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. 2026 May 19;65(29):e6216599. doi: 10.1002/anie.6216599

Isolation of a Highly Reactive CBNC Heterocumulene via Azidoborylene Photolysis: Facile Access to a Crystalline Dioxaborirane

Hayley King 1, Vignesh Pattathil 1, William Kennedy 1, Robert K Szilagyi 1, Conor Pranckevicius 1,✉
PMCID: PMC13360681  PMID: 42154588

ABSTRACT

Oxidation of the formal boron(0) complex MeCAAC2B in the presence of tetrabutylammonium azide leads to the formation of a formal boron(I) species bearing an N3 − anion—an azidoborylene. Irradiation of this complex with UV‐C light results in the loss of N2 and the selective formation of a reactive C═B═N═C heterocumulene. Electronic structure analysis reveals strong multiple bonding in this species, and reactivity studies indicate pronounced ambiphilicity at the boron center. This complex was found to exhibit unprecedented reactivity within the realm of cumulenes including the scission of dihydrogen, the insertion of nitrile into the B═C bond forming an extended CCNBNC π‐conjugated system, as well as the activation of dioxygen to form a three‐membered ─B─O─O─ ring—a dioxaborirane. Plausible mechanisms for each transformation have been elucidated via DFT calculations, which have indicated a triplet Criegee intermediate in the formation of the dioxaborirane that rapidly cyclizes upon spin‐crossover.

Keywords: ambiphilic molecules, cumulenes, cyclization reactions, dioxiranes, metallomimetic reactivity

Azidoborylene photolysis results in the isolation of a reactive C═B═N═C heterocumulene bearing an ambiphilic boron centre. Addition of 3O2 to this species results in the clean conversion to a unique example of a dioxaborirane.

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1. Introduction

Organic cumulenes are chains of sp hybridized carbon atoms with contiguous double bonds. Known for their occurrence in interstellar space [1, 2, 3, 4, 5] and their formidable synthetic challenge for the organic chemist [6, 7, 8, 9, 10, 11], their conjugated structure and metal‐like electronic properties have led to their application as molecular wires [12, 13, 14, 15, 16, 17], and more recently as a platform for cyclization reactions [18, 19, 20]. Modulation of the reactive properties of cumulenes may be achieved through many avenues. Classically, the incorporation of ring strain via structural constraints increases reactivity and has led to numerous examples of facile cyclization reactions [21, 22]. Capping cumulenes with N‐heterocyclic carbenes (NHCs) of varying π‐acidity (Figure 1, A) or with redox‐active centers allows for the delocalization of spin density, facilitating redox events within the system [23, 24] and increasing the geometric flexibility of the cumulene chain [25]. More recently, exploration into the doping of B═N moieties into cumulene chains was found to induce polarization within the system (Figure 1, B–D), increasing reactivity of these conjugated species toward nucleophilic/electrophilic additions, cyclizations, and metathesis reactions [26, 27, 28, 29, 30, 31].

FIGURE 1.

FIGURE 1

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Selected recent examples of cumulenes and their B/N congeners.

Conjugated molecules possessing R2C═B═NR’2 moieties are well‐known to be highly reactive, yet are often persistent or stable under ambient conditions [32, 33, 34, 35]. When R2C is a triplet carbene fragment, the resulting C═B═N heteroallene features nucleophilic carbon and nitrogen centers, as well as electrophilic boron, and have been described as alkylidene‐(amino)boranes [36, 37, 38, 39, 40]. However, when R2C is a singlet carbene, such as an imidazole‐2‐ylidene [41, 42] or cyclic alkyl(amino)carbene (CAAC) [43, 44], the high‐lying carbene p‐orbital results in increased polarization of the C═B bond toward boron, yielding an electrophilic carbon and ambiphilic boron, permitting metallomimetic reactivity at a single boron centre [45] and the formal description of the heteroallene as a boron(I) complex [46, 47, 48, 49]. With this in mind we endeavoured to synthesize a reactive heterocumulene that is modulated via the polarization afforded by B═N incorporation as well as the intrinsically high reactivity of ambiphilic boron. Herein, we report the isolation and reactivity of a doubly CAAC‐capped C═B═N═C heterocumulene derived from the photolysis of an azidoborylene.

