Skip to main content
NCBI home page
Royal Society of Chemistry logoLink to Royal Society of Chemistry
. 2026 Jul 10;13(16):6803–6815. doi: 10.1039/d6qi01030j

Synthesis, structural analysis and reactivity of alkynyl sulfide anions

Sunita Mondal a,b,†, Quentin Le Dé a,†, Daniel A Santos Oliveira b,c, Daniela Rodrigues Silva b, Angela De Feudis a, F Matthias Bickelhaupt b,d,e,✉, Viktoria H Gessner a,✉
PMCID: PMC13383285  PMID: 42518945

Abstract

Ketenyl anions are versatile, isolable reagents that facilitate the formation of ketenes, carbonyl-containing compounds, and functionalized heterocycles. In contrast, their thio analogues have only been prepared in situ and their alkali metal complexes remain elusive. Here, we report the facile synthesis and isolation of a series of thioketenyl anions through CS-for-CO exchange, using carbon disulfide or thioisocyanates as CS transfer reagents. Spectroscopic and crystallographic studies, combined with quantum chemical calculations, reveal that the electronic structure of these anions is best described by the alkynyl sulfide form with a C–C triple bond, with a minor contribution from the thioketenyl structure. This differs from previously reported related anions and can be attributed to the enhanced π-accepting properties of the carbon monosulfide ligand, which can be rationalized by the Dewar–Chatt–Duncanson model. This insight bridges the bonding in these carbanionic species with that in transition metal complexes. The unique bonding in alkynyl sulfides is reflected in their reactivity patterns, opening pathways to sulfur-heterocycles and neutral alkynyl sulfides via S-centered reactivity.

Structure elucidation, reactivity studies and detailed bonding analysis of alkali metal alkynyl sulfides are reported.graphic file with name d6qi01030j-ga.jpg

Introduction

Thio compounds, particularly sulfur heterocycles, play a significant role in pharmaceutical1–3 and material chemistry,4,5 such as for the preparation of sulfur-containing drugs like Plavix, Seroquel or Cymbalta (Fig. 1a). Alkynyl sulfides (thioalkynes) represent versatile sulfur-containing building blocks that provide access to a range of functionalized organosulfur compounds, including sulfur-containing heterocycles.6–8 The synthesis of alkynyl sulfides is achieved through various methods,9 including the transition metal-catalyzed coupling of terminal alkynes and thiols10–12 or the reaction of alkynyl anions with disulfides or other sulfur electrophiles (Fig. 1b).13,14 Furthermore, dehydrohalogenation reactions of β-halovinyl thioethers15 and the coupling of electrophilic alkyne reagents, such as hypervalent iodine compounds,16 have been reported. In contrast to other heteroatom-functionalized alkynes, such as ynamines or alkynyl phosphines, alkynyl sulfides are usually stable reagents. However, in certain cases, they were found to undergo [3,3]-sigmatropic17,18 or [1,3]-sigmatropic19,20 rearrangements to form thioketene derivatives. The close relationship between alkynyl sufides and thioketenes becomes evident from ylidenethioketenes. Their structure is best described by both, the alkynyl sulfide (R+ –C Created by potrace 1.16, written by Peter Selinger 2001-2019 C–S−) and the thioketene form (R Created by potrace 1.16, written by Peter Selinger 2001-2019 C Created by potrace 1.16, written by Peter Selinger 2001-2019 C Created by potrace 1.16, written by Peter Selinger 2001-2019 S).21,22

Fig. 1. (a) Examples of sulfur-containing drug molecules, (b) structure and synthesis of alkynyl sulfides, (c) canonical structures of anionic alkynyl sulfides and coordination modes with transition metals and (d) synthesis of free alkynyl sulfide anions reported in this work.

Fig. 1

Open in a new tab

Anionic alkynyl sulfides, R–C Created by potrace 1.16, written by Peter Selinger 2001-2019 C–S−, serve as a versatile starting point for the synthesis of alkynyl sulfides and more complex thio compounds (Fig. 1c). They can be prepared by deprotonative cleavage of thiadiazoles23,24 and addition of elemental sulfur to lithium acetylides,25–28 or can be generated in the coordination sphere of transition metals through oxidative addition29–32 or reductive S–C bond cleavage in alkynyl thioethers.33,34 Like neutral alkynyl sulfide, the anions can be described by two mesomeric forms: as alkynyl sulfide with a linear geometry and the negative charge localized on the sulfur atom, or as bent thioketenyl anion, with the negative charge residing on the carbon atom. Isolation and structure analysis of various transition metal complexes of alkynyl sulfides revealed a preferred coordination of the anionic alkynyl sulfides either via the sulfur atom25,26 or the C–C triple bond,33,34 suggesting a preference of the alkynyl sulfide form (Fig. 1c). A rearrangement to the thioketenyl form and exclusive coordination to the C1 carbon atom have rarely been discussed.25 In contrast, alkali metal alkynyl sulfides have only been utilized as in situ-generated reagents and have never been isolated despite their applicability in the synthesis of heterocycles.35–37

Previously, we reported the synthesis of the anionic cyano-substituted alkynyl sulfide [NCCCS]− (2CN) through the addition of carbon disulfide (CS2) to the corresponding ketenyl anion [NCCCO]−1CN.38 Unfortunately, 2CN could not be obtained in crystalline form, preventing its experimental structure elucidation. However, density functional theory (DFT) calculations indicated that 2CN – in contrast to the cyanoketenyl anion – adopts a linear geometry, consistent with its description as alkynyl sulfide anion. This conclusion is in line with earlier computational investigations of the parent H-substituted system.39 To date, no other alkali metal alkynyl sulfide has been isolated, thus leaving not only their structural and electronic properties, but also their principal reactivity virtually unexplored. Herein, we close this gap by isolating a series of alkynyl sulfide anions, including the first crystal structure analyses. In contrast to the linear structure of 2CN predicted by quantum-chemical calculations, these anions adopt slightly bent geometries and exhibit diverse reactivities.

Results and discussion

Synthesis of alkynyl sulfide anions

We began our studies with targeting the phosphinoyl-substituted anions 2PO and 2PS. We initially adopted a previously reported synthetic route involving carbon disulfide cycloaddition followed by cycloreversion with carbonyl sulfide (OCS) elimination.22,40 Addition of one equivalent of CS2 to the potassium salts of ketenyl anions 1PO and 1PS resulted in the formation of a single compound, as evidenced by 31P{1H} NMR spectroscopy, showing resonances at 2.4 and 12.5 ppm, respectively (Scheme 1).41,42 Both compounds could be isolated as yellow solids in excellent 97% yields. X-ray diffraction (XRD) analysis of single crystals of both compounds obtained by addition of one equivalent of 18-crown-6 (18-c-6), confirmed the formation of the targeted alkynyl sulfide anions.

Scheme 1. Synthesis of the alkynyl sulfide anions 2PO, 2PS and 2Ts. a Proposed intermediate, not isolated. b Reported in ref. 38.

Scheme 1

Open in a new tab

The facile formation of the potassium salts of 2PO and 2PS contrasts our previous observations with the cyano system 1CN. Here, the addition of CS2 at room temperature afforded the four-membered ring compound 3CN, which only upon heating transformed into the alkynyl sulfide anion 2CN. This observation prompted us to investigate whether the formation of 2PO and 2PS also proceeds through the cyclic intermediates 3PO and 3PS, respectively. To validate this hypothesis, we monitored the reaction between 1PO and CS2 using real-time IR spectroscopy at 0 °C. Upon addition of CS2, compound 1PO is rapidly consumed (blue line, Fig. 2), and an intermediate forms, exhibiting an IR band at 1732 cm−1 (green line), consistent with the CO stretching frequency calculated for heterocycle 3PO. This intermediate subsequently reacts to the final product, exhibiting an IR band at 1964 cm−1 (orange line), which matches the spectroscopic features of isolated alkynyl sulfide 2PO. Thus, we concluded that the observed intermediate corresponds to heterocycle 3PO. Indeed, when the reaction between 1PS and CS2 was performed at −40 °C, compound 3PS could be obtained as crystalline solid and its identity was confirmed by XRD analysis (see SI, Fig. S73).

