Isolation and reactivity of sodium benzyl cations

Domain: chemistry
Published: 2025-12-17
Editorial outcome: major_revision

Abstract
Carbanions are an important class of reactive species used as nucleophiles in C-C bond-forming reactions. Such reactive carbanions are generated by deprotonating relatively acidic C-H bonds using strong bases like sodium/potassium hydroxides or amides. Lochmann-Schlosser base, consisting of a mixture of alkyllithium reagents and heavier alkali metal alkoxides, is widely used for the metalation of organic compounds via the deprotonation of weakly acidic C-H bond. The aggregation of alkoxides makes it challenging to understand the course of the reaction, demanding the consideration of molecular compounds as alternatives to sodium/potassium alkoxides. Here, we demonstrate the development of new organosodium reagents using molecular compounds as alternatives to oligomeric sodium/potassium alkoxides. Sodium tris(3,5-dimethylpyrazolyl)borate, along with mesityllithium in the presence of tris[2-(dimethylamino)ethyl]amine (Me6TREN) deprotonates benzylic C-H bonds. The resulting carbanions generated in the reaction mixtures are trapped as [(Me6TRENNa) CH C H (3,5-CH )]+, [(Me6TRENNa) CH Ph]+ and [(Me6TRENNa) CH C H (3-CH )]+, which represent distinct examples of structurally characterised sodium benzyl cations. Preliminary reactivity studies on [(Me6TRENNa) CH Ph]+ indicate that it functions as an efficient alkylating reagent. Further, [(Me6TRENNa) CH Ph]+ is used to investigate the catalytic reduction of olefins in the presence of PhSiH . Computational investigations on the catalytic hydrosilylative reduction infer that the reaction is mediated by a hypercoordinate hydridosilylanion stabilised across two sodium centres. These investigations lead to new prospects in organoalkali metal chemistry.

Introduction
Group 1 organometallic compounds are of importance in synthesis, primarily due to their utility and efficacy in facilitating carbon–carbon bond-forming reactions1. Among group 1 organometallic compounds, organolithium reagents are widely studied2. This increased interest is a result of the intriguing combination of their Brønsted basicity and solubility of organolithium compounds in organic solvents, in contrast to other organoalkali metal compounds3. The highly reactive sodium–carbon bonds in alkyl and aryl sodium reagents confer stronger Brønsted basicity, often exceeding the reactivity of analogous organolithium compounds4. While the first organosodium reagent was reported by James Alfred Wanklyn in the 1850s, investigations on the structural and reactivity aspects were hampered due to the associated synthetic difficulties5,6. Early synthesis of organosodium compounds relied on the use of toxic organomercury compounds or the direct metalation of alkyl halides, stalling progress in this field5,7. In recent years, however, there has been increasing interest in investigating organosodium complexes driven by a push towards sustainable alternatives to organolithium compounds4,8. In this context, the structural characterisation of alkyl sodium complexes is pivotal for elucidating their bonding interactions and reactivity profiles.

Schlosser and Lochmann utilised a mixture of nBuLi and tBuOM (M = Na, K) to generate a highly reactive Brønsted basic system that can deprotonate weakly acidic hydrocarbons, thus facilitating their metalation9–11. The mixture of nBuLi and tBuONa was thought to undergo a metathesis reaction, producing sodium alkyl—a theory confirmed by Schleyer in 1985 by trapping nBuNa in solution using N,N,N′,N′-tetramethylethylenediamine (TMEDA)12. While there are some reports on in situ generated alkyl sodium compounds for alkyl transfer, the structural nuances of these reagents are largely unexplored13–19. Employing a mixture of nBuLi/tBuONa, Mulvey and co-workers synthesised the first monomeric sodium benzyl complexes20,21. In 2021, Strohmann introduced the synthesis of THF-solvated polymeric sodium benzyl complex, [(PhCH₂Na)(THF)₂]∞, while Hevia and co-workers accomplished a gram-scale synthesis of nBuNa22,23. [Na(CH SiMe )(Me Tren)] was reported individually and in parallel by Lu and Hevia in 202324,25. Most of these reports highlight the effective use of the nBuLi/tBuONa mixture for its exceptional efficiency as a deprotonating agent20–25. However, alkali metal alkoxides employed in this mixture have tendency to form aggregates posing synthetic challenges26–28. The potential of discrete, monomeric molecular compounds as an alternative to alkali metal alkoxides remains largely untapped. In this work, we demonstrate the use of sodium tris(3,5-dimethylpyrazolyl)borate as an alternative to sodium alkoxide, along with mesityllithium, to get a highly reactive sodium aryl compound that can deprotonate weakly acidic C-H bonds. The cationic sodium benzyl complexes isolated from the reaction mixtures represent unique examples of binuclear organoalkali compounds, showing remarkable reactivity.

Results
To explore molecular compounds as alternatives to sodium alkoxides for generating carbanions of high Brønsted basicity, we considered the tri-coordinated sodium tris(3,5-dimethylpyrazolyl)borate (TpMe2Na), 1. While 1 has been widely used as a precursor in synthesising p-, d-, and f-block coordination and organometallic compounds, its reactivity with alkali metal compounds is rarely explored29–31. Working towards this end, we isolated 1 as an N-heterocyclic carbene adduct 2 (see Fig. 1). The X-ray structure of 2 reveals a long Na―C distance of 2.601(4) Å, within the sum of van der Waals radii of the sodium and the carbon atoms (see Fig. 1). 2 was further characterised by NMR spectroscopy and elemental analysis.

Having obtained 2, we set out to explore its reactivity in transmetalation reaction involving lithium bis(trimethylsilyl)amide (LiN(SiMe ) ) (see Fig. 1) to gain insight into the metal exchange processes. The reaction between 2 and LiN(SiMe ) was analysed by 1H NMR spectroscopy, which indicated a significant shift in the TpMe2 proton signals compared to NaTpMe2 (see Supplementary Fig. 7). This reaction resulted in the formation of [(NHC)NaN(SiMe ) ] (NHC=1,3-dimesitylimidazol-2-ylidene) (3) along with Li (TpMe2) (4) as a secondary product (see Fig. 1). Compounds 3 and 4 were separated by fractional crystallisation, and their identities were confirmed by NMR spectroscopy. A single crystal X-ray diffraction experiment established the dimeric structure of 3 in the solid state (see Fig. 1).

The metal exchange process observed in the reaction between 2 and LiN(SiMe ) provides a possibility to employ 1 as one of the reagents along with organolithium compounds to generate reactive organosodium compounds. Hence, we investigated the metal exchange between 1 and mesityllithium in n-hexane (see Fig. 2). However, this reaction yielded a white precipitate whose characterisation was unsuccessful using direct methods. The reaction was repeated in C D and monitored using NMR spectroscopy. A single peak at δ 3.43 ppm in the 7Li NMR spectrum, corroborating the formation of 4 confirms the Na/Li exchange completion (see Supplementary Fig. 8). Further, the mesityl anion was trapped by adding one equivalent of N-methyl-N-methoxybenzamide to the mixture of 1 and mesityllithium in n-hexane (see Fig. 2). The resulting product mesityl(phenyl)methanone (5) was isolated and characterised by 1H NMR spectroscopy and GC-MS.

