A crystalline stannyne

doi:10.21203/rs.3.rs-3050761/v1

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A crystalline stannyne

https://doi.org/10.21203/rs.3.rs-3050761/v1

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published 17 Jun, 2024

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The synthesis of heteronuclear alkyne analogs incorporating heavier group 14 elements (R¹−C≡E−R², E = Si, Ge, Sn, Pb) has posed a longstanding challenge, with no previous reports on isolable compounds of this nature. Until now, neutral silynes (R¹−C≡Si(L)−R²) and germynes (R¹−C≡Ge(L)−R²) stabilized by a Lewis base have achieved sufficient stability for structural characterization at low temperatures. Here we show the isolation of a base-free stannyne (R¹−C≡Sn−R²) at room temperature, achieved through the strategic use of a bulky cyclic phosphino ligand in combination with a bulky terphenyl substituent. Despite an allenic structure with strong delocalization of π-electrons, this compound exhibits adjacent ambiphilic carbon and tin centers, forming a unique carbon-tin multiple bond with ionic character. The stannyne demonstrates reactivity similar to carbenes or stannylenes, reacting with 1-adamantyl isocyanide and 2,3-dimethyl-1,3-butadiene. Additionally, its carbon-tin bond can be saturated by Et₃N·HCl or cleaved by isopropyl isocyanate.

Physical sciences/Chemistry/Coordination chemistry/Organometallic chemistry/Chemical bonding

Physical sciences/Chemistry/Chemical synthesis/Reactive precursors

Alkynes are ubiquitous organic compounds containing a carbon-carbon triple bond (Fig. 1a). They possess valuable versatility, participating in various reactions that lead to the formation of diverse functional groups and structures.¹ Consequently, alkynes play significant roles in both chemistry and biology. Substituting the carbon atoms involved in the triple bond of alkynes with heavier group 14 elements such as silicon, germanium, tin, and lead provides access to unique compounds known as heavier homonuclear alkyne analogs, namely disilyne,^2,3 digermyne,⁴ distannyne,⁵ and diplumyne⁶ (R¹−E≡E−R², E = Si, Ge, Sn, Pb) (Fig. 1a). The groups led by Power,^4-6 Sekiguchi² and Wiberg³ made significant contributions by isolating these compounds, opening up avenues for further exploration.^7-15 These compounds possess distinct characteristics compared to linear alkynes due to the second-order Jahn-Teller effect^16-19 observed in the heavier main group analogs. This effect leads to a slipped π-bond and substantial geometric distortion, providing a trans-bent molecular geometry. These unique electronic features render the heavier element centers ambiphilic, enabling them to display reactivity towards small molecules with strong enthalpic bonds.^7-11,20-23

By replacing one carbon atom in alkynes with a heavier group 14 element, their heteronuclear analogs are obtained: silyne, germyne, stannyne, and plumyne (R¹−C≡E−R², E = Si, Ge, Sn, Pb) (Fig. 1a). Theoretical predictions suggest that similar to R¹−E≡E−R², the R¹−C≡E−R² compounds adopt a trans-bent molecular geometry.^24-30 However, without Lewis base stabilization, these compounds are completely unknown as isolable species. A major challenge in synthesizing R¹−C≡E−R² is the energetically favored isomerization of R¹−C≡E−R² into R¹R²C=E, especially when R¹ and R² are small substituents.^24-30 Indeed, the isolation of these compounds as stable, isolable species has been a long-standing objective. As of now, the only neutral species proven to be sufficiently stable for structural characterization below –30 °C are silyne B³¹ and two germynes C,³² which were stabilized by a Lewis base, as reported by Kato and Baceiredo over a decade ago (Fig. 1b). It has been observed that they undergo intramolecular rearrangement reactions above this temperature threshold.^31,32 More recently, Kato isolated a base-stabilized cationic silyne D with moderate stability at room temperature (t_1/2 = 7 days in THF).³³ By contrast, stannyne and plumyne have not yet been identified as isolable species, even in the presence of a Lewis base for stabilization. Based on UV-vis spectroscopic observations, Kira and Sakamoto demonstrated the transient existence of stannyne F³⁴ during low-temperature photolysis of the corresponding diazo precursor (–196 °C). However, F is considered a highly transient species at room temperature, defying direct observation.^34,35 These findings underscore the inherent difficulty of isolating these highly reactive compounds under typical laboratory conditions.

Landmark studies by Bertrand,³⁶ as well as more recent work by Kato,^31,32 Baceiredo,^31,32 and our group,^37,38 have showcased the remarkable potential of phosphinodiazomethyl anion salt as a versatile synthon for introducing a singlet carbyne anion (R−C^–) fragment to both main group and transition metal centers. This unique reactivity has led to the preparation of unusual species such as singlet carbene A and B-E (Fig. 1b). In our previous work, we isolated a copper phosphinocarbyne anion complex E by employing a bulky phosphino substituent.³⁸

Complementary computational studies conducted by Su have shed light on the properties of stannynes and suggested that appropriate bulky substituents can encapsulate the central C≡Sn unit, protecting it and enabling its isolation as a stable species.²⁹ Herein, we demonstrate the isolation of a base-free crystalline stannyne via the strategic combination of a bulky cyclic phosphino and a bulky terphenyl substituent. This species represents an example of a base-free heteronuclear analog of alkynes containing a heavier group 14 element, and it is also the unprecedented main group species to possess diverse adjacent ambiphilic centers. This work has significant implications for the future design of adjacent bis-ambiphile main group systems.

Synthesis and characterization

In our pursuit of a stannyne, we aimed to introduce a π-donor substituent at the carbon center. This substitution has proven to effectively stabilize the singlet state of low-valent carbon species.^39,40 Additionally, increasing the steric bulk of the substituents at both carbon and tin atoms would provide desirable kinetic protection.⁵ To achieve this goal, we synthesized a stannylenyl diazomethane 2 (³¹P NMR: 125.5 ppm) as a precursor, bearing a bulky cyclic phosphino at the carbon center and a bulky terphenyl substituent at the tin center (Fig. 2). This compound was prepared by treating 1³⁷ with potassium tert-butoxide (^tBuOK) in THF followed by 2,6-Mes₂C₆H₃SnCl⁴¹ (Mes = mesityl) in the absence of light. The infrared absorption ν(CN₂) in 2 occurs at 1966 cm^–1, showing similarity to the corresponding absorption observed in metal-substituted phosphinodiazaomethanes.^37,38 Yellow single crystals of 2 were obtained by slowly evaporating its concentrated pentane solution at –30 ℃, and its structure was confirmed by X-ray diffraction (Fig. 3a).