Fig. 2. Real-time IR spectroscopic monitoring of the addition of CS2 to ketenyl anion 1PO at 0 °C. Before the addition of CS2, only 1PO is observed (blue line; νcco = 2092 cm−1 [solid state IR data νcco = 2093 cm−1]), which subsequently converts to 3PO (green line; νco = 1732 cm−1 [gas phase calculate data νco = 1786 cm−1]) and finally to 2PO (orange line; νccs, sym = 1964 cm−1 [solid state IR data νccs, sym = 1950 cm−1]).

Fig. 2

Open in a new tab

To further probe the generality of the alkynyl sulfide formation from the corresponding ketenyl anions, we applied the aforementioned strategy to the sodium salt of tosyl ketenyl anion 1Ts.43 Addition of 1 equivalent of CS2 to 1Ts resulted in the formation of an orange compound in an 86% yield, which was identified as intermediate 3Ts based on NMR and XRD analyses (Fig. 3). In contrast to the phosphinoyl-substituted anions, compound 3Ts proved stable towards COS release at room temperature. Even heating a solution of 3Ts in deuterated THF or deuterated 1,2-difluorobenzene for two days in a sealed Young NMR tube at reflux, did not yield the desired alkynyl sulfide. In contrast, heating a THF solution of 3Ts at reflux under static vacuum in a Schlenk tube for two hours, led to the complete conversion to 2Ts, as confirmed by NMR spectroscopy and XRD analysis (Fig. 5).

Fig. 3. Molecular structures of the crown-ether complexes of 3Ts, 4aPO and 4Ts in the solid state. Hydrogen atoms and disordered parts in the molecules are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level.

Fig. 3

Open in a new tab

Fig. 5. Molecular structures of the crown-ether complexes of the alkynyl sulfide anions 2 in the solid state. Hydrogen atoms and disordered parts in the molecules are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level. Crystallographic details are given in the SI.

Fig. 5

Open in a new tab

To understand the influence of the Z substituent on the reaction conditions required for the synthesis of 2PO and 2Ts, we performed DFT calculations at the ZORA44–46-BP8647–49/TZ2P50 level of theory to elucidate the underlying reaction pathways (Fig. 4). The reaction starts with a [2 + 2] cycloaddition affording the four-membered ring intermediate 3. This step is thermodynamically favorable (ΔG = −2.8 kcal mol−1 for 2PO, −11.6 kcal mol−1 for 2Ts) with activation barriers of 20.8 and 18.8 kcal mol−1, consistent with both reactions occurring at ambient temperature. Subsequent OCS extrusion from 3 furnishes the corresponding alkynyl sulfide 2. While for the tosyl system OCS release occurs via a concerted [2 + 2] cycloreversion process and is calculated to be endergonic with respect to 3Ts (ΔΔG = +2.5 kcal mol−1), the phosphinoyl-substituted system undergoes a stepwise exergonic (ΔΔG = −6.3 kcal mol−1) COS release. These findings are consistent with the experimental observations, rationalizing the need for elevated temperature and constant vacuum to yield 2Ts from 3Ts, whereas the reaction for the phosphinoyl system proceeds readily at room temperature. The concerted cycloreversion of the tosyl derivative can be rationalized by the instability of the corresponding intermediate INT2Ts, which is expected to be less stable than its phosphinoyl analog due to the stronger electron-withdrawing ability of the tosyl group, reducing the nucleophilicity of alkynyl sulfide 2Ts.

Fig. 4. Reaction pathway calculated at the ZORA-BP86/TZ2P level of theory for the formation of 2PO (blue line) and 2Ts (pink line).

Fig. 4

Open in a new tab

After successful synthesis of the alkynyl sulfides from CS2, we examined whether a similar transformation could also be achieved using other sulfur-containing heteroallenes, such as isothiocyanates. We started our investigation with phenyl isothiocyanate and 1PO as model substrates. Treatment of 1 equiv. of PhNCS with 1PO at room temperature yielded a bright yellow solution. The 31P{1H} NMR spectrum indicated selective formation of a new species, characterized by a signal appearing at δP = 14.5 ppm. XRD analysis of single crystals grown in presence of 18-c-6 (Fig. 3) identified 4aPO as a four-membered thiete. In contrast to the CS2 addition product 3PO, which immediately underwent OCS release at room temperature, 4aPO proved to be stable at this temperature, but converted to the alkynyl sulfide anion 2PO upon heating of a THF solution at 60 °C. Mechanistically, formation of 2PO from 4aPO is proposed to proceed through initial rearrangement to azetidine ring (INT3A), which subsequently undergoes stepwise [2 + 2] cycloreversion to release PhNCO and thioketenyl anion 2PO (see the SI section 5.5 for details). Since the reaction was not selective, isolation of 2PO from the reaction mixture proved challenging, and was only achieved by crystallization in presence of 18-c-6. Therefore, we examined the use of tert-butyl isothiocyanate as alternative CS transfer reagent. While no reaction was observed at room temperature, heating at 45 °C in presence of 1 equiv. of crown ether led to the selective formation of the crown ether complex of 2PO, which could be isolated in a good 62% yield.

To assess the generality of this method, we also examined the reactivity of other ketenyl anions with isothiocyanates. Treatment of potassium ketenyl 1PS with PhNCS at room temperature afforded the corresponding four-membered heterocycle 4aPS as a brown powder in a good yield of 82%. Heating the THF solution 4aPS at 60 °C in presence of 1 equiv. of 18-c-6 led to the formation of crown ether complex of 2PS (δP = 10.5 ppm) in moderate yield of 52%. Reaction of tBuNCS with 1PS showed no detectable conversion to heterocycle 4bPS at room temperature but directly led to the formation of 2PS upon heating of the reaction mixture in presence of crown ether at 45 °C. Reaction of the tosyl system 1Ts with PhNCS at room temperature afforded the cycloaddition product 4Ts in a good yield of 69% (Fig. 3). Unfortunately, heating a THF solution of 4Ts at 60 °C did not yield detectable amounts of 2Ts. These observations demonstrate that alkynyl sulfide formation via cycloaddition of ketenyl anions with thioisocyanates and cycloreversion through isocyanates release is a more general approach, which however depends on the applied thioketenyl anion and the used thioisocyanate.

Spectroscopic and crystallographic studies

With the series of isolable anionic alkynyl sulfides at hand, we conducted a systematic investigation of their structural and spectroscopic properties to elucidate whether these anions are more appropriately described as anionic alkynyl sulfides 2 or thioketenyl anions 2′ (Scheme 1). The anions feature a signal in the range between 51 and 63 ppm in the 13C{1H} NMR spectrum, corresponding to the C1-CS carbon (Table 1). This signal appears significantly high-field shifted relative to those reported for neutral thioketenes (e.g., 86 ppm for (Mes)2C Created by potrace 1.16, written by Peter Selinger 2001-2019 C Created by potrace 1.16, written by Peter Selinger 2001-2019 S)51 and neutral alkynyl sulfides (e.g., 75 ppm for TolC Created by potrace 1.16, written by Peter Selinger 2001-2019 CSTol),52 indicating the presence of an electron pair on the C1 carbon and supporting the thioketenyl form. However, comparison of the 13C{1H} NMR spectroscopic data of thioketenyl anion 2PO with those of the corresponding ketenyl anion 1PO,41 keteniminyl anion 5 53 and diazomethanide 6 54 reveals that 2PO features the most deshielded C1 signal, indicating reduced charge accumulation on the C1 carbon in 2PO relative to the other anions. The IR spectra of 2 display two characteristic CCS stretching bands: an asymmetric stretch at 2009–2024 cm−1 and a symmetric stretch at 1950–1957 cm−1,55 which fall within the range of values reported for neutral thioketenes (around 1750 cm−1)51 and neutral alkynyl sulfides (around 2100 cm−1).56 Overall, this suggests an intermediate bonding situation between the thioketenyl 2′ and alkynyl sulfide 2 form, but more shifted towards the alkynyl form.

