected to a vacuum-gas line and the contents were dried for 1 h. Next, 0.9 mmol of 4-methoxystyrene and 5 mL of anhydrous dimethylformamide (DMF) were added under an inert gas atmosphere. The mixture was heated in a closed system at 140 °C, in an oxygen-free and anhydrous atmosphere for 24 h. After this time, the mixture was cooled to 22 °C and concentrated to 1 mL volume. The separated precipitate was filtered through a layer of celite and washed successively with 5 mL of hexane and 5 mL of diethyl ether. The crude product was purified by column chromatography on silica gel using hexane: methylene chloride mixture in a ratio of 20:1 as eluent. The isolated product was dried in vacuum for 2 h. Finally, 10,10′-bis((E)-4-methylstyryl)-9,9′-bianthracene was obtained with an isolation yield of 80% (0.18 g). ¹H NMR (600 MHz, CDCl₃) δ 8.54 (d, J = 8.9 Hz, 4H, anthracene), 8.06 (d, J = 16.5, 2H, -CH=CH-), 7.68 (d, J = 7.6 Hz, 4H, Ar), 7.48–7.42 (m, 4H, anthracene), 7.33 (d, J = 7.6 Hz, 4H, Ar), 7.21–7.15 (m, 8H, anthracene), 7.12 (d, J = 16.5 Hz, 2H, -CH=CH-), 2.47 (s, 6H, CH₃). ¹³C NMR (151 MHz, CDCl₃) δ 138.07, 137.63, 134.62, 133.81, 133.09, 131.49, 129.63, 129.60, 127.35, 126.59, 126.41, 125.60, 125.29, 124.07, 21.35; HRMS (ESI+): calc for [C₄₆H₃₄O₂]⁺: 586.2661; found: 586.2548.

3.2.4. Synthesis of 10,10′-bis((E)-4-Chlorostyryl)-9,9′-bianthracene (3c)

A 100 mL Schlenk flask equipped with a magnetic stirrer was charged with 0.51 g (1.0 mmol) of 10,10′-dibromo-9,9′-bianthracene, 3.0 mmol of K₂CO₃, 0.05 mmol of palladium acetate Pd(OAc)₂, 0.1 mmol of X-Phos and 0.2 g of dried 4Å molecular sieves. The Schlenk flask was then connected to a vacuum-gas line and the contents were dried for 1 h. Next, 2.2 mmol of 4-chlorostyrene and 12 mL of anhydrous dimethylformamide (DMF) were added in an inert gas atmosphere. The reaction mixture was heated in a closed system at 140 °C, in an oxygen-free and anhydrous atmosphere for 24 h. After this time, the mixture was cooled to 22 °C and evaporated in vacuo. The crude product was isolated from the solid residue by column chromatography on silica gel using a 10:1 hexane: dichloromethane mixture as eluent. The isolated product was dried in vacuo for 2 h. Finally, 10,10′-bis((E)-4-chlorostyryl)-9,9′-bianthracene was obtained with the yield of 75% (0.46 g). ¹H NMR (400 MHz, CDCl₃) δ 8.50–8.48 (m, 4H, anthracene), 8.08 (d, J = 16.6 Hz, 2H, -CH=CH-), 7.71–7.69 (m, 4H, Ar), 7.49–7.47 (m, 4H, Ar), 7.47–7.41 (m, 4H, anthracene), 7.18–7.15 (m, 8H, anthracene), 7.09 (d, J = 16.6 Hz, 2H, -CH=CH-). ¹³C NMR (151 MHz, CDCl₃) δ 136.48, 135.80, 133.79, 133.36, 133.19, 131.44, 129.57, 129.07, 127.85, 127.37, 126.19, 125.78, 125.70, 125.51; HRMS (ESI+): calc for [C₄₆H₃₄O₂]⁺: 626.1568; found: 626.1564.