We observed an intriguing phenomenon whereby N₂ was gradually eliminated from a C₆D₆ solution of 2 at room temperature over a period of approximately 7 hours (Supplementary Fig. S17). This elimination was concurrent with the intensity loss of the infrared ν(CN₂) absorption, affording species 3. Alternatively, irradiating (303 nm) a solid of 2 at room temperature for 30 minutes followed by washing with cold pentane resulted in the isolation of 3 as a yellow solid with a 96% yield (217 mg, 0.254 mmol). The ³¹P NMR resonance of 3 displays a singlet at 67.9 ppm accompanied by a satellite doublet arising from the P-Sn coupling (168.7 Hz). Meanwhile, its ¹¹⁹Sn NMR signal shows a doublet at 1149.3 ppm (168.7 Hz). This stands in stark contrast to the spectroscopic characteristics of 2, where no two-bond P-Sn coupling was observed and singlet resonances were detected in both the ³¹P (125.3 ppm) and ¹¹⁹Sn NMR (92.7 ppm) spectra.

Surprisingly, we found that 3 was exceptionally stable in both its solid and solution states at room temperature and could be safely stored for several months in a glove box with a nitrogen atmosphere. However, it should be noted that 3 is sensitive to air and gradually decomposes into unknown substances in 1 h (Supplementary Fig. S22). The electronic spectrum of 3 reveals the presence of two broad absorption bands, ranging from 320 to 360 nm and 400 to 480 nm (Supplementary Fig. S60), which are responsible for its characteristic yellow color. Time-dependent density functional theory (TD-DFT) calculations indicate that these bands originate from HOMO to LUMO and HOMO–1 to LUMO transitions, respectively (Supplementary Fig. S71).

Compound 3 crystalized as yellow crystals from a concentrated pentane solution at –30 ℃, and its X-ray diffraction analysis confirmed its formulation as [(CH₂)(NDipp)]₂PCSn(C₆H₃-2,6-Mes) (Dipp = 2,6-diisopropylphenyl; Mes = mesityl) (Fig. 3b). In contrast to the pyramidalization observed at P(1) in 2 (Fig.3a), the P(1) atom of 3 adopts a trigonal planar geometry with a sum of angles of 358.6°. Notably, the P(1)−C(1) bond in 3 is significantly shortened (1.561(6) Å) compared to that of 2 (1.879(8) Å), indicating strong P-to-C π-donation and resulting in multiple bond character. This is similar to observations in Bertrand’s (phosphino)(silyl)carbene Me₂Si(^tBuN)₂PCSiMe₃⁴² and our copper phosphinocarbyne anion complex [(CH₂)(NDipp)]₂PCCu(IPent) (IPent = 1,3-bis(2,6-di(3-pentyl)phenyl)imidazol-2-ylidene).³⁸ Additionally, the C(1)−Sn(1) bond length in 3 (2.082(6) Å) is shortened relative to 2 (2.134(8) Å) and lies between Pyykkö’s standard values for C−Sn single (2.15 Å) and double bonds (1.97 Å).⁴³ For comparison, the Sn(1)−C(2) bond length in 3 is 2.217(5) Å. These data indicate the presence of a multiple bond between C(1) and Sn(1) in 3. The bond angles of P(1)−C(1)−Sn(1) (136.7(3)°) and C(1)−Sn(1)−C(2) (98.0(2)°) in 3 are slightly more acute than those in 2 (138.0(5) and 105.6(5)°, respectively).

Computational studies

We conducted quantum chemical calculations to elucidate the electronic structure of compound 3. The optimized structural parameters of 3 obtained at the BP86-D3(BJ)/def2-TZVPP level of theory are in good agreement with the X-ray data (Supplementary Table 7). NBO analysis (BP86-D3(BJ)/def2-TZVPP) revealed that P(1) (1.59 a.u.) and Sn(1) (1.09 a.u.) atoms carry considerable positive charges, while C(1) (–1.45 a.u.) and C(2) (–0.39 a.u.) atoms are negatively charged. This charge separation is due to the lower electronegativity of phosphorus (2.19) and tin (1.96) compared to nitrogen (3.04) and carbon (2.55) elements.

Furthermore, the Wiberg bond indexes (WBIs) of P(1)−C(1), C(1)−Sn(1), and Sn(1)−C(2) are 2.08, 0.80, and 0.60, respectively. These values indicate a pronounced multiple bond character for P(1)−C(1) and a relatively stronger bonding interaction between C(1) and Sn(1) than between Sn(1) and C(2). Notably, the WBI for the C(1)−Sn(1) bond in 3 (0.80) is slightly higher compared to those in 5 (0.77) and 6 (0.72) (vide infra) (Supplementary Table 8). This distinction can be attributed to the absence of a lone pair and a vacant 5p orbital at Sn(1) in 5 and 6, which mitigates the extent of π-interaction with adjacent atoms (vide infra). It is important to acknowledge, however, that WBI values may not always precisely reflect the nature of multiple bonds, especially those with high ionic character, as exemplified by the relatively low WBI (0.89) of an Al−N triple bond in an iminoalane.⁴⁴

To gain further insights into the bonding situation of 3, frontier molecular orbital (FMO), intrinsic bond orbital (IBO)^45,46 and electron localization function (ELF)⁴⁷ calculations were carried out (Fig. 4 and Supplementary Fig. S67). The HOMO (–4.47 eV) consists of the P(1)−C(1) π-bonding orbital and the lone pair orbital at Sn(1) (Fig. 4a). The HOMO–1 (–4.94 eV) corresponds to the P(1)−C(1)−Sn(1) out-of-plane 3-center-2-electron (3c2e) π-bonding orbital (Fig. 4b). Further, the HOMO–2 level, at –5.40 eV, is primarily composed of a slipped C(1)−Sn(1) π bond, exhibiting lone pair characteristics at both C(1) and Sn(1) (Fig. 4c). This form of slipped π bond contributes to the bent geometry observed at C(1) and is a feature commonly associated with heavier main group elements forming multiple bonds,^7-9 as seen in disilyne,² digermyne,⁴ distannyne,⁵ and diplumbyne.⁶ Moreover, the LUMO (–2.01 eV) represents a C(1)−Sn(1) π*-antibonding orbital with a significant vacant 5p orbital character at Sn(1), along with the P−N σ*-antibonding orbitals (Fig. 4d). The LUMO+2 (–1.45 eV) features the P(1)−C(1) π*-antibonding orbital (Fig. 4e). Overall, this FMO analysis reveals the multiple bond character of the P(1)−C(1)−Sn(1) chain in 3 (see resonance forms in Fig. 2) and suggests that both C(1) and Sn(1) exhibit ambiphilicity. Notably, the ELF plot of 3 shows the ionic interaction between the C and Sn atoms in the P(1)−C(1)−Sn(1) plane, with limited electron density localized at the C(1)−Sn(1) and Sn(1)−C(2) bonds (Fig. 4f), whereas the P(1)−C(1) bond exhibits a strong covalent character.

Our IBO analysis indicates that C(1) forms two σ bonds, one each with P(1) and Sn(1) (IBO1 and IBO5, Supplementary Fig. S67). Additionally, there is a slipped P(1)−C(1) π bond (IBO2), arising from the donation of a lone pair by P(1). The lone pair on Sn(1) remains highly localized (IBO4), while IBO3 illustrates a 3c2e π bond centered at C(1), consistent with the HOMO–1 of 3.

Natural resonance theory (NRT) calculations on a simplified model of 3 (where Dipp groups are replaced by H atoms and the Ter group by a CH₃), the predominant resonance form is identified as the allenic structure (26.65%) (Supplementary Figure S68). Other significant resonance forms include P(1)−C(1)=Sn(1) (11.02%) and P(1)−C(1)≡Sn(1) (5.35%), along with two forms of P(1)≡C(1)−Sn(1) contributing 10.33% and 7.67%, respectively. Taken together, these results, combined with the FMO and IBO findings, suggest that the electronic structure of 3 is most appropriately represented as an allenic structure 3A. This structure is characterized by considerable π-electron delocalization across the P(1)−C(1)−Sn(1) atoms, with P bearing a formal positive charge and Sn a negative charge. Despite an allenic structure of 3, both NRT and FMO analyses (HOMO–1 and HOMO–2) suggest a minor contribution of the stannye form of P(1)−C(1)≡Sn(1).

A salient structural characteristic of 3 is the near-perpendicular orientation of the N(1)−P(1)−N(2) plane to the P(1)−C(1)−Sn(1) plane (Fig. 3b). The trigonal-planar configuration of the phosphino moiety exhibits a pronounced twist relative to the P(1)−C(1)−Sn(1) plane, indicated by a torsion angle of –97.9(6)° for N(1)−P(1)−C(1)−Sn(1). Notably, this angle exceeds those reported for germmyne C,³² which has a torsion angle of –73.6(6)°, and the methylenephosphonium salt [(ⁱPr₂N)₂P=C(TMS)₂][OTf], with a torsion angle of –59.5(3)°.⁴⁸ The distinct spatial configuration observed in 3 can be largely attributed to π-interactions. These interactions involve the lone pairs present on P(1) and Sn(1) and the formally unoccupied p orbital on C(1). Furthermore, the delocalization of the C(1) lone pair into the vacant p orbital of Sn(1) and into the N−P σ* antibonding orbitals plays a significant role (Supplementary Fig. S66). This type of out-of-plane negative hyperconjugation, emanating from the C(1) lone pair to the N−P σ* antibonding orbitals, is in line with stabilization approaches for a unique carbene with a σ⁰π² electronic configuration.⁴⁹ Upon performing a constrained geometry optimization, it has been determined that the alternative co-planar conformation is energetically disfavored by 4.2 kcal/mol relative to the experimentally observed structure of 3 (Supplementary Fig. S65).

Reactivity

Diarylstannylene with electron-withdrawing aryl substituents reacts with isocyanide, forming Lewis acid-base adducts.^50,51 However, treatment of 3 with 1-adamantyl isocyanide (AdNC) at room temperature yields the sole product 4 (³¹P NMR: 112.2 ppm; ¹¹⁹Sn NMR: 1486.9 ppm) (Fig. 5), regardless of the amount of AdNC used. Through multi-nuclear NMR and X-ray diffraction data, 4 is identified as a (phosphino)(stannylenyl)ketenimine with the stannylene center remaining intact (Fig. 6a). This reaction demonstrates the synthetic potential of stannynes for unique stannylenes with unconventional substituents.⁵²

The stannyne 3 not only functions as a carbene but also exhibits properties of stannylene. While the [4+1] cycloaddition of stannylenes with dienes is typically limited to stannylenes with electropositive substituents like germyl⁵³ and boryl,⁵⁴ the addition of excess 2,3-dimethyl-1,3-butadiene to a THF solution of 3 generates species 5 (³¹P NMR: 3.7 ppm; ¹¹⁹Sn NMR: –43.6 ppm) (Fig. 5). Isolation of 5 as colorless X-ray quality crystals in 65% yield confirms its formulation as a (phosphino)(stannyl)carbene (Fig. 6b). Contrasting with 3, the phosphino group in 5 adopts a co-planar arrangement concerning the P(1)−C(1)−Sn(1) plane. This structural arrangement can be attributed to the absence of a lone pair and an unoccupied 5p orbital at Sn(1) in 5. It is noteworthy that (phosphino)(stannyl)carbenes were previously considered reactive intermediates incapable of isolation,⁵⁵ making 5 the first example of its kind. This reaction highlights the versatility of stannynes as a versatile synthon for novel carbenes with unusual substituents.⁴⁰ To the best of our knowledge, 3 represents the first example of a main group compound with diverse adjacent ambiphilic centers.

We then investigated the reactivity of the C(1)−Sn(1) multiple bonding character in 3. When 3 was treated with dry HCl in dioxane, a complex mixture was observed. Nonetheless, addition reactions of 3 with excess Et₃N·HCl at –35 ^oC, a mild Brønsted acid, proceeded smoothly, giving rise to the formation of 6 (³¹P NMR: 111.3 ppm; ¹¹⁹Sn NMR: –13.2 ppm). X-ray diffraction analysis confirmed that 6 is a double addition product, with two hydrogen atoms and two chlorine atoms attached to C(1) and Sn(1), respectively (Figure 6c). The C(1)−Sn(1) bond length in 6 elongates to 2.126(4) Å compared to 2.082(6) Å in 3. By adjusting the reaction ratio of 3:Et₃N·HCl to 1:1, we observed the formation of 6 as well as a major intermediate (³¹P NMR: 90.7 ppm), along with unreacted 3 (Supplementary Fig. S35). Although we were unable to isolate the intermediate, our calculations suggest that it is likely the monoaddition intermediate, specifically the stannaalkene [(CH₂)(NDipp)]₂PC(H)=Sn(Cl)(C₆H₃-2,6-Mes) (calc. ³¹P NMR: 97.6 ppm, Supplementary Figure S72) (for a proposed mechanism, refer to Supplementary Fig. S61).

