Facile Heck coupling synthesis and characterization of a novel tris(4-(pyridine-4-vinyl)phenyl)methylsilane tridentate core European Journal of Chemistry 15 (1) (2024) 71-73 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2024 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.15.1.71-73.2505 European Journal of Chemistry View Journal Online View Article Online Facile Heck coupling synthesis and characterization of a novel tris(4-(pyridine-4-vinyl)phenyl)methylsilane tridentate core Okpara Sergeant Bull * and Chioma Don-Lawson Department of Chemistry, Faculty of Science, Rivers State University, Port Harcourt City, P.M.B. 5080, Nigeria * Corresponding author at: Department of Chemistry, Faculty of Science, Rivers State University, Port Harcourt City, P.M.B. 5080, Nigeria. e-mail: bull.okpara@ust.edu.ng (O.S. Bull). 10.5155/eurjchem.15.1.71-73.2505 Received: 24 December 2023 Received in revised form: 17 February 2024 Accepted: 23 February 2024 Published online: 31 March 2024 Printed: 31 March 2024 Aromatic rigid ligands with carboxylate, phosphate, or pyridyl terminals are highly important today for application in the manufacturing of metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and other supramolecular structures. Aromatic rigid ligands give rigidity to MOFs and COFs materials. In addition, building units are important in that their judicious selection can result in a 2-D or 3-D framework with moderate or high surface area. Most aromatic linkers are based on carbon centres which are associated with a negative impact on the environment. However, in contrast, silicon-based centres are scarce and benign to the environment, even though they can be prepared facilely via metathesis. Here, we report the facile preparation of a new tris (4-(pyridine-4-vinyl)phenyl) methylsilane using the classical Heck coupling reaction. The bridging ligand was synthesized via the standard Heck coupling of 4-vinylpyridine with tris(4-bromophenyl)(methyl)silane. Aromatic Heck-coupling 4-Vinylpyridine Silicon-based centre Tris(4-Bromophenyl)(methyl)silane Tris(4-(Pyridine-4-vinyl)phenyl)methylsilane Cite this: Eur. J. Chem. 2024, 15(1), 71-73 Journal website: www.eurjchem.com 1. Introduction The importance of the availability of a wide range of ligands with the potential to bridge two remote metal centres cannot be overemphasized in coordination chemistry [1]. However, there are only a handful of ligands with three or more binding sites linked to a central spacer that can bind metal ions in a polygonal array [2]. Such ligands would be of considerable importance as precursors for the preparation of modern materials such as Metal Organic Frameworks (MOFs) [3-5] or Covalent Organic Frameworks (COFs) [6], which have been reported in the literature to have a variety of potential applications such as gas storage [7], gas purification [8], adsorption of heavy metals [9], catalysis [10,11], drug delivery [12], etc. as well as other supramolecular compounds [13]. Whether MOFs, COFs, or other supramolecular compounds, their preparation requires the presence of aromatic rigid ligands [14]. However, commercially available ligands are so small that the need for novel, tuneable, and functional materials to tackle the gamut challenges of the present day. Additionally, available linkers are carbon-based, which have been reported to be the culprit for a variety of environmental problems associated with a conti- nuous and completely dependent on the carbon-centre linker [15]. One way to reduce such dependence on commercially available carbon-based linkers is to move in favour of silicon, which is a congener of carbon. However, silicon is safer than carbon, and silicon centres can be easily prepared by metathesis [1,16]. To this end, it is still desirable to design new linkers with custom-designed dimensionality or pendant functional groups so as to have control of the physicochemical properties of the resulting