3.2.5. Synthesis of 10,10′-bis((E)-4-tert-butylstyryl)-9,9′-bianthracene (3d)

A 100 mL Schlenk flask equipped with a magnetic stirrer was charged with 0.51 g (1.0 mmol) of 10,10′-dibromo-9,9′-bianthracene, 3.0 mmol of K₂CO₃, 0.05 mmol of palladium acetate Pd(OAc)₂, 0.1 mmol of X-Phos and 0.2 g of dried 4Å molecular sieves. The Schlenk flask was then connected to a vacuum-gas line and the contents were dried for 1 h. After this time, 2.2 mmol of 4-(ttert-butyl)styrene and 12 mL of anhydrous dimethylformamide (DMF) were added in an inert gas atmosphere. The reaction mixture was heated in a closed system at 140 °C, in a strictly oxygen-free and anhydrous atmosphere for 24 h. After this time, the mixture was cooled to 22 °C and evaporated in vacuo. The crude product was isolated from the solid residue by column chromatography on silica gel using a 10:1 hexane:dichloromethane mixture as eluent. The isolated product was dried under vacuum for 2 h. Finally, 10,10′-bis((E)-4-(tert-butyl)styryl)-9,9′-bianthracene was obtained with the yield of 79% (0.53 g). ¹H NMR (400 MHz, CDCl₃) δ 8.53 (dt, J = 8.9, 1.0 Hz, 4H, anthracene), 8.07 (d, J = 16.6 Hz, 2H, -CH=CH-), 7.74–7.72 (m, 4H, Ar), 7.56–7.72 (m, 4H, Ar), 7.43 (ddd, J = 8.9, 5.2, 2.4 Hz, 4H, anthracene), 7.19–7.15 (m, 8H, anthracene), 7.12 (d, J = 16.6 Hz, 2H, -CH=CH-), 1.39 (s, 18H, t-Bu). ¹³C NMR (151 MHz, CDCl₃) δ 151.38, 137.51, 134.61, 133.83, 133.11, 131.48, 129.64, 127.35, 126.43, 126.41, 125.85, 125.60, 125.28, 124.32, 34.76, 31.36; HRMS (ESI+): calc for [C₄₆H₃₄O₂]⁺: 670.3600; found: 670.3581.

3.2.6. Single Crystal X-Ray Crystallography

The diffraction data for the crystal of 3a was collected at 130 K with an Oxford Diffraction SuperNova diffractometer (Oxford Diffraction Ltd., Yarnton, Oxfordshire, England) using Cu Kα radiation (λ = 1.54184 Å) equipped with mirror monochromator. The intensity data were collected and processed using CrysAlis PRO software (Rigaku OD Yarnton, Oxfordshire, England), version 1.171.43.143a). For crystals 3b and 3c the diffraction data were collected at 100 K with an D8 QUEST system equipped with a Microfocus source Incoatec ImS DII (Bruker AXS, Karlsruhe, Germany) (Cu, λ = 1.54184 Å). The frames were integrated with the Bruker SAINT software package using a narrow-frame algorithm (Bruker AXS LLC (Karlsruhe, Germany), 2019; SAINT V8.40B). Data were corrected for absorption effects using the Multi-Scan method (SADABS) [15].

All crystal structures were solved by direct methods with the program SHELXT 2018/2 [16] and refined by full-matrix least-squares method on F2 with SHELXL 2018/3 [17]. The carbon-bound hydrogen atoms were refined as riding on their carriers and their displacement parameters were set equal to 1.5 Ueq(C) for the methyl groups and 1.2 Ueq(C) for the remaining H atoms.

A summary of the crystallographic data and refinement details are given in the Supplementary Materials. Molecular graphics were generated with Olex2 v.1.3 [18] and Mercury 2024.3.1 software [19].

4. Conclusions

The Heck coupling of 10,10′-dibromo-9,9′-bianthracene and styrene derivatives is an effective method for synthesising 10,10′-bis((E)-2-aryl-vinyl)-9,9′-bianthracenes. Four compounds not described in the literature were synthesised in good yields (83%, 80%, 75% and 79%, respectively) as a result of Heck cross-coupling of 10,10′-dibromo-9,9′-bianthracene with 4-methoxy-, 4-methyl-, 4-chloro- and 4-tert-butylstyrene. This process allows for the highly selective formation of new bianthracene structures, providing convenient access to materials with potential applications in organic electronics. The disadvantage of the method is the undesirable minor competitive hydrodehalogenation. The scope of the process can be extended to allow coupling of 10,10′-dibromo-9,9′-bianthracene with a variety of vinyl derivatives.