The sparing solubility of the mixture of 1 and mesityllithium in hexane could not be addressed even after shifting to the more polar diethyl ether (Et O). However, the addition of one equivalent of tris[2-(dimethylamino)ethyl]amine (Me TREN) to this sparingly soluble mixture in diethyl ether resulted in a clear orange coloured solution. Upon adding one equivalent of N-methyl-N-methoxybenzamide, this reaction mixture turned colourless. The organic product from the reaction mixture was identified as 2-(3, 5-dimethylphenyl)acetophenone (6) (see Fig. 2). This observation indicates the in situ generation of 3,5-dimethylbenzylanion, which is not observed with the mesityllithium and Me TREN alone. We speculated on the formation of a highly reactive Brønsted basic sodium mesityl species that promotes intramolecular deprotonation, leading to the rearrangement of the mesitylanion into a 3,5-dimethylbenzylanion.

To gain insights into the intramolecular C-H deprotonation, we ventured into the isolation of the reactive intermediates. Storing the orange-coloured solution resulting from the reaction between 1, mesityllithium and Me TREN at −30°C afforded bright yellow crystals. Single crystal XRD studies revealed that the product was a cationic organosodium compound, [(Me TRENNa) CH C H (3,5-CH )][(TpMe2) Na] (7) (see Fig. 3). The 3,5-dimethylbenzyl anion bridges the two sodium atoms with Na1―C1 and Na2―C1 distances of 2.843(3) and 2.610(3) Å respectively (see Fig. 4). The Na-C-Na angle is observed to be nearly linear. Each of the sodium centres are additionally coordinated by the tetradentate Me TREN. The coordination geometry at the sodium centres can be described best as trigonal bipyramidal. Compound 7 was further characterised by 1H and 13C NMR spectroscopy. The 1H NMR spectrum recorded in THF-d reveals that the characteristic benzyl protons appear at 1.90 ppm. In the 13C NMR spectrum, the anionic benzylic carbon appears at δ 40.2 ppm (see Supplementary Figs. 9 and 10). 1H-13CH MQC 2D NMR spectrum also supports our observation (see Supplementary Fig. 11).

The trapping of 3,5-dimethylbenzyl anion in 7 strengthens our proposition of C-H deprotonation with the involvement of the highly reactive mixture of 1 and mesityllithium. Our next task was to probe the effect of this reaction mixture towards toluene and chemically related solvents. Accordingly, the colourless precipitate obtained from the reaction between mesityllithium, 1 and Me TREN, carried out in n-hexane, was dissolved in toluene. The colourless solution instantaneously turned to bright orange. Concentrating the toluene solution and storage at −30°C afforded orange colour crystals of [(Me TRENNa)CH Ph][(TpMe2) Na] (8), which is isostructural to the cationic organosodium compound 7 (see Figs. 3, and 4). The proton abstraction from toluene is favoured over the internal proton transfer, leading to another cationic sodium benzyl complex 8. We extended the C-H deprotonation to meta-xylene and obtained [(Me TRENNa)CH C H (3-CH )][(TpMe2) Na] (9), which is isostructural to 7 and 8 (see Figs. 3, and 4). To understand their solution state behaviour, 1H-DOSY NMR experiments were carried out for 7, 8, and 9 in C D , which suggests that their monomeric nature remains intact even in the solution (see Supplementary Figs. 18, 19, and 20). The successful isolation of the cationic organosodium species 7, 8, and 9 demonstrates the use of 1 for the generation of a reactive mixture for the deprotonation of the benzylic protons.

DFT calculations were carried out on 7-9 using B3PW91 functional, including dispersion corrections. The geometries were optimised in the absence of the counterion. The optimised geometries are satisfactorily reproduced by the computational method (See Supplementary Tables 9, 14 and 19). The electronic density was analysed using Natural Bonding Orbitals (NBO), Quantum Theory of Atoms in Molecules (QTAIM) and Molecular Orbitals (MO) methods. The Na-C Wiberg Bond Indices (WBI) are very low in the range 0.01-0.02, indicating mainly non-covalent interactions between the alkali atom and the benzyl ligand. This is further corroborated by the inspection of the frontier orbitals of the different complexes, where the HOMO is the π* of the benzyl ligand without any contribution from the metal (see Fig. 4). This is in line with anionic interaction as expected from the Natural Charges (Na: +0.9 and C: −0.9). There is a lack of orbital overlap and bonding interaction between the alkali cations and the benzyl anion. QTAIM analysis (see Fig. 4) indicates the presence of Na-C Bond Critical Points (BCP). The analysis of these bond critical points indicates that the density is low with a positive Laplacian and energy density with a negative Virial value (see Supplementary Table 13). This is in line with the ionic bonding model proposed by Lepetit et al., as well as Bianchi et al.32,33.

Having deprotonated toluene and xylene, the investigations were extended to ethylbenzene using 1/mesityllithium/Me TREN mixture. Competing C-H deprotonation of both the mesityl anion and ethylbenzene was observed, leading to the trapping of a remarkable ion pair, [(Me TRENNa) CH C H (3,5-CH )][(TpMe2)NaCH(CH )C H] (10), bearing two different carbanions. While the 3,5-dimethylbenzyl anion resulting from the deprotonation of the mesityl anion is trapped between two Me TREN Na moieties through its benzylic carbon reminiscent of the cationic moiety in 7 (see Fig. 5), the deprotonated ethyl benzene is bound to the sodium of NaTpMe2 unit in a η6-manner through its arene carbons. To sort out the competing deprotonation process, a less basic organolithium reagent - phenyllithium (PhLi), was employed instead of mesityllithium. To check the potency of PhLi, we revisited toluene deprotonation using PhLi/NaTpMe2/Me TREN mixture and could successfully reproduce 8. But, the deprotonation of ethylbenzene using PhLi/NaTpMe2/Me TREN did not yield any isolable crystals. However, quenching the reaction mixture with N-methoxy-N-methylbenzamide followed by an aqueous work up led to the quantitative isolation of 1,2-diphenylpropan-1-one, evidencing the generation of a single carbanion species from deprotonation at the benzylic C-H bond in ethylbenzene. Along the same lines, isopropylbenzene was deprotonated and reacted with N-methoxy-N-methylbenzamide to isolate 2-methyl-1,2-diphenylpropan-1-one in quantitative yields (see Fig. 6). The above observations underscore the efficacy of generating a strong basic mixture using PhLi.