framework materials [17]. Several synthetic routes have been used for the syntheses of varieties of rigid aryl systems based on silicon centres with pyridyl pendants [17,18]. Furthermore, after the preparation of the silicon centre linker, such linkers can be coupled to other rigid aromatic groups via the famous Heck coupling reaction [2]. The Heck reaction has not been fully used for the preparation of pyridyl pendants. In this study, we report the preparation of a novel silicon- centred pyridyl ligand binding site linked via alkene bridges to phenyl spacers. This novel silicon-centre ligand has the potential to form 2-D or 3-D MOF with metals or COF with other non-metals. The preparation of tris(4-(pyridine-4-vinyl) phenyl)methylsilane (L) (a new linker), was analogous to the standard Heck reaction in the literature [2] as well as the preparation of tris(4-bromophenyl)(methyl)silane [1], as shown in Scheme 1. ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.15.1.71-73.2505 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.15.1.71-73.2505 mailto:bull.okpara@ust.edu.ng http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.15.1.71-73.2505&domain=pdf&date_stamp=2024-03-31 72 Bull and Don-Lawson / European Journal of Chemistry 15 (1) (2024) 71-73 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.71-73.2505 Scheme 1. Pathway for the synthesis of tri(4-(pyridine-4-vinyl)phenyl)methylsilane (L). 2. Experimental 2.1. Chemicals and reagents All chemicals, reagents, and solvents used in this work were commercially purchased from Sigma-Aldrich and used as received, unless otherwise noted. Spectroscopy: 1H, 13C{1H}, and 29Si{1H} NMR spectra were recorded on a Bruker AVANCE III HD 400 MHz spectrometer in CDCl3 solvent unless otherwise stated. The chemical shifts (δ) for 1H, 13C{1H}, and 29Si{1H} are quoted in ppm with reference to Me4Si. The coupling constants are reported in Hz. 2.2. Preparation of tris(4-bromophenyl)(methyl)silane (E) In a dry three-neck round bottom flask equipped with a magnetic stirrer bar, 1,4-dibromobenzene (7.5 g, 30 mmol) was dissolved in dry ether (100 mL) and the mixture was stirred and cooled to -76 °C under N2. nBuLi (2.5 M in hexanes, 12 mL, 30 mmol) was taken using a dry syringe with needle and the content was carefully added into the solution dropwise while stirring. At the end of the addition, the mixture was stirred for 1 h. Then, methyltrichlorosilane (1.18 mL, 10 mmol) was taken using a dry syringe with needle and the content was carefully added dropwise at -76 °C. At the end of the addition, the reaction mixture was slowly increased to room temperature and stirred for 24 h. The reaction mixture was then quenched with 30 mL of H2O, and the organic layer was separated and collected. The aqueous portion was washed twice with 30 mL of Et2O, and the organic layer separated and collected. The two separate portions of the collected organic layers were combined, washed with brine, dried over anhydrous MgSO4, and then filtered. Removal of the solvents under vacuum gave a crude product, which was recrystallized in hexane to give colourless crystals. Tris(4-Bromophenyl)(methyl)silane (E): Color: White. Yield: 90%. M.p.: 120.0-120.7 °C. 1H NMR (400 MHz, CDCl3, δ, ppm): 0.79 (s, 3H, CH3), 7.30 (d, 6H, J = 8.4 Hz, Ar-H), 7.50 (d, 6H, J = 8.4 Hz, Ar-H). 2.3. Preparation of tris(4-(pyridine-4-vinyl)phenyl) methylsilane (L) In a clean dry round bottom flask, a mixture of tris(4- dibromophenyl)methylsilane (E) (1.70 g, 3.33 mmol), 4- vinylpyridine (D) (1.32 g, 12.53 mmol, 1.35 mL), stoichiometric base, trimethylamine (1.27 g, 12.53 mmol, 1.75 mL), which is generally needed to react with the acid produced to regenerate the active catalyst, [Pd(OAc)2] (0.023 g, 0.10 mmol), PPh3 (0.053 g, 0.20 mmol) and magnetic stirrer bar were mixed under N2 and then degassed to remove oxygen. The degassed mixture was heated under a gaseous flow of N2, refluxed at 100 °C for 48 h to keep the solution free of oxygen and water, which also helps for high conversion. The resulting solid mass was partitioned between CH2Cl2 and water. The organic layer was separated and evaporated to dryness. The crude brown product was recrystal- lized from acetone to give the brown product. Tris(4-(Pyridine-4-vinyl)phenyl)methylsilane (L): Color: Brown. Yield: 80%. M.p.: 169.4 -170.2 °C. 1H NMR (400 MHz, CDCl3, δ, ppm): 0.89 (s, 3H, CH3), 7.07 (d, J = 16 Hz, 3H, CHCH), 7.31 (d, J = 16 Hz, 3H, CHCH), 7.35-7.37 (m, 6H, m-C5H4N), 7.54 (s, 12H, o,m-C4H4), 8.46-8.58 (m, 6H o-C5H4N). 13C NMR (100.61 MHz, CDCl3, δ, ppm): -3.45, 120.90, 126.49, 126.83, 132.91, 135.74, 136.54, 137.31, 144.40, 150.24. 29Si NMR (79.5 MHz, CDCl3, δ, ppm): -11.09. 3. Results and discussion Compound E, tris(4-dibromophenyl)(methyl)silane, was synthesized and characterized using standard analytical and spectroscopic methods. For example, the 1H NMR spectrum of the compound is comparable to the literature [17-19], and showed well-resolved resonances with aromatic proton signals found within the range δ 7.30-7.50 ppm, while nonaromatic methyl protons are found at δ 0.79 ppm. Trichloro(methyl)silane (CH3SiCl3) was added to the lithiation product, which resulted in the formation of tris(4- dibromophenyl)(methyl)silane as a colorless powder product after aqueous work in a 90% yield of the compound (Lit. 82%, 83.5%) [17,19]. At the end of the reaction, the reaction mixture was partitioned between aqueous and organic layers to give a Bull and Don-Lawson / European Journal of Chemistry 15 (1) (2024) 71-73 73 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.71-73.2505 brown powder, which was washed with ethyl acetate to give an 80% yield of tris(4-(pyridine-4-vinyl)phenyl)(methyl)silane (L) as brown powder. The 1H NMR spectrum of compound L showed well-resolved resonances with aromatic proton signals found within δ 7.07-8.58 ppm, which are consistent with aromatic vinylpyridine compounds (δ 7.14-8.63 ppm) in the literature [2], while non-aromatic methyl protons were found at δ 0.89 ppm (starting material E = δ 0.79 ppm), (Lit. δ 0.94 ppm for similar Si-CH3) [17]. The 13C{1H} NMR spectrum of L shows signals for aromatic carbons in the range of δ 120.90- 150.24 ppm, which is consistent with the values in the literature [2], while the methyl carbon signal was found at δ -3.45 ppm, which is also consistent with similar compounds in the literature with values such as δ -4.30 ppm, for tris(4- bromophenyl)(methyl)silane, and δ -2.70 ppm, for tris(3,5- difluorophenyl)methylsilane [19]. Furthermore, the 29Si{1H} NMR spectrum of compound L shows a singlet at δ -11.09 ppm. The Heck coupling reaction has thus been applied in this study to create novel silicon-centred pyridyl ligand binding sites linked via alkene bridges to phenyl spacers. The use of this novel ligand in the preparation of MOFs and COFs is being explored. 4. Conclusion A novel silicon-centre pyridyl ligand tris(4-(pyridine-4- vinyl)phenyl)methylsilane has been prepared by the Heck coupling reaction of 4-vinylpyridine with tris(4-bromophenyl) (methyl)silane. The product was made as a brown powder with a yield of 80%. Therefore, this ligand should be explored for the preparation of silicon-based MOFs, COFs, and other supra- molecular structures. Acknowledgements We gratefully acknowledge the financial support given to us by the Nigerian Government through the Petroleum Technology Development Fund (PTDF), the Tertiary Education Trust Fund (TETFUND), Nigeria and the Rivers State University, Port Harcourt Nigeria. Disclosure statement Conflict of interest: The authors declare that they have no conflict of interest. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. CRediT authorship contribution statement Conceptualization: Okpara Sergeant Bull, Chioma Don-Lawson; Methodology: Okpara Sergeant Bull; Formal Analysis: Okpara Sergeant Bull; Investigation: Okpara Sergeant Bull; Resources: Okpara Sergeant Bull; Data Curation: Okpara Sergeant Bull; Writing - Original Draft: Okpara Sergeant Bull; Writing - Review and Editing: Chioma Don-Lawson; Visualization: Chioma Don- Lawson; Funding acquisition: Okpara Sergeant Bull; Supervision: Okpara Sergeant Bull; Project Administration: Chioma Don-Lawson. ORCID and Email Okpara Sergeant Bull bull.okpara@ust.edu.ng https://orcid.org/0000-0002-5810-1483 Chioma Don-Lawson chioma.don-lawson@ust.edu.ng https://orcid.org/0009-0005-2593-7873 References [1]. Bull, O. S.; Okpa, E. Application of green chemistry for the one-pot preparation of Tris (4-bromophenyl) chlorosilane. Int. J. Appl. Chem. 2023, 10, 1–5. [2]. Amoroso, A. J.; Maher, J. P.; McCleverty, J. A.; Ward, M. D. Magnetic spin exchange interactions between several metal centres in paramagnetic complexes with new polynucleating bridging ligands. J. Chem. Soc. Chem. Commun. 1994, 1273–1275. [3]. Bull, O. S.; Bull, I.; Amadi, G. K.; Obaalologhi Odu, C.; Okpa, E. O. A review on metal- organic frameworks (MOFS), synthesis, activation, characterisation, and application. Orient. J. Chem. 2022, 38, 490–516. [4]. Bull, O. S. Solvothermal Synthesis and Characterization of a New 3D Potassium Metal-Organic Framework (MOF) Structure. J. Chem. Soc. Niger. 2020, 45, 126–134. [5]. Sergeant Bull, O.; Monsuru Adewale, S.; Okpa, E. Production of biodiesel from waste cooking oil using A zinc-based metal-organic framework (Zn-MOF) as catalyst. Int. J. Appl. Chem. 2024, 11, 1–6. [6]. Bull, O. S.; Bull, I.; Amadi, G. K.; Odu, C. O. Covalent Organic Frameworks (COFS): A Review. J. Appl. Sci. Environ. Manage. 2022, 26, 145–179. [7]. Li, J.-R.; Ma, Y.; McCarthy, M. C.; Sculley, J.; Yu, J.; Jeong, H.-K.; Balbuena, P. B.; Zhou, H.-C. Carbon dioxide capture-related gas adsorption and separation in metal-organic frameworks. Coord. Chem. Rev. 2011, 255, 1791–1823. [8]. Prasad, T. K.; Suh, M. P. Control of interpenetration and gas-sorption properties of metal–organic frameworks by a simple change in ligand design. Chemistry 2012, 18, 8673–8680. [9]. Xie, Z.; Xu, W.; Cui, X.; Wang, Y. Recent progress in metal–organic frameworks and their derived nanostructures for energy and environmental applications. ChemSusChem 2017, 10, 1645–1663. [10]. Evans, J. D.; Garai, B.; Reinsch, H.; Li, W.; Dissegna, S.; Bon, V.; Senkovska, I.; Fischer, R. A.; Kaskel, S.; Janiak, C.; Stock, N.; Volkmer, D. Metal–organic frameworks in Germany: From synthesis to function. Coord. Chem. Rev. 2019, 380, 378–418. [11]. Odu, C. 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This work is published and licensed by Atlanta Publishing House LLC, Atlanta, GA, USA. The full terms of this license are available at https://www.eurjchem.com/index.php/eurjchem/terms and incorporate the Creative Commons Attribution-Non Commercial (CC BY NC) (International, v4.0) License (http://creativecommons.org/licenses/by-nc/4.0). By accessing the work, you hereby accept the Terms. This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution, or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (https://www.eurjchem.com/index.php/eurjchem/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). mailto:bull.okpara@ust.edu.ng https://orcid.org/0000-0002-5810-1483 mailto:chioma.don-lawson@ust.edu.ng https://orcid.org/0009-0005-2593-7873 https://spiral.imperial.ac.uk/handle/10044/1/83674 https://www.eurjchem.com/index.php/eurjchem/terms http://creativecommons.org/licenses/by-nc/4.0 https://www.eurjchem.com/index.php/eurjchem/terms 1. Introduction 2. Experimental 2.1. Chemicals and reagents 2.2. Preparation of tris(4-bromophenyl)(methyl)silane (E) 2.3. Preparation of tris(4-(pyridine-4-vinyl)phenyl) methylsilane (L) 3. Results and discussion 4. Conclusion Acknowledgements Disclosure statement CRediT authorship contribution statement ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField20: PrintField21: PrintField22: