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Article

Straightforward Superbase-Mediated Reductive O-Phosphorylation of Aromatic and Heteroaromatic Ketones with Red Phosphorus in the Superbase Suspension KOH/DMSO(H2O)

by
Vladimir A. Kuimov
1,
Svetlana F. Malysheva
1,
Natalia A. Belogorlova
1,
Ruslan I. Fattakhov
1,
Alexander I. Albanov
1,
Irina Yu. Bagryanskaya
2,
Nikolay I. Tikhonov
1 and
Boris A. Trofimov
1,*
1
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences, 1 Favorsky Str., Irkutsk 664033, Russia
2
N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090, Russia
*
Author to whom correspondence should be addressed.
Molecules 2025, 30(6), 1367; https://doi.org/10.3390/molecules30061367
Submission received: 18 February 2025 / Revised: 10 March 2025 / Accepted: 15 March 2025 / Published: 18 March 2025
(This article belongs to the Special Issue Exclusive Contributions by the Editorial Board Members (EBMs) of the Organic Chemistry Section of Molecules)
Browse Figures
Versions Notes

Abstract

It was shown for the first time that diaryl(hetaryl)ketones are capable of directly phosphorylating with red phosphorus in the superbase suspension KOH/DMSO(H2O) at 85 °C for 1.5 h to afford potassium bis(diaryl(hetaryl)methyl)phosphates that were earlier inaccessible in a yield of up to 45%. The ESR data demonstrate that unlike previously published phosphorylation with elemental phosphorus, this new phosphorylation reaction proceeds via a single electron transfer from polyphospide anions to diaryl(hetaryl)ketones. This is the first example of the C-O-P bond generation during the phosphorylation with elemental phosphorus in strongly basic media, which usually provides C-P bond formation.

1. Introduction

Now, it is commonly admitted [1,2,3,4,5,6,7,8,9,10,11] that the methods for the synthesis of organophosphorus compounds (OPCs) from elemental phosphorus (both white and red) and appropriate electrophiles might be potentially of lower cost and less negative ecological impact compared to traditional technologies based on phosphorus chloride [12]. Therefore, the search for and development of chlorine-free syntheses of OPCs still remains a challenge of modern chemistry [13,14,15,16]. White phosphorus (P4) is known to be an intermediate (via its chlorides) for the industrial-scale synthesis of phosphorus-containing herbicides, battery electrolytes, pharmaceuticals, detergents, and catalyst ligands [8,17,18,19,20,21]. In recent years, significant advances (on the laboratory level) towards the utilization of P4 for the chlorine-free synthesis of value-added OPCs such as secondary and tertiary phosphines and phosphine oxides [22,23] as well as aminophosphonates [24] and tertiary phosphates [25] have been reached. Though red phosphorus (Pred) is a product of the high-temperature transformation of P4, it is considerably less toxic and much safer in handling than its white modification [8,26,27,28]. This makes Pred a competitive intermediate in the synthesis of OPCs [29].
Since 1988, we pioneered the systematic study of the activation of Pred in simple and available superbase suspensions of the type alkali metal hydroxide/strongly polar complexing solvent (ligand) [30,31] that allowed a number of new environmentally friendly methods for the synthesis of various important OPCs to be developed. Among them are secondary and tertiary phosphines and phosphine oxides, as well as phosphinic and phosphonic acids [29,31]. In multiphase superbase suspensions such as Pred/KOH/DMSO(H2O), three-dimensional phosphorus molecules are disassembled to polyphosphide anions having supernucleophilic properties, which are capable of reacting with various electrophiles (organyl halides [31,32,33], alkenes [31,34,35], acetylenes [31,36,37], and oxiranes [38]) securing the easy and mild formation of the corresponding OPCs. Altogether these syntheses represent an efficient general approach to the direct formation of the C-P bond. It is important that, in no case, the products with С-O-P (phosphates and other phosphorus esters) were formed seemingly due to the proneness of such systems to alkaline hydrolysis.
Meanwhile, OPCs play an important role in life-sustaining activity and human practice. Thus, organic phosphates are widely employed as pesticides [39], extractants [40,41], plasticizers [42], and flame retardants [43,44] due to the successful combination of their physicochemical properties. In our case, it is important to underline that phosphoric acid diesters are utilized as wetting agents [45], antistatics for textiles [46], emulsifiers for cosmetics [47,48], corrosion inhibition in metalworking, cutting and grinding fluids [49], surfactants [50,51], lubricants [52], agrochemical additives [39,53], cleaners formulations [51], organocatalysts [54], in emulsion polymerization reactions [55], etc. For example, commercially available dibenzylphosphate and diphenylphosphate are used as phosphorylating agents [56,57], Brønsted acid catalysts for many reactions [58,59,60].
Organic phosphates play an important role in biological systems [61,62,63,64], since they perform numerous vital functions in living species (DNA, RNA, ATP, etc.) [65,66,67,68,69]. Phosphates such as perifosine, miltefosine, inositol phosphates, and citicoline exhibit antiviral, anticancer, and antiproliferative activities [62].
Currently, for the synthesis of organic phosphates, phosphorus chlorides (PCl3 or POCl3) [70] or phosphorus(V) oxide or polyphosphoric acid and alcohols [19] are mostly employed. Usually, these methods are not selective and mixtures of mono-, di-, and triphosphates, often difficult to separate, are formed. Phosphates with diarylmethyl (benzhydryl) or triarylmethyl (trityl) substituents remain understudied due to their inaccessibility. There are only two methods for the preparation of bis- and tris(diphenylmethyl)phosphates [71] utilizing diphenyldiazamethane and phosphoric acid or benzophenone hydrazone, (diacetoxyiodo)benzene, and phosphoric acid [72,73,74].
Thus, complementing the chemistry of organic phosphates with new chlorine-free, and hence ecologically neutral (as generating no hazardous waste) phosphorylation technology employing available, inexpensive and safe starting materials and catalysts/mediators (aromatic or heteroaromatic ketones, red phosphorus, KOH, and DMSO) is an awaited task.
All of these facts justify the efforts we spent to elaborate a straightforward method for the synthesis of so far less accessible diesters of phosphoric acids. For this, we took diaryl(hetaryl)ketones as electrophiles of choice, which due to their carbonyl might be involved in the generation of C-O-P bond systems while reacting with Pred in strongly basic compositions.
At the same time, according to the known phosphorylation of arylacetylenes stereoselectively providing tris(Z-styryl)phosphine [36], the formation of the C-P bond here seemed to be more preferable. In other words, in this case, the synthesis of tris(diphenylhydroxymethyl)phosphine should be expected.
However, against this expectation, when benzophenone 1a reacted with red phosphorus under the conditions analogous to those developed for the synthesis of tris(Z-styryl)phosphine (60 °C, 1.5 h), we isolated bis(diphenylmethyl)phosphate (2a), thereby proving our initial assumption. The synthesis was accompanied by the formation of phosphorus-free products, diphenylcarbinol (3a) and diphenylmethane (4a), the reduced derivatives of benzophenone (Scheme 1).
Consequently, it was the first event when a compound with the C-О-P bond system was selectively obtained in the reaction of electrophiles with Pred in strongly basic conditions.
From structure of phosphate 2a it followed that we dealt with a new process cardinally different from previously investigated reactions of electrophiles with red phosphorus in multiphase superbase media, which as mentioned above provided exclusively the compounds with a P-C bond [29,31].
This essential difference results from the steric shielding of the carbon atom of the keto group by the ortho-hydrogen of two phenyl substituents and the oxidizing properties of benzophenone itself.
After this first result, it became clear that we encounter a new reaction, which needs to be systematically developed.

