Magnetically recyclable borane Lewis acid catalyst for hydrosilylation of imines and reductive amination of carbonyls

Magnetically Recyclable Borane Lewis Acid Catalyst for Hydrosilylation of Imines and Reductive Amination of Carbonyls Vitthal B. Saptal,[a] Prabodh Ranjan,[b] Radek Zbořil,[c, d] Marek Nowicki,[a, e] and Jędrzej Walkowiak*[a] Fluorinated arylborane-based Lewis acid catalysts have shown remarkable activity and serve as ideal examples of transition metal-free catalysts for diverse organic transformations. However, their homogeneous nature poses challenges in terms of recyclability and separation from reaction mixtures. This work presents an efficient technique for the heterogenization of boron Lewis acid catalysts by anchoring Piers’ borane to allylfunctionalized iron oxide. This catalyst demonstrates excellent activity in the hydrosilylation of imines and the reductive amination of carbonyls using various silanes as reducing agents under mild reaction conditions. The catalyst exhibits broad tolerance towards a wide range of functional substrates. Furthermore, it exhibits good recyclability and can be easily separated from the products using an external magnetic field. This work represents a significant advance in the development of sustainable heterogenous metal-free catalysts for organic transformations. Introduction In the field of organic synthesis, transition metal catalysts (TMCs) have been extensively employed over the past few decades.[1] These catalysts have played a significant role in advancing the synthesis of important organic scaffolds. However, their usage comes with certain challenges. The separation of TMCs from the reaction mixture is difficult, often resulting in the sacrifice of the catalyst during product purification. Furthermore, traces of metals tend to persist in the final products. These limitations restrict the applications of TMCs in the synthesis of essential compounds related to biology, medicine, food, and cosmetics,[2] and the design of transitionmetal-free catalysts has gained increasing attention as a highly favorable alternative. This approach brings forth a multitude of advantages in the synthesis of valuable organic compounds while also fostering sustainability.[3] Transition-metal-free catalysts possess the distinct advantage that they can be directly utilized in medicinal and biological applications. Moreover, they facilitate the simplification of purification and separation procedures, resulting in cost reductions. In particular, the elimination of expensive, moisture-sensitive, and air-sensitive TMCs makes processes more efficient and economical. Fluorinated aryl boranes as transition-metal-free Lewis acid catalysts have garnered notable attention for diverse organic reactions in recent times.[4] Tris(pentafluorophenyl)borane (B- (C6F5)3) has a firmly established reputation as an exceptional Lewis acid catalyst and reagent owing to its extraordinary qualities, including exceptional thermal stability and outstanding solubility in commonly employed organic solvents and poses a lower environmental impact in comparison to TMCs.[4a] Hence, in comparison to boron trihalides (BX3=F, Cl, and Br), B(C6F5)3has proven to be a superior choice in molecular catalysis.[4b] The utility of this borane has been further demonstrated in frustrated Lewis pairs (FLPs) of acid and base for the activation of small molecules like CO2, H2, CO, etc.[5] Moreover, these boranes have exhibited remarkable activity in a wide range of chemical processes. Their effectiveness has been extensively demonstrated in several important reactions such as polymerization,[6] hydrogenation,[7] hydrosilylation,[8] CO2 reduction,[9] CH bond activation,[10] functionalization reactions[11] and other transformations. In addition, boron Lewis acids, when combined with chiral substituents, show great potential as chiral catalysts for asymmetric reactions, including hydrogenation and hydrosilylation.