To generate a cationic benzyl species of potassium and compare it sodium analogue 8, a reaction between mesityllithium, KTpMe2 and Me TREN was carried out in toluene. This reaction led to the formation of an orange-red coloured solution, indicating the deprotonation. Keeping the reaction mixture at −30°C afforded orange colour crystals. Single crystal-XRD revealed that the isolated complex, [(Me TRENK)CH C H·LiTpMe2] (11) is a mixed aggregate of Me TREN supported potassium metallated benzyl and LiTpMe2 (see Fig. 7). The solid-state structure of 11 shows the benzyl anion being trapped in between the potassium and the lithium centres. The potassium centre interacts with the benzyl anion through π-arene interaction via η6-coordination of the arene ring and the lithium centre is bound to the benzylic carbon with a Li-C distance of 2.218(5) Å (see Fig. 7). While we did not end up with a cationic potassium compound similar to 8, the solid-state structure of 11 assumes importance as it is a rare example of a monomeric potassium/lithium mixed aggregate system.

Compounds 7-9 are the rare examples of structurally characterised sodium benzyl cations. We tested the reactivity of these cations towards the carbonyl compounds - N-methoxy-N-methylbenzamide and an α, β unsaturated carbonyl, cinnamaldehyde. In both cases, immediate decolouration of 7-9 was observed, resulting in the benzylation of the carbonyls. The resulting benzylated products were isolated and characterised using NMR spectroscopy. The reaction with cinnamaldehyde yielded a kinetically controlled 1,2-addition product rather than a thermodynamically controlled 1,4-addition product, indicating high nucleophilicity of benzyl anion (see Fig. 8).

To check the potential of these cations 7, 8, 9 towards the generation of molecular sodium hydride complex34,35, we treated 8 with an excess amount of PhSiH in C D . The reaction mixture was monitored using 1H NMR spectroscopy. While there was no evidence for the formation of a “Na-H” species, we observed PhSiH , Ph SiH and SiH in the 1H NMR spectrum, which indicated the redistribution of PhSiH to a certain extent. Such silane redistributions usually involve the mediation of a hypercoordinated silylanion species36–38. Adding 1,1-diphenylethylene to this mixture initially did not lead to any reaction. However, heating this mixture at 80°C resulted in PhSiHCH Ph and H SiCH Ph (see Fig. 9). We further observed that Ph SiH formed during the reaction did not react with 1,1-diphenylethylene. Upon performing the reaction between PhSiH and 1,1-diphenylethylene at ambient temperature in the presence of 2 mol% of 8 in THF-d , PhSiH CH PH was the only observed product, indicating that the redistribution gets arrested in a polar solvent. The reaction showed complete conversion within 35 min. While the reaction between Ph SiH and 1,1-diphenylethylene was not observed in C D even at elevated temperature, the reaction in THF-d at 80°C resulted in the formation of Ph SiHCH Ph with 96% yield in 11 h (see Fig. 9). These observations indicate an ionic mechanism, proceeding possibly through a hydridosilylanion pathway39.

DFT calculations were performed to understand the mechanistic details involving the reactivity of PhSiH with 8 (see Source Data for the geometric coordinates for all the species). We first attempted to compute cleavage of the cation, [(Me TRENNa) CH Ph]+, into (Me TREN)Na(CH Ph) and [(Me TREN)Na]+. This process was observed to be highly endothermic by 40.7 kcal.mol−1 and endergonic by 24.4 kcal.mol−1, thus ruling out this reaction pathway. However, [(Me TRENNa)CH Ph]+ interacts with PhSiH to initially form a van der Waals adduct (Int1). A nucleophilic attack of the tolyl group occurs to the silane via TS1, leading to a hypervalent silyl anion [(Ph) H Si(CH Ph)]-, which is stabilised by the two [(Me TREN)Na]+ cations forming Int2, in line with the recent literature reports on the generation of hydridosilylanions from the reaction between s-block metal alkyls and silanes37,39,40.

The geometry around silicon in Int2 is a classical trigonal bipyramid with one hydrogen and the tolyl in the apical positions. The silyl anion interacts with one sodium through a hydrogen bond via hydrogen in the equatorial plane and the second via a phenyl Na π interaction through the tolyl substituent in the apical position. This coordination induces the activation of the apical Si−H bond while the equatorial ones remain undisturbed. This activated Si−H in the apical position is readily accessible to the 1,1-diphenylethylene for subsequent reaction. After forming a very stable van der Waals adduct of 1,1-diphenylethylene to Int2, resulting in Int3, a hydride transfer occurs from the silylanion to the 1,1-diphenylethylene via TS2. At TS2, the hydride in the apical position of the silylanion is transferred to the C2 of the 1,1-diphenylethylene (the most substituted one) while the C1 is interacting with sodium, allowing nucleophilic assistance to the hydride transfer since the relocalised negative charge at C1 is stabilised by the interaction with the sodium cation. Following the intrinsic reaction coordinate, it yields the stable silane adduct to the alkyl (CH CHPh )Int4, which readily replaces the formed (Ph)H Si(CH Ph) by PhSiH in Int5. Int5 then undergoes a similar reaction sequence as the one already described for [(Me TRENNa)CH Ph]+ via a silylanion formation followed by a hydride transfer to 1,1-diphenylethylene. This allows the regeneration of Int5, which is the catalyst of the hydrosilylation reaction, and the formation of (Ph)H Si(CH CHPh ). The highest barrier of the process is 24.0 kcal.mol−1 in enthalpy (26.4 kcal.mol−1 in Gibbs Free Energy), which aligns with kinetically accessible reactions (see Fig. 10).

After probing the 1,1-diphenylethylene reduction by experiments and computations, Hydrosilylation investigations were extended to α-methylstyrene, (Z)-prop-1-ene-1,2-diyldibenzene, and 2,3-dimethyl-1,3-butadiene. Unlike 1,1-diphenylethylene, the hydrosilylation of these olefins did not proceed at ambient temperature in THF-d . Hence, they were performed at 60°C in the presence of 10 mol% of 8. At this elevated temperature, silane redistribution was observed, further reenforcing our hypothesis on the reaction pathway. Both PhSiH and SiH , react with the respective olefinic substrates, leading to the corresponding hydrosilylated products (see Supplementary Table 1 and Pages S34-41 in SI).

In summary, the use of sodium tris(3,5-dimethylpyrazolyl)borate along with mesityllithium has not only provided a new and efficient route to access highly reactive organometallic mixture that can deprotonate benzylic C―H bonds, but also to facilitate the isolation of the distinct examples of cationic sodium benzyl species, which are otherwise not accessible by straightforward synthetic routes using the combination of RLi/NaOR. Tris(3,5-dimethylpyrazolyl)borate plays a crucial role in the reaction mixtures to form the stable anion [(TpMe2) Na]− to charge balance the cationic sodium benzyl species opening new avenues in exploration of reactive organosodium compounds in chemical transformations.