Table 1. Comparison of the spectroscopic and crystallographic data of the alkynyl sulfide anions 2 with related ketenyl anion 1, keteniminyl anion 5 and diazomethanide 6.

graphic file with name d6qi01030j-u1.jpg
  2Ts 2PS 2PO 1PO a 5b 6c
δ(C1) (ppm) 62.7 51.6 54.0 3.1 40.2 19.8
δ(C2) (ppm) 145.8 140.4 141.6 140.8 151.4 —
1 J PC (Hz) — 189.8 207.6 209.6 133.8 57.6
IR (cm−1) 2018, 1957 2024, 1957 2009, 1950 2093 1981 1970
C1–C2 (Å) 1.228(9) 1.226(2) 1.223(2) 1.240(2) 1.283(6) —
C2–S1 (Å) 1.618(6) 1.626(1) 1.631(1) — — —
Z–C1–C2 (°) 157.9(6) 150.9(1) 170.0(1) 148.9(1) 139.3(4) 125.9(2)
Open in a new tab
a

NMR and structure parameters are taken from ref. 41.

b

NMR and XRD parameters are taken from ref. 53.

c

NMR and structure parameters are taken from ref. 54.

The solid-state structures of the alkynyl sulfide anions 2 were elucidated by XRD analysis (Fig. 5). The alkali metal salts were crystallized as crown ether complexes, which feature distinctly different anion cation interactions. In 2PO and 2PS, the potassium ion forms direct contacts to the anion, binding to the phosphinoyl group in 2PO and to the sulfur atom of the alkynyl sulfide moiety in 2PS. In contrast, 2Ts represents a “free” alkynyl sulfide anion. In this case, the two 12-crown-4 (12-c-4) molecules fully encapsulate the sodium cation, eliminating any direct metal–anion interaction, enabling a discussion of the alkynyl sulfide structure without interference of the counter cation. Regardless of the presence or nature of the cation anion interaction, all structures exhibit an almost linear, yet slightly bent geometry, with E–C1–C2 angles ranging between 150.9(1) and 170.0(1)°. This contrasts the linear geometry of the cyano system predicted by DFT studies, indicating significant substituent effects on the bending angle.38 However, the observed trend in the bending angle (2PS < 2Ts < 2PO) does not align with typical substituent properties such as electron-withdrawing ability, implying that cation–anion interactions or even packing effects in the crystal structure override simple electronic effects. The C1–C2 and S1–C2 bond lengths vary only slightly in the different alkynyl sulfide anions. The free anion 2Ts exhibits the shortest S1–C2 bond length (1.618(6) Å), which lies between typical C–S single and double bond values, and the longest C1–C2 bond length of 1.228(9) Å, consistent with an elongated C–C triple bond and the most pronounced thioketenyl character in this anion. Comparison of the structural parameters of the alkynyl sulfide anion 2PO with the ketenyl anion 1PO, keteniminyl anion 5 and diazomethanide 6 reveals that the bending angle decreases with increasing acceptor ability of the ligand at C1 (CS, CO, CNCy, N2) in the order 2PO > 1PO > 5 > 6. Similarly, the C1–C2 bond length increases in the same order from the alkynyl sulfide to the keteniminyl anion. These trends, together with the IR spectroscopic data, clearly confirm the more pronounced contribution of the alkynyl sulfide structure to the bonding situation.

Computational analysis of the bonding in alkynyl sulfide anions

To shed light on the electronic structure of the alkynyl sulfide anions, we carried out DFT calculations at the ZORA-BP86/TZ2P level of theory. To assess the influence of substituents independent of cation effects, we analyzed the free anions 2 [Z–C–CS]− with Z = P(O)Ph2 (2PO) and Z = SO2Tol (2Ts). The energy-optimized gas-phase structure of 2Ts shows a more acute bending angle of 161.7° at C1 atom compared to 2PO (176.9°), in agreement with the experimentally observed trend (Table S5). Likewise, the tosyl system also features a shorter C–S bond than 2PO (1.619 and 1.625 Å, respectively), suggesting that the thioketenyl resonance form 2′ (Scheme 1) is more strongly favored in 2Ts than in 2PO. This preference is attributed to the stronger electron-withdrawing ability of the tosyl substituent, which more efficiently stabilizes the negative charge at carbon in the thioketenyl form. Accordingly, the calculated Voronoi deformation density (VDD)57 atomic charges at both the C1 atom [Q(C1) = −0.26] and the CS moiety [Q(CS) = −0.39] in 2Ts are less negative than the corresponding values in 2PO (Q(C1) = −0.30 and Q(CS) = −0.43), reflecting an increased charge transfer to the tosyl group (Fig. 6a). Similarly, the calculated Mayer bond order (MBO)58,59 of the C1–C2 bond in 2Ts (2.22) is smaller than in 2PO (2.25), further supporting that more electron-withdrawing substituents favor the thioketenyl resonance form 2′. However, analysis of the frontier orbitals of both anions 2 reveals that the two highest molecular orbitals (HOMO and HOMO−1) in both 2Ts and 2PO (Fig. 6b and Table S6) correspond to the π-bonds of the C–C–S linkage, suggesting a C Created by potrace 1.16, written by Peter Selinger 2001-2019 C triple bond, yet with a polarization towards the C1 carbon atom. The LUMO is predominantly localized on the Z group.

Fig. 6. Bonding situation in the alkynyl sulfide anions. (a) Comparison of the Voronoi deformation density (VDD) atomic charges (in electrons) and Mayer bond orders in 2PO and 2Ts. (b) Display of the isosurface (at 0.03 au) of the HOMO and HOMO−1 of 2Ts. Computed at ZORA-BP86/TZ2P level of theory.

Fig. 6

Open in a new tab

After understanding the effect of the Z group, we next analyzed the electronic structure of alkynyl sulfide anion 2PO {[Ph2P(O)–C–L2]−; L2 = CS} in comparison with the isoelectronic ketenyl anion 1PO {L2 = CO}, keteniminyl anion 5 {L2 = CNCy}, and diazomethanide 6 {L2 = N2}. To the best of our knowledge, this compound series represents the only set of isolated compounds featuring a systematic variation of these fundamental ligands and therefore provides general insights into their intrinsic properties. The calculated geometries of the naked anions 2PO, 1PO, 5, and 6 (Table S5) exhibit bending angles at the C1 atom that follow the trend CS > CO > CNCy > N2, in good agreement with the experimental data. This series of anions, featuring bent geometry and negative partial charge accumulation (Table S10) around the C1 atom, shows close resemblance with carbones, where a divalent C(0) atom retains its valence electrons as two lone pairs, and the chemical bonds are best described as dative interactions with concomitant L2 → C ← L2 σ-donation and L2 ← C → L2 π-backdonation.60,61 In carbone systems, the Dewar–Chatt–Duncanson model62,63 (often used for transition metal complexes) was used to demonstrate that the bending angle around C atom becomes more acute with decreasing π-acceptor strength of the ligands [e.g., C(CO)(CO) (156°); C(CO)(PPh3) (152°); C(PPh3)(PPh3) (146°)].64 Similarly, in our case, with decreasing π-acceptor strength of the L2 ligands (CS > CO ≈ CNCy > N2),65–67 the bending angle around C1 decreases 2PO > 1PO > 5 > 6.

To gain further insight into the nature of the chemical bonding, we analyzed the bonding energy (ΔE) between [Me2P(O)C]− and L2 [L2 = CS (2POS), CO (1POS), CNMe (5S) and N2 (6S)] along the bending coordinate around C1, using the Activation Strain Model (ASM)68–73 combined with the Energy Decomposition Analysis (EDA)74–76 (see the SI for technical details). To reduce computational cost, simplified model systems (2POS, 1POS, 5S, and 6S; Fig. S83) were employed, in which all aryl and alkyl substituents were replaced by methyl groups. All trends in C–L2 bond strength observed in the actual system [Ph2P(O)–C–L2]− are reproduced in the simplified model systems [Me2P(O)–C–L2]− (Tables S5 and S9). The calculated electronic bonding energy (ΔE) of the C–L2 bond in [Me2P(O)–C–L2]− becomes less stabilizing from CS to CO, CNMe, and N2. Note that the potential energy surface as a function of the P–C–L2 is flat, and the trends in ΔE remain the same at any given P–C–L2 bending angle. In general, these trends in ΔE arise from the trends in the interaction energy ΔEint (Fig. 7a). Only for L2 = CNMe (5S), the strain energy ΔEstrain is more destabilizing than for the other L2 ligands, which offsets ΔEint and causes a bond weakening for CNMe (5S) relative to CO (1POS).

