Orthogonal tandem catalysis involving Au(I)-hydroacyloxylation and Rh(I)-hydroformylation reactions

Abstract

We report an orthogonal tandem catalysis (OTC) involving Au(I)-hydroacyloxylation and Rh(I)-hydroformylation highlighting their compatibility when these metals are employed in a reaction of homogeneous catalysis. Moreover, this OTC allows the synthesis of different carbaldehydes. Several derivatizations were performed at the end of the OTC procedure, giving access to two series of alcohol and oxime derivatives. ³¹P NMR experiments and kinetic studies carried out on the OTC allowed a detailed understanding of the catalytic cycles involved, highlighting the competitive ligand coordination between the gold and rhodium catalysts.

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Introduction

Since the early 2000s, interest in multi-catalytic reactions in homogeneous media has continued to grow.¹ This is due to the fact that, in nature, biological transformations, often catalyzed, occur sequentially in the same environment. This interest is growing both in academia and in industry.² However, designing such bio-inspired reaction sequences poses a significant challenge for organic chemists. When multiple independent catalytic systems are simultaneously involved in the reaction sequence, these transformations fall into the category of orthogonal tandem catalysis (OTC, Scheme 1a).³ This represents a specific one-pot reaction in which all reactants are present at the beginning of the reaction, unlike classical sequential one-pot reactions, and for which sequential catalytic cycles are carried out without interference between them. OTC reactions caught organic chemists’ attention due to the opportunity to build complex systems in which several chemical transformations could be done successively.⁴ The others advantages of OTC reactions over sequential one-pot reactions are manifold: (a) the non-intervention of an operator during the process, (b) the possibility to directly consume intermediate B when unstable, (c) avoid poisoning of catalyst by intermediate B and (d) promote equilibrium reaction until total conversion by coupling it directly with the next reaction cycle (thermodynamic leveraging). On the other hand, the conception of such multi-catalytic systems assumes a fine understanding of the catalytic cycles involved because many pitfalls are likely to disrupt the planned chemical mechanics (poisoning of catalysts, interactions between catalysts, solvents and temperatures compatibilities, side reactions, etc.).

Scheme 1 OTC reactions, preview attempts and our proposed Au(I)/Rh(I) OTC.

In organometallic catalysis, many metal pairs have been studied, particularly those involving gold(I)⁵ or rhodium(I)⁶ in combination with another metal. Unexpectedly, no OTC procedure involving these two metals has yet been developed. Two attempts to combine them have been made, but they have failed. In 2013, Hashmi and Lautens developed a one-pot two-step procedure aimed at the enantioselective synthesis of β-functionalized ketones from propargyl alcohol derivatives (Scheme 1b).⁷

Unfortunately, the transposal of such a one-pot bimetallic procedure to the corresponding OTC procedure failed due to the over-functionalization process. In 2017, Yu provided a sequential procedure involving the Au(I)/Rh(I) couple toward the preparation of polycyclic molecules derivating from tetrahydroisoquinolinone. Attempts to add all components together from the start also failed (Scheme 1c).⁸

In this context, we aimed to develop an OTC procedure combining Au(I)-hydroacyloxylation and Rh(I)-hydroformylation reactions (Scheme 1d). For that purpose, we have selected substrate 1 having an aryl moiety bearing an acid function and terminal alkyne, which can be transformed into the corresponding lactone 2 by gold(I) catalysis. This latter feature an exocyclic double bond that is an appropriate target for undergoing functionalization via rhodium(I)-catalyzed hydroformylation. This sequence was considered because both reactions are highly efficient and would result in functionalized heterocyclic compounds.

Results and discussion

Before considering the OTC process, we have concentrated our effort on the optimization of each steps independently: the gold(I)-catalyzed hydroacyloxylation reaction, then the rhodium(I)-catalyzed hydroformylation reaction.

Our first objective was to carry out the hydroacyloxylation reaction under compatible conditions with an OTC procedure, i.e., with simple conditions and the highest possible selectivity (Table 1).