[12] Likewise, fluoroarenesubstituted boranes offer notable advantages, such as high catalytic activity and selectivity. Furthermore, the properties of [a] Dr. V. B. Saptal, Dr. M. Nowicki, Dr. J. Walkowiak Center for Advanced Technology, Adam Mickiewicz University, Uniwersytetu Poznanskiego Poznań, 10, 61–614 Poznan, Poland E-mail: [email protected] [b] Dr. P. Ranjan Department of Chemistry, Indian Institute of Technology, Kanpur, India (208016) [c] Prof. Dr. R. Zbořil Regional Centre of Advanced Technologies and Materials, Czech Advanced Technology and Research Institute, (CATRIN), Palacký University Olomouc, Šlechtitelů 27, 779 00, Olomouc, Czech Republic [d] Prof. Dr. R. Zbořil CEET, Nanotechnology Centre, VSB-Technical University of Ostrava, 17. listopadu 2172/15, 708 00, Ostrava-Poruba, Czech Republic [e] Dr. M. Nowicki Institute of Physics, Faculty of Materials Engineering and Technical Physics, Poznan University of Technology, Piotrowo 3, 60-965 Poznan, Poland Supporting information for this article is available on the WWW under https://doi.org/10.1002/cssc.202400058 © 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Wiley VCH Freitag, 02.08.2024 2415 / 353816 [S. 92/98] 1 ChemSusChem 2024,17, e202400058 (1 of 7) © 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH ChemSusChem www.chemsuschem.org Research Article doi.org/10.1002/cssc.202400058 these boranes can be finely tuned by modifying the arene ligands, allowing for greater control and versatility in their application.[11] The application of boranes as catalysts is hindered by several drawbacks, including challenges in their synthesis and handling, as well as the moisture sensitivity of their precursors.[13] Their synthesis often involves multistep procedures, and exhibit instability upon recycling, making them difficult to separate from products. However, a potential solution to these issues lies in the heterogenization of fluoroarene boranes and other Lewis acids. This approach could facilitate their easy recovery and recycling, reducing the potential for environmental harm.[14] Heterogenization of boranes is challenging due to their high reactivity and Lewis acidity, which readily leads to the formation of dimers or higher oligomers that are difficult to immobilize onto solid supports without disrupting the active sites.[15] Their large size and hydrophobic nature also impede their dispersion on solid supports, resulting in low surface area and limited accessibility. Additionally, their strong Lewis acidity can lead to undesired reactions with the support material or other functional groups on the surface, leading to the formation of inactive surface complexes. Despite these challenges, the development of effective strategies for the heterogenization of boranes and other highly reactive Lewis acids remains a crucial research area in the field of catalysis, especially from the perspective of sustainability. Finding ways to overcome these obstacles and successfully immobilize boranes onto solid supports while preserving their catalytic activity is an important goal for advancing the application of borane-based catalysts in the field of green chemistry.[16] Several efforts have been undertaken to heterogenize borane catalysts, incorporating the use of specialized ligands and supports (Scheme 1A). The majority of these approaches involve covalent grafting onto polymers,[17] immobilization onto the surface of silica[18] anchoring on materials like metal organic frameworks (MOFs),[19] among others. Alternative approaches have been explored, where boron Lewis acids are designed using heterogeneous FLP systems. In these systems, either one FLP partner (acid or base) is externally added, or both components are grafted onto the surface of porous or polymeric materials.[5c,20] Continuing our exploration of sustainable catalyst design for hydroelementation (hydrosilylation and hydroboration) and coupling reactions in the synthesis of organoboron and organosilicon compounds, our focus is on evaluating alternative catalysts that are free of expensive noble metals.[21] By investigating these precious transition metal-free catalysts, we aim to develop greener and more environmentally-friendly catalytic systems. This article presents an innovative method, showcasing the first-ever demonstration of a unique approach to incorporate a fluorinated aryl borane-based Lewis acid onto an iron oxide (Fe3O4) surface. This technique enables effortless and efficient recyclability, eliminating the need for complex, multistep procedures.