In comparison, our experiments with a previous copper carbyne anion complex demonstrated that protonation of the [(CH₂)(NDipp)]₂PC^– anion produced a transient monosubstituted carbene, spontaneously dimerizing into the alkene [(CH₂)(NDipp)]₂P(H)C=C(H)P[(NDipp)(CH₂)]₂.³⁸ However, when treating 3 with an equivalent of Et₃N·HCl, the same alkene did not form, implying a minimal contribution from the stannyliumylidene resonance form (i.e. a complex of [(CH₂)(NDipp)]₂PC^– anion and [(C₆H₃-2,6-Mes)Sn]⁺ cation).

Remarkably, 3 exhibited a facile reaction involving cleavage of the C−Sn bond when treated with isopropyl isocyanate (ⁱPrNCO) (Fig. 5). The reaction, conducted with either one or two equivalents of ⁱPrNCO, predominantly produced 7, while in the former case a portion of 3 remained unchanged. In the ³¹P and ¹¹⁹Sn NMR spectra of 7, singlet resonances were observed at 15.7 and 342.9 ppm, respectively. To our surprise, single-crystal X-ray diffraction analysis of colorless crystals of 7 revealed complete splitting of the C−Sn bond through the formal insertion of two ⁱPrNCO molecules, accompanied by rearrangement involving H- and O-shifts (Figure 6d) (for a proposed mechanism, refer to Supplementary Fig. S63). This O-migration bears resemblance to the rearrangement observed in phosphaketenes to phosphaheteroallenes.⁵⁶

More than two decades after Power's groundbreaking work on distannyne⁵ and a decade following the seminal contributions of Kato and Baceiredo in base-stabilized silyne and germyne,^31,32 the isolation of 3 stands as a testament to the feasibility of stabilizing base-free stannynes at room temperature. Compound 3, featuring adjacent ambiphilic carbon and tin atoms, represents an unprecedented example of a main group species with such diverse ambiphilic centers. It showcases a carbon-tin multiple bond with ionic characteristics. Intriguingly, this stannyne can act as either a singlet carbene or a stannylene depending on the substrates involved, highlighting its versatility as a precursor for unique carbenes and stannylenes. Given the substantial impact of alkynes and their heavier homonuclear analogs across various disciplines, we believe that with continued development and research, their heteronuclear heavier counterparts will similarly find widespread applications in a variety of fields.

Acknowledgement

We gratefully acknowledge financial support from the National Natural Science Foundation of China (22350004; 22271132; 22101114), Shenzhen Science and Technology Innovation Program (JCYJ20220530114806015), Guangdong Innovation & Entrepreneurial Research Team Program (2021ZT09C278), and Guangdong Provincial Key Laboratory of Catalysis (2020B121201002). We also acknowledge the assistance of SUSTech Core Research Facilities. The theoretical work was supported by the Center for Computational Science and Engineering at SUSTech.

Author contributions

L.L.L. conceptualized and supervised the project. X.F.W. and R.W. performed the experimental work. L.L.L., X.F.W., C.H, and R.W. performed the computational work. X.F.W., C.P.H., J.C.L., R.W. and X.Z. performed the X-ray crystallographic analyses. L.L.L. wrote the paper with the input from all authors. All authors discussed the results in detail and commented on the paper.

Competing interests

The authors declare no competing interests.

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Experimental details

Synthetic methods. All manipulations were conducted within a nitrogen-filled glovebox or under a dry nitrogen atmosphere, employing standard Schlenk techniques, unless otherwise specified. Toluene, n-hexane, n-pentane, and tetrahydrofuran were subjected to distillation over sodium or LiAlH₄and subsequently stored over activated molecular sieves in the glove box. Commercial reagents were obtained from Energy Chemical, J&K, or TCI Chemical Co. and were used without further purification. The reagents 1³⁷ and 2,6-Mes₂C₆H₃SnCl⁴¹ were prepared according to the reported literature. Note: Although we have not experienced any problems, cautions should be exercised when handling diazo reagents due to their potentially explosive nature, especially for large scale reactions.

Spectroscopic methods. NMR spectra were acquired at 298 K on a Bruker Avance 400 (¹H: 400 MHz, ³¹P: 162 MHz, ¹³C: 101 MHz, ¹¹⁹Sn: 149 MHz) or 500 (¹H: 500 MHz, ³¹P: 202 MHz, ¹³C: 126 MHz) or 600 (¹H: 600 MHz, ³¹P: 243 MHz, ¹³C: 151 MHz) NMR spectrometer. The ¹H, ¹³C{¹H} spectra were referenced to residual internal C₆H₆, ³¹P spectra was referenced externally to an 85% H₃PO₄ solution in H₂O, while ¹¹⁹Sn spectra was referenced with respect to SnMe₄. The provided data is presented as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, sept = septet, m = multiplet and/or multiple resonances), coupling constant in hertz (Hz), integration and attribution). Deuterated solvent, such as C₆D₆, THF-d₈, CDCl_3, were degassed by employing three freeze-pump-thaw cycles and stored over activated molecular sieves in the glove box. High-resolution mass spectrometry (HRMS) was conducted using a Thermo Fisher Scientific Q-Exactive MS System. Infrared spectra were recorded on a FT-IR spectrometer (Bruker ALPHA II) using a DLaTGS detector. UV-Vis absorption spectra were recorded on Lambda 365 spectrophotometer (PerkinElmer) at room temperature. Elemental analyses (C, H, N) were conducted utilizing a Vario Micro Cube analyzer (Elementar, Germany).