Fig. 7. (a) Activation strain model (ASM) and (b) energy decomposition analysis (EDA) of the C–L2 bond in anionic systems [Me2P(O)–C–L2]− (where L2 = CS, CO, CNMe, N2) as a function of the P–C–L2 bond angle, computed at ZORA-BP86/TZ2P level of theory.

Fig. 7

Open in a new tab

Further insights into the interaction energy ΔEint are obtained by decomposing it into electrostatic interactions ΔVelstat, Pauli (steric) repulsion ΔEPauli, and stabilizing orbital interactions ΔEoi (Fig. 7b). Overall, all EDA terms increase in magnitude as the P–C–L2 bending angle becomes more acute, that is, ΔEPauli becomes more destabilizing, whereas ΔVelstat and ΔEoi become more stabilizing. Most importantly, the observed trends in ΔEint are mainly dictated by the trends in ΔEoi, and to a lesser extent by ΔVelstat, which becomes less stabilizing along CS(2POS), CNMe(5S), CO(1POS), and N2(6S). In contrast, the trends in the Pauli repulsion (ΔEPauli) along L2 are inconsistent and, therefore, do not determine the observed trends in bonding energy ΔE.

Quantitative molecular orbital analysis reveals a metallomimetic nature of these anionic systems, which are dominated by the [(POMe2)C]− ← L2 σ-donation and the in-plane and out-of-plane [(POMe2)C]− → L2 π-backdonation, in accordance with the classical Dewar–Chatt–Duncanson model (Fig. 8a). Further decomposition of the orbital-interaction term ΔEoi into ΔEoi,A′ and ΔEoi,A″ components reveals that the orbital interactions primarily originate from the interactions in the ΔEoi,A′ (Fig. 8b), which become less stabilizing along CS(2POS), CO(1POS), CNMe(5S), and N2(6S). The ΔEoi,A′ term includes both [(POMe2)C]− ← L2 σ-donation and the in-plane [(POMe2)C]− → L2 π-backdonation (depicted in red in Fig. 8a). Analysis at a consistent geometry with the P–C–L2 angle fixed at 120° (Fig. S86) shows that the in-plane π*-antibonding orbital of the L2 ligand rises in energy going from CS to CNMe to CO to N2, indicating a reduction of π-acceptor ability of the L2 ligand.

Fig. 8. (a) Molecular orbital diagram of the bonding interactions (σ-donation and π-backdonation) between [P(O)Me2C]−and L2 in [P(O)Me2C–L2]− (where L2 = CS, CO, CNMe, N2) at P–C–L2 = 120°. (b) Decomposition of the orbital interaction (ΔEoi) term in the A′ and A″ irreducible representations of CS symmetry as a function of the P–C–L2 bond angle. All values computed at ZORA-BP86/TZ2P level of theory.

Fig. 8

Open in a new tab

Overall, CS is the best π-acceptor ligand, which experiences the strongest π-backdonation, both in-plane (ΔEoi,A′) and out-of-plane (ΔEoi,A″). The stronger the π-backdonation, the larger the C Created by potrace 1.16, written by Peter Selinger 2001-2019 L2 triple bond character. Therefore, the weakening of the π-backdonation from CS(2POS), CO(1POS), CNMe(5S), and N2(6S) is perfectly in line with the experimentally observed decrease of the bending angle along this series of ligands and confirms that the alkynyl resonance form 2 is predominant for CS.

Reactivity studies of 2

With the first isolable alkynyl sulfide anions at hand, we next investigated their reactivity, in particular the chemoselectivity toward different electrophiles. We particularly focused on reactivity studies of the phosphinoyl substituted alkynyl sulfide 2PO due to its ease of isolation. Reaction of the anions 2 with methyl iodide afforded thioalkynes 7 through selective methylation at the sulfur end. This reactivity contrasts the observations made for ketenyl anions, which showed selective methylation at the C1 carbon center, and underscores the more pronounced alkynyl character. The thioalkynes 7a and 7b were isolated in excellent yields of 90 and 81%, confirming that 2 can indeed serve as an effective precursor for thioalkyne synthesis (Fig. 9).

Fig. 9. Reactivity studies of anionic alkynyl sulfides 2. For details on reaction conditions, see the SI. For clarity only the anionic component of the salts 10 and 11 are depicted. The cation [K·(18-c-6)], solvents and disordered parts in the solid-state structures have been omitted for clarity. Thermal ellipsoids are shown at the 50% level. a NMR yield; all others are isolated yields. b Crystal data of low quality.

Fig. 9

Open in a new tab

Following this successful S-centered reaction, we examined whether other electrophiles would promote reactivity at the nucleophile C1 site, thereby enabling access to neutral thioketenes. Indeed, reaction of 2PO with trityl chloride selectively yielded the neutral thioketene 8, indicating that softer electrophiles preferentially react at the C1 carbon atom. Single crystals of compound 8 suitable for XRD analysis were obtained by slow evaporation of benzene solution and unambiguously confirmed the C-centered reactivity. Analysis of the molecular structure of 8 revealed an elongation of the C1–C2 bond from 1.223(2) Å in 2PO to 1.316(2) Å, accompanied by a shortening of the C2–S1 bond from 1.632(1) Å in 2PO to 1.552(1) Å. These changes are consistent with a transformation from a thioalkyne to a thioketene. In contrast to the phosphinoyl-substituted alkynyl sulfide, the tosyl system exhibited low selectivity towards both electrophiles, indicating that excessive stabilizing of the negative charge into the backbone substituent complicates selective transformations.

While trimethylsilyl chloride (TMSCl) showed no selective reaction with both 2PS and 2Ts, its reaction with 2PO led to a further reactivity pattern. Addition of 1 equiv. of TMSCl to a THF solution of 2PO at room temperature resulted in the selective formation of new species 9, exhibiting a slightly down-field resonance signal at δP = 8.5 ppm. This signal was assigned to the product of the silylation at the oxygen center of the phosphinoyl group. The strong oxophilicity of the silicon directs the reactivity of TMSCl to the oxygen rather than the carbon or sulfur center (Fig. 9). Compound 9 features an almost linear geometry in the solid state with a P–C–C angle of 165.0(2)° and a C2–C2 distance of 1.232(2) Å.

Besides their reactivity towards electrophiles, the alkali metal salts of 2 showed high reactivity toward unsaturated compounds. Reaction of 2 with carbon disulfide or phenyl isothiocyanate furnished the highly functionalized heterocycles 10 and 11, respectively, via [2 + 2] cycloaddition reactions across the C–C triple bond (Fig. 9). Both reactions proceeded selectively, enabling the isolation of the resulting heterocycles as solids in good yields of 77 to 80%. Both heterocycles represent novel scaffolds that, until now, have only been synthesized once as neutral species with either PPh3 or an N-heterocyclic carbene ligand as exocyclic substituents.40,77 These thiete scaffolds represent untapped functional groups in pharmaceuticals.78,79

In addition, we examined whether the alkali metal salts of 2 could also be used for the transmetalation to alkynyl sulfide transition-metal complexes. While no reaction was observed upon treatment of 2PO with 1 equiv. of IPrCuCl (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) at room temperature, addition of 0.5 equiv. of CS2 to the reaction mixture in THF led to the formation of a new species, characterized by two low-field shifted 31P{1H} NMR resonances at δP = 4.60 and 29.73 ppm. Single-crystal XRD analysis revealed the formation of copper complex 12, featuring a cyclobutene-1,3-dithione scaffold with an exocyclic bound CS2 moiety. In the complex, each copper center is coordinated by one sulfur atom of the CS2 unit and the sulfur atom from the two former alkynyl sulfide anions. Interestingly, cyclobutene-1,3-dithione 12 is not obtained upon treatment of thiete 10a with the copper complex. This suggests that complex 12 instead forms via a copper-stabilized CS2 adduct of the alkynyl sulfide that undergoes cyclization with a second equivalent of the alkynyl sulfide.