2. Results and Discussion

We commenced the work with the investigation of the reference reaction between benzophenone 1a and Pred in KOH/DMSO suspension to find the conditions providing the best yield of the target phosphate 2a (Table 1).
As mentioned above, the second major product was diphenylcarbinol (3a) inherently associated with the reaction mechanism (see below mechanistic rationale).
Initially, the synthesis was implemented under the conditions established for the preparation of tris(Z-styryl)phosphine [36]. The varying reaction parameters were benzophenone/Pred/KOH ratio, water content, complexing solvent, temperature, and time, while the controlling (optimizing) functions were the conversion of 1a and yields of phosphate 2a, alcohol 3a, and diphenylmethane 4a.
Note that, during the process, the elemental phosphorus is partially oxidized mostly to inorganic phosphite and also in a degree to hypophosphite, which are not extractable by organic extractants. This is why the combined amounts of organophosphorus and organic products are always less than 100%, even at a complete conversion of the starting materials.
The experiments show that the most influencing reaction factor was the nature of the solvent and base (for the screening of bases, see Supplementary Materials Section S2.2), which remarkably affects the conversion of 1a, yields, and ratio of the products. The reaction medium of choice appeared to be the KOH/DMSO [75] suspension, ensuring the best yield of phosphate 2a and decreasing the amount of 3a and 4a (entry 10).
Another reaction parameter governing the outcome of the phosphorylation was the molar ratio of 1a and Pred, the optimum of which was found to be 1:3 (entry 10), while the higher or lower content of 1a gave inferior results (entry 5, 8). Also, the yield of phosphate 2a noticeably depends on water additives to the reaction mixture: the most suitable result (45% yield) was reached with 21 mmol of water per 73 mmol of Pred, while a higher amount of additives (167 mmol) of water led to the formation of 2a in 24% yield (entry 1), but without specially added water this dropped to 39% (entry 13). When commercial DMSO (~2% of water), used in all the experiments, was replaced by dry DMSO, the yield of 2a was further decreased (31%, entry 14). As seen from entry 11, when 1a was slowly (dropwise) added to the reaction mixture under the best condition (entry 10), carbinol 3a was almost cleanly formed (84% yield), whereas the yield of phosphate 2a dropped to 11%.
Temperature and time, which covered 60–96 °C and 1.5–6 h, with average values of 85 °C and 1.5 h being optimal, had less effect on the reaction efficiency. The experimental details imply the radical anion character of the process. Indeed, just after the contact of the reactants, the reaction mixture acquired the red color, quickly turning via bright purple to red-brownish, that commonly accompanies the presence of radical ions. In the presence of 10 mol% (relative to 1a) of typical radical scavengers (hydroquinone, TEMPO, and quinhydrone), the yield of 2a dropped to 22, 29, and 18%, correspondingly. Since the radical scavengers were taken in amounts much less than equimolar compared to the ketones, they trap only a small part of forming radicals, while a main part of the starting compounds further participate in the major process. In addition, the free-radical species may not come to the solution from anion–radical pairs. In the ESR spectra, typical signals of benzophenone radical anions and signals attributable to the polyphosphinyl radical were observed (Figure 1, see also Supplementary Materials). In the 31P NMR spectra of the reaction mixtures obtained in the presence of the above radical scavengers, characteristic signals assignable to intermediate P-C adducts are observed (see Supplementary Materials), implying the initial attack of the carbonyl carbon by a P-centered free radical and subsequent phospha-Brook rearrangement [76,77,78,79] to the final C-O-P products.
Since the initial splitting of the P-P bond by OH− gives P− and H-O-P-terminated species [29,31], the reaction of the latter with diarylcarbinol in a nucleophilic substitution manner might lead to the corresponding C-O-P product. However, the control reaction between carbinol 3a and Pred under the optimum conditions did not produce any amount of phosphate 2a, thus ruling out such a method for the formation of phosphate 2a.
Next, the substrate scope of this reaction was assessed using a variety of diaryl(hetaryl)ketones, mostly asymmetrical ones (Scheme 2). The yields of phosphates 2 spanned 5–45% and were very sensitive to substitution in the benzene ring and to the nature of the heterocyclic ring attached to the carbonyl group.
However, because of the physical–chemical complexity of this multi-phase process, no clear-cut regularities in the structure/yield relationship can be deduced. Meanwhile, the expected radical anion character of at least one step of the cascade sequence should be facilitated by electron-withdrawing groups due to the decrease in LUMO level, i.e., the higher electron affinity of the intermediates and stabilization of the ion radical intermediate, while electron-donating ones should have an opposite influence. In fact, this is confirmed by the elevated yields of the target phosphates in the case of pyridine ketones 1m,n, which contain π-acceptor substituents (see below).
At the same time, the higher than average yields of the corresponding phosphates (2c, 2e, and 2h) for ketones with certain electron-donating substituents (3-Me, 4-tBu, and 4-MeS), give a clue that electron-deficient intermediates such as free radicals, formed by the quenching of radical anion with protons, also play an important role in the phosphorylation cascade. The lower yields of phosphates 2f, 2i, and 2o for ketones with electron-donating substituents (4-MeO-, 4-BnO-, and 2-Thiophenyl) are likely due to competition between two steps: (i) the reduction of ketones and (ii) their phosphorylation. Consequently, the more active radical anions generated from the ketones having the donor substituents are rapidly transformed to carbinols 3, while the phosphorylation becomes the minor direction. Accordingly, the case with two stronger electron-donating groups (i-Pr) in both benzene rings directed the reaction exclusively towards the corresponding carbinol and diarylmethane (see Supplementary Materials). The ketones with stronger π-donors in one of the benzene rings, such as 4-Me2N-, 4-OH, 4-C6H13O, and 4-MeSCH2O, did not afford a phosphorylation product, and only in some cases, small amounts of the corresponding carbinols were detectable (1H NMR) in the reaction mixtures, which is consistent with the ion-radical character of the process. Although the electron-donating powers of 4-MeO, 4-BnO, and 4-C6H13O groups are close (σ ≈ −0.25, −0.42, −0.34) [80], the latter long-chain substituent should create impassable spatial encumbrance for the interaction of 3D-oligomeric phosphorus-centered radicals with ketones. In the cases of 4-OVin and 4-O, all substituents in one of the benzene rings, the oligomerization over the double bonds likely prevails, since nether carbinols nor phosphorylated products were formed.