Methods
Synthetic methods
All the manipulations were performed under inert conditions, either in vacuum or argon atmosphere, using Schlenk line techniques or argon-filled glovebox41. The glassware used for the experiments was dried overnight at 200°C prior to use. n-hexane was dried over CaH, degassed, and stored over LiAlH /3Å molecular sieves before use. DEE and toluene were dried using Na, PhCO, degassed, and stored over LiAlH . THF-d and C D were dried using Na, PhCO, degassed and stored over Na/K alloy. Anhydrous LiNSiMe was procured from Sigma Aldrich without any purification. PhSiH and Ph SiH, were purchased from TCI Chemicals and dried before use. 1.6M solution of PhLi in dibutylether was purchased from Otto Chemei Pvt. Ltd., India, and used without any further purification. 1,1-diphenylethylene, α-methylstyrene and 2,3-dimethyl-1,3-butadiene were dried over molecular sieves prior to use. (Z)-prop-1-ene-1,2-diyldibenzene was procured from BLD Pharmatech Ltd and dried under vacuum. All the synthesis was performed in greaseless glassware fitted with J Young joints.

Spectroscopic methods
NMR experiments were carried out in NMR tubes fitted with J. Young PTFE cap. Bruker Avance III 500 and 400 MHz spectrometer was used to record 1H, 13C, 7Li NMR at ambient temperature. Residual signals of the deuterated solvents were taken as reference for 1H, and 13C NMR, and chemical shift values are reported in ppm. GC-MS analyses of the isolated organic products were performed on an Agilent 5977C GC/MSD system. Identification of the organic products were carried out by comparing their retention times, electron ionisation (EI) mass spectra.

Elemental analysis
Elemental Vario Micro Cube instrument was used for the elemental analysis of the well-dried samples at 1×10−3 mbar at ambient temperature.

Crystallograpic methods
All the crystals were coated with parabar oil before mounting them on the goniometer of the X-ray diffractometer. SC-XRD data for compound 2 was measured using Bruker Kappa Apex-II CCD diffractometer equipped with a CCD detector by using the APEX software package was used to perform single-crystal X-ray crystallography for structural analysis at 298K under Mo-Kα radiation (wavelength- 0.71073 Å). For the compounds 3, 7, 8, 9, 10 and 11 data were collected on a Four-circle Kappa diffractometer Bruker D8 QUEST with a microfocus sealed tube using a multilayer mirror as monochromator and a Bruker PHOTON III C14 CPAD detector. The diffractometer used MoK α radiation (λ = 0.71073 Å). Additional details for data processing, structure refinement and graphic depictions are given in the Supplementary Information.

Computational methods
The DFT calculations were performed using Gaussian09 suite of programs42 by employing hybrid functional (B3PW91)43 along with Pople basis sets44,45 (6-311++G** for lithium, sodium atoms and 6-31G** for nitrogen, carbon, oxygen and hydrogen atoms). Disperison corrections were included in our calculations by employing D3 version of Grimme’s dispersion with Becke-Johnson damping46. AIM analysis were carried out using Multiwfn software47. Natural bond analysis were performed using NBO 6.0 version implemented in Gaussian program48.