Overall, these reactivity patterns demonstrate that alkynyl sulfide anions – unlike the corresponding ketenyl anions – exhibit a pronounced tendency to react at the sulfur atom, as well as high reactivities toward cyclization reactions involving the C–C triple bond. Thus, these anions serve not only as entry into the diverse chemistry of neutral alkynyl sulfides, but also offer potential for the synthesis of heterocycles.80,81

Conclusions

In conclusion, we report the synthesis of isolable alkynyl sulfide anions through reaction of ketenyl anions with either carbon disulfide or isothiocyanates. Both reactions proceed via a [2 + 2] cycloaddition reaction to a four-membered thiete intermediate, which subsequently undergoes cycloreversion through elimination of carbonyl sulfide and isocyanates, respectively. The electronic structure of these anions is best represented by the alkynyl sulfide form, featuring a C–C triple bond, as supported by the IR and NMR data. However, a minor contribution from the thioketenyl structure causes a slight bending of [R–C–CS]− linkage. This differs from previously reported related anions of the type [R–C–L]−, such as ketenyl anions (L = CO) or diazomethanides (L = N2), which exhibit a strong contribution of the structure with a lone pair at carbon. DFT studies reveal that the trends in the bonding situation in these anions are primarily governed by orbital interactions, particularly the in-plane π-backdonation from carbon to ligand L. This backdonation increases from N2 to CO and CS, reflecting fundamental ligand properties observed in transition metal chemistry, thereby unifying bonding concepts between carbanionic compounds and coordination complexes. The distinctive bonding in alkynyl anions is reflected in their reactivity patterns, which include a pronounced tendency for S-centered reactivity relative to the corresponding ketenyl anions and addition reactions across the C–C triple bond. These unique reactivities render alkynyl sulfides as powerful reagents for the synthesis of sulfur-containing heterocycles.

Author contributions

S. M. performed all synthetic experiments and spectroscopic analyses, except for compound 3Ts, 2Ts and 10b, which were synthesized by Q. L., A. D. F. helped with the isolation of compound 7 and 9. Q. L. carried out the in situ IR experiments. V. H. G. designed and supervised the experimental part of the project. S. M. carried out the quantum chemical calculations with help of D. A. S and D. R. S. The theoretical part of the work was supervised by F. M. B.

Conflicts of interest

There are no conflicts to declare.

Supplementary Material

QI-013-D6QI01030J-s001
QI-013-D6QI01030J-s002
QI-013-D6QI01030J-s003

Acknowledgments

This work has been funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy – EXC-2033-390677874 – RESOLV, the European Union (ERC, CarbFunction, 101086951), and the Netherlands Organization for Scientific Research (NWO). DFT calculations were carried out on the ADA (VU) Cluster and the Dutch national e-infrastructure, with support from the SURF Cooperative. D. A. S. O. acknowledges the São Paulo Research Foundation (FAPESP) (Grants #2022/01685-6 and #2024/03646-3) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (Grant #162366/2021-3) for funding their doctoral scholarship. Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them.

Data availability

The data supporting this article has been included as part of the supplementary information (SI). Supplementary information: the primary experimental data (NMR, IR files) as well as the coordinates of the optimized structures (xyz). See DOI: https://doi.org/10.1039/d6qi01030j.

CCDC 2528269–2528277 contain the supplementary crystallographic data for this paper.82a–i

The CCDC numbers and compound assignments are provided in the tables in the SI. We have included these cif files and the corresponding checkcif reports.