Table 1 Optimization of the hydroacyloxylation reaction step^a

Entry	Catalyst	Time (min)	1a/2a ^c
a Reactions were performed by adding catalyst (1 mol%) to a solution of 1a in DCE (0.25 M) at RT. b 70 °C. c Measured by ^1H NMR in the crude mixture.
1	Cat. A	60	100/0
2	Cat. A + AgSbF6	15	0/100
3^b	Cat. B + AgSbF6	60	60/40
4^b	Cat. C + AgSbF6	15	0/100
5	Cat. D	15	0/100

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Based on previously reported procedures for this transformation,⁹ the entire screening was conducted under the following conditions: substrate 1a (1 equiv.), gold catalyst (1 mol%), possible additive (1 mol%), in dichloroethane (DCE, 0.25 M). We began by testing gold(I) chloride as catalyst.^9a,b We first used a phosphite gold(I) chloride (Cat. A) (entry 1), which failed to convert the substrate. However, when the cationic gold(I) complex is formed by the addition of silver hexafluoroantimonate (entry 2), substrate 1a is completely converted into lactone 2a within 15 minutes at room temperature. A full regioselectivity in favor of the 6-endo-dig cyclization was obtained as we never observed the formation of compound 3a bearing the seven-membered ring. With the same conditions, the NHC-based Cat. B and Cat. C proved ineffective. Their reactivity was restored at 70 °C, albeit with a lower conversion for Cat. B (entries 3 and 4). In contrast, the reaction carried out in the presence of a pre-activated cationic gold(I) complex, the commercially available catalyst [(JohnPhos)Au(MeCN)][SbF₆] (Cat. D), leads to complete formation of 2a without any additional additive within 15 minutes at room temperature (entry 5).

Once the hydroacyloxylation reaction was optimized, we investigated if it would be possible to apply the hydroformylation reaction to lactones 2a. Indeed, the literature does not mention any example of the application of this transformation to such substrates. First, we determined the best ligand for the hydroformylation, the latter having a significant impact on the conversion of the reaction and its selectivity (Table 2). Three compounds can be obtained: iso-aldehyde 4a, n-aldehyde 5a, and compound 6a, the latter resulting from the side hydrogenation reaction. This screening was carried out using lactone 2a as substrate under reaction conditions commonly used: Rh(CO)₂(acac) (1 or 2 mol%), ligand L (1, 2 or 4 mol%) in toluene at 70 °C under the pressure of 20 bars of syngas (CO/H₂, 1 : 1).¹⁰ Monodentate phosphite ligands, such as P(OPh)₃ (L3), demonstrated better catalytic performance in the hydroformylation of 2a than monodentate phosphine ligands, such as PPh₃ (L1) or JohnPhos (L2) (entries 1–3). On other side, bidentate phosphite ligands such as BiPhePhos (L4) did not allow a good conversion in 4a (entry 4). We then explored various substituents on the aryl group of the monodentate phosphite ligands. Indeed, it is well established that the substitution pattern of aryl groups plays a key role in the activity and stability of the rhodium–phosphite complex.¹¹ An alkyl group in the ortho position improves the conversion to 4a only minimally, if at all (L5–L8, entries 5–8). The ligand with a methoxy group in para-position (L9) was not performant at all, unlike the same group in ortho-position (L10) which gave an excellent result with 86% of conversion into 4a (entries 9 and 10). The presence of the methoxy group in the ortho-position electronically enriches the aromatic ring, thereby enhancing the catalytic activity of the complex, while protecting the phosphorus atom against hydrolysis. We then decided to decrease the amount of ligand L10 and to change the solvent of the reaction to DCE in order to standardize reaction conditions of the two transformations (hydroacyloxylation/hydroformylation). The result was exactly the same. This catalytic system was also efficient with the use of 1 mol% of Rh(CO)₂(acac) and 2 mol% of ligand L10 (entry 12). It is noteworthy that during the development of the purification conditions of carbaldehyde 4a, we found that it was unstable under both standard and reversed-phase chromatography conditions. Consequently, all the results presented in this part correspond to the conversions obtained by integrating the ¹H NMR spectrum of the crude reaction. Moreover, throughout the optimization of this reaction, we never observed the formation of the n-aldehyde 5a or of the hydrogenated substrate 6a.