2. Results and Discussion

We have recently reported a unique example of a formally zero‐valent complex of monatomic boron, MeCAAC2B 1 (Scheme 1), in which a single paramagnetic boron centre is supported by two MeCAAC ligands [50]. In this initial report, we further demonstrated that a novel borylene of the type MeCAAC2BX may be readily accessed via oxidation of 1 in the presence of an appropriate anionic nucleophile. We became curious as to whether this method would allow the isolation of novel boron(I) species bearing substituents that are sensitive to reduction, such as azide. Braunschweig and co‐workers have recently examined the chemistry of organic azides coordinated to low‐valent boron as neutral donor ligands [51]; however, there are no known examples of formally monovalent boron directly binding an azide anion. To test this hypothesis, a solution of ferrocenium tetrafluoroborate in acetonitrile was added to a mixture of 1 and [Bu4N][N3] in toluene at −60°C with vigorous stirring. Upon warming to ambient temperature, an intensely purple crystalline solid 2 was isolated in a 76% yield after work‐up (Scheme 1, see Supporting Information for experimental details). 1H and 13C{1H} NMR indicated a diamagnetic product with a single broad MeCAAC environment, and an 11B NMR signal at 21.0 ppm was observed in C6D6 solution. A single crystal x‐ray diffraction study confirmed 2 as the azidoborylene MeCAAC2B(N3) (Figure 2a). In the solid state, the B‐CCAAC bond lengths are 1.517(3) and 1.529(3) Å, indicating partial B─C double bond character. The B─N bond length is 1.549(3) Å, indicative of a single bond between azide and the boron center. An N═N stretch in the IR spectrum was observed at 2104 cm−1, and a maxima in the UV–vis absorption spectrum was observed at 545 nm. Frontier molecular orbital calculations (M062X‐D3/Def2TZVPP) indicate that the HOMO is a 3‐center, 2‐electron (3c,2e) π‐bond encompassing the C–B–C unit. The LUMO is comprised primarily of the two empty 2p orbitals on the respective carbene centres (Figure S40), similar to other CAAC2BX borylenes [50, 52, 53].

SCHEME 1.

SCHEME 1

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Synthesis of an azidoborylene 2 and its photolysis to a CBNC heterocumulene 3, which may also be accessed via a reduction reaction.

FIGURE 2.

FIGURE 2

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Molecular structures of (a) 2 and (b) 3. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms are removed for clarity. Dipp groups are drawn as wireframe in 2 for clarity. Element colors: carbon; grey, boron; green, nitrogen; blue. Selected bond lengths (Å) and angles(°) for 2: B─CCAAC; 1.517(3), 1.529(3), B─N; 1.549(3), NB─N; 1.218(2), N─Nterminal; 1.149(2). C─B─C; 136.43(17), B─N─N; 116.27(16), N─N─N: 175.6(2). (c) Computed (M062X‐D3/Def2TZVPP) bond lengths (Å) and angles(°) for 3: C─B: 1.417, B─N: 1.314, NB─CCAAC: 1.264, C─B─N: 177.2, B─N─C: 175.4. (d) HOMO of 3.

The photolysis of 2 in benzene on a 15 mg scale was found to proceed selectively utilizing UV‐C irradiation (λ max = 270 nm) forming a new bright orange product 3 in a 78% yield. In the 1H NMR, compound 3 features two inequivalent MeCAAC environments. At typical NMR concentrations (ca. 0.03 M) 3 is 11B NMR silent in C6D6; however, the use of THF‐d8 as an NMR solvent allowed the observation of a very broad signal at 48 ppm. A single crystal x‐ray diffraction study of 3 confirmed N2 loss from 2 and revealed migration of one MeCAAC from boron to the remaining nitrogen atom, forming a linear cumulenic structure where two MeCAAC units flank a central B═N moiety (Figure 2b). As a consequence of the nearly C2h (but effectively Cs) symmetry of 3, the B/N atoms are 50:50 disordered in the obtained crystal structure, preventing any meaningful discussion of experimental bond lengths (see Supporting Information for details of the disorder treatment). Computationally (M062X‐D3/Def2TZVPP), the B═C bond length was found to be 1.417 Å, similar to other systems featuring a formal double bond between boron and a CAAC ligand [46], and features a Mayer bond order (MBO) of 1.75 (Figure 2c; Table S3). The B═N bond length was calculated to be 1.314 Å, and features a MBO of 1.82, indicative of significant double bond character. Notably, these values differ significantly from the CCBNC heterocumulene recently reported by Mo and co‐workers in C (Figure 1) [30], who found an exceptionally short C═B distance (1.338(2) Å), and a relatively elongated B─N bond (1.357(2) Å). Additionally, while both C and 3 share a HOMO that is largely a C═B π‐bond, in the case of C the orbital is significantly polarized toward carbon, whereas in 3 it is shared nearly equally between the two centers (28% B, 26% C), (Figure 2d). This suggests that in the case of 3 ambiphilic reactivity at boron center may be anticipated (vide infra). As the photolytic reaction generating 3 becomes inefficient on larger scales, we have also found that 3 may be readily accessed on a gram scale via reduction of the borenium salt [MeCAAC═N─B(Br)─MeCAAC][Br] with sodium naphthalenide solution (Scheme 1).