References

  1. Pluta K. Morak-Młodawska B. Jeleń M. Recent progress in biological activities of synthesized phenothiazines. Eur. J. Med. Chem. 2011;46:3179–3189. doi: 10.1016/j.ejmech.2011.05.013. [DOI] [PubMed] [Google Scholar]
  2. Ilardi E. A. Vitaku E. Njardarson J. T. Data-Mining for Sulfur and Fluorine: An Evaluation of Pharmaceuticals To Reveal Opportunities for Drug Design and Discovery. J. Med. Chem. 2014;57:2832–2842. doi: 10.1021/jm401375q. [DOI] [PubMed] [Google Scholar]
  3. Laxmikeshav K. Kumari P. Shankaraiah N. Expedition of sulfur-containing heterocyclic derivatives as cytotoxic agents in medicinal chemistry: A decade update. Med. Res. Rev. 2022;42:513–575. doi: 10.1002/med.21852. [DOI] [PubMed] [Google Scholar]
  4. Rahate A. S. Nemade K. R. Waghuley S. A. Polyphenylene sulfide (PPS): state of the art and applications. Rev. Chem. Eng. 2013;29:471–489. [Google Scholar]
  5. Dadashi-Silab S. Aydogan C. Yagci Y. Shining a light on an adaptable photoinitiator: advances in photopolymerizations initiated by thioxanthones. Polym. Chem. 2015;6:6595–6615. doi: 10.1039/C5PY01004G. [DOI] [Google Scholar]
  6. Hilt G. Lüers S. Harms K. The First Broad Application of Alkynyl Sulfides as Dienophiles in Cobalt(I)-Catalyzed Diels−Alder Reactions. J. Org. Chem. 2004;69:624–630. doi: 10.1021/jo0302915. [DOI] [PubMed] [Google Scholar]
  7. Commandeur M. Commandeur C. Paolis M. D. Edmunds A. J. F. Maienfisch P. Ghosez L. Studies related to the total synthesis of the sesquiterpene core of the pyrrolobenzoxazine natural products CJ-12662 and CJ-12663. Tetrahedron Lett. 2009;50:3359–3362. doi: 10.1016/j.tetlet.2009.02.105. [DOI] [Google Scholar]
  8. Xie L.-G. Shaaban S. Chen X. Maulide N. Metal-Free Synthesis of Highly Substituted Pyridines by Formal [2+2+2] Cycloaddition under Mild Conditions. Angew. Chem., Int. Ed. 2016;55:12864–12867. doi: 10.1002/anie.201606604. [DOI] [PubMed] [Google Scholar]
  9. Santandrea J. Godin E. Collins S. K. A synthetic guide to alkynyl sulfides. Org. Biomol. Chem. 2020;18:4885–4893. doi: 10.1039/D0OB00908C. [DOI] [PubMed] [Google Scholar]
  10. Yang Y. Dong W. Guo Y. Rioux R. M. Cu(I)-catalyzed aerobic cross-dehydrogenative coupling of terminal alkynes with thiols for the construction of alkynyl sulfides. Green Chem. 2013;15:3170–3175. doi: 10.1039/C3GC41330F. [DOI] [Google Scholar]
  11. Wang W. Peng X. Wei F. Tung C.-H. Xu Z. Copper(I)-Catalyzed Interrupted Click Reaction: Synthesis of Diverse 5-Hetero-Functionalized Triazoles. Angew. Chem., Int. Ed. 2016;55:649–653. doi: 10.1002/anie.201509124. [DOI] [PubMed] [Google Scholar]
  12. Kanemoto K. Yoshida S. Hosoya T. Synthesis of Alkynyl Sulfides by Copper-Catalyzed Thiolation of Terminal Alkynes Using Thiosulfonates. Org. Lett. 2019;21:3172–3177. doi: 10.1021/acs.orglett.9b00875. [DOI] [PubMed] [Google Scholar]
  13. Bieber L. W. da Silva M. F. Menezes P. H. Short and efficient preparation of alkynyl selenides, sulfides and tellurides from terminal alkynes. Tetrahedron Lett. 2004;45:2735–2737. doi: 10.1016/j.tetlet.2004.02.042. [DOI] [Google Scholar]
  14. Arisawa M. Fujimoto K. Morinaka S. Yamaguchi M. Equilibrating C−S Bond Formation by C−H and S−S Bond Metathesis. Rhodium-Catalyzed Alkylthiolation Reaction of 1-Alkynes with Disulfides. J. Am. Chem. Soc. 2005;127:12226–12227. doi: 10.1021/ja0527121. [DOI] [PubMed] [Google Scholar]
  15. Arens J. F. Doornbos T. The chemistry of acetylenic ethers XVI. Acetylenic thioethers. Recl. Trav. Chim. Pays-Bas. 1956;75:481–486. doi: 10.1002/recl.19560750414. [DOI] [Google Scholar]
  16. Frei R. Waser J. A Highly Chemoselective and Practical Alkynylation of Thiols. J. Am. Chem. Soc. 2013;135:9620–9623. doi: 10.1021/ja4044196. [DOI] [PubMed] [Google Scholar]
  17. Schaumann E. Lindstaedt J. Thioketen-Synthesen, VII. Substituenteneffekte auf die Thio-Claisen-Umlagerung von Alkinyl(allyl)sulfiden. Chem. Ber. 1983;116:1728–1738. doi: 10.1002/cber.19831160504. [DOI] [Google Scholar]
  18. Schaumann E. Lindstaedt J. Förster W. Eine neue Synthese und Reaktionsverhalten von (Aminoethinyl)sulfiden. Chem. Ber. 1983;116:509–513. doi: 10.1002/cber.19831160211. [DOI] [Google Scholar]
  19. Nørkjær K. Senning A. 1-Alkynyl Disulfides: Their Characterization and Their 1-Thiapropargyl—3-Thiaallenyl Rearrangements. Chem. Ber. 1993;126:73–77. doi: 10.1002/cber.19931260113. [DOI] [Google Scholar]
  20. Siegbahn P. E. M. Yoshimine M. Pacansky J. A theoretical study of the lowest singlet and triplet surfaces of C2H2S. J. Chem. Phys. 1983;78:1384–1389. doi: 10.1063/1.444879. [DOI] [Google Scholar]
  21. Birum G. H. Matthews C. N. Cycloaddition reactions of triphenylphosphoranylideneketene. J. Am. Chem. Soc. 1968;90:3842–3847. doi: 10.1021/ja01016a045. [DOI] [Google Scholar]
  22. Antoni P. W. Reitz J. Hansmann M. M. N2/CO Exchange at a Vinylidene Carbon Center: Stable Alkylidene Ketenes and Alkylidene Thioketenes from 1,2,3-Triazole Derived Diazoalkenes. J. Am. Chem. Soc. 2021;143:12878–12885. doi: 10.1021/jacs.1c06906. [DOI] [PubMed] [Google Scholar]
  23. Cerrada E. Laguna M. Lardíes N. Bis(1,2,3-thiadiazole)s as Precursors in the Synthesis of Bis(alkynethiolate)gold(I) Derivatives. Eur. J. Inorg. Chem. 2009;2009:137–146. doi: 10.1002/ejic.200800861. [DOI] [Google Scholar]
  24. Lardiés N. Romeo I. Cerrada E. Laguna M. Skabara P. J. Synthesis and properties of alkynethiolate gold(I) complexes. Dalton Trans. 2007:5329–5338. doi: 10.1039/B708966J. [DOI] [PubMed] [Google Scholar]
  25. Weigand W. Metallkomplexe mit funktionalisierten Schwefelliganden, I / Metal Complexes of Functionalized Sulphur Containing Ligands, I: Eisen(II)-, Ruthenium(II)- und Platin(II)-1-alkin-1-thiolato- und -2-propen-1-thiolato-Komplexe / Synthesis of Iron(II), Ruthenium(II) and Platinum(II) 1-Alkyne-1-thiolato and 2-Propene-1-thiolato Complexes. Z. Naturforsch., B: J. Chem. Sci. 1991;46:1333–1337. doi: 10.1515/znb-1991-1010. [DOI] [Google Scholar]
  26. Weigand W. Robl C. Metallkomplexe mit funktionalisierten Schwefel-Liganden, VI[1]. Stabilisierung von 1-Alkin-1-thiolato-Liganden [R–C≡C–S–; R = SiMe3,(η5-C5H4)Fe(η5-C5H5)] in Ru(II)- und Pt(II)-Komplexen. Kristallstrukturanalyse von cis-(Ph3P)2Pt[C≡C–(η5C5H4)Fe(η5-C 5H5)]2. Chem. Ber. 1993;126:1807–1809. doi: 10.1002/cber.19931260808. [DOI] [Google Scholar]
  27. Ara I. Delgado E. Forniés J. Hernández E. Lalinde E. Mansilla N. Moreno M. T. The first alkynethiolate derivatives of bis(substituted cyclopentadienyl)titanium(IV) and their role in the synthesis of heterobimetallic compounds. Crystal structures of [Ti(η 5 -C 5 H 4 SiMe 3) 2 (SC[triple bond, length half m-dash]CBu t) 2 ] and [(η 5 -C 5 H 4 SiMe 3)(SC[triple bond, length half m-dash]CBu t)Ti(µ-η 5 ∶κ- P -C 5 H 4 PPh 2)(µ-SC[triple bond, length half m-dash]CBu t)Pt(C 6 F 5) 2 ]†. J. Chem. Soc., Dalton Trans. 1998:3199–3208. doi: 10.1039/A803806F. [DOI] [Google Scholar]
  28. Brandsma L., Synthesis of Acetylenes, Allenes and Cumulenes, Elsevier, Amsterdam, 2004, p. 25 [Google Scholar]
  29. Rosenberger C. Steunou N. Jeannin S. Jeannin Y. Synthesis of [Fe2(CO)6(μ-SC2H5)(μ-CCR)] (R = CH3 or C6H5) and reactivity with electron-rich molecules, triphenylphosphine, diphenylacetylene, ethylthio(phenyl) ethyne and (diethylamino) propyne. Preparation of [Fe2(CO)6(μ-SCCC6H5)(μ-CCC6H5)] and formation of [Fe4(CO)12(μ4-S)(μ-CCC6H5)2] J. Organomet. Chem. 1995;494:17–35. doi: 10.1016/0022-328X(94)05298-P. [DOI] [Google Scholar]
  30. Isabel Alcalde M. Delgado E. Donnadieu B. Hernández E. Paz Martín M. Zamora F. Asymmetric acetylenic thioethers in ruthenium cluster chemistry. J. Organomet. Chem. 2004;689:552–556. doi: 10.1016/j.jorganchem.2003.11.006. [DOI] [Google Scholar]
  31. Alcalde M. I. Carty A. J. Chi Y. Delgado E. Donnadieu B. Hernández E. Dallmann K. Sánchez-Nieves J. Syntheses of new ruthenium clusters containing sulfur, ynyl and diynyl ligands. Crystal structures of [Ru3(CO)9(μ-η2-SCCSiMe3)(μ3-η2-CCSiMe3)], [Ru4(CO)12(μ4-S)(μ-η2-CCSiMe3)2] and [Ru4(CO)9(μ-CO)2(μ4-S)(μ4-η2-C(SiMe3)C(CCSiMe3)] J. Chem. Soc., Dalton Trans. 2001:2502–2507. doi: 10.1039/B103202J. [DOI] [Google Scholar]
  32. Delgado E. Hernández E. Nievas Á. Villa M. Martín A. Alonso B. Synthesis, characterization and reactivity studies of the new compound [Os3(CO)9(μ3-η2,η3,η3-{C5H5FeC5H3CCC(S)C(Fc)CHO}] J. Organomet. Chem. 2007;692:5453–5458. doi: 10.1016/j.jorganchem.2007.09.003. [DOI] [Google Scholar]
  33. Seidel W. W. Meel M. J. Hupka F. Weigand J. J. Acetylenedithiolate as directional bridging ligand in cobalt(I) alkyne platinum dithiolato bimetallic complexes. Dalton Trans. 2009;39:624–631. doi: 10.1039/B913859E. [DOI] [PubMed] [Google Scholar]
  34. Seidel W. W. Sánchez B. L. Meel M. J. Hepp A. Pape T. Electronic Control of the Rotational Barrier in η2-Alkyne-1-thio Complexes. Eur. J. Inorg. Chem. 2007;2007:936–943. doi: 10.1002/ejic.200600619. [DOI] [Google Scholar]
  35. Wang Y. Zhao F. Chi Y. Zhang W.-X. Xi Z. Substituent-Controlled Selective Synthesis of N-Acyl 2-Aminothiazoles by Intramolecular Zwitterion-Mediated C–N Bond Cleavage. J. Org. Chem. 2014;79:11146–11154. doi: 10.1021/jo502123k. [DOI] [PubMed] [Google Scholar]
  36. Wang Y. Zhang W.-X. Wang Z. Xi Z. Procedure-Controlled Selective Synthesis of 5-Acyl-2-iminothiazolines and their Selenium and Tellurium Derivatives by Convergent Tandem Annulation. Angew. Chem., Int. Ed. 2011;50:8122–8126. doi: 10.1002/anie.201101948. [DOI] [PubMed] [Google Scholar]
  37. Wang Z. Wang Y. Zhang W.-X. Hou Z. Xi Z. Efficient One-Pot Synthesis of 2,3-Dihydropyrimidinthiones via Multicomponent Coupling of Terminal Alkynes, Elemental Sulfur, and Carbodiimides. J. Am. Chem. Soc. 2009;131:15108–15109. doi: 10.1021/ja9069419. [DOI] [PubMed] [Google Scholar]
  38. Le Dé Q. Zhang Y. Zhao L. Krischer F. Feichtner K.-S. Frenking G. Gessner V. H. Isolation and Structure Elucidation of the Heterocumulene Anions [NCC-L]− (L=CO, CS, N2) Angew. Chem. 2025;137:e202422496. doi: 10.1002/ange.202422496. [DOI] [PubMed] [Google Scholar]
  39. Bernasconi C. F. Wenzel P. J. Carbon-to-Carbon Identity Proton Transfer from Allene, Ketene, Ketenimine, and Thioketene to Their Respective Conjugate Anions in the Gas Phase. An ab Initio Study. J. Am. Chem. Soc. 2001;123:7146–7153. doi: 10.1021/ja010368b. [DOI] [PubMed] [Google Scholar]