Crystallographic methods. Crystal data was collected on a Bruker D8 VENTURE Diffractometer equipped with an Excillum METALJET diffractometer utilizing Ga-Kα (λ = 1.34139) radiation by APEX-Ⅲ software suite.⁵⁷ SAINT was employed for integrating frames data. And the data was corrected for absorption effects using the empirical multi-scan method (SADABS).⁵⁸ The structures were solved using the SHELXT⁵⁹ structure solution program through the Intrinsic Phasing solution method and refined through Least Squares minimization method using SHELXL⁶⁰ in the graphical user interface Olex2.⁶¹ Anisotropic refinement was applied to all non-hydrogen atoms, while structure factor calculations accounted for hydrogen atoms. The hydrogen atoms were positioned according to idealized geometric positions.

Synthesis of 2. A solution of ^tBuOK (21.5 mg, 0.19 mmol) in THF (3.0 mL) was gradually added to a THF solution of 1 (100 mg, 0.19 mmol) (3.0 mL) at a temperature of –35℃. The resulting mixture was stirred for 10 minutes at –35℃, followed by warming to room temperature and subsequent stirring for 7 hours. This reaction resulted in the complete consumption of 1, yielding the formation of 1a (³¹P NMR (THF): 131 ppm (s)). The solution was then cooled back to –35℃, and a THF (3.0 mL) solution of 2,6-Mes₂C₆H₃SnCl (89.4 mg, 0.19 mmol) was added slowly. After 10 minutes of stirring in the absence of light, all volatile components were removed under vacuum, resulting in the formation of a deep red oil. Pentane was introduced into the mixture, which was then filtered through a Celite pad, yielding a red solution. The remaining volatiles were subsequently removed under vacuum, and the resulting red powder was washed with cold pentane (3.0 mL), resulting in the isolation of 2 as a yellow solid (133 mg, 0.15 mmol) in a yield of 79%. Yellow crystals of 2 suitable for single-crystal X-ray diffraction were obtained by allowing a concentrated pentane solution to undergo slow evaporation at –30℃. ¹H NMR (500 MHz, C₆D₆): δ (ppm) 1.01 (d, ³J_H-H= 6.8 Hz, 6H, two sets of CH(CH₃)₂of Dipp), 1.21 (d, ³J_H-H= 7.1 Hz, 6H, two sets of CH(CH₃)₂of Dipp), 1.30 (d, ³J_H-H= 6.9 Hz, 12H, four sets of CH(CH₃)₂of Dipp), 1.97 (s, 12H, four sets of o-CH₃ of Ter-Mes), 2.21 (s, 6H, two sets of p-CH₃ of Ter-Mes), 3.11 (sept, ³J_H-H= 7.1 Hz, 2H, two sets of CH(CH₃)₂ of Dipp), 3.55 – 3.62 (m, 2H, NCH₂), 3.94 (sept, ³J_H-H= 6.9 Hz, 2H, two sets of CH(CH₃)₂ of Dipp), 3.98 – 4.09 (m, 2H, NCH₂), 6.55 (s, 4H, m-Mes), 6.86 (d, ³J_H-H = 7.5 Hz, 2H, m-C₆H₃of Ter), 7.08 – 7.16 (m, 4H, Ar-H), 7.25 (t, ³J_H-H = 7.6 Hz, 3H, Ar-H). ¹³C{¹H} NMR (126 MHz, C₆D₆): δ (ppm) 21.3, 21.5 (d, ⁴J_P-C = 4.0 Hz, CH(CH₃)₂), 24.0, 24.2, 25.8, 26.1, 27.9, 29.0 (d, ⁴J_P-C = 9.1 Hz, CH(CH₃)₂), 55.2 (d, ²J_P-C= 6.7 Hz, NCH₂), 124.6, 124.7, 127.5, 128.9, 129.0, 129.5, 136.4, 137.2, 139.4 (d, ²J_P-C = 13.9 Hz, P-N-C_Ar), 146.9, 149.0, 150.1, 174.8 (d, ³J_P-C = 15.0 Hz, Sn-o-C_Ar). (Note: The signal corresponding to the quaternary carbon in close proximity to both Sn and P was not observed in the spectrum.). ³¹P NMR (243 MHz, C₆D₆): δ (ppm) 125.3 (s). ¹¹⁹Sn NMR (149 MHz, C₆D₆): δ (ppm) 92.7 (s). HRMS [M-N₂+H]⁺ C₅₁H₆₄N₂PSn⁺ calc. 855.38236 m/z, found 855.38195 m/z. IR (ATR, neat): v = 2901, 1966 (N=N stretching), 1440, 1103, 961, 519 cm^–¹.

Synthesis of 3. A sample of compound 2 (234 mg, 0.265 mmol) was sealed in thick-walled pressure bottle. Subsequently, the solid was exposed to 303 nm light for a duration of 30 minutes at room temperature, resulting in the clean formation of compound 3. Afterward, the resulting brown powder was washed with 2 mL of cold pentane. This procedure yielded compound 3 as a yellow solid (217 mg, 0.254 mmol, 96% yield). To obtain suitable single-crystal samples for X-ray diffraction analysis, yellow crystals of compound 3 were grown by gradually evaporating a concentrated pentane solution at a temperature of –30 °C over a duration of 48 hours. ¹H NMR (600 MHz, C₆D₆): δ (ppm) 1.20 (d, ³J_H-H= 6.9 Hz, 12H, four sets of CH(CH₃)₂of Dipp), 1.23 (d, ³J_H-H= 6.8 Hz, 12H, four sets of CH(CH₃)₂of Dipp), 2.13 (s,12H, four sets of o-CH₃ of Ter-Mes), 2.26 (s, 6H, two sets of p-CH₃ of Ter-Mes), 3.26 (d, ³J_H-H= 6.2 Hz, 4H, two sets of NCH₂), 3.45 (sept, ³J_H-H= 6.9 Hz, 4H, four sets of CH(CH₃)₂of Dipp), 6.56 (s, 4H, m-Mes), 6.98 (d, ³J_H-H = 7.5 Hz, 2H, m-C₆H₃of Ter), 7.11 (d, ³J_H-H = 7.5 Hz, 4H, Ar-H), 7.24 (q, ³J_H-H = 8.0 Hz, 3H, Ar-H). ¹³C {¹H} NMR (151 MHz, C₆D₆): δ (ppm) 21.5, 21.8, 24.7, 25.0, 29.2, 47.8 (d, ²J_P-C= 8.1 Hz, NCH₂), 124.5, 127.5, 127.6, 128.3, 128.5, 128.6, 130.5 (d, ¹J_P-C = 50.1 Hz, PCSn), 134.9 (d, ²J_P-C = 3.8 Hz, P-N-C_Ar), 135.7, 136.6, 138.3, 146.5, 148.6, 179.5 (d, ³J_P-C = 35.4 Hz, Sn-o-C_Ar). ³¹P NMR (243 MHz, C₆D₆): δ (ppm) 67.9 (singlet with two satellites, ²J_Sn-P= 168.7 Hz). ¹¹⁹Sn NMR (149 MHz, C₆D₆): δ 1149.3 (d, ²J_Sn-P= 168.7 Hz). HRMS [M+H]⁺ C₅₁H₆₄N₂PSn⁺ calc. 855.38236 m/z, found 855.38196 m/z. IR (ATR, neat): v = 2952, 1364, 1178, 909, 755, 537 cm^–¹. Anal. Calcd for C₅₁H₆₃N₂PSn: C, 71.75; H, 7.44; N, 3.28; Found: C, 70.62; H, 7.41; N, 3.35.