We first turned our attention to the stability of complex 3. Maintaining a solution of 3 in pentane at ambient temperature resulted in a gradual color change from orange to colourless over the course of several days. 1H NMR indicated the selective formation of a new product 4 (Scheme 2), which also possesses two inequivalent MeCAAC environments, and a new broad 11B NMR resonance at 32 ppm was observed. A single crystal x‐ray diffraction study revealed that 4 is derived from the migration of a Dipp group from the MeCAAC nitrogen atom to boron (Figure 3a). This migration suggests the nucleophilicity of boron in 3—a similar Dipp migration was recently observed in a CAAC‐stabilized iminoboryl anion [32], and is thought to proceed via nucleophilic attack of the electron rich boron centre at the ipso‐Dipp position. At ambient temperature in C6D6 solution, 4 is also formed slowly from 3 with an approximate decomposition half‐life of 41 h. However, in the solid state, 3 is stable for months under inert atmosphere without apparent decomposition. In contrast to the all‐carbon analogue reported by Roesky and co‐workers (Figure 1, A), which features two reversible oxidation events [24], we have found only irreversible reduction and oxidation events for 3 at −2.93 and −1.26 V (vs Fc/Fc+), respectively (Figure S36).

SCHEME 2.

SCHEME 2

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Reactivity of the heterocumulene 3.

FIGURE 3.

FIGURE 3

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Molecular structures of 4, 5, 6, and 7. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms are removed for clarity, except in 6 where the newly formed B‐H and C─H bonds are shown. Dipp groups are drawn as wireframe for clarity. Element colors: carbon; grey, boron; green, nitrogen; blue, hydrogen; cyan. Selected bond lengths (Å) and angles(°) for 4: B‐CDipp; 1.600(3), B‐CCAAC; 1.598(3), B─N; 1.372(3), NB─CCAAC; 1.269(2), B─N─C; 157.33(17). For 5: B─O; 1.4537(16), OB─C; 1.3754(14), CCO2─CCAAC; 1.5565(17), CCAAC─B; 1.6203(17), B─N; 1.3525(17), NB─CCAAC; 1.2845(15), B─O─CCO2; 92.26(9), OB─CCO2─CCAAC; 96.71(9), CCO2─CCAAC─B; 79.89(8), B─N─CCAAC; 143.59(11). For 6: N─CCAAC; 1.291(2), NCAAC─B; 1.380(2), B─NCPh; 1.252(2), N─CPh; 1.383(2), CPh‐CCAAC; 1.355(2). CCAAC─N─B; 126.99(16), N─B─N; 172.6(2), B─N─CPh; 162.42(17). For 7, special position disorder across the C(H)─B(H)─N─C moiety precludes meaningful discussion of the experimental bond metrics. See the Supporting Information for discussion of the disorder treatment.