Table 2 Optimization of the hydroformylation reaction step^a

Entry	Ligand (L)	Ratio 2a/4a ^b	Entry	Ligand (L)	Ratio 2a/4a ^b
a Reaction conditions: Rh(CO)2(acac) (2 mol%), ligand (8 mol%), toluene. b Measured by ^1H NMR in the crude mixture. c Ligand (4 mol%). d Rh(CO)2(acac) (2 mol%), L10 (4 mol%), DCE. e Rh(CO)2(acac) (1 mol%), L10 (2 mol%), DCE.
1	PPh3 (L1)	82/18	7	(2,4-Di-tBu-PhO)3P (L7)	49/51
2	JohnPhos (L2)	98/2	8	(2,6-Di-Me-PhO)3P (L8)	92/8
3	(PhO)3P (L3)	55/45	9	(4-MeO-PhO)3P (L9)	76/24
4^c	BiPhePhos (L4)	91/9	10	(2-MeO-PhO)3P (L10)	14/86
5	(2-Me-PhO)3P (L5)	46/54	11^d	(2-MeO-PhO)3P (L10)	14/86
6	(2-tBu-PhO)3P (L6)	55/45	12	(2-MeO-PhO) 3 P (L10)	13/87

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Since in the OTC procedure all catalytic species required must be present from the beginning, we studied the impact of the presence of ligand and rhodium(I) complex on the gold(I)-catalyzed hydroacyloxylation reaction (Table 3). We first observed that Cat. D [(L2)Au(MeCN)][SbF₆], which has been identified as the most efficient catalyst to achieve regioselective hydroacyloxylation of 2a, loses its catalytic performance at room temperature after 1 h when it is placed in the presence of 2 equivalents of the L10 ligand (entries 1 and 2). These results led us to hypothesize that in the presence of an excess of ligand, the loss of the catalytic performances of the gold(I) complex, could be related to the predominant formation of new organometallic species, [(L2)Au(L10)][SbF₆], catalytically inert at room temperature in the hydroacyloxylation reaction. On the other hand, in the presence of ligand L10, when a rhodium(I) source is introduced into the reaction medium, we observe that the catalytic performances of the gold catalysts are regenerated (entry 3).

Table 3 Impact of L10/Rh(CO)₂(acac) on gold(I)-catalyzed hydroacyloxylation^a

Entry	[Rh]	L	Product (%)
a Measured by ^1H NMR in the crude mixture.
1	—	—	2a (100)
2	—	L10	1a (100)
3	Rh(CO) 2 (acac)	L10	2a (100)

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The presence of the rhodium(I) source could thus allow the release of a sufficient quantity of the catalytically active organogold species to complete the reaction. To confirm the possible interaction between Cat. A, Rh(CO)₂(acac), and ligand L10, we conducted a study by ³¹P NMR regarding several mixtures of the catalytic species involved at the beginning of our OTC procedure (Fig. 1).

Fig. 1 ³¹P NMR analyses (162 MHz, CDCl₃) of different species involved in the OTC. Complete study and full spectrum are shown in ESI.† (a) Rh(CO)₂(acac) (1 equiv.), L10 (2 equiv.), CDCl₃. (b) Cat. D (1 equiv.), L10 (2 equiv.), CDCl₃. (c) Rh(CO)₂(acac) (1 equiv.), Cat. D (1 equiv.), L10 (1 equiv.), CDCl₃ or Rh(CO)(L10)(acac) (1 equiv.), Cat. D (1 equiv.), CDCl₃. (d) Rh(CO)₂(acac) (1 equiv.), Cat. D (1 equiv.), L10 (2 equiv.), CDCl₃.