In the case of halo-substituted ketones (2j and 2k), the yields of the target products are decreased because of the reductive elimination of the halogens that leads to the halogen-free phosphate 2a which was isolated. The ketones with F, Cl, and Br substituents in 2- and 4- positions gave only unsubstituted phosphate 2a in up to a 37% yield, meaning that the reductive elimination of the halogens takes place during the phosphorylation. The reaction of 2,4-difluorophenyl-(phenyl)ketone proceeds as a nucleophilic substitution of fluorine atom by the phosphinate moiety [32]. Apparently, here the SRN1 reaction occurs, involving the initial intermediate radical anions (detected by ESR), which eliminate the halogen anion, followed by the recombination of the radical formed with either the hydrogen or polyphosphinyl radical. Since the SRN1 reaction is commonly determined [81,82] as involving radical anions, such a scheme may be considered as justifiable. Thus, this reductive elimination of halogens once again supports the radical anion character of the phosphorylation studied (see Supplementary Materials).
Ketones with electron-rich aromatic heterocyclic substituents (2-Th and 2-Fu) were found to be almost inert in this phosphorylation, which corresponds to their lower activity in single-electron transfer processes (SETs). Consequently, the ketones having π-electron-deficient aromatic substituents (3-Py and 4-Py) such as 1m,n gave yields close to the better ones (35 and 38%). Unfortunately, such functional groups as ester, amide, cyano, nitro, and others, which are sensitive to strongly basic media, do not tolerate the reaction conditions. The condensed aromatic ketones (like 1-naphthyl-phenylketone) mainly undergo reduction to the corresponding carbinol and 1-naphthylphenylmethane (isolated in 51% yield). This results from its susceptibility to the reduction and the anticipated steric shielding of the radical anion center in the initial intermediate by the bulky naphthyl substituents that almost prevents the attack by P-centered free-radicals. This is supported by the fact that Ph-2-MeO-naphthylketone under the aforementioned conditions was not phosphorylated at all, giving the corresponding carbinol in a 32% yield. Expectedly, fatty aromatic ketones were not able to be phosphorylated owing to the domination of the aldol-krotone processes. The testing ketones there are acetophenone, dibenzylketone, ([1,1′-biphenyl]-4-yl)(benzyl)ketone, anthrone, 1,2,3,4-tetrafluoro-9-fluorenone, and 9-fluorenone.
The stability of potassium bis(diphenylmethyl)phosphate was evaluated (KOH/DMSO(H2O), 85 °C, 1.5 h): 64% of the initial product was recovered along with 36% of potassium phosphate, diphenylcarbinol, benzophenone, and diphenylmethane, thus indicating the partial solvolysis of the target phosphates 2 under the reaction conditions. Consequently, this, in a degree, lowers the reaction efficiency, but leaves room for a further finer optimization.
According to the X-ray diffraction data of molecule 2a, the crystal is situated on the inversion center (Figure 2). XRD study proved the structure of 2a in which atom K is five coordinate (see Supplementary Materials, Figures S13 and S14) through four K π-arene interactions with the phenyl substituent and four atoms of O phosphate-groups. The K–C(sp2) distances are in the range of 3.308(3)–3.385(3) Å [83,84], the distance between the centroid of the Ph ring and K is 3.078 Å, and the K–O distances are 2.944(1), 2.591(1), and 2.575(1) Å for O1, O3, and O4 correspondingly. This coordination of K with O4 leads to four-membered planar metallocycles—K1O4K1O4. The coordination of K with the atom O1 leads to the coordination dimer (Figure S15) and finally, the coordination of K with the atom O3 leads to the resulting structure in the crystal—the chained coordination polymer along the crystallographic axis a (Figure S16).
In the light of the above experimental details, the preliminary mechanistic rationale of the C=O bond phosphorylation in aryl(hetaryl)ketones by the superbase Pred/KOH/DMSO(H2O) can be proposed as follows below, though a special theoretical and physical–chemical study is required to establish the true mechanism of this reaction. In any case, the cleavage of the P-P bond of elemental phosphorus by hydroxide anions in superbase media (e.g., KOH/DMSO) to deliver P-centered polyphosphide anions like intermediate A (Scheme 3) is now commonly accepted in numerous publications; for references, see reviews [31,85,86]. The aggregation between polar ketone molecules and DMSO may also contribute to the reaction mechanism [87,88]. Meanwhile, the ESR spectral detection of both P-centered and diaryl ketone-derived radical species (Figure 1) as well as the suppression of the reaction by standard radical scavengers (hydroquinone, TEMPO, and quinhydrone), and the characteristic coloration of the reaction mixture may be considered as evidence in favor of the proposed mechanism.
The P-P bond of the 3D-polymer Pred is cleaved by the superbasic hydroxide-anion to deliver the polyphospide anion (A) and polyphosphinite B (Scheme 3a) [31]. Then follows the single-electron transfer (SET) from intermediate A to ketones.
This thereby generates radical anion C and polyphosphinyl radical D (Scheme 3b), which further recombine with the participation of water molecules to give either P-С-bonds (pathway a) or Р-О-С bonds (pathway b, intermediates F and G, correspondingly). Intermediate E can also interact with polyphosphide anion A to furnish the new anion-radical H; SET from H to 1a renders intermediate F. The intermediate F undergoes P-P bond cleavage by the OH anion to produce intermediate I (P=O) and the new polyphosphide anion (A*). The polyphosphinite anion J, formed after the abstraction of a proton from polyphosphinite I and phospha-Brook rearrangement [76,77,78,79] (PBR), adds to the next molecule of benzophenone to release alkoxide anion K. Then follows the PBR of K to polyphosphonate L, and after the cleavage of the remaining P-P bond by the hydroxide anion, we arrive at the final phosphorylation product, which is isolable as potassium salt 2a. The formation of the intermediate P-C bonds (Figures S1–S5) was detected in the 31P NMR of the reaction mixture (see Supplementary Materials).
The appearance of diaryl(hetaryl)carbinols is the expected result of the competitive recombination of the initial radical anion C with hydrogen radicals. The hydride transfer in the carbinols via the disproportionation [89] gave diaryl(hetaryl)methanes and the corresponding ketones.
The straightforward alkylation of salts 2 may open an easy route to a series of asymmetrical phosphates as exemplified by the methylation of 2a (MeI, MeCN, 50 °C, 1 day, 5a), Scheme 4. Consequently, this, in a degree, lowers the reaction efficiency, but leaves room for a further finer optimization.