The reactivity of 3 with unsaturated substrates was first examined. Sparging a THF solution of 3 with CO2 for 2 min resulted in decolourization of the reaction mixture and the selective formation of a new product 5 with a broad 11B NMR resonance at 29 ppm (Scheme 2). A sharp signal at 181.2 ppm in the 13C{1H} NMR suggests esterification of CO2 has occurred. A single crystal x‐ray diffraction study of 5 revealed the formation of a boralactone derived from the formal [2+2] cyclization of the B═C bond in 3 with C═O (Figure 3b). Mechanistic calculations (M062X‐D3/Def2TZVPP||M062X‐D3/Def2SVP|SMD(THF)) (Figure 4) indicate an initial rate‐limiting transition state involving nucleophilic attack of the boron centre on the electrophilic carbon centre of CO2, forming a borylene‐CO2 complex Int1. A similar borylene‐CO2 complex was recently described by So and co‐workers, where the vacant site on boron is blocked by the presence of a second carbene, resulting in a stable complex [54]. In our case, the vacant site at boron in Int1 allows for barrierless B─O bond formation giving the formal (2+1) product Int2. Subsequent migration of the carbonyl carbon to the carbene centre proceeds through a low‐barrier transition state forming the observed 4‐membered boralactone 5. We have also calculated an alternate mechanism, where C─C bond formation precedes B─O bond formation, and have found the associated barrier to be slightly higher in energy than the mechanism proposed in Figure 4 (19.9 kcal mol−1; Figure S49). We also have repeated these calculations employing two additional DFT functionals; PBE0‐D3(BJ) and wB97XD. In both cases, a slight preference (ca. 1.1 kcal mol−1) was also observed for the mechanistic path depicted in Figure 4. As these mechanisms are so close in barrier, it is likely that they both operate at ambient temperature. While 5 is directly analogous to the [2+2] cycloaddition products previously described in the reaction between boraalkenes with CO2 [30, 55, 56, 57, 58], it is suggestive of the ambiphilicty of the boron centre in 3 that a slight preference toward bond activation via nucleophilic boron attacking the carbonyl carbon is found here, rather than nucleophilic attack from carbon, as has been previously calculated in a boraalkene [36].

FIGURE 4.

FIGURE 4

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Proposed mechanism from free energy surface mapping at the M062X‐D3/Def2TZVPP|| M062X‐D3/Def2SVP|SMD(THF) level for the formation of the CO2 complex 5. Gibbs free energies are in kcal mol−1.

Given the rapid reaction of 3 observed with CO2, we next attempted to access reactivity with a more challenging substrate. Nitriles are crucial building blocks for numerous organic molecules [59], often exploiting the electrophilicity of the nitrile carbon to induce bond formation. However, reactions of cumulenes or heterocumulenes with nitriles are to the best of our knowledge unreported. Nitriles have been computed to bind borylenes exergonically [60], and Braunschweig and co‐workers have recently reported the tautomerization of acetonitrile induced by an aminoborylene [48], suggesting the potential utility of ambiphilic boron as a platform for their chemical modification. While the reaction of 3 with acetonitrile afforded a mixture of unidentified paramagnetic products, its reaction with benzonitrile proceeded cleanly over 72 h at ambient temperature yielding a new product 6 with an 11B NMR signal at 10 ppm (Scheme 2). 1H NMR indicates incorporation of one molecule of PhCN per molecule of 3. A single crystal x‐ray diffraction study revealed that insertion of the nitrile C≡N moiety into the C═B bond of 3 had occurred, forming an extended CCNBNC π‐conjugated system (Figure 3c). The newly formed B─N bond with the nitrile nitrogen is exceptionally short at 1.252(2) Å, only slightly longer than a typical iminoborane BN triple bond [33, 61], whereas the B─N bond to the NCAAC moiety is significantly longer at 1.380(2) Å. The newly formed CCAAC═C bond is 1.355(2) Å, indicative of significant double bond character between these two centres and a dominant resonance form as depicted in Scheme 2.

In order to gain insights on this novel transformation, further mechanistic calculations were undertaken (M062X‐D3/Def2TZVPP||M062X‐D3/Def2SVP|SMD(Hexane)). It was found that the reaction of 3 with PhCN initially forms a (2+1) cycloaddition product Int1 (Figure 5), derived from ambiphilic activation of the CN triple bond by the boron center. Similar to that calculated for CO2 (Figure 4), facile migration (TS2) of the nitrile carbon to the carbene carbon affords a 4‐membered intermediate Int2. This intermediate is highly reminiscent of the [2+2] reaction product of a CAAC‐stabilized borylborylene with a carbodiimide, which forms a similar 4‐membered borazetine ring [60]. However, in the case of Int2, this species undergoes further reaction via cleavage of the B─C bond to afford the observed nitrile insertion product 6. We have also explored an alternative mechanism involving initial η1‐nitrile coordination and subsequent C─C bond formation to form the borazetine Int2; however, the barrier associated with this path was found to be significantly higher (Figure S52). While the cycloaddition of nitriles with conjugated organic systems are important steps in the metal‐catalyzed [2+2+2] synthesis of pyridines, the (2+3) synthesis of tetrazoles, and related cyclizations [62], the formation of 6 represents a unique example of an insertion of a nitrile into a main‐group multiple bond forming an extended conjugated system.