We first characterized the rhodium pre-catalyst of our hydroformylation reaction, generated in situ by chelation of the commercial rhodium salt (Rh(CO)₂(acac), 1 equiv.) by ligand L10 (2 equiv.). This complex is characterized by a doublet at 123.53 ppm with a ³¹P–¹⁰³Rh coupling constant of 293 Hz (spectrum a). It is interesting to note that the ligand L10 was detected in the reaction medium in its free form (at 134.35 ppm) suggesting that the rhodium is bearing only one ligand (Rh(CO)(L10)(acac)).¹² The ³¹P NMR of Cat. D, shows one singlet at 57.02 ppm (not shown here, see ESI†) and the mixture of this catalyst with ligand L10 shows two NMR signals (63.97 and 131.49 ppm) appearing as doublets due to a ³¹P–³¹P coupling (J = 434 Hz) through the gold atom, suggesting the formation of the [(L2)Au(L10)][SbF₆] complex (spectrum b).¹³ These chemical shifts were used as a reference to study the affinity of ligand L10 in the presence of the bimetallic couple Au(I)/Rh(I). Indeed, when ligand L10 (1 equiv.) is added to a mixture of the two metallic species (1 equiv. each), we have observed the appearance in ³¹P NMR of the characteristic signal of the [(L2)Au(L10)][SbF₆] complex (spectrum c). This observation shows that ligand L10 has a greater affinity for Au(I) than Rh(I). The same result is observed if Au(I) (1 equiv.) is added into a mixture of Rh(I) (1 equiv.) and ligand L10 (1 equiv., spectrum c), confirming a weaker binding force between the ligand and Rh(I). The last experience shows an equimolar distribution of the ligand L10, in case of using 2 equiv. of L10 facing to one equivalent of each metal (spectrum d). It is important to note that the ligand JohnPhos (L2) was never detected in the reaction medium, either in its free form or in the form of complex Rh(I)-JohnPhos, inactive in the hydroformylation reaction applied to our heterocycles (cf.Table 2, entry 2). In order to evaluate the potential impact of syngas on the complexation of L10 with the gold complex, we bubbled syngas through a solution containing Au(I) and L10 in a 1 : 2 ratio. No change was observed, and the obtained spectrum was identical to spectrum b (Fig. 1). One equivalent of Rh(I) was subsequently added, and the recorded spectrum remained identical to spectrum d (Fig. 1). All these experiments only provide an insight into the initial state of the catalytic system in the OTC. We then focused the study on the Au(I)/Rh(I) OTC reaction, thus, seeking to find a compatibility between the two organometallic systems. In this regard, we have combined the reaction conditions as the best for either of the transformations involved. The objective was the formation of the carbaldehyde of interest 4a, by adding Cat. D (1 mol%) to a solution of 2-(2-ethynylphenyl)acetic acid 1a, Rh(CO)₂(acac) (1 mol%) and P(2-MeOPhO)₃ (L10, 2 mol%) in DCE at 70 °C under the pressure of 20 bars of syngas (Table 4, entry 1).

Table 4 OTC optimization^a,b

Entry	x	y	z	4a	2a	7a	8a/9a
a Reaction conditions: Cat. D (x mol%), Rh(CO)2(acac) (y mol%), L10 (z mol%), DCE (0.25 M), CO/H2 (1 : 1, 20 bars), 70 °C, 16 h. b Ratio measured by ^1H NMR in the crude mixture.
1	1	1	2	84	9	2	5
2	0	1	2	0	11	0	89
3	1	0	2	0	100	0	0
4	1	1	0	2	94	2	2
5	1	1	2	2	84	3	11
6	1	2	4	84	3	3	10
7	1	4	4	90	5	0	5

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The combination of the two previously optimized reaction conditions (1 mol% of Cat. D and Rh(CO)₂(acac) and 2 mol% of L10) allowed a total conversion of acid 1a, the acquisition of carbaldehyde 4a with a conversion of 84%, and further information on the composition of the crude of reaction of such a transformation. We observed residual traces of intermediate lactone 2a (9%) and identified three secondary products. Aldehydes 8a and 9a are derived from over-functionalization, which arises directly from the presence of reactive species from the initial moment of the procedure. Here, this phenomenon takes the form of a hydroformylation-reduction reaction applied directly to the unsaturation of 2-(2-ethynylphenyl)acetic acid 1a.¹⁴ The acetophenone 7a derived from the hydrolysis of lactone intermediate 2a. Moreover, as expected, without gold catalyst, product 8a and 9a from hydroformylation–reduction reaction were mostly recovered with little part of 2a showing that Rh(I) was able to catalyze hydroacyloxylation but not as fast as the hydroformylation reaction (entry 2). Without Rh(I) catalyst, only 2a was recovered (entry 3) and without L10 the hydroformylation reaction was not efficient at all (entry 4).

With these reaction conditions in hand, Cat. D (1 mol%), Rh(CO)₂(acac) (1 mol%), L10 (2 mol%), DCE (0.25 M), CO/H₂ (1 : 1, 20 bars), 70 °C, we studied the kinetic of this OTC (Fig. 2).