3. Materials and Methods

3.1. General Information

All manipulations were carried out under argon atmosphere. 1H, 13C, 31P, and 19F NMR spectra were recorded at 400.13, 100.62, 161.98, and 376.50 MHz, respectively, in DMSO or CDCl3 solutions with a Bruker (Bruker Corp., Karlsruhe, Germany) DPX-400 and AV-400 spectrometers. Chemical shifts were reported in δ (ppm) relative to DMSO_d6 or CDCl3 (1H and 13C) as internal standards or H3PO4 (31P) as an external standard. The assignment of signals in the 1Н NMR spectra was made using COSY experiments (XWinNMR ver. 2.6). Resonance signals of carbon atoms were assigned based on 1H-13C HSQC and 1H-13C HMBC experiments (XWinNMR ver. 2.6). IR spectra were run on a Vertex 70 (Bruker Optics GmbH, Karlsruhe, Germany) spectrometer. The EI mass spectra were obtained on a Shimadzu (KRATOS Analytical Ltd., Manchester, UK) GSMS-QP5050 mass spectrometer. Melting points were established using a Kofler micro hot-stage apparatus (Wagner&Munz GmbH, München, Germany) and are uncorrected. Commercially available red phosphorus (KSAN Sia, Riga, Latvia) was purified by consecutive washing with aq. NaOH (1–2%), H2O, EtOH, and Et2O to remove all acidic impurities, dried in vacuum at 25–30 °C to a constant weight, and stored under inert atmosphere (N2). Commercially available undried DMSO (~1% of water) was used (Vekton, St. Petersburg, Russia). Commercially available potassium hydroxide (from Sigma-Aldrich, Saint Louis, MO, USA) of composition KOH (~85%) and H2O (≤15%) that almost exactly corresponds to the formula KOH∙0.5H2O [90,91] was used without further purification. The water content in KOH∙0.5H2O was determined using moisture analyzer (HB43-S Halogen, METTLER TOLEDO, Powai, Mumbai, India). Most of the diaryl(hetaryl)ketones are commercial products: 1a–f,j,l–o, 9H-fluoren-9-one, and anthracen-9(10H)-one. Other ketones (3-Methoxybenzophenone (1g), (4-(methylthio)phenyl)(phenyl)methanone (1h), benzyloxybenzophenone (1i), 3-fluorobenzophenone (1k), 1-naphthyl(phenyl)methanone (1l), 2-benzoylfurane (1p), and 2-methoxynaphthalen-1-yl(phenyl)methanone) were synthesized according to the literature methods (see Supplementary Materials). The EPR spectra of the samples were recorded with the ELEXSYS E-580 spectrometer (Bruker BioSpin GmbH, Karlsruhe, Germany), X-band 9.7 GHz. Raman spectra were obtained on an ATP 8900Ad Raman vacuum Fourier transform infrared spectrometer (Optosky Photonics, Xiamen, China), 785 and 1064 nm. The C, H microanalyses were performed on a Flash 2000 CHNS analyzer (Thermo Fisher Scientific, Delft, The Netherlands).

3.2. Synthetic Procedures

3.2.1. Procedure for the Preparation of the Potassium Phosphate 2a

(1). A 250 mL round-bottom flask was sequentially charged with red phosphorus (2.25 g, 73 mmol), ketone 1a (24 mmol), DMSO (50 mL), freshly machine-powdered KOH·0.5H2O (10.00 g, 154 mmol), and H2O (0.38 g, 21 mmol) and flushed with argon from the balloon. The flask was sunk into a preliminarily heated oil bath and the reaction mixture was stirred (500–700 rpm) for 1.5 h at 84–85 °C. After the reaction completion, the flask was cooled down to r.t., one part of water (25 mL) was added, and the reaction mixture was transferred into a separation funnel. A separated aqueous basic layer (~18 g), consisting of inorganic phosphates and KOH, was discarded. To the remaining aqueous organic layer, another portion of water (25 mL) and CHCl3 (25 mL) were added. The CHCl3 layer was separated and the aqueous organic layer was further extracted twice with CHCl3 (2 × 25 mL). Therefore, the CHCl3 extract contains DMSO, the target product 2a, carbinol 3a, and diphenylmethane 4a. After the evaporation of CHCl3 and DMSO (3 mmHg, 50 °C), 3a and 4a are consequentially washed out by the diethyl ether (3 × 15 mL) and chloroform (2 × 2 mL). The residue was dried in vacuum to give 2.53 g (45%) of the phosphate 2a.
Potassium bis(diphenylmethyl)phosphate (2a). Yield: 2.53 g (45%), clear crystals, mp 293 °C (hexane/DMF). 1H NMR (400.13 MHz, DMSO_d6): δ = 6.08 (d, 3JPOCH = 10.1 Hz, 2H, POCH), 7.13–7.20 (m, 20 H, Ho,m,p in Ph) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 77.1 (d, 2JPC = 5.2 Hz, POCH), 126.3 (Cp in Ph), 126.5 (Co in Ph), 127.7 (Cm in Ph), 144.5 (d, 3JPC = 4.2 Hz, Ci in Ph) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −0.17 (t, 3JPOCH = 10.1 Hz) ppm. IR (KBr): 3435, 3028, 3058, 2932, 1657, 1599, 1493, 1453, 1261, 1188, 1103, 1008, 884, 859, 707, 573, 487 сm−1. Raman (785 nm): 219, 272, 620, 648, 748, 841, 1004, 1189, 1352, 1604, 3060 сm−1. Anal. Calcd. for C26H22 KO4P (m.w. 468.52): C, 66.65; H, 4.73. Found: C, 64.68; H, 5.09. This salt is very soluble in DMSO, DMF, MeOH, EtOH, and iPrOH, but sparingly soluble in MeCN, dioxane, THF, DME, and C6H6 and very poorly soluble in CHCl3, DCM, ethyl acetate, acetone, H2O, Et2O, and CCl4.