Synthesis of 4. A solution of 1-adamantyl isocyanide (AdNC) (6 mg, 0.374 mmol) in tetrahydrofuran (THF) (2.0 mL) was slowly introduced into another THF solution containing 3 (32 mg, 0.374 mmol) (2.0 mL) at room temperature. The resulting mixture was stirred at room temperature for 20 minutes, followed by the removal of volatiles under vacuum. The resulting yellow powder was subsequently washed with 1.0 mL of cold hexane, resulting in the formation of yellow solid 4 (25 mg, 0.0246 mmol) with a yield of 66%. To obtain yellow crystals suitable for single-crystal X-ray diffraction analysis, a concentrated hexane solution of compound 4 was subjected to slow evaporation at –30°C. ¹H NMR (600 MHz, C₆D₆): δ (ppm) 0.98 (d, ³J_H-H= 6.7 Hz, 6H, two sets of CH(CH₃)₂ of Dipp), 1.26 (d, ³J_H-H= 6.8 Hz, 6H, two sets of CH(CH₃)₂ of Dipp), 1.31 (d, ³J_H-H= 6.9 Hz, 6H, two sets of CH(CH₃)₂ of Dipp), 1.35 (d, ³J_H-H= 6.9 Hz, 6H, two sets of CH(CH₃)₂ of Dipp), 1.39 – 1.44 (m, 2H, Ad-H), 1.46 (s, 6H, Ad-H), 1.48 (s, 1H, Ad-H), 1.54 – 1.57 (m, 1H, Ad-H), 1.66 (s, 1H, Ad-H), 1.87 (s, 4H, Ad-H overlapped with o-CH₃ of Ter-Mes), 1.89 (s, 9 H, three sets of o-CH₃), 2.24 (s, 9H, Ad-H overlapped with p-CH₃ of Ter-Mes), 3.14 – 3.23 (m, 2H, NCH₂), 3.76 (sept, ³J_H-H= 6.9 Hz, 2H, two sets of CH(CH₃)₂), 3.86 (sept, ³J_H-H= 6.9 Hz, 2H, two sets of CH(CH₃)₂), 3.92 – 4.07 (m, 2 H, NCH₂), 6.55 (s, 4H, m-Mes), 6.87 (d, ³J_H-H = 7.4 Hz, 2H, m-C₆H₃of Ter), 7.14 (s, 1H, Ar-H), 7.20 – 7.26 (m, 4H, Ar-H), 7.31 (t, ³J_H-H= 7.6 Hz, 2H, Ar-H). ¹³C {¹H} NMR (151 MHz, C₆D₆): δ (ppm) 21.3, 21.4, 23.6, 25.1, 26.1, 26.8, 27.7, 28.8 (d, ⁴J_P-C = 6.5 Hz, CH(CH₃)₂), 30.1, 36.2, 44.7, 55.3 (d, ²J_P-C= 7.3 Hz, NCH₂), 57.5, 102.3 (d, ^JJ_P-C= 156.1 Hz, PCSn), 124.8 (d, ²J_P-C= 59.9 Hz, CCN), 127.1, 128.8, 136.7, 136.9, 141.0 (d, ²J_P-C = 14.2 Hz, P-N-C_Ar), 146.9, 149.4, 150.1, 161.9, 177.0 (Sn-o-C_Ar). ³¹P NMR (243 MHz, C₆D₆): δ (ppm) 112.2 (s). ¹¹⁹Sn NMR (149 MHz, C₆D₆): δ (ppm)1486.8 (s). HRMS [M+H]⁺ C₆₂H₇₉N₃PSn⁺ calc. 1016.50281 m/z, found 1016.50629 m/z.

IR (ATR, neat): v =2908, 1967 (CCN stretching), 1441, 1056, 804, 766 cm^–¹. Anal. Calcd for C₆₂H₇₈N₃PSn: C, 73.37; H, 7.75; N, 4.14; Found: C, 72.97; H, 7.83; N, 4.21.