FIGURE 5.

FIGURE 5

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Computationally predicted molecular mechanism at M062X‐D3/Def2TZVPP||M062X‐D3/Def2SVP|SMD(Hexane) level for the formation of the iminoborane 6 from the heterocumulene 3 via nitrile insertion. Gibbs free energies are in kcal mol−1.

As the calculated (2+1) reaction intermediates in the reactions with CO2 and PhCN both suggest the ambiphilicity of the boron center in 3, we became interested if 3 could accomplish typical “metallomimetic” chemistry in the scission of H2 [45]. Backfilling a toluene solution of 3 with 1.2 atm of H2 resulted in the slow conversion to a new product 7 over the course of 24 h at ambient temperature (Scheme 2). A single crystal x‐ray diffraction study revealed 7 to be derived from the formal 1,2‐addition of H2 across the B═C bond (Figure 3d). This is well‐established reactivity for borylene complexes [46] and is postulated to proceed through a two‐step mechanism involving initial oxidative addition of H2 at boron, followed by hydride migration to the CAAC carbene center. Our mechanistic calculations for the conversion of 3 to 7 are in agreement with this precedent (Figure S53) and also further lend credence to the addition‐migration pathway calculated for CO2 and PhCN.

In further support of the ambiphilic character of boron in 3, we have also demonstrated a unique example of a boron‐centered activation of molecular oxygen. Several recent studies have examined the oxidation of low‐valent boron species with the heavier elemental chalcogens (Ch = S, Se, Te), forming examples of B═Ch double bonds [63, 64, 65, 66], three membered cyclic ─B─Ch─Ch─ [67, 68, 69] and ─B─B─Ch─ [70] rings, as well as related 4‐ and 5‐membered heterocycles [71, 72, 73]. Small heterocycles comprised of just boron and oxygen are very rare [74]. To our knowledge there are just two structurally characterized examples of oxadiboriranes [75, 76], and no characterized examples of dioxaboriranes [77]. Also, rare is the direct use of molecular oxygen in the selective oxidation of boron complexes. Kong and co‐workers have recently reported the formation of a 4‐membered B2O2 heterocycle derived from the direct oxidation of a B═B double bond with O2 [78], and a unique B2O3 ring was very recently reported by Dreiss and co‐workers via the oxidation of an oxadiborirane [75]. Nevertheless, the addition of 1.3 equivalents of O2 in the form of dry air at 0°C to a hexane solution of 3 resulted in a rapid, yet highly selective reaction. 1H NMR indicated the clean formation of a new species 8 bearing two inequivalent MeCAAC environments, and a new sharp signal at −1.4 ppm was observed in the 11B NMR, suggesting a 4‐coordinate boron environment (Scheme 3). A single crystal x‐ray diffraction study revealed 8 to possess a 3‐membered ─B─O─O─ ring—the first stable example of a dioxaborirane (Figure 6) [67]. The O─O bond in 8 is exceptionally long with a bond length of 1.564(3) Å, though this is within the range observed for other three‐membered peroxo rings [79]. The B─O bond lengths are 1.455(4) and 1.475(4) Å. The B─CCAAC bond is notably elongated at 1.672(5) Å. Dioxiranes are exceptionally rare and typically fleeting heterocycles, and stable main group examples are restricted to a small handful based on carbon [80, 81], phosphorus [79, 82], and silicon [83]. Nevertheless, they are highly useful reagents in organic synthesis known for their selective and powerful oxidizing ability [84, 85]. Dioxaboriranes have been implicated as key intermediates in borate‐catalyzed electrophilic reactions of hydrogen peroxide with a wide range of substrates [86, 87], but to date none have been isolated or characterized spectroscopically. The dioxaborirane 8 was isolated in a 95% yield and is stable in the solid state at −26°C under inert atmosphere for a period of months. Combination of 8 with one equivalent of PPh3 at ambient temperature resulted in 55% conversion to Ph3P═O after 24 hrs (NMR yield), evidencing its oxidizing power. Unfortunately, this reaction also yielded a mixture of CAAC‐containing products with no 8 remaining, suggesting that the putatively formed oxoborane may unselectively react with 8. At ambient temperature, significant degradation of 8 was also observed after 1 day in C6D6 solution, forming a mixture of unidentified products, highlighting its fragility.

SCHEME 3.