3.2.2. General Procedure for the Preparation of the Potassium Phosphates 2m,n

A mixture of red phosphorus (2.25 g, 73 mmol), freshly machine-powdered KOH·0.5H2O (10.00 g, 154 mmol), H2O (0.38 g, 21 mmol), and phenylpyridylketone (1m,n, 24 mmol) in 50 mL of DMSO was stirred for 1.5 h at 84–85 °C (oil bath). After the reaction completion, one portion of water (25 mL) was added, and the aqueous basic layer (~13–18 g) was separated and discarded (consisting of non-organic phosphates and KOH). The reaction mixture was diluted with another portion of water (25 mL) and extracted with chloroform (3 × 25 mL); chloroform was dried on CaCl2 and removed to obtain the corresponding phenylpyridylcarbinol (48–52%). The remaining aqueous layer was carefully acidified with aq. HCl (18%) up to pH ~7, and water and DMSO were removed in vacuum. The resulting solid mass was washed with CHCl3 (3 × 15 mL), chloroform was removed, and the residue was dried in vacuum to give phosphate 2m,n as wax masses in a yield of 35–38%.
Potassium bis[(2-methylphenyl)(phenyl)methyl]phosphate (2b). Following the general procedure, 2b was prepared from 1b (24 mmol, 4.71 g). 2b was isolated as white powder (1.43 g, 24% yield), mp 264–266 °C. 1H NMR (400.13 MHz, DMSO_d6): δ = 2.03, 2.04 (s, 6 H, CH3), 6.20, 6.22 (d, 3JPOCH = 10.2 Hz, 2 H, POCH), 6.98–7.02 (m, 2 H, H-3 in C6H4), 7.07–7.17 (m, 6 H, H-4,5,6 in C6H4 and 8 H, Ho,m in Ph), 7.31–7.36 (m, 2 H, Hp in Ph) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 19.2 (CH3), 74.6 (d, 2JPC = 4.7 Hz, POCH), 125.5 (C-5 in C6H4), 126.4, 126.5 (C-4 in C6H4), 126.5 (Cp, in Ph), 127.1, 127.2 (Co in Ph), 127.1, 127.2 (C-6 in C6H4), 127.6 (Cm in Ph), 129.8 (C-3 in C6H4), 134.4 (d, 4JPC = 1.6 Hz, C-2 in C6H4), 142.0, 142.1 (d, 3JPC = 3.3 Hz, C-1 in C6H4), 143.4, 143.5 (d, 3JPC = 4.6 Hz, Ci in Ph) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −0.05 (t, 3JPOCH = 10.1 Hz) ppm. IR (KBr): 3435, 3027, 2921, 1608, 1493, 1453, 1244, 1156, 1103, 1019, 933, 875, 710, 625, 578, 509 сm−1. Raman (1064 nm): 339, 624, 795, 847, 1000, 1028, 1102, 1185, 1611, 3059 cm−1. Anal. Calcd for C28H26KO4P (m.w. 496.58): C, 67.72; H, 5.28. Found: C, 67.38; H, 5.18.
Potassium bis[(3-methylphenyl)(phenyl)methyl]phosphate (2c). Following the general procedure, 2c was prepared from 1c (24 mmol, 4.71 g). 2c was isolated as white powder (2.09 g, 35% yield), mp 220–222 °C. 1H NMR (400.13 MHz, DMSO_d6): δ = 2.20 (s, 6 H, CH3), 6.03 (d, 3JPOCH = 9.9 Hz, 2 H, POCH), 6.94–7.20 (m, 18 H, H-2,4,5,6 in C6H4 and Hm,o,p in Ph) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 21.2 (CH3), 77.24 (d, 2JPC = 5.0 Hz, POCH), 123.7, 123.8 (C-6 in C6H4), 126.4 (Cp, in Ph), 126.5, 126.5 (Co in Ph), 127.1 (C-4 in C6H4), 127.1 (C-2 in C6H4), 127.7 (C-5 in C6H4), 127.8 (Cm in Ph), 136.7 (C-3 in C6H4), 144.3 (d, 3JPC = 3.8 Hz, C-1 in Ph) 144.4 (d, 3JPC = 4.1 Hz, Ci in Ph) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −0.32 (t, 3JPOCH = 9.8 Hz) ppm. IR (KBr): 3434, 3059, 3060, 3027, 2920, 1606, 1491, 1452, 1243, 1194, 1155, 1100, 1057, 1018, 933, 914, 875, 795, 772, 709, 654, 624, 578, 511, 452 сm−1. Raman (785 nm): 224, 273, 527, 618, 652, 736, 780, 847, 1002, 1107, 1195, 1238, 1380, 1448, 1604, 3061 cm−1. Anal. Calcd for C28H26KO4P (m.w. 496.58): C, 67.72; H, 5.28. Found: C, 67.61; H, 4.97.
Potassium bis[(4-methylphenyl)(phenyl)methyl]phosphate (2d). Following the general procedure, 2d was prepared from 1d (24 mmol, 4.71 g). 2d was isolated as white powder (1.73 g, 29% yield), mp 234–236 °C. 1Н (DMSO_d6): δ = 2.23 (s, 6 H, CH3), 6.03 (d, 3JPOCH = 10.0 Hz, 2 H, POCH), 6.96–6.98 (m, 4 H, H-3,5 in C6H4), 7.05–7.07 (m, 4 H, H-2,6 in C6H4), 7.12–7.18 (m, 10 H, Ho,m,p in Ph) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 20.8 (CH3), 77.0 (d, 2JPC = 5.1 Hz, POCH), 126.3 (Cp in Ph), 126.5 (Co in Ph), 126.6 (d, 4JPC = 2.6 Hz, C-2,6 in C6H4), 127.7 (d, 5JPC = 0.9 Hz, Cm in Ph), 128.3 (d, 5JPC = 1.3 Hz, C-3,5 in C6H4), 135.3 (d, 6JPC = 1.8 Hz, C-4 in C6H4), 141.5 (d, 3JPC = 4.1 Hz, C-1 in C6H4), 144.7 (d, 3JPC = 4.5 Hz, Ci in Ph) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −0.51 (t, 3JPOCH = 9.9 Hz) ppm. IR (KBr): 3435, 3030, 2923, 1631, 1513, 1453, 1255, 1190, 1098, 1004, 881, 897, 572 сm−1. Raman (785 nm): 337, 497, 645, 798, 849, 1004, 1029, 1105, 1187, 1382, 1454, 1611, 3061 cm−1. Anal Calcd for C28H26KO4P (m.w. 496.58): C, 67.72; H, 5.28. Found: C, 67.62; H, 5.17.