[22] The resultant system features an immobilized Piers’ borane (HB(C6F5)2) on an allyl-functionalized Fe3O4material, which exhibited excellent catalytic activity in the hydrosilylation of imines and the one-pot reductive amination of carbonyl group with amines, and silanes as the reducing agents. Moreover, this boron catalyst has demonstrated tolerance toward a broad scope of substrates and could be recycled for up to four cycles with only a slight loss of activity. Results and Discussion Our research commenced with the objective of immobilizing Piers’ borane (HB(C6F5)2, PB) onto the surface of Fe3O4. To achieve this, we synthesized the catalyst PB@Fe3O4through a two-step synthetic process. Initially, we functionalized the Fe3O4 support with allylic moeities on its surface. This entailed utilizing allyltrimethoxysilane (ATMS) as a modifier/linker to incorporate alkene functional groups. The surface functionalization was accomplished using the hydrolysis method, wherein ATMS and Fe3O4were subjected to a reaction in the presence of NH4OH (Scheme S4 in ESI). Subsequently, we introduced borane Lewis acidic sites by hydroboration of the supported allyl functional groups with Piers’ borane (Scheme S5 in ESI). The PB was synthesized according to Piers’ method by the reaction of B(C6F5)3as a boron source with Et3SiH as a reducing agent (Scheme 2a).[23] Synthesized PB@Fe3O4was characterized using various analytical techniques. In infrared spectroscopy (FT-IR), a sharp peak was observed at 1633 cm1, which is indicative of the successful installation of alkene functional groups on the Fe3O4 Scheme 1. A. Previous methods used for the heterogenization of borane catalysts, a) ref. [18d] b) ref. [17a], c) ref. [17c] d) ref. [17b], B. Strategy used for the synthesis of PB@Fe3O4, C. Application of PB@Fe3O4for the hydrosilylation of imines and reductive amination. Wiley VCH Freitag, 02.08.2024 2415 / 353816 [S. 93/98] 1 ChemSusChem 2024,17, e202400058 (2 of 7) © 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202400058 1864564x, 2024, 15, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202400058 by Technical University Ostrava, Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License support (ESI, Figure S3). This peak at 1633 cm1indicates the stretching vibration of the C=C bond in the alkene group, confirming its presence on the Fe3O4surface following allylic functionalization. The presence of peaks near 3000 cm1and 1000 cm1in the FT-IR spectrum indicated CH bond stretching, further supporting the successful functionalization of Fe3O4with allyl groups. Following the hydroboration of Allyl-Fe3O4with Piers’ borane, several IR signals in the aliphatic region (near 900–1400 cm1) were observed. These signals provided conclusive evidence for the successful immobilization of Piers’ borane (PB@Fe3O4) on the modified support. Additionally, the efficiency of the hydroboration of allyl groups with PB was verified by a reaction with allyltrimethoxysilane conducted in an NMR tube in CDCl3(Scheme 2b). A 1H NMR spectrum was recorded after five minutes. The appearance of new peaks at 1.1, 1.3, and 1.6 ppm and the disappearance of alkene signals at 4.9 and at 5.8 ppm provided evidence of the functionalization of the allyl moiety with PB. The reaction proceeded rapidly at room temperature (ESI, Figure S1–2). Furthermore, the weight loss observed via thermogravimetric (TGA) analysis in both Allyl-Fe3O4and PB@Fe3O4, attributable to the removal of organic material, serves as confirmation of the successful immobilization of the catalyst (ESI, Figure S4). Moreover, the TGA analysis demonstrated the good stability of the allyl-functionalized Fe3O4and PB@Fe3O4catalyst, as indicated by minimal weight loss. This suggests that both the support and the catalyst retained their structural integrity and remained stable throughout the process. Scanning electron microscopy (SEM) revealed a significant morphological change from Fe3O4(Figure 1a) to PB@Fe3O4, characterized by increased particle size, confirming successful allyl group installation (Figure 1b). Further variations in morphology, linked to particle size, suggested hydroboration of the allyl group with borane, leading to additional morphological changes. Transmission electron microscopy (TEM) analysis reveals the even and effective deposition of an ATMS layer onto the Fe3O4 surface, as depicted in Figure 1c. Moreover, TEM images of PB@ Fe3O4illustrate an enhanced clarity of these layers, indicating the successful functionalization of PB onto the surface of allyl functional groups (Figure 1c–d). The elemental analysis revealed the presence of C, Si with O, and Fe, which strongly indicates the successful loading of the ATMS group onto the Fe3O4surface. Further, detection of F element merged with Fe confirms loading of PB (ESI, Figure S2a and S2b and Table S1). After successful immobilization of PB, we considered the Lewis acidity of the boron catalyst to activate the silane for hydrosilylation reactions. The hydrosilylation of imines is a practical and efficient method to obtain substituted amines, which serve as valuable building blocks for organic synthesis.