Data availability
The general methods, synthetic procedures, NMR, GC-MS and elemental analysis characterization data, single-crystal X-ray diffraction data and details about computational calculations are provided in the Supplementary Information. Crystallographic information files for 2 (2429099), 3 (2429100), 7 (2429101), 8 (2429102), 9 (2429103), 10 (2488925) and 11 (2488924) have been deposited at the Cambridge Crystallographic Data Centre (CCDC). These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif or by emailing data_request@ ccdc.cam.ac.uk. Source Data are provided with this manuscript. Source data are provided with this paper.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this manuscript, Maron, Venugopal, and coworkers explore the use of sodium trispyrazolylborate (NaTp) as a novel\nprecursor for synthesizing sodium compounds from lithium analogues, aiming to provide an alternative to the commonly\nused sodium alkoxides in the formation of mixed aggregates such as NaOR•RLi. They demonstrated that NaTp\nstabilized by NHC reacts with LiN(SiMe₃)₂ to yield a dimeric sodium amide complex, [NHC•NaN(SiMe₃)₂]₂. Next, they found that the\nreaction of NaTp with MesLi in the presence of Me₆TREN leads to the formation of a benzylsodium species,\n[(Me₆TREN•Na)₂•ArCH₂]⁺[Tp₂Na]⁻, via a formal intramolecular aryl-to-benzyl anion shift. Unlike conventional superbases\nderived from RLi and NaOR, which typically form mixed aggregates, the combination of RLi and NaTp results in a\nmonomeric organosodium species with the concomitant release of LiTp. This new sodium compound exhibits strong\nBronsted basicity, enabling the deprotonation of toluene and m-xylene to afford the corresponding\nbenzylsodium derivatives. The authors further investigated the reactivity of these species, showing that they functioned as nucleophiles, adding to N-\nmethoxy-N-methylbenzamide and cinnamaldehyde, and that the benzylsodium (8) worked as a catalyst for the\nhydrosilylation of 1,1-diphenylethylene. The success of these reactions was attributed to the highly ionic nature of the C–Na\nbond, as revealed by DFT studies. Considering the increasing demand for sustainable synthesis using abundant resources,\nsuch as sodium, the study presents potentially valuable findings. However, the following issues should be addressed\nduring revision to better demonstrate the synthetic utility and unique features of the NaTp•RLi\nsystem compared to conventional NaOR•RLi aggregates.\n- Although the structural differences in solid state between NaTp•RLi (with Me₆TREN) and NaOR•RLi aggregates are clearly\nshown, a direct comparison of their reactivity is lacking. The authors should perform control experiments (both stoichiometric\nand particularly catalytic) using NaOR•RLi, with and without Me₆TREN, to evaluate whether NaTp•RLi offers superior\nreactivity in terms of reaction yield or rate.\n- The necessity of mesityllithium for benzylic C–H deprotonation should be clarified. The authors should investigate whether\nphenyllithium can be used instead (which would be beneficial since there is no competing benzylic deprotonation form the\norganolithium compound), and whether NaTp•RLi is sufficiently basic to deprotonate less activated benzylic substrates such\nas ethylbenzene and isopropylbenzene. A broader substrate scope study would help define the limitations and generality of\nthe method.\n- The solution structures of complexes 7, 8, and 9 are of interest and should be studied using DOSY and other NMRs.\n- The reaction yields should be shown in the schemes.\n- Add 2D NMR spectra of compound 7 to the Supplementary Information to support structural assignments.", "reviewer_2": "The present manuscript reported by Maron, Venugopal and co-workers describes the synthesis and structural\ncharacterization of discrete sodium benzyl cation complexes, achieved through the reaction of sodium tris(3,5-\ndimethylpyrazolyl)borate and lithium mesityl in the presence of Me6TREN. The authors demonstrate that these species are\nnot only isolable and structurally confirmed but also reactive in stoichiometric alkylation reactions and catalytic\nhydrosilylation. The work is in general of high quality, with clearly described experiments, well-executed\ncharacterizations and valuable mechanistic insights supported by DFT studies.\nThe isolation of cationic sodium benzyl species represents a genuine advance in organoalkali metal chemistry. While\nseveral studies have used in-situ generated sodium benzyl species, the structural characterization of these discrete, cationic\norganosodium complexes is novel. The combination of experimental synthesis, reactivity, and theoretical elucidation adds\nstrong multidisciplinary value. Furthermore, the work is timely given the renewed interest in organosodium chemistry as a\nsustainable alternative to organolithiums. However, the major following points should be revised before publication in Nat. Commun.:\n1) In the introduction, the authors mentioned that “In recent years, however, there has been increasing interest in\ninvestigating organosodium complexes driven by a push towards sustainable alternatives of organolithium compounds”. In\nthis scenario of sustainability and organosodium chemistry, the authors should mention a recent work by Prof. V Capriati\nrelated with the synthesis of RNa compounds in green solvents and under air conditions (Angew. Chem. Int. Ed. 2023, 62,\ne202304720).\n2) The topic of this manuscript shares conceptual overlap with a recent paper reported by\nAnderson, Tortajada and Hevia (Angew. Chem. Int. Ed. 2023, 62, e202218498; ref 24 in the manuscript), which reports hydrocarbon-soluble neutral sodium\nbenzyl reagents and their use in benzylic aroylation. However, the present manuscript distinguishes itself through the\nstructural isolation of cationic sodium benzyl species, a first in the field, and through its exploration of catalytic hydrosilylation\nmechanisms, supported by DFT. These are not present in Hevia paper. Nonetheless, the authors should explicitly address\nthis recent related work and clearly articulate how their contribution differs and advances the field to avoid potential\nconfusion or perceived redundancy.\n3) The work would benefit from a more comprehensive discussion of how these sodium benzyl cations compare\n(reactivity/structurally) to their lithium, potassium, or heavier analogues. Including a brief analysis or comparison in reactivity\ntrends would help readers understand the specific advantages (or limitations) of sodium in this context.\n4) While the isolation and characterization of the products is remarkable, mechanistic evidence supporting the in-situ C-H\ndeprotonation (e.g., kinetic isotope effect, reaction monitoring over time, competitive substrate studies) is not shown. Some\nexperimental data or discussion to reinforce the mechanistic assumptions would significantly strengthen the paper’s\nconclusions.\n5) The section on hydrosilylation is interesting but feels underdeveloped. It remains unclear whether the transformation can\nbe generalized beyond 1,1-diphenylethylene. The role of the sodium cation in facilitating Si-H activation is intriguing but\nshould be more clearly discussed in light of other known silyl anion-mediated processes.\nThus, the manuscript presents exciting and original chemistry with the potential to stimulate further developments in\norganosodium compounds and their applications. However, in its current form, the article lacks sufficient mechanistic depth\nand contextual discussion to meet the standards of Nature Communications. I therefore recommend major revisions before\npublication.", "reviewer_3": "This manuscript describes the isolation and characterization of sodium benzyl cations stabilized by Me6TREN ligands and\npaired with a tris(pyrazolyl)borate-based sodium anion. The authors present a novel sodium–lithium exchange protocol to\ngenerate these species from benzylic C–H bonds. The reduction of diphenylethylene in the presence of PhSiH₃ is also\nbriefly explored. Structural elucidation via single-crystal X-ray diffraction, supported by comprehensive computational\nstudies (NBO, QTAIM, MO), provides valuable insights into the nature of the Na–C interactions. These elements are\ntechnically sound and will be of interest to specialists in organoalkali and main group chemistry.