Potassium bis[(4-tert-butylphenyl)(phenyl)methyl]phosphate (2e). Following the general procedure, 2e was prepared from 1e (24 mmol, 5.72 g). 2e was isolated as white powder (2.51 g 36% yield), mp 263–265 °C. 1H NMR (400.13 MHz, DMSO_d6): δ = 1.24 (s, 18 H, CH3), 6.03 (d, 3JPOCH = 10.0 Hz, 2 H, POCH), 7.10–7.21 (m, 8 H in C6H4 and 10 H in Ph) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 31.3 (CH3), 34.1 [C(CH3)3], 77.0 (d, 2JPC = 4.8 Hz, POCH), 124.5 (C-2,6 in C6H4), 126.29 (Cp in Ph), 126.3 (C-3,5 in C6H4), 126.5 (Co in Ph), 127.7 (Cm in Ph), 141.6 (d, 3JPC = 3.6 Hz, Ci in Ph), 144.7 (d, 3JPC = 3.7 Hz C-1 in C6H4), 148.6 (C-4 in C6H4) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −0.15 (t, 3JPOCH = 9.9 Hz) ppm. IR (KBr): 3421, 3061, 2983, 1639, 1513, 1454, 1410, 1363, 1231, 1100, 1007, 891, 861, 804, 704, 626, 580, 528 сm−1. Anal. Calcd for C34H38KO4P (m.w. 580.73): C, 70.32; H, 6.60. Found: C, 69.96; H, 6.64.
Potassium bis[(4-methoxyphenyl)(phenyl)methyl]phosphate (2f). Following the general procedure, 2f was prepared from 1f (24 mmol, 5.09 g). 2f was isolated as white powder (1.00 g, 16% yield), mp 195–196 °C. 1H NMR (400.13 MHz, DMSO_d6): δ = 3.69 (s, 6 H, OCH3), 6.05 (d, 3JPOCH = 10.0 Hz, 2 H, POCH), 6.72–6.75 (m, 4 H, H-3,5 in C6H4), 7.08–7.11 (m, 4 H, H-2,6 in C6H4), 7.13–7.19 (m, 10 H in Ph) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 55.2 (OCH3), 77.2 (d, 2JPC = 4.4 Hz, POCH), 113.4 (C-3,5 in C6H4), 126.7 (Cp,o in Ph), 128.0 (C-2,6 in C6H4), 128.1 (Cm in Ph), 136.5 (C-1 in C6H4), 144.6 (Ci in Ph), 158.2 (C-4 in C6H4) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −0.69 (t, 3JPOCH = 9.9 Hz) ppm. IR (KBr): 3434, 3029, 2934, 2837, 1611, 1512, 1453, 1252, 1175, 1098, 1003, 926, 887, 785, 703, 576 сm−1. Anal Calcd for C28H26KO6P (m.w. 528.57): C, 63.62; H, 4.96. Found: C, 63.42; H, 4.93.
Potassium bis[(3-methoxyphenyl)(phenyl)methyl]phosphate (2g). Following the general procedure, 2g was prepared from 1g (24 mmol, 5.09 g). 2g was isolated as white powder (0.70 g, 11% yield), mp 156–157 °C. 1H NMR (400.13 MHz, DMSO_d6): δ = 3.65 (s, 6 H, OCH3), 6.01 (d, 3JPOCH = 10.1 Hz, 2 H, POCH), 6.68 (dt, 3J4–5 = 8.4 Hz, 4J4–2~4J4–6 = 2.5 Hz, 2H, H-4 in C6H4), 6.74 (d, 3J6–5 = 7.7 Hz, 2H, H-6 in C6H4), 6.79 (br.s, 2 H, H-2 in C6H4), 7.08 (ddd, 3J5–6 = 7.7 Hz, 3J5–4 = 8.4 Hz, 5J5–2 = 2.1 Hz, 2H, H-5 in C6H4), 7.10–7.18 (m, 10 H in Ph) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 54.9 (OCH3), 77.1 (d, 2JPC = 4.8 Hz, POCH), 111.8 (C-4 in C6H4), 112.2 (d, 4JPC = 4.3 Hz, C-2), 118.8 (C-6 in C6H4), 126.4 (Cp, in Ph), 126.5 (Co in Ph), 127.7 (Cm in Ph), 128.8 (C-5 in C6H4), 144.4 (d, 3JPC = 4.5 Hz, Ci in Ph), 146.0 (d, 3JPC = 4.5 Hz, C-1 in C6H4), 158.9 (C-3 in C6H4) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −0.64 (t, 3JPOCH = 10.1 Hz) ppm. IR (KBr): 3432, 3027, 2920, 2835, 1601, 1490, 1242, 1157, 1103, 1021, 879, 776, 694, 599, 519 сm−1. Anal. Calcd for C28H26KO6P (m.w. 528.57): C, 63.62; H, 4.96. Found: C, 63.22; H, 4.92.
Potassium bis{[4-(methylthio)phenyl](phenyl)methyl}phosphate (2h). Following the general procedure, 2h was prepared from 1h (24 mmol, 5.48 g). 2h was isolated as white powder (2.01 g, 30% yield), mp 158–159 °C. 1H NMR (400.13 MHz, CDCl3): δ = 2.39, 2.40 (s, 6 H, SCH3), 6.00, 6.02 (d, 3JPOCH = 9.3 Hz, 2 H, POCH), 7.04–7.21 (m, 8 H in C6H4, 10 H in Ph) ppm. 13C NMR (100.62 MHz, CDCl3): δ = 15.6 (SCH3), 78.3 (d, 2JPC = 4.1 Hz, POCH), 126.1, 126.2 (Co in Ph), 126.6, 126.7 (C-3,5 in C6H4), 127.0, 127.1 (C-2,6 in C6H4), 127.3, 127.3 (Cp in Ph), 128.4, 128.4 (Cm in Ph), 137.3 (C-4 in C6H4), 139.1, 139.3 (C-1 in C6H4), 142.8, 143.0 (Ci in Ph) ppm. 31P NMR (161.98 MHz, CDCl3): δ = −0.61 (br.t) ppm. IR (KBr): 3436, 3027, 2918, 1959, 1905, 1700, 1600, 1493, 1403, 1242, 1100, 1006, 886, 795, 701, 623, 571 сm−1. Anal. Calcd for C28H26KO4PS2 (m.w. 560.71): C, 59.98; H, 4.67. Found: C, 60.42; H, 4.91.
Potassium bis[[4-(benzyloxy)phenyl](phenyl)methyl]phosphate (2i). Following the general procedure, 2i was prepared from 1i (24 mmol, 6.92 g). 2i was isolated as white powder (0.90 g, 16% yield), mp 244 °C. 1H NMR (400.13 MHz, DMSO_d6): δ = 5.03 (s, 4 H, OCH2), 6.00 (d, 3JPOCH = 10.1 Hz, 2 H, POCH), 6.80 (d, 3JHH = 8.4 Hz, 4 H, H-3,5 in C6H4), 7.05 (d, 3JHH = 8.0 Hz, 4 H, H-2,6 in C6H4), 7.11–7.16 (m, 10 H, Ho,m,p in PhCH), 7.31–7.43 (m, 10 H, Ho,m,p in PhCH2) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 69.2 (OCH2), 76.8 (d, 2JPC = 5.1 Hz, POCH), 114.0 (C-3,5 in C6H4), 126.3 (Cp in PhCH), 126.5 (Co in PhCH), 127.6 (Co in PhCH2), 127.7 (Cm in PhCH), 127.8 (Cp in PhCH2), 127.9 (C-2,6 in C6H4), 128.5 (Cm in PhCH2), 136.9 (C-1 in C6H4), 137.3 (Ci in PhCH2), 144.8 (Ci in PhCH), 157.1 (C-4 in C6H4) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −0.21 (t, 3JPOCH = 10.0 Hz) ppm. IR (KBr): 3430, 2301, 1613, 1512, 1454, 1399, 1247, 1175, 1099, 1001, 888, 897, 574 сm−1. Anal. Calcd for C40H34 O6P (m.w. 468.52): C, 70.57; H, 5.03. Found: C, 70.28; H, 5.09.
Potassium bis[(3-chlorophenyl)(phenyl)methyl]phosphate (2j). Following the general procedure, 2j was prepared from 1j (24 mmol, 5.20 g). 2j was isolated as white powder (0.32 g, 5% yield), mp 198 °C. 1H NMR (400.13 MHz, DMSO_d6): δ = 6.07 (d, 3JPOCH = 9.9 Hz, 2 H, POCH), 7.14–7.26 (m, 10 H, in Ph and 8 H in C6H4) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 76.5 (d, 2JPC = 4.7 Hz, POCH), 125.0, 125.1 (C-6 in C6H4), 126.1 (Cp, in Ph), 126.5 (Co in Ph), 126.7 (C-2 in C6H4), 127.8 (C-4 in C6H4), 127.9 (Cm in Ph), 129.7 (C-5 in C6H4), 132.7 (C-3 in C6H4), 143.6 (d, 3JPC = 4.3 Hz, Ci in Ph), 146.8 (d, 3JPC = 4.2 Hz, C-1 in C6H4) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −1.37 (t, 3JPOCH = 10.1 Hz) ppm. IR (KBr): 2922, 2833, 2258, 2129, 1651, 1495, 1454, 1292, 1229, 1029, 1025, 886, 826, 764, 701, 574 сm−1. Anal. Calcd for C26H20Cl2KO4P (m.w. 537.41): C, 58.11; H, 3.75. Found: C, 58.02; H, 3.71.
Potassium bis[(3-fluorophenyl)(phenyl)methyl]phosphate (2k). Following the general procedure, 2k was prepared from 1k (24 mmol, 4.80 g). 2k was isolated as white powder (1.57 g, 26% yield), mp 236–238 °C. 1H NMR (400.13 MHz, DMSO_d6): δ = 6.07 (d, 3JPOCH = 10.0 Hz, 2 H, POCH), 6.92 (t, 3J4–5~3J4-F = 8.5 Hz, 2 H, H-4 in C6H4), 7.00 (d, 4 H, 3J2-F~3J6–5 = 7.8 Hz, H-2,6 in C6H4), 7.15–7.20 (m, 12 H, Ho,m,p in Ph, H-5 in C6H4) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 76.6 (d, 2JPC = 4.6 Hz, POCH), 113.0, 113.2 (d, 2JCF = 20.2 Hz, C-2,4 in C6H4), 122.4 (C-6 in C6H4), 126.5 (Co in Ph), 126.8 (Cp, in Ph), 127.9 (Cm in Ph), 129.7 (d, 3JCF = 8.2 Hz, C-5 in C6H4), 143.8 (Ci in Ph), 147.3 (C-1 in C6H4), 162.0 (d, 1JCF = 242.9 Hz, C-3 in C6H4) ppm. 31P NMR (161.98 MHz, DMSO_D6): δ = −0.96 (t, 3JPOCH = 9.9 Hz) ppm. 19F NMR (376.50 MHz, DMSO_d6): δ = −113.42 ppm. IR (KBr): 3031, 2919, 2850, 1592, 1450, 1245, 1103, 1018, 941, 874, 791, 706, 522 сm−1. Anal. Calcd for C26H20F2KO4P (m.w. 504.50): C, 61.90; H, 4.00. Found: C, 61.28; H, 3.99.
Potassium bis(naphthalen-1-yl(phenyl)methyl)phosphate (2l). Following the general procedure, 2l was prepared from 1l (24 mmol, 5.57 g). 2l was isolated as light beige crystalline solids (0.48 g, 7% yield), mp 176–178 °C. 1H NMR (400.13 MHz, DMSO_d6): δ = 6.73, 6.72 (d, 3JPOCH = 10.1 Hz, 2 H, POCH), 7.06–7.09 (m, 6 H, Hm,p in Ph), 7.11–7.16 (m, 4 H, Ho in Ph), 7.31 (br.t, 3J3–2~3J3–4 = 7.5 Hz, 2 H, H-3 in C5H4), 7.32 (t, 3J6–7~3J6–5 = 8.2 Hz, 2 H, H-6 in C5H4), 7.41 (t, 3J7–6~4J7–8 = 8.2 Hz, 2 H, H-6 in C5H4), 7.49 (d, 3J2–4 = 7.5 Hz, 2 H, H-2 in C5H4), 7.86 (d, 3J8–7 = 8.2 Hz, 2 H, H-8 in C5H4), 7.88, 7.90 (d, 3J8–7 = 8.2 Hz, 2 H, H-5 in C5H4), ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 75.5 (POC), 124.7 (C-5 in Napht.), 125.0 (C-2 in Napht.), 125.3 (C 3, 7 in Napht.), 125.5 (C-6 in Napht.), 126.6 (Cp in Ph), 127.1 (Co, in Ph), 127.4 (C-4 in Napht.), 127.7 (Cm in Ph), 128.4 (C-8 in Napht.), 130.1 (C-9 in Napht.), 133.5 (C-10 in Napht.), 139.0, 143.6 (Ci in Ph) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −0.22 (t, 3JPOCH = 9.7 Hz) ppm. IR (KBr): 509, 607, 696, 779, 798, 884, 921, 989, 1048, 1082, 1101, 1185, 1248, 1268, 1453, 1494, 1510, 1597, 1634, 2924, 3030, 3058, 3086. Anal. Calcd for C34H26KO4P (m.w. 568.64): C, 71.81; H, 4.61; Found: C, 71.79; H, 4.60.