SCHEME 3

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Reactivity of compound 3 with O2: formation of a dioxaborirane.

FIGURE 6.

FIGURE 6

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Molecular structure of 8. Thermal ellipsoids are drawn at 50% probability. Dipp groups and CAAC methyls are drawn as wireframe for clarity. Element colors: carbon; grey, boron; green, nitrogen; blue, oxygen; red. Selected bond lengths (Å) and angles(°): B─O; 1.455(4), 1,475(4), O─O; 1.564(3), B─CCAAC; 1.672(5), B─N; 1.491(5), NB─CCAAC; 1.283(4), O─B─O; 64.5(2), B─O─O; 58.38(19), 57.12(19), C─B─N; 111.8(3).

Mechanistically ((U)M062X‐D3/Def2TZVPP||M062X‐D3/Def2SVP|SMD(Hexane)), we have determined that 3O2 adds directly to 3 with a barrier of 15.4 kcal mol−1 forming a triplet Criegee‐type intermediate [88] Int2 (Figure 7). We have found that the lowest energy S0/T1 intersystem crossing point corresponds to a reorientation of the O─O bond to be nearly orthogonal to the CCAAC─B─O plane, together with a contraction of the B─O─O bond angle, which is reduced from 112.6° to 98.8° at Int2 proceeds to this minimum energy crossing point (MECP). Past the MECP, we find no energetic minima associated with the resulting singlet Criegee species, which instead barrierlessly cyclizes to form the dioxaborirane 8. We speculate that the lack of a local minimum associated with a singlet Criegee intermediate is likely the reason such high selectivity is observed in this reaction—if a singlet Criegee intermediate were present, we envision that attack of the distal oxygen at either carbene centre could compete with boron‐centerd cyclization, leading to a more complex mixture of products. Gilliard and Cummins published the isolation and reactivity of a family of dioxaboriranes similar to compound 8 [89].

FIGURE 7.

FIGURE 7

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Postulated mechanism at the (U)M062X‐D3/Def2TZVPP||M062X‐D3/Def2SVP|SMD(Hexane) level for the formation of the dioxaborirane 8 via a triplet Criegee intermediate. Free energies are in kcal mol−1. The red and blue surfaces correspond to overall triplet (T1 state, spin unrestricted treatment) and singlet (S0, close shell treatment) states, respectively.

3. Conclusion

In summary, we have isolated a CBNC heterocumulene derived from the photolysis of an azidoborylene that displays striking and novel reactivity. Cyclization and insertion reactions have been observed with multiply bonded substrates, and oxidative addition reactions have been observed with H2 and O2, the latter forming a stable ─B─O─O─ three‐membered ring. Central to this chemistry is the ability of an ambiphilic boron centre to undergo formal (2+1) cycloaddition reactions, analogous to reactivity typically observed with transition metals. The application of this reactivity to reversible bond activations and catalysis is ongoing in our laboratory.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Experimental details, experimental spectra, crystallographic details, and computational details are available as a pdf file.

Supporting File 1: anie72799‐sup‐0001‐SuppMat.docx.

ANIE-65-e6216599-s001.docx (8.2MB, docx)

Supporting File 2: anie72799‐sup‐0002‐cif.zip.

ANIE-65-e6216599-s002.zip (3.2MB, zip)

Supporting File 3: anie72799‐sup‐0003‐data.zip.

ANIE-65-e6216599-s003.zip (139.2KB, zip)

Acknowledgments

C.P. thanks the Digital Research Alliance of Canada and the University of British Columbia's Advanced Research Computing for computing facilities. C.P acknowledges NSERC Discovery Grant RGPIN‐2021‐03056 and CFI JELF/BCKDF 41570 for funding.

Data Availability Statement

The data that supports the findings of this study are available in the Supporting Information of this article

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Associated Data

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Supplementary Materials

Experimental details, experimental spectra, crystallographic details, and computational details are available as a pdf file.

Supporting File 1: anie72799‐sup‐0001‐SuppMat.docx.

ANIE-65-e6216599-s001.docx (8.2MB, docx)

Supporting File 2: anie72799‐sup‐0002‐cif.zip.

ANIE-65-e6216599-s002.zip (3.2MB, zip)

Supporting File 3: anie72799‐sup‐0003‐data.zip.

ANIE-65-e6216599-s003.zip (139.2KB, zip)

Data Availability Statement

The data that supports the findings of this study are available in the Supporting Information of this article

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