Fig. 2 Kinetic study of [Au(I)]/[Rh(I)] OTC reaction of 1a. Red and blue plained curves, OTC reaction, conditions: Cat. D (1 mol%), Rh(CO)₂(acac) (1 mol%), L10 (2 mol%), DCE (0.25 M), CO/H₂ (1 : 1, 20 bars), 70 °C. Dashed red curve, hydroacyloxylation of 1a, conditions: Cat. D (1 mol%), DCE, RT. Dashed blue curve, hydroformylation of 2a, conditions: Rh(CO)₂(acac) (1 mol%), L10 (2 mol%), DCE (0.25 M), CO/H₂ (1 : 1, 20 bars), 70 °C, 16 h.

When the OTC reaction was stopped after 1 h, 97% of the starting substrate 1a has been converted into 2a, without formation of product 4a (Fig. 2, red and blue plained curves). This is comparable with the rate of hydroacyloxylation reaction of 1a (Fig. 2, dashed red curve). After 4 h, the OTC reaction does not seem to have evolved much, the starting substrate 1a is still not completely consumed and only 2% of the expected product 4a is formed. After 8 h of reaction, the substrate is completely converted. The desired product proportion 4a has reached 6% conversion. After 10 h of reaction, the results observed have hardly changed, indicating little progress in the OTC between 1 h and 10 h. The progress of the reaction increases sharply from 10 h onwards. Indeed, the conversion of 2a into 4a reached 48%, at 12 h suggesting that Rh(I) hydroformylation takes place from the 10 h threshold. After 16 h, the reaction is almost complete, with only 9% of product 2a remaining. Compared to the hydroformylation of 2a (Fig. 2, blue dashed curves), only 4 h is necessary to reach 50% conversion into 4a and 8 h for the completion of the reaction. Moreover, under these reaction conditions, the OTC reaction proved to be non-reproducible, with the lactone 2a as the major products (Table 4, entries 1 and 5). The slowdown of the hydroformylation reaction, combined with the lack of reproducibility of the OTC reaction, led us to double the amount of rhodium complex and ligand (respectively 2 and 4 mol%, entry 6).

This restored good conversion to the targeted aldehyde 4a, but also favored the hydroformylation of 1a over its hydroacyloxylation, as 10% of aldehydes 8a/9a is recovered. Therefore, we then increased the quantity of rhodium to 4 mol% to limit the amount of free L10 (Table 4, entry 7). In this way, we succeed to obtain carbaldehyde 4a with a conversion of 90% and good reproducibility. Eventually, the use of Cat. D (1 mol%), Rh(CO)₂(acac) (4 mol%) and L10 (4 mol%) in DCE (0.25 M) under syngas pressure (20 bars) at 70 °C proved to be the conditions of choice for this OTC reaction.

Based on competitive ligand coordination between the two metal complexes, we propose the mechanism detailed in Scheme 2 for this Au(I)/Rh(I) OTC. As shown by experiments on interactions between catalytic systems, as well as the kinetic study performed on the OTC, competitive ligand coordination between the gold and rhodium catalysts lead to their partial and reversible deactivations. On the one hand, at the beginning of the reaction, since ligand L10 coordinates more easily gold than rhodium, an equilibrium is established. A low amount of L10 facilitates its decoordination from gold in favor of substrate 1a. L10 can then be intercepted by rhodium and the hydroacyloxylation reaction can take place. After protodeauration, lactone 2a is formed. On the other hand, the bimetallic equilibrium would also allow the formation of the active rhodium complex bearing only one ligand L10, through competitive coordination with the gold complex. At this stage, a sufficient amount of both Rh(I) complex and L10 are necessary to promote the hydroformylation reaction. If so, this allows the reaction of lactone 2a with the rhodium complex, which, after carbon monoxide insertion, dihydrogen addition, and reductive elimination, would yield aldehyde 4a.

Scheme 2 Proposed mechanism of the Au(I)/Rh(I) OTC reaction from 1a to 4a.

Then, we explored the scope of the reaction. As illustrated in Scheme 3, the OTC transformation is efficient on a broad range of substrate 1 with good to excellent conversions in favor of aldehydes 4 (55–94%). As in case of 1a, all of these transformations proved remarkably regioselective as only one compound was obtained in each case. A wide range of aryls exhibiting electron-donating or withdrawing groups are well tolerated at any position without affecting the conversion (for example compounds 12e–h).