Synthesis of 5. An excess of 2,3-dimethyl-1,3-butadiene was introduced into a solution of compound 3 (31 mg, 0.0364 mmol) in THF (1.0 mL). The resulting mixture was stirred for 16 hours at room temperature. Subsequently, all volatiles were removed under vacuum, resulting in the formation of a brown oil. The brown oil was dissolved in 0.5 mL of hexane and stored at -35°C in a freezer for a duration of one week, leading to the formation of colorless crystals of product 5 (22 mg, 0.0235 mmol) with a yield of 65%. ¹H NMR (600 MHz, C₆D₆): δ (ppm) 0.34 (d, ²J_H-H= 15.7 Hz, 2H, SnCH₂), 0.81 (d, ²J_H-H= 15.5 Hz, 2H, SnCH₂), 1.24 (d, ³J_H-H= 5.4 Hz, 12H, four sets of CH(CH₃)₂ of Dipp), 1.30 (d, ³J_H-H= 5.4 Hz, 12H, four sets of CH(CH₃)₂ of Dipp), 1.62 (s, 6H, two sets of CH₃ of SnCH₂CCH₃), 2.04 (s,12H, four sets of o-CH₃ of Ter-Mes), 2.31 (s, 6H, four sets of p-CH₃ of Ter-Mes), 3.23 (d, ³J_H-H= 5.4 Hz, 4H, four sets of CH(CH₃)₂), 3.40 – 3.51 (m, 4H, two sets of NCH₂), 6.83 (s, 4H, m-Mes), 6.87 (d, ³J_H-H = 7.6 Hz, 2H, m-C₆H₃of Ter), 7.08 (d, ³J_H-H = 7.4 Hz, 4H, Ar-H), 7.16 – 7.20 (m, 3H, Ar-H). ¹³C{¹H} NMR (151 MHz, C₆D₆): δ (ppm) 21.4, 21.4, 21.6, 24.7, 25.0, 27.3, 29.3, 47.7 (d, ²J_P-C= 6.1 Hz, NCH₂), 124.4, 127.6, 128.4, 128.6, 128.6, 129.1, 130.9, 130.9 (d, ¹J_P-C = 34.0 Hz, PCSn), 135.5, 135.6, 136.7, 142.0, 148.7, 150.0. ³¹P NMR (243 MHz, C₆D₆): δ (ppm) 3.7 (singlet with two satellites, ²J_Sn-P=181.4 Hz). ¹¹⁹Sn NMR (149 MHz, C₆D₆): δ (ppm) –43.6 (d, ²J_Sn-P=181.4 Hz). HRMS [M+H]⁺ C₅₇H₇₄N₂PSn⁺ calc. 937.46061 m/z, found 937.46191 m/z. IR (ATR, neat): v = 2960, 1442, 1256, 1074, 847, 802 cm^–¹. Anal. Calcd for C₅₇H₇₃N₂PSn: C, 73.15; H, 7.86; N, 2.99; Found: C, 71.29; H, 7.86; N, 3.09.

Synthesis of 6. Inside the glovebox, a pre-cooled solution of THF (3 mL) was added dropwise to a mixture comprising compound 3 (38.6 mg, 0.0452 mmol) and Et₃N·HCl (12.4 mg, 0.0904 mmol). Following stirring at –35°C for 15 minutes, the resulting mixture was filtered through a Celite pad, resulting in the formation of a white solution. Subsequently, all volatiles were removed under vacuum. The resulting white powder was then washed with 3.0 mL of cold hexane, affording white solid 6 (28.5 mg, 0.307 mmol) with a yield of 68%. To obtain colorless crystals suitable for single-crystal X-ray diffraction analysis, a concentrated hexane solution of compound 6 was subjected to slow evaporation at –30°C. ¹H NMR (600 MHz, C₆D₆): δ (ppm) 1.21 (d, ³J_H-H= 6.6 Hz, 6H, two sets of CH(CH₃)₂ of Dipp), 1.28 (m, 12H, four sets of CH(CH₃)₂ of Dipp), 1.41 (d, ³J_H-H= 6.6 Hz, 6H, two sets of CH(CH₃)₂ of Dipp), 1.64 (d, ²J_H-H= 5.0 Hz, 2H, PCH₂), 2.00 (s, 12H, four sets of o-CH₃ of Ter-Mes), 2.18 (s, 6H, two sets of p-CH₃ of Ter-Mes), 3.08 – 3.20 (m, 2H, NCH₂), 3.26 – 3.38 (m, 2H, two sets of CH(CH₃)₂of Dipp), 3.61 (sept, ³J_H-H= 6.6 Hz, 2H, two sets of CH(CH₃)₂of Dipp), 3.72 (m, 2H, NCH₂), 6.66 (s, 4H, m-Mes), 6.78 (d, ³J_H-H = 7.5 Hz, 2H, m-C₆H₃of Ter), 7.08 (t, ³J_H-H = 7.5 Hz, 1H, p-C₆H₃of Ter), 7.15 (s, 2H, Ar-H), 7.17 (s, 2H, Ar-H), 7.19 – 7.23 (m, 2H, Ar-H). ¹³C{¹H} NMR (151 MHz, C₆D₆): δ (ppm) 21.3, 21.6 (d, ⁴J_P-C = 3.0 Hz, CH(CH₃)₂), 24.0, 24.8, 26.5, 29.0, 29.2 (d, ⁴J_P-C = 11.9 Hz, CH(CH₃)₂), 36.2 (d, ¹J_P-C = 89.2 Hz, PCH₂), 55.1 (d, ²J_P-C= 6.1 Hz, NCH₂), 124.5, 124.8, 127.0, 128.3, 129.1, 129.6, 131.9, 136.8, 138.0, 138.2, 140.2 (d, ²J_P-C = 12.5 Hz, P-N-C_Ar), 141.6, 148.0, 149.0, 149.4. ³¹P NMR (243 MHz, C₆D₆): δ (ppm) 111.3 (singlet with two satellites, ²J_Sn-P= 263.1 Hz). ¹¹⁹Sn NMR (149 MHz, C₆D₆): δ (ppm) –13.2 (d, ²J_Sn-P= 263.1 Hz). HRMS [M]⁺ C₅₁H₆₅N₂Cl₂PSn⁺ calc. 926.32789 m/z, found 926.32904 m/z. HRMS [M]⁺ C₅₁H₆₅N₂Cl³⁷ClPSn⁺ calc. 928.32494 m/z, found 928.33063 m/z. IR (ATR, neat): v = 2963, 1443, 1070, 850, 804, 757 cm^–¹. Anal. Calcd for C₅₁H₆₅Cl₂N₂PSn: C, 66.10; H, 7.07; N, 3.02; Found: C, 63.11; H, 7.00; N, 2.93.