  40. Feuerstein W. Varava P. Fadaei-Tirani F. Scopelliti R. Severin K. Synthesis, structural characterization, and coordination chemistry of imidazole-based alkylidene ketenes. Chem. Commun. 2021;57:11509–11512. doi: 10.1039/D1CC05161J. [DOI] [PubMed] [Google Scholar]
  41. Jörges M. Mondal S. Kumar M. Duari P. Krischer F. Löffler J. Gessner V. H. Phosphinoyl-Substituted Ketenyl Anions: Synthesis and Substituent Effects on the Structural Properties. Organometallics. 2024;43:585–593. doi: 10.1021/acs.organomet.3c00530. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Jörges M. Krischer F. Gessner V. H. Transition metal–free ketene formation from carbon monoxide through isolable ketenyl anions. Science. 2022;378:1331–1336. doi: 10.1126/science.ade4563. [DOI] [PubMed] [Google Scholar]
  43. Krischer F. Jörges M. Leung T.-F. Darmandeh H. Gessner V. H. Selectivity Control of the Ligand Exchange at Carbon in α-Metallated Ylides as a Route to Ketenyl Anions. Angew. Chem., Int. Ed. 2023;62:e202309629. doi: 10.1002/anie.202309629. [DOI] [PubMed] [Google Scholar]
  44. van Lenthe E. Baerends E. J. Snijders J. G. Relativistic total energy using regular approximations. J. Chem. Phys. 1994;101:9783–9792. doi: 10.1063/1.467943. [DOI] [Google Scholar]
  45. van Lenthe E. Ehlers A. Baerends E.-J. Geometry optimizations in the zero order regular approximation for relativistic effects. J. Chem. Phys. 1999;110:8943–8953. doi: 10.1063/1.478813. [DOI] [Google Scholar]
  46. van Lenthe E. Baerends E. J. Snijders J. G. Relativistic regular two-component Hamiltonians. J. Chem. Phys. 1993;99:4597–4610. doi: 10.1063/1.466059. [DOI] [Google Scholar]
  47. Becke A. D. Density-functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A. 1988;38:3098–3100. doi: 10.1103/PhysRevA.38.3098. [DOI] [PubMed] [Google Scholar]
  48. Perdew J. P. Erratum: Density-functional approximation for the correlation energy of the inhomogeneous electron gas. Phys. Rev. B: Condens. Matter Mater. Phys. 1986;34:7406. doi: 10.1103/PhysRevB.34.7406. [DOI] [PubMed] [Google Scholar]
  49. Perdew J. P. Density-functional approximation for the correlation energy of the inhomogeneous electron gas. Phys. Rev. B: Condens. Matter Mater. Phys. 1986;33:8822–8824. doi: 10.1103/PhysRevB.33.8822. [DOI] [PubMed] [Google Scholar]
  50. Van Lenthe E. Baerends E. J. Optimized Slater-type basis sets for the elements 1–118. J. Comput. Chem. 2003;24:1142–1156. doi: 10.1002/jcc.10255. [DOI] [PubMed] [Google Scholar]
  51. Selzer T. Rappoport Z. Bis(dimesitylmethylene)-1,3-dithietane, -1,2,4-trithiane, and -1,2,4,5-tetrathiane. Conformation and DNMR Study. Observable Dimesityl Thioketene. J. Org. Chem. 1996;61:7326–7334. doi: 10.1021/jo960911k. [DOI] [PubMed] [Google Scholar]
  52. Chen Y. Wen S. Tian Q. Zhang Y. Cheng G. Transition Metal-Free C–H Thiolation via Sulfonium Salts Using β-Sulfinylesters as the Sulfur Source. Org. Lett. 2021;23:7905–7909. doi: 10.1021/acs.orglett.1c02912. [DOI] [PubMed] [Google Scholar]
  53. Mondal S. Zhang Y. Duari P. Feichtner K.-S. Das A. Zhao L. Frenking G. Gessner V. H. PPh3/Isocyanide and N2/Isocyanide Exchange: Pathways to Isolable Alkali Metal Keteniminyl Anions. Angew. Chem., Int. Ed. 2025;64:e202504325. doi: 10.1002/anie.202504325. [DOI] [PMC free article] [PubMed] [Google Scholar]
  54. Ward R. J. Jörges M. Remm H. Kiliani E. Krischer F. Le Dé Q. Gessner V. H. An Azide-Free Synthesis of Metallodiazomethanes Using Nitrous Oxide. J. Am. Chem. Soc. 2024;146:24602–24608. doi: 10.1021/jacs.4c07999. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Brar A. Nadella K. Unruh D. K. Bouley B. Krempner C. New Phosphoranylideneketenes and Phosphoranylidenethioketenes-Synthesis, Structure, Spectroscopy, and Lewis Base Properties. Chem. – Eur. J. 2025;31:e02777. doi: 10.1002/chem.202502777. [DOI] [PubMed] [Google Scholar]
  56. Voets M. Smet M. Dehaen W. Synthesis of alkynyl sulfides resulting from a novel ring cleavage of 5-chloro-1,2,3-thiadiazoles in the presence of organometallic reagents. J. Chem. Soc., Perkin Trans. 1. 1999:1473–1476. doi: 10.1039/A901355E. [DOI] [Google Scholar]
  57. Fonseca Guerra C. Handgraaf J.-W. Baerends E. J. Bickelhaupt F. M. Voronoi deformation density (VDD) charges: Assessment of the Mulliken, Bader, Hirshfeld, Weinhold, and VDD methods for charge analysis. J. Comput. Chem. 2004;25:189–210. doi: 10.1002/jcc.10351. [DOI] [PubMed] [Google Scholar]
  58. Mayer I. Charge, bond order and valence in the AB initio SCF theory. Chem. Phys. Lett. 1983;97:270–274. doi: 10.1016/0009-2614(83)80005-0. [DOI] [Google Scholar]
  59. Mayer I. Bond order and valence: Relations to Mulliken's population analysis. Int. J. Quantum Chem. 1984;26:151–154. doi: 10.1002/qua.560260111. [DOI] [Google Scholar]
  60. Tonner R. Frenking G. Divalent Carbon(0) Chemistry, Part 1: Parent Compounds. Chem. – Eur. J. 2008;14:3260–3272. doi: 10.1002/chem.200701390. [DOI] [PubMed] [Google Scholar]
  61. Frenking G. Tonner R. Klein S. Takagi N. Shimizu T. Krapp A. Pandey K. K. Parameswaran P. New bonding modes of carbon and heavier group 14 atoms Si–Pb. Chem. Soc. Rev. 2014;43:5106–5139. doi: 10.1039/C4CS00073K. [DOI] [PubMed] [Google Scholar]
  62. Chatt J. Duncanson L. A. J. Chem. Soc. 1953:2939–2947. doi: 10.1039/JR9530002939. [DOI] [Google Scholar]
  63. Frenking G. Understanding the nature of the bonding in transition metal complexes: from Dewar's molecular orbital model to an energy partitioning analysis of the metal–ligand bond. J. Organomet. Chem. 2001;635:9–23. doi: 10.1016/S0022-328X(01)01154-8. [DOI] [Google Scholar]
  64. Frenking G. Dative Bonds in Main-Group Compounds: A Case for More Arrows! Angew. Chem., Int. Ed. 2014;53:6040–6046. doi: 10.1002/anie.201311022. [DOI] [PubMed] [Google Scholar]
  65. Moltzen E. K. Klabunde K. J. Senning A. Carbon monosulfide: a review. Chem. Rev. 1988;88:391–406. doi: 10.1021/cr00084a003. [DOI] [Google Scholar]
  66. Perrin L. Clot E. Eisenstein O. Loch J. Crabtree R. H. Computed Ligand Electronic Parameters from Quantum Chemistry and Their Relation to Tolman Parameters, Lever Parameters, and Hammett Constants. Inorg. Chem. 2001;40:5806–5811. doi: 10.1021/ic0105258. [DOI] [PubMed] [Google Scholar]
  67. Lichtenberger D. L. Fenske R. F. Electronic structure of transition metal thiocarbonyl complexes. Inorg. Chem. 1976;15:2015–2022. doi: 10.1021/ic50163a001. [DOI] [Google Scholar]
  68. Vermeeren P. van der Lubbe S. C. C. Fonseca Guerra C. Bickelhaupt F. M. Hamlin T. A. Understanding chemical reactivity using the activation strain model. Nat. Protoc. 2020;15:649–667. doi: 10.1038/s41596-019-0265-0. [DOI] [PubMed] [Google Scholar]
  69. Bickelhaupt F. M. Houk K. N. Analyzing Reaction Rates with the Distortion/Interaction-Activation Strain Model. Angew. Chem., Int. Ed. 2017;56:10070–10086. doi: 10.1002/anie.201701486. [DOI] [PMC free article] [PubMed] [Google Scholar]
  70. Wolters L. P. Bickelhaupt F. M. The activation strain model and molecular orbital theory. Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2015;5:324–343. doi: 10.1002/wcms.1221. [DOI] [PMC free article] [PubMed] [Google Scholar]
  71. Bickelhaupt F. M. Understanding reactivity with Kohn–Sham molecular orbital theory: E2−SN2 mechanistic spectrum and other concepts. J. Comput. Chem. 1999;20:114–128. doi: 10.1002/(SICI)1096-987X(19990115)20:1<114::AID-JCC12>3.0.CO;2-L. [DOI] [Google Scholar]
  72. Fernández I. Bickelhaupt F. M. The activation strain model and molecular orbital theory: understanding and designing chemical reactions. Chem. Soc. Rev. 2014;43:4953–4967. doi: 10.1039/C4CS00055B. [DOI] [PubMed] [Google Scholar]
  73. van Zeist W.-J. Bickelhaupt F. M. The activation strain model of chemical reactivity. Org. Biomol. Chem. 2010;8:3118–3127. doi: 10.1039/B926828F. [DOI] [PubMed] [Google Scholar]
  74. van Meer R. Gritsenko O. V. Baerends E. J. Physical Meaning of Virtual Kohn–Sham Orbitals and Orbital Energies: An Ideal Basis for the Description of Molecular Excitations. J. Chem. Theory Comput. 2014;10:4432–4441. doi: 10.1021/ct500727c. [DOI] [PubMed] [Google Scholar]
  75. Bickelhaupt F. M. and Baerends E. J., in Reviews in Computational Chemistry, John Wiley & Sons, Ltd, 2000, pp. 1–86 [Google Scholar]
  76. Hamlin T. A., Vermeeren P., Fonseca Guerra C. and Bickelhaupt F. M., in Complementary Bonding Analysis, ed. S. Grabowsky, De Gruyter, 2021, pp. 199–212 [Google Scholar]
  77. Bestmann H. J. Schmid G. Über die Umsetzung von N-Phenyliminoketenyliden-triphenylphosphoran mit Kohlendioxid, Kohlenoxisulfid und Schwefelkohlenstoff. Tetrahedron Lett. 1977;18:3037–3038. doi: 10.1016/S0040-4039(01)83150-6. [DOI] [Google Scholar]
  78. Eisold M. Müller-Deku A. Reiners F. Didier D. Parallel Approaches for the Functionalization of Thietes: α-Metalation versus C-H Activation. Org. Lett. 2018;20:4654–4658. doi: 10.1021/acs.orglett.8b01961. [DOI] [PubMed] [Google Scholar]
  79. Didier D. Reiners F. Uncommon Four-Membered Building Blocks – Cyclobutenes, Azetines and Thietes. Chem. Rec. 2021;21:1144–1160. doi: 10.1002/tcr.202100011. [DOI] [PubMed] [Google Scholar]
  80. Xie L.-G. Shaaban S. Chen X. Maulide N. Metal-Free Synthesis of Highly Substituted Pyridines by Formal [2+2+2] Cycloaddition under Mild Conditions. Angew. Chem., Int. Ed. 2016;55:12864–12867. doi: 10.1002/anie.201606604. [DOI] [PubMed] [Google Scholar]
  81. Aurelio L. Volpe R. Halim R. Scammells P. J. Flynn B. L. Synthesis of Thieno-Fused Heterocycles through Reiterative Iodocyclization. Adv. Synth. Catal. 2014;356:1974–1978. doi: 10.1002/adsc.201400072. [DOI] [Google Scholar]
  82. (a) CCDC 2528269: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw2k [DOI]; (b) CCDC 2528270: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw3l [DOI]; (c) CCDC 2528271: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw4m [DOI]; (d) CCDC 2528272: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw5n [DOI]; (e) CCDC 2528273: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw6p [DOI]; (f) CCDC 2528274: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw7q [DOI]; (g) CCDC 2528275: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw8r [DOI]; (h) CCDC 2528276: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw9s [DOI]; (i) CCDC 2528277: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvwbt [DOI]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Citations