[1a] Although homogeneous transition metals are typically the preferred choice for this transformation, their toxicity, cost, and lack of recyclability pose significant drawbacks.[24] Homogeneous borane catalysts have been well-established for facilitating hydride transfers to unsaturated functional groups, such as imines, carbonyls, and others.[25] Our objective was to leverage the hydride activation potential of boron Lewis acids and utilize PB@F3O4as a catalyst for imine hydrosilylation. Hence, we tested the synthesized PB@Fe3O4catalyst in the hydrosilylation of imines to amines. This transformation was achieved by utilizing different silanes as reducing agents using the Nbenzylideneaniline (1a) as a model imine substrate (Table 1). Initially, the hydrosilylation of compound 1a to amine 2a with dimethylphenylsilane was examined at room temperature, and it resulted in only 14% yield after 24 hours of reaction time (Table 1, entry 1). Upon increasing the reaction temperatures to Scheme 2. a) Synthetic method for the Piers’ Borane, b) Hydroboration of allyl trimethoxysilane (linker) using Piers’ borane. Figure 1. a) SEM image of Fe3O4b) SEM of PB@Fe3O4, c) TEM images of Allyl@Fe3O4, d–f) TEM of PB@Fe3O4. Wiley VCH Freitag, 02.08.2024 2415 / 353816 [S. 94/98] 1 ChemSusChem 2024,17, e202400058 (3 of 7) © 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202400058 1864564x, 2024, 15, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202400058 by Technical University Ostrava, Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License a range of 50–80°C, the yields of compound 2a increased (90%, Table 1, entries 2–3). Furthermore, elevating the temperature to 90°C and 100°C provided marginally higher yields, albeit the increment was only modestly superior (93 %) to that attained at 80°C, while also reducing the reaction time from 24 hours to 18 hours (Table 1, entry 4–6). Subsequently, we conducted the reaction without the catalyst at 80°C, which only yielded a trace amount of the desired product (Table 1, entry 7). This experiment clearly demonstrated the necessity of the catalytic components to achieve high conversion of the reactant molecules. Moreover, investigations were conducted with other silanes such as PhCH2(Me)2SiH (80%), Et3SiH (75%), and PhSiH3(72%) all of which displayed good to moderate yields, albeit lower when compared to PhMe2SiH (Table 1, entries 8–10). The utilization of a polar solvent like THF, as well as carrying out the reaction under solvent-free conditions, led to lower yields in contrast to previous reaction conditions (Table 1, entries 11–12). With the optimized reaction conditions established, the scope of various imines was explored for hydrosilylation reactions using PhMe2SiH. Imines containing electron-donating substituents on the phenyl ring, such as methoxy (86 %) and nbutyl groups (88%), exhibited excellent tolerance to the reaction conditions and resulted in high yields of the desired amines (Scheme 3, 2b–2c). Imines substituted with benzyl ether and fluorine atom also gave excellent yields (Scheme 3, 2d). The hydrosilylation of methyl-substituted imine (N-(1phenylethylidene)aniline, 1e) led yield up to 85% of 2 e, indicating the effectiveness of the reaction with this class of imines. No significant activity was noted in the imines containing aliphatic amines (1f–1h), although a low yield was observed after an extended reaction time to 48 h (2g, 30%). This observation could be attributed to their strong electrondonating ability. Sterically hindered primary imines, such as diphenylmethanimine (1i), and silyl-substituted imines (1j), instead of yielding the desired compounds, led to the formation of self-coupled products with lower yields. This suggests that steric hindrance and reactivity of imines play a role in the selectivity and efficiency of the reaction. After the successful application of PB@Fe3O4in hydrosilylation of imines, the same system was further explored for its effectiveness in the reductive amination (RA) of carbonyl compounds (Scheme 4). The RA reaction is one of the most straightforward, efficient, and versatile method for synthesizing substituted amine molecules.