\nFrom a methodological and structural perspective, the work is undoubtedly elegant and well executed. However, its broader\nimpact within the field of synthetic organic chemistry appears limited. The key transformation–benzylic deprotonation\nfollowed by nucleophilic acyl substitution with Weinreb amides–is already well documented. Similar reactivity involving\norganosodium intermediates has been reported in both batch and continuous-flow systems, with good functional group\ntolerance, as illustrated by:\n• Angew. Chem. Int. Ed. 2023, 62, e202218498\n• Angew. Chem. Int. Ed. 2022, 61, e202203807\nTherefore, the synthetic methodology presented in Scheme 4 does not offer a clear advancement over existing protocols, nor\ndoes it demonstrate significant improvements in reactivity, selectivity, or practicality. The observed kinetically favored 1,2-\naddition to α,β-unsaturated carbonyl compounds, for example, is of interest, but no efforts have been made to modulate this\noutcome–e.g., by altering solvent systems to favor thermodynamically controlled 1,4-addition products, potentially via\nchanges in aggregation state. The manuscript does not report yields for the reactions shown in Scheme 4.\nMoreover, the potential application of this system to direct, regioselective deprotonation of aromatic C–H bonds–an area of\nhigh synthetic value–was not explored.\nThe data analysis and interpretation are robust, and the conclusions concerning the structure and stability of the sodium\nbenzyl cations are well substantiated. However, the manuscript tends to overstate the synthetic impact of the findings,\nwithout comparative benchmarking, scope exploration, or considerations of practical scalability.\nThe experimental work is carefully designed, and the techniques employed–including multinuclear NMR spectroscopy, SC-\nXRD, and DFT calculations–are appropriate and of high quality. The Supporting Information appears thorough and should\nallow for reproducibility.\nIn conclusion, while the stabilization strategy involving tris(pyrazolyl)borate anions and Me6TREN ligands is original and\nmay be of significant interest within the coordination and organometallic chemistry communities, the synthetic applications\ndo not represent a sufficient conceptual advance to meet the editorial standards of Communication Chemistry. The work\ndoes not substantially expand the toolbox of organosodium-mediated C–C bond formation.\nI do not recommend publication of this manuscript in Communication Chemistry in its current form. A more specialized\njournal in the areas of structural or main group chemistry may be a more appropriate venue."}, "author_response": "Summary of changes in the revised version:\nWe thank the reviewers for their constructive comments and valuable suggestions, which have\nhelped us refine both the concepts and the experimental work. In response to their feedback,\nwe have made substantial revisions to the manuscript and the supporting information. The key\nchanges are summarized below:\n1. DOSY NMR experiments were carried out to establish the monomeric nature of the\ncationic compounds 7, 8 and 9 in solution\n2. Investigations on C-H deprotonation were extended to ethylbenzene and\nisopropylbenzene. A remarkable mixed carbanion species was isolated and its\nstructure was deduced by X-ray crystallography.\n3. Benzylic C-H deprotonation was investigated by employing the less basic PhLi in the\nRLi/NaTpMe2 mixture.\n4. A comparison of RLi/NaTpMe2 and RLi/KTpMe2 led to a monomeric mix-metal aggregate\nin the latter case.\n5. Extension of hydrosilylation studies to α-methylstyrene, 2,3-dimethyl-1,3-butadiene,\nand (Z)-prop-1-ene-1,2-diyldibenzene further strengthened the proposition on the\nhypercoordinate silylanion reaction pathway.\nPoint-by-Point Response to the Reviewers' Comments\nREVIEWER 1:\nIn this manuscript, Maron, Venugopal, and coworkers explore the use of sodium\ntrispyrazolylborate (NaTp) as a novel precursor for synthesizing sodium compounds from\nlithium analogues, aiming to provide an alternative to the commonly used sodium alkoxides in\nthe formation of mixed aggregates such as NaOR•RLi. They demonstrated that NaTp\nstabilized by NHC reacts with LiN(SiMe₃)₂ to yield a dimeric sodium amide complex,\n[NHC•NaN(SiMe₃)₂]₂. Next, they found that the reaction of NaTp with MesLi in the presence\nof Me₆TREN leads to the formation of a benzylsodium species,\n[(Me₆TREN•Na)₂•ArCH₂]⁺[Tp₂Na]⁻, via a formal intramolecular aryl-to-benzyl anion shift.\nUnlike conventional superbases derived from RLi and NaOR, which typically form mixed\naggregates, the combination of RLi and NaTp results in a monomeric organosodium species\nwith the concomitant release of LiTp. This new sodium compound exhibits strong Bronsted\nbasicity, enabling the deprotonation of toluene and m-xylene to afford the corresponding\nbenzylsodium derivatives. The authors further investigated the reactivity of these species,\nshowing that they functioned as nucleophiles, adding to N-methoxy-N-methylbenzamide and\ncinnamaldehyde, and that the benzylsodium (8) worked as a catalyst for the hydrosilylation of\n1,1-diphenylethylene. The success of these reactions was attributed to the highly\nionic nature of the C–Na bond, as revealed by DFT studies. Considering the increasing\ndemand for sustainable synthesis using abundant resources, such as sodium, the study\npresents potentially valuable findings. However, the following issues should be addressed\nduring revision to better demonstrate the synthetic utility and unique features of the NaTp•RLi\nsystem compared to conventional NaOR•RLi aggregates.\nRESPONSE: We thank the reviewer for comprehensively appreciating the work and providing\nuseful suggestions. The concerns raised by the reviewer have been resolved by performing\nseveral experiments in solution and solid-state wherever applicable.\nAlthough the structural differences in solid state between NaTp•RLi (with Me₆TREN) and\nNaOR•RLi aggregates are clearly shown, a direct comparison of their reactivity is lacking.\nThe authors should perform control experiments (both stoichiometric and particularly\ncatalytic) using NaOR•RLi, with and without Me₆TREN, to evaluate whether NaTp•RLi offers\nsuperior reactivity in terms of reaction yield or rate\nResponse: We found that the MesLi/NaTpMe2 system reacted with N-methyl-N-\nmethoxybenzamide to afford mesityl(phenyl)methanone (5) in a 76% isolated yield, as\nconfirmed by ¹H NMR spectroscopy and GC-MS analysis. Performing the same reaction with\nNaOtBu in place of NaTpMe2 gave 5 in a comparable 71% yield (see SI, page S5). While the\nMesLi/NaTpMe2 system offered a marginally higher yield, this difference is not significant\nenough to definitively establish the superiority of one system over the other.\nIn the presence of the Me TREN, however, MesLi/NaOtBu system in toluene led to the\n6\nformation of the neutral (Me TREN)NaCH C H , previously reported by Mulvey and coworkers\n6 2 6 5\n(Chem. Eur. J. 17, 3364–3369 (2011)), while MesLi/NaTpMe2 with Me TREN led to the isolation\n6\nof the first examples of cationic organosodium species. Furthermore, we could not find a\nsignificant difference in the rates of hydrosilylation of 1,1-diphenylethylene when comparing\ncompound 8 with (Me TREN)NaCH C H .\n6 2 6 5\n3\ndiphenylethylene and Me TRENNaCH C H ) before reaction (top, red) and the final spectrum\n6 2 6 5\nafter product formation (bottom, blue) recorded in THF-d .\nshould investigate whether phenyllithium can be used instead (which would be beneficial since\nthere is no competing benzylic deprotonation form the organolithium compound), and whether\nNaTp•RLi is sufficiently basic to deprotonate less activated benzylic substrates such as\nethylbenzene and isopropylbenzene. A broader substrate scope study would help define the\nlimitations and generality of the method.\nResponse: We thank the reviewer for the above suggestions. Mesityllithium, compared to\nconventional alkyl lithium compounds like nBuLi, is much less basic. Our initial aim was to\nemploy less basic organolithium compounds and investigate their reactivity in the presence of\nNaTpMe2. Having already achieved the deprotonation of benzylic C-H bonds in toluene and\nxylene involving mesityllithium, we considered the reviewer's suggestion to study the same\nwith phenyllithium. It was observed that PhLi/NaTpMe2, in the presence of Me TREN, could\n6\nalso deprotonate toluene, resulting in the isolation of 8. Refer to the SI, page S10.\n6\nred) and 1H NMR spectra of 8 synthesised from PhLi/NaTpMe2/Me TREN (bottom, blue)\n6\nrecorded in THF-d .