Scheme 3 Au(I)-hydroacyloxylatio/Rh(I)-hydroformylation OTC followed with derivatization reactions. ^a (1) Cat. D (1 mol%), Rh(CO)₂(acac) (4 mol%), L10 (4 mol%), DCE (0.25 M), CO/H₂ (1 : 1, 20 bars), 70 °C, (2) NaBH₃CN (2 equiv.), DCM, RT, 16 h. ^b (1) Cat. D (1 mol%), Rh(CO)₂(acac) (4 mol%), L10 (4 mol%), DCE (0.25 M), CO/H₂ (1 : 1, 20 bars), 70 °C, (2) NaBH₄ (2 equiv.), MeOH, RT, 16 h. ^c (1) Cat. D (1 mol%), Rh(CO)₂(acac) (4 mol%), L10 (4 mol%), DCE (0.25 M), CO/H₂ (1 : 1, 20 bars), 70 °C, (2) NaOAc (2 equiv.), NH₂OH·HCl (2 equiv.), EtOH, RT, 16 h.

As discussed above, due to the inherent instability of the various carbaldehydes obtained, we have developed several derivatization reactions to be applied at the end of the Au(I)/Rh(I) OTC procedure to obtain sufficiently stable compounds to be isolated and characterized. First, we focused on the classical reduction of aldehydes in the corresponding primary alcohol (compounds 10 and 13, Scheme 3). For this, we performed a screening of different reduction systems (NaBH₄, NaBH₃CN, NaBH(OAc)₃, DIBAL-H). It appeared that the best conditions to transform carbaldehydes 4 into alcohols 10 was the use of NaBH₃CN in DCM, while for the transformation of carbaldehydes 11 into 13, it was the use of NaBH₄ in MeOH. The application of the OTC procedure Au(I)/Rh(I) hydroacyloxylation/hydroformylation followed by the reduction reaction allowed the preparation of 11 heterocycles 10 and 13 with yields ranging from 24 to 52%. The structures of two compounds were confirmed by crystallization: compound 10a and 13a.

A second derivatization reaction have been developed. We were interested in the condensation of carbaldehydes 4 and 12 with hydroxylamine to give the corresponding oximes 14 and 15 (Scheme 3). The crude mixture from the OTC reaction was thus directly solubilized in ethanol, and sodium acetate and hydroxylammonium chloride were added. The application of the OTC/hydroxylamine condensation procedure allowed the preparation of 12 new heterocycles bearing an oxime moiety with yields ranging from 25 to 69%. These yields are, for the most part, closer to the conversions observed after the OTC procedure than those obtained with the previous derivatization.

Conclusion

In summary, we have developed an orthogonal tandem catalysis involving Au(I)-hydroacyloxylation and Rh(I)-hydroformylation, demonstrating that these two metals are compatible with each other. The application of the Au(I)/Rh(I) hydroacyloxylation/hydroformylation OTC procedure gave access to 14 carbaldehydes of interest. After derivatization reactions, 11 alcohols and 12 oximes were obtained, with yields ranging from 24 to 52% and from 25 to 69%, respectively. ³¹P NMR experiments and a kinetic study carried out on the OTC allowed a detailed understanding of the catalytic cycles involved, highlighting the competitive ligand coordination between the gold and rhodium catalysts. These studies allowed for the determination of the optimal catalytic conditions, leading to the development of the first OTC Au(I)/Rh(I) reaction.

Author contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Data availability

All the data are available in the ESI† including ¹H, ¹³C, ³¹P and ¹⁹F description and spectra.

The data for 10a and 13a will be provided when this article is accepted. CCDC 2384274 for 10a and 2111415† for 13a contains the supplementary crystallographic data for this paper.

A checkcif is provided in the list of documents supplied for compounds 10a and 13a.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work of the Interdisciplinary Thematic Institute InnoVec, as part of the ITI 2021-2028 program of the University of Strasbourg, CNRS and Inserm, was supported by IdEx Unistra (ANR-10-IDEX-0002) and SFRI (STRAT'US project) under the framework of the French Investments for the Future Program. The doctoral grant for E.S. was financed by the “Ministère de l'Enseignement Supérieur, de la Recherche et de l'Innovation”. We thank the leading committee of our laboratory (LIT, UMR 7200) for the technical support, the platform PACSI (GDS 3670) for NMR and mass analyses and Lydia Karmazin and Corinne Bailly (GDS 3648) for X-ray analyses.

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Footnote

† Electronic supplementary information (ESI) available. CCDC 2384274 and 2111415. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d5qo00084j

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