[26] It serves as a crucial tool in organic synthesis, allowing in one step for the formation of amines including chiral ones, which are essential building blocks in organic synthesis. The reaction involves the condensation of carbonyl compounds with amines in the presence of a reducing agent.[27] We explored PB@Fe3O4catalyst for the RA using the same optimized conditions. A model reaction was conducted involving benzaldehyde, aniline, and PhMe2SiH. The reaction yielded the secondary amine 4a with an excellent yield of 85%. Encouraged by these results, aldehydes with electron-donating groups such as OMe and electron-withdrawing groups like NO2 were tested, and good yields were obtained for the corresponding products (4b and 4c). The aldehyde with a nitro group at the ortho position resulted in only a trace amount of the Table 1. Optimization of reaction conditions. Entry Silane Solvent Temp. (°C) Time (h) Yield (%)[b] 1 PhMe2SiH Toluene Rt 24 14 2 PhMe2SiH Toluene 50 24 56 3 PhMe2SiH Toluene 80 24 92 4PhMe2SiH Toluene 80 18 90 5 PhMe2SiH Toluene 90 18 92 6 PhMe2SiH Toluene 100 18 93 7[c] PhMe2SiH Toluene 80 18 <7 8 PhCH2Me2SiH Toluene 80 24 80 9 Et3SiH Toluene 80 24 75 10 PhSiH3Toluene 80 24 72 11 PhMe2SiH THF 80 24 65 12 PhMe2SiH – 80 12 58 [a] Reaction conditions: i) imine (1 a) (1 mmol), silane (1.2 mmol), PB@Fe3O4(10 mg), inert atmosphere, solvent (2 mL) ii) KOH, H2O/MeOH (1:1), rt. [b] Determined by GC-MS analysis. [c] Without PB@Fe3O4. Scheme 3. Substrate scope for the hydrosilylation of imines with PhMe2SiH catalyzed by heterogeneous PB@Fe3O4. Reaction conditions: 1(1 mmol), silane (1.2 mmol), PB@Fe3O4(10 mg), Toluene (2 mL), inert atmosphere, 18 h, KOH, H2O/MeOH (1:1), rt. N.R. (no results). Wiley VCH Freitag, 02.08.2024 2415 / 353816 [S. 95/98] 1 ChemSusChem 2024,17, e202400058 (4 of 7) © 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202400058 1864564x, 2024, 15, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202400058 by Technical University Ostrava, Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License product. This observation could be attributed to the combined effects of steric hindrance and electronic factors, which might sluggish the reaction and lower the yield (4d). Fluoro substituted product at para position tolerated excellent yield with RA (4e). Subsequently, ketones such as acetophenone and substituted acetophenones with halide like I, and Br at para position were tested in the reaction and gave good to moderate yields (4g–4h). Also, electron withdrawing NO2(4i, 50%) and donating functional groups like OMe (4 k, 68%) were tested and good to moderate yields of products were obtained. While, phenyl substitution lowered the yield of product 4j. Methyl substitution at meta position also gave excellent yield with RA (4l). Interestingly, it was discovered that the aliphatic aldehyde (3m), which possessed both the alkene and the carbonyl group, exhibited a selectivity towards RA rather than hydrosilylation of the C=C bond (4m). Ketones substituted with a naphthalene group provided a yield of 68% (4n). However, when a bulky benzophenone (3o) was used, no conversion was observed under the given reaction conditions. Various heterocyclic aldehydes and ketones containing furan and thiophene heteroatoms (3p–3s) demonstrated excellent yields in RA reactions. Finally, anilines substituted with methoxy (3t), methyl (3u), dimethoxy (3v) ethyl (3w), and bromo (3x) functional groups were tested, and it was observed that they provided good to excellent yields of 4t–x. The RA of benzylamine 3y was found to be very slow, resulting in only a trace amount of the desired product (4y). The immobilization of Piers’ borane on Fe3O4allowed for easy separation of the catalyst from the reaction products using an external magnetic field. This magnetic separation method enabled testing the recyclability of the catalyst in the hydrosilylation of imine (1a) and the reductive amination of 3a with aniline using PhMe2SiH as a reducing agent. The catalyst demonstrated successful recycling for four cycles, yielding the desired products with high efficiency. No contamination with the catalyst was observed. However, a gradual decrease in product yields over time was noted (Figure 2). This decrease could potentially be attributed to factors such as catalyst weight loss or coordination with moisture or other reagents, which may have affected its activity. By utilizing the reported methods and computational calculations, we have proposed a reaction mechanism for imine hydrosilylation using catalyst 1(ESI, S6).