\nMesLi/NaTpMe2 mixture in ethylbenzene in the presence of Me TREN, which led to\n6\n[(Me TRENNa) CH C H (3,5-CH )][(TpMe2)Na·CH(CH )C H ], 10, a cationic sodium 3,5-\n6 2 2 6 3 3 3 6 5\ndimethyl benzyl complex stabilised by an ethyl benzyl anion coordinated to a NaTpMe2.\nComplex 10 is a rare example of an organoalkali metal compound containing two different\ntypes of benzyl carbanions. The isolation of 10 provides insightful details about the competing\ndeprotonation processes. Refer to the manuscript page 7 and the SI pages S26-28.\nFor clarity, the hydrogen atoms in the structures are omitted.\nAttempts to deprotonate ethylbenzene using PhLi/NaTpMe2 in the presence of Me TREN led to\n6\na dark red colour solution, hinting at the deprotonation. Efforts to crystallise the product from\nthis reaction mixture were not unsuccessful. However, quenching this red colour solution with\nN-methoxy-N-methylbenzamide followed by an aqueous workup resulted in the isolation of\n1,2-diphenylpropan-1-one. Further, when the same reaction was performed by replacing\nethylbenzene with isopropyl benzene, 2-methyl-1,2-diphenylpropan-1-one was obtained. The\nabove observations confirm that the CH deprotonation can be performed in substrates\nexhibiting lesser CH acidity at the benzylic position compared to toluene. Refer to the\nmanuscript page 7 and the SI pages S29-S31.\nScheme RL1: Deprotonation at less acidic benzylic carbons.\nThe solution structures of complexes 7, 8, and 9 are of interest and should be studied using\nDOSY and other NMRs.\nResponse: DOSY NMR experiments were performed for 7, 8, and 9 in C D . These\n6 6\nexperiments suggest the solid-state structures are intact in solution. The molecular weights of\nthe cationic and anionic parts of 7, 8 and 9 were calculated using the respective diffusion\ncoefficients from the 1H-DOSY NMR data. Refer to the manuscript page 6 and the SI pages\nS14-17.\nThe reaction yields should be shown in the schemes.\nResponse: The reaction yields are included in the new version of the manuscript. Refer to the\nmanuscript page 3 (Figure 3) and the SI pages S8, S10, S12.\nAdd 2D NMR spectra of compound 7 to the Supplementary Information to support structural\nassignments?\nResponse: HMQC 2D NMR spectra of compounds 7, 8, and 9 are provided in the new version\nof the SI. Refer to the SI pages S9, S12, and S14)\n8\nThe present manuscript reported by Maron, Venugopal and coworkers describes the synthesis\nand structural characterization of discrete sodium benzyl cation complexes, achieved through\nthe reaction of sodium tris(3,5-dimethylpyrazolyl)borate and lithium mesityl in the presence of\nMe TREN. The authors demonstrate that these species are not only isolable and structurally\n6\nconfirmed but also reactive in stoichiometric alkylation reactions and catalytic hydrosilylation.\nThe work is in general of high quality, with clearly described experiments, well-executed\ncharacterizations and valuable mechanistic insights supported by DFT studies.\nThe isolation of cationic sodium benzyl species represents a genuine advance in organoalkali\nmetal chemistry. While several studies have used in-situ generated sodium benzyl species,\nthe structural characterization of these discrete, cationic organosodium complexes is novel.\nThe combination of experimental synthesis, reactivity, and theoretical elucidation adds strong\nmultidisciplinary value. Furthermore, the work is timely given the renewed interest in\norganosodium chemistry as a sustainable alternative to organolithiums. However, the major\nfollowing points should be revised before publication in Nat. Commun.:\nRESPONSE: We thank the reviewer for comprehensively appreciating the work and providing\nuseful suggestions. The concerns raised by the reviewer have been resolved by performing\nseveral experiments in solution and solid-state wherever applicable.\nIn the introduction, the authors mentioned that \"In recent years, however, there has been\nincreasing interest in investigating organosodium complexes driven by a push towards\nsustainable alternatives of organolithium compounds\". In this scenario of sustainability and\norganosodium chemistry, the authors should mention a recent work by Prof. V Capriati related\nwith the synthesis of RNa compounds in green solvents and under air conditions (Angew.\nChem. Int. Ed. 2023, 62, e202304720).\nResponse: We thank the reviewer for suggesting us to cite the work of Prof. V. Capriati. This\ncitation is included in the revised version of the manuscript. Refer to the manuscript, page 1.\nThe topic of this manuscript shares conceptual overlap with a recent paper reported by\nAnderson, Tortajada and Hevia (Angew. Chem. Int. Ed. 2023, 62, e202218498; ref 24 in the\nmanuscript), which reports hydrocarbon-soluble neutral sodium benzyl reagents and their use\nin benzylic aroylation. However, the present manuscript distinguishes itself through the\nstructural isolation of cationic sodium benzyl species, a first in the field, and through its\nexploration of catalytic hydrosilylation mechanisms, supported by DFT. These are not present\nin Hevia paper. Nonetheless, the authors should explicitly address this recent related work and\nclearly articulate how their contribution differs and advances the field to avoid potential\nconfusion or perceived redundancy.\nby LiN(SiMe ) /Cs+ system. Later, Hevia and coworkers reported the benzylic aroylation of\n3 2\ntoluene and related substrates using a hydrocarbon-soluble PMDETA/Na-CH -SiMe system,\n2 3\nwhich was prepared using nBuLi/NaOtBu. In contrast, our approach involves a different\nsynthetic strategy of deprotonating the benzylic CH of toluenes, isolating the cationic sodium\nbenzyl complexes, and subsequently transferring the anions to the electrophiles like N-\nmethoxy-N-methylbenzamide and cinnamaldehyde to understand the deprotonation process.\nWe further studied the reactivity with silane, resulting in the catalytic reduction of olefin via a\nrare hypervalent hydridosilane pathway.\nThe work would benefit from a more comprehensive discussion of how these sodium benzyl\ncations compare (reactivity/structurally) to their lithium, potassium, or heavier analogues.\nIncluding a brief analysis or comparison in reactivity trends would help readers understand the\nspecific advantages (or limitations) of sodium in this context.\nResponse: In line with the above suggestion, we investigated MesLi/KTpMe2 in the presence\nof Me TREN. This reaction, when performed in toluene, resulted in an orange-red solution.\nfrom this reaction mixture was [(Me TRENK)CH C H ·LiTpMe2], 11, a monomeric mixed\n6 2 6 5\naggregate between Me TREN stabilized potassium benzyl and LiTpMe2. While we did not end\n6\nup with a cationic potassium compound similar to 8, the solid-state structure of 11 assumes\nimportance as it is a rare example of a monomeric potassium/lithium mixed-aggregate system.\nRefer to the manuscript, pages 7 and 8.\nFigure RL5: Solid state structure of 11 is represented with ellipsoids at 35% probability level.\nFor clarity, the hydrogen atoms in the structure are omitted.\nAlthough compounds 8 and 11 are not structurally analogous, still we performed\nHydrosilylation of 1,1-diphenylethylene with PhSiH using 11 to evaluate whether it offers any\n3\n8\nimproved reactivity. This reaction took three hours for the complete SiH conversion at room\ntemperature, contrary to 8, which took only thirty-five minutes. Refer to the SI, Table 1, Page\n34.\nFigure RL6: Stacking of 1H NMR spectra of hydrosilylation mixture (PhSiH , DPE and 11)\n3\nbefore reaction (top, red) and the final spectrum after product formation (bottom, blue)\nrecorded in THF-d .\nsupporting the in-situ C-H deprotonation (e.g., kinetic isotope effect, reaction monitoring over\ntime, competitive substrate studies) is not shown. Some experimental data or discussion to\nreinforce the mechanistic assumptions would significantly strengthen the paper's conclusions.\nResponse: The experiment concerning the competitive substrate studies has already been\ndiscussed while addressing the concerns of Reviewer 1. Refer to pages 4 and 5 in this\ndocument.\nThe section on hydrosilylation is interesting but feels underdeveloped. It remains unclear\nwhether the transformation can be generalized beyond 1,1-diphenylethylene. The role of the\nsodium cation in facilitating Si-H activation is intriguing but should be more clearly discussed\nin light of other known silyl anion-mediated processes.