  1. (a) CCDC 2528269: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw2k [DOI]
  2. (b) CCDC 2528270: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw3l [DOI]
  3. (c) CCDC 2528271: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw4m [DOI]
  4. (d) CCDC 2528272: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw5n [DOI]
  5. (e) CCDC 2528273: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw6p [DOI]
  6. (f) CCDC 2528274: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw7q [DOI]
  7. (g) CCDC 2528275: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw8r [DOI]
  8. (h) CCDC 2528276: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvw9s [DOI]
  9. (i) CCDC 2528277: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2qvwbt [DOI]

Supplementary Materials

QI-013-D6QI01030J-s001
QI-013-D6QI01030J-s001.pdf (8.8MB, pdf)
QI-013-D6QI01030J-s002
QI-013-D6QI01030J-s002.xyz (55.6KB, xyz)
QI-013-D6QI01030J-s003
QI-013-D6QI01030J-s003.cif (10.8MB, cif)

Data Availability Statement

The data supporting this article has been included as part of the supplementary information (SI). Supplementary information: the primary experimental data (NMR, IR files) as well as the coordinates of the optimized structures (xyz). See DOI: https://doi.org/10.1039/d6qi01030j.

CCDC 2528269–2528277 contain the supplementary crystallographic data for this paper.82a–i

The CCDC numbers and compound assignments are provided in the tables in the SI. We have included these cif files and the corresponding checkcif reports.

Articles from Inorganic Chemistry Frontiers are provided here courtesy of Royal Society of Chemistry

RESOURCES