[26–27] Previous mechanisms have predominantly centered around B(C6F5)3catalyst with alkene, carbonyl and imines as substrates. Here, PB@F3O4 has been considered, which exhibits sufficient Lewis acidity and follows a similar pathway, albeit with one less electron-withdrawing fluorosubstituted phenyl group. In the presence of PB@F3O4, mechanism involves initial activation of the SiH bond of PhMe2SiH through the SN2-Si pathway, resulting in the formation of intermediates A1 and A2 via reversible η1 coordination (ESI, Scheme S6–S7). The Si of A2 acts as Lewis acid, wherease imine (II) attacks as a nucleophile (nitrogen acts as Lewis base). Consequently, a hydride transfer occurs at the boron center of the catalyst, generating borohydride B1 and silyliminium intermediate B2. Further, hydride transfer takes place from B1 to B2, which leads to the formation of amine (III) and regeneration of catalyst 1(Scheme 5). Scheme 4. Substrate scope for RA of aldehydes and ketones with amines using silane. Reaction conditions: 3 (1 mmol), amine (1 mmol), silane (1.2 mmol), PB@Fe3O4(10 mg), Toluene (2 mL), MS (300 mg), inert atmosphere. KOH, H2O/MeOH (1:1), rt. Figure 2. Recyclability investigation featuring the PB@Fe3O4catalyst for imine (1a) hydrosilylation (green) and reductive amination of benzaldehyde (orange). Wiley VCH Freitag, 02.08.2024 2415 / 353816 [S. 96/98] 1 ChemSusChem 2024,17, e202400058 (5 of 7) © 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202400058 1864564x, 2024, 15, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202400058 by Technical University Ostrava, Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Conclusions We have successfully developed a novel and efficient approach for heterogenizing borane Lewis acid catalysts on a magnetically separable material. This catalyst was synthesized through a simple two-step functionalization of Fe3O4using allyltrimethoxysilane, followed by the hydroboration of the C=C bond with Piers’ borane. The resulting PB@Fe3O4catalyst exhibited exceptional catalytic performance in the hydrosilylation of imines to amines under mild reaction conditions. Furthermore, the catalyst demonstrated its versatility in reductive amination reactions, showcasing its efficacy with various silanes, carbonyl compounds, and amines, with dimethylphenylsilane yielding the best results. The developed strategy represents a more sustainable and environmentally friendly approach towards the use of heterogenous metal-free catalysts in organic synthesis. Moreover, the catalyst design allows facile magnetic separation thus decreasing costs and enhancing the potential of its transfer into the industrial practice. Acknowledgements This work was supported by the National Science Centre in Poland, grant no. UMO-2018/31/G/ST4/04012. The authors would like to thank Ondrej Tomanec and Priti Sharma for TEM analysis and Kinga Stefanowska for TG analysis. This article has been produced with the financial support of the European Union under the REFRESH – Research Excellence for Region Sustainability and High-tech Industries project number CZ.10.03.01/00/22_003/0000048 via the Operational Programme Just Transition. PR would like to thank the computer center (CC) at the Indian Institute of Technology Kanpur (IITK) for granting access to their high-performance computing facilitates. PR is also grateful to the department of chemistry, IITK for the institute’s postdoctoral fellowship. Conflict of Interests The authors declare no conflict of interest. Data Availability Statement The data that support the findings of this study are available in the supplementary material of this article. Keywords: heterogeneous borane ·Lewis acid ·amine synthesis ·hydrosilylation ·precious metal-free catalysis [1] a) A. Trowbridge, S. M. Walton, M. J. Gaunt, Chem. Rev. 2020,120, 2613– 2692; b) V. B. Saptal, V. Ruta, M. A. Bajada, G Vilé, Angew. Chem.Int. 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ChemSusChem published by Wiley-VCH GmbH ChemSusChem Research Article doi.org/10.1002/cssc.202400058 1864564x, 2024, 15, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202400058 by Technical University Ostrava, Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License