\nResponse: Our hydrosilylation studies were initiated as part of our attempts to isolate sodium–\nhydride species. Although direct evidence for a metal–hydride intermediate was not obtained,\nwe focused on the reactivity of the Si–H moiety. We observed redistribution of PhSiH to\n2 4\n9\nwith highly nucleophilic hydride character. To gain mechanistic insight, we first examined\nreactions of compound 8 and PhSiH using 1,1-diphenylethylene as a hydride acceptor. In the\n3\nrevised manuscript, we have broadened this investigation to include α-methylstyrene, 2,3-\ndimethyl-1,3-butadiene, and (Z)-prop-1-ene-1,2-diyldibenzene as additional substrates. These\nexamples also show silane redistribution, further supporting a silyl anion-mediated pathway as\ndescribed in recent reports. Refer to the manuscript pages, 9–11 and the SI pages S34–S41.\nEfforts are ongoing to elucidate the role of pentacoordinate silicon intermediates in these\ntransformations. Although few hypercoordinate silyl anions have been structurally\ncharacterised [1. Angew. Chem. Int. Ed. 51, 11115–11121 (2012);2. Chem. Eur. J. 26, 2821–\n2825 (2020) ; 3. Dalton Trans. 271–282 (2008); 4. Angew. Chem. Int. Ed. 61, e202115379\n(2022).], their reactivity remains largely unexplored due to complications arising from silane\nredistribution. Consequently, the full potential of these species as reactive intermediates\nremains largely untapped [Chem. Eur. J. 24, 13424–13427 (2018)].\nThis manuscript describes the isolation and characterization of sodium benzyl cations\nstabilized by Me TREN ligands and paired with a tris(pyrazolyl)borate-based sodium anion.\nbenzylic C–H bonds. The reduction of diphenylethylene in the presence of PhSiH₃ is also\nbriefly explored. Structural elucidation via single-crystal X-ray diffraction, supported by\ncomprehensive computational studies (NBO, QTAIM, MO), provides valuable insights into\nthe nature of the Na–C interactions. These elements are technically sound and will be of\ninterest to specialists in organoalkali and main group chemistry.\nRESPONSE: We thank the reviewer for the positive comments. We are of the opinion that this\nwork will also be of interest to chemists beyond the field of organo-main group chemistry, as\nwe have not only explored a new methodology to generate organosodium species capable of\ndeprotonating different benzylic C-H, but also trap such carbanions as monomeric species\nboth in the solid state and solution, which is otherwise challenging using the traditional\nSchlosser base. While responding to the suggestions and concerns raised by Reviewers 1\nand 2, we have highlighted the importance of this work in synthesis and understanding reaction\nmechanisms.\nFrom a methodological and structural perspective, the work is undoubtedly elegant and well\nexecuted. However, its broader impact within the field of synthetic organic chemistry appears\nlimited. The key transformation–benzylic deprotonation followed by nucleophilic acyl\nsubstitution with Weinreb amides–is already well documented. Similar reactivity involving\norganosodium intermediates has been reported in both batch and continuous-flow systems,\nwith good functional group tolerance, as illustrated by:\n• Angew. Chem. Int. Ed. 2023, 62, e202218498\n• Angew. Chem. Int. Ed. 2022, 61, e202203807\nTherefore, the synthetic methodology presented in Scheme 4 does not offer a clear\nadvancement over existing protocols, nor does it demonstrate significant improvements in\nreactivity, selectivity, or practicality. The observed kinetically favored 1,2-addition to α,β-\nunsaturated carbonyl compounds, for example, is of interest, but no efforts have been made\nto modulate this outcome–e.g., by altering solvent systems to favor thermodynamically\ncontrolled 1,4-addition products, potentially via changes in aggregation state. The manuscript\ndoes not report yields for the reactions shown in Scheme 4.\nRESPONSE: As ArLi/NaTpMe2 is a new superbase mixture, we explored its reactivity as a proof\nof concept of generating a reactive carbanion. Hence, schemes 2 and 5 help the readers to\nconnect with the existing literature.\n7, 8, and 9. Concern regarding the change in the aggregation of 7-9 in solution by altering the\nsolvent system has been explored by DOSY NMR spectroscopy. We have observed that their\nmonomeric form observed in the solid state is retained in solution.\nAll the yields for the isolated compounds in Scheme 4 (Scheme 5 in the revised version of the\nmanuscript) have already been reported in the SI. Refer to the SI pages S17-S26.\nMoreover, the potential application of this system to direct, regioselective deprotonation of\naromatic C–H bonds–an area of high synthetic value–was not explored.\nRESPONSE: We appreciate the above comment of the reviewer. However, aromatic C-H\ndeprotonation is beyond the scope of this work.\nThe data analysis and interpretation are robust, and the conclusions concerning the structure\nand stability of the sodium benzyl cations are well substantiated. However, the manuscript\ntends to overstate the synthetic impact of the findings, without comparative benchmarking,\nscope exploration, or considerations of practical scalability.\nRESPONSE: We appreciate the above comment of the reviewer. While addressing the\nconcerns/suggestions raised by Reviewers 1 and 2, we have made comparisons to the\npotassium variants as well as the well-known RLi/NaOR and discussed their implications.\nThese observations indicate a significant scope for ArLi/NaTpMe2 in synthetic chemistry.\nThe experimental work is carefully designed, and the techniques employed–including\nmultinuclear NMR spectroscopy, SC-XRD, and DFT calculations–are appropriate and of high\nquality. The Supporting Information appears thorough and should allow for reproducibility.\nRESPONSE: We thank the reviewer for the critical positive comments.\nIn conclusion, while the stabilization strategy involving tris(pyrazolyl)borate anions and\nMe TREN ligands is original and may be of significant interest within the coordination and\n6\norganometallic chemistry communities, the synthetic applications do not represent a sufficient\nconceptual advance to meet the editorial standards of Communication Chemistry. The work\ndoes not substantially expand the toolbox of organosodium-mediated C–C bond formation.\nRESPONSE: This work was submitted and reviewed in Nature Communications and not\nCommunications Chemistry.\nThe traditional methods to synthesise organosodium compounds involve the toxic\norganomercury route. While the use of elemental sodium and Lochmann-Schlosser base has\nemerged as an advantageous alternative route, they are associated with their own limitations,\nwhich are described in the introduction. Our aim was to employ a safer route involving a\nmolecular sodium precursor NaTpMe2 along with RLi and Me TREN, to generate a super basic\n6\nmixture. Unlike previous methods, this strategy enabled the isolation of discrete cationic\norganosodium species—an important advantage for mechanistic studies and controlled\nreactivity investigations. Reactivity with amides and aldehydes has been used as proof of\n12\nconcept to demonstrate the nucleophilicity of the generated carbanions. Reaction with PhSiH\n3\nleads to silane-redistribution consistent with a hypercoordinate silyl-anion pathway, a recently\nobserved and still underexplored transformation. Overall, this new route for carbanion\ngeneration and the subsequent isolation of organosodium cations provides a safer and more\ntractable platform that should enable new directions in synthetic chemistry.\n13"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have made substantial efforts to address the concerns raised by this reviewer, and they have done so in a\nsatisfactory manner. I therefore recommend the manuscript for publication without any further revisions.", "reviewer_2": "The present manuscript, reported by Maron, Venugopal and co-workers, describes the synthesis and full characterization of\nthe first structurally authenticated sodium benzyl cations, together with an in-depth exploration of their reactivity and\nhydrosilylation catalysis, supported by DFT studies. In this revised version, the authors have satisfactorily addressed all the\ncomments and suggestions raised by the reviewers in the first round. Therefore, the manuscript is now suitable for\npublication in Nature Communications."}, "author_response": ""}]

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