Synthesis of 7. A solution of isopropyl isocyanate (ⁱPrNCO) (10 mg, 0.12 mmol) in THF (2.0 mL) was slowly introduced into another THF solution containing 3 (50 mg, 0.059 mmol) (2.0 mL) at –35°C. The resulting mixture was stirred at room temperature for 10 minutes, followed by the removal of volatiles under vacuum. The resulting white powder was subsequently washed with 1.0 mL of cold pentane, resulting in the formation of white solid 7 (32 mg, 0.031 mmol) with a yield of 54%. To obtain colorless crystals suitable for single-crystal X-ray diffraction analysis, a concentrated pentane and toluene solution of compound 7 was subjected to slow evaporation at –30°C. ¹H NMR (500 MHz, C₆D₆): δ (ppm) 0.16 (t, ³J_H-H= 7.5 Hz, 6H, two sets of NCH(CH₃)₂), 0.54 (s, 3H, NC(CH₃)₂N), 0.70 (s, 3H, NC(CH₃)₂N), 1.04 (d, ³J_H-H= 6.7 Hz, 3H, CH(CH₃)₂ of Dipp), 1.16 (d, ³J_H-H= 6.7 Hz, 3H, CH(CH₃)₂ of Dipp), 1.26 (d, ³J_H-H= 6.9 Hz, 3H, CH(CH₃)₂ of Dipp), 1.40 (d, ³J_H-H= 6.6 Hz, 6H, two sets of CH(CH₃)₂ of Dipp), 1.45 (d, ³J_H-H= 6.9 Hz, 3H, CH(CH₃)₂ of Dipp), 1.68 (d, J = 6.7 Hz, 3H, CH(CH₃)₂ of Dipp), 1.72 (d, ³J_H-H= 6.6 Hz, 3H, CH(CH₃)₂ of Dipp), 2.06 (s, 3H, CH₃ of Ter-Mes), 2.20 (s, 3H, CH₃ of Ter-Mes), 2.30 (s, 3H, CH₃ of Ter-Mes), 2.34 (s, 3H, CH₃ of Ter-Mes), 2.40 (t, ³J_H-H= 7.5 Hz, 1H, NCHMe₂), 2.49 (s, 3H, CH₃ of Ter-Mes), 2.55 (s, 3H, CH₃ of Ter-Mes), 3.25 – 3.39 (m, 1H, NCH₂), 3.64 (sept, ³J_H-H= 6.7 Hz, 1H, CH(CH₃)₂of Dipp), 3.68 – 3.75 (m, 1H, NCH₂), 3.77 – 3.86 (m, 1H, NCH₂), 4.01 (sept, ³J_H-H= 6.9 Hz, 1H, CH(CH₃)₂of Dipp), 4.22 – 4.31 (m, 1H, NCH₂), 4.35 (sept, ³J_H-H= 6.7 Hz, 1H, CH(CH₃)₂of Dipp), 4.43 (sept, ³J_H-H= 6.6 Hz, 1H, CH(CH₃)₂of Dipp), 6.77 – 6.90 (m, 4H, Ar-H), 6.94 – 7.03 (m, 1H, Ar-H), 7.16 – 7.21 (m, 3H, Ar-H), 7.20 – 7.26 (m, 4H, Ar-H), 7.30 (t, ³J_H-H = 7.7 Hz, 1H, p-C₆H₃of Ter), 7.41 (d, ³J_P-H = 12.0 Hz, 1H, PCCH). ¹³C{¹H} NMR (126 MHz, C₆D₆): δ (ppm) 21.0, 21.4, 21.8, 21.9, 22.5, 22.6, 22.9, 23.1, 25.0, 25.3, 25.5, 25.9, 26.0, 26.2, 26.6, 27.1, 27.4, 27.6, 28.8, 29.2, 29.4, 47.7 (NCH), 48.8 (d, ²J_P-C = 13.6 Hz, NCH₂), 50.5 (d, ²J_P-C = 13.4 Hz, NCH₂), 75.8 (NCN), 90.3 (d, ¹J_P-C = 192.1 Hz, P-C), 124.2, 125.2, 125.4, 128.8 (d, ²J_P-C = 12.0 Hz, P-N-C, Ar-C), 129.2, 129.9, 135.4, 135.5, 136.1, 136.8, 137.0, 138.0, 139.6, 142.7, 146.2, 148.2, 150.7, 150.9 (d, ³J_P-C = 3.3 Hz, P-N-C-C, Ar-C), 151.0, 151.2, 154.7 (d, ²J_P-C = 16.2 Hz, PCCH), 169.0 (d, ²J_P-C = 6.1 Hz, O-C-N), 174.3 (Sn-o-C_Ar). ³¹P NMR (243 MHz, C₆D₆): δ (ppm) 15.7. ¹¹⁹Sn NMR (149 MHz, C₆D₆): δ (ppm) 342.9. HRMS [M+H]⁺ C₅₉H₇₈N₄O₂PSn⁺ calc. 1025.48789 m/z, found 1025.49072 m/z. IR (ATR, neat): v = 2946, 1587, 1442, 1292, 1094, 805 cm^–¹. Anal. Calcd for C₅₉H₇₇N₄O₂PSn: C, 69.21; H, 7.58; N, 5.47; Found: C, 66.72; H, 7.64; N, 5.77.

Computational details

Geometry optimizations were carried out using the Gaussian 16 package⁶² with the BP86 functional^63,64 augmented with the D3BJ version of Grimme’s empirical dispersion correction.^65,66,67 The def2-TZVPP basis set was used for all the atoms. Frequency calculations at the same level of theory were performed to identify the number of imaginary frequencies (zero for local minimum). Natural bond orbital (NBO) calculations and natural resonance theory (NRT) calculations were carried out using NBO 7.0 program⁶⁸ at the BP86-D3(BJ)/def2-TZVPP level of theory, intrinsic bond orbitals (IBOs) were carried out using ORCA program⁶⁹ at the same level. Optimized structures were visualized by the Chemcraft⁷⁰ or IBOview program.⁴⁶The electron localization function (ELF) analysis⁴⁷ were carried out using Amsterdam Modeling Suite⁷¹ at the BP86-D3(BJ)/TZP level of theory using the BP86-D3(BJ)/def2-TZVPP optimized geometries, the relativistic scalar effect was included by using the zeroth-order regular approximation (ZORA).^72,73TD-DFT calculations were carried out at the M062X/def2-TZVP level of theory. Isotropic shifts for Int2A were computed at the GIAO-B97-2⁷⁴/Def2-TZVP^75,76//BP86-D3(BJ)/def2-SVP level of theory.

Data availability

Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition numbers 2261177 (2), 2261179 (3), 2261180 (4), 2261178 (5), 2261181 (6) and 2261213 (7). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/. All other data are presented in the main text and the Supplementary Information, and are also available from the corresponding authors on reasonable request.

Methods-only references

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There is NO Competing Interest.

figure5.cdx
Compound2.cif
Supplementary Data Set 1
Compound3.cif
Supplementary Data Set 2
Compound4.cif
Supplementary Data Set 3
Compound5.cif
Supplementary Data Set 4
Compound6.cif
Supplementary Data Set 5
Compound7.cif
Supplementary Data Set 6
CartesianCooradinates.xlsx
Supplementary Data Set 7
SupportingInformation.pdf

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A crystalline stannyne

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