Potassium bis[phenyl(pyridin-4-yl)methyl]phosphate (2m). Following the general procedure, 2m was prepared from 1m (24 mmol, 4.40 g). 2m was isolated as white powder (2.13 g, 38% yield), mp 125–127 °C. 1H NMR (400.13 MHz, CDCl3): δ = 6.23 (d, 3JPOCH = 9.6 Hz, 2 H, POCH), 7.14–7.27 (m, 10 H, Ho,m,p in Ph), 7.36, 7.40 (d, 3JPH = 5.4 Hz, 4 H, H-3,5 in C5H4), 8.28 (br.s, 4 H, H-2,6 in C5H4) ppm.13C NMR (100.62 MHz, CDCl3): δ = 76.8 (POCH), 122.3 (C-5 in C5H4), 126.6 (Co in Ph), 127.6 (Cp, in Ph), 128.4 (Cm in Ph), 134.9 (C-4 in C5H4), 138.6 (C-3 in C5H4), 141.4 (Ci in Ph), 147.4 (C-2 in C5H4), 167.6 (C-6 in C5H4) ppm. 31P NMR (161.98 MHz, CDCl3): δ = −1.10 (br.t) ppm. IR (KBr): 3405, 3063, 2923, 2852, 1638, 1495, 1554, 1232, 1048, 889, 796, 700, 563 сm−1. Anal. Calcd for C24H20KN2O4P (m.w. 470.50): C, 61.27; H, 4.28; N, 5.95. Found: C, 61.20; H, 4.27; N, 5.15.
Potassium bis[phenyl(pyridin-3-yl)methyl]phosphate (2n). Following the general procedure, 2n was prepared from 1n (24 mmol, 4.40 g). 2n was isolated as white powder (1.98 g, 35% yield), mp 195–197 °C. 1H NMR (400.13 MHz, CDCl3): δ = 6.15 (d, 3JPOCH = 9.2 Hz, 2 H, POCH), 6.94–6.96 (m, 2 H, H-5 in C5H4), 7.09–7.16 (m, 10 H, Ho,m,p in Ph), 7.38–7.40 (m, 2 H, H-5 in C5H4), 8.24 (d, 3J6–5 = 5.0 Hz, 2 H, H-6 in C5H4), 8.57 (br.s, 2 H, H-2 in C5H4) ppm. 13C NMR (100.62 MHz, CDCl3): δ = 76.8 (POCH), 123.3 (C-5 in C5H4), 126.6 (Co in Ph), 127.6 (Cp, in Ph), 128.4 (Cm in Ph), 134.9 (C-4 in C5H4), 138.6 (C-3 in C5H4), 141.4 (Ci in Ph), 147.4 (C-2 in C5H4), 147.6 (C-6 in C5H4) ppm. 31P NMR (161.98 MHz, CDCl3): δ = −1.06 (t, 3JPOCH = 9.1 Hz) ppm. 15N NMR (40.5 MHz, CDCl3): δ = −77.6 ppm. IR (KBr): 3429, 3030, 2922, 2853, 2388, 2300, 1632, 1579, 1495, 1426, 1192, 1049, 881, 700, 565 сm−1. Anal. Calcd for C24H20KN2O4P (m.w. 470.50): C, 61.27; H, 4.28; N, 5.95. Found: C, 61.19; H, 4.26; N, 5.35.
Potassium bis[phenyl(2-thienyl)methyl]phosphate (2o). Following the general procedure, 2o was prepared from 1o (24 mmol, 4.52 g). 2o was isolated as white powder (0.46 g, 8% yield), mp 180 °C. 1H NMR (400.13 MHz, DMSO_d6): δ = 6.30 (d, 3JPOCH = 9.8 Hz, 2 H, POCH), 6.77–6.78 (m, 2 H, H-3 in C4H3S), 6.82–6.84 (m, 2 H, H-4 in C4H3S), 7.21–7.24 (m, 10 H in Ph), 7.30 (dd, 3J5–4 = 5.0 Hz, 4J5–3 = 1.8 Hz, 2 H, H-5 in C4H3S) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 73.5, 73.6 (d, 2JPC = 5.0 Hz, 2JPC = 4.9 Hz, POCH), 124.4, 124.5 (C-3 in C4H3S), 124.9, 125.0 (C-5 in C4H3S), 126.1, 126.2 (C-4), 126.2, 126.3 (Co in Ph), 126.8, 126.9 (Cp in Ph), 127.8 (Cm in Ph), 143.8 (d, 3JPC = 3.5 Hz, Ci in Ph), 148.5, 148.6 (d, 3JPC = 4.5 Hz, C-2 in C4H3S) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −1.03 (t, 3JPOCH = 9.9 Hz) ppm. IR (KBr): 3430, 3062, 2931, 2301, 1613, 1512, 1454, 1399, 1247, 1175, 1099, 1001, 888, 833, 697, 574, 468 сm−1. Anal. Calcd for C22H18KO4PS2 (m.w. 480.58): C, 54.98; H, 3.78. Found: C, 44.51; H, 3.75.
Furan-2-yl(phenyl)methylhypophosphite (2p). Yield: (traces); oil. 1H NMR (400.13 MHz, DMSO_d6): δ = 6.06 (m), 6.07 (d, 3JPH = 11.9 Hz), 6.29 (dt, 4J3,5 = 1.5, 3J3,4 = 3.1 Hz), 7.05 (d, 1JPH = 454.2 Hz), 7.19–7.25 (m, 5H), 7.45 (ddd, J = 0.8, 1.63, 4.3 Hz) ppm. 31P NMR (161.98 MHz, DMSO_d6): δ = −2.82 (t, 1JPH = 460 Hz) ppm. There was too little substance to record 13C NMR. Anal. Calcd for C11H11O3P (m.w. 222.18): C, 59.47; H, 4.99. Found: C, 59.31; H, 5.09.
The structure of furan-2-yl(phenyl)methylhypophosphite 2p follows from 1H and 31P NMR spectra of the reaction mixture and their comparison with the known spectra of similar compounds [92].
Diphenylmethanol (3a) [93]. Following the general procedure, 3a was prepared from 1a (24 mmol, 4.71 g). 3a was isolated as light beige crystals (1.64 g 37% yield), mp 60–62 °C (hexane). 1H NMR (400.13 MHz, DMSO_d6): δ = 5.71 (s, 1 H, CH), 5.90 (s, 1 H, OH), 7.18–7.40 (m, 10 H, Ho,m,p in Ph) ppm. 13C NMR (100.62 MHz, DMSO_d6): δ = 74.4 (CH), 126.3 (Co in Ph), 126.8 (Cp in Ph), 128.1 (Cm in Ph), 145.8 (Ci in Ph) ppm. IR (KBr): 1960, 1896, 1628, 1597, 1492, 1454, 1316, 1274, 1184, 1084, 1018, 917,830, 740, 701, 601, 548 сm−1. Anal. Calcd for C13H12O (m.w. 184.23): C, 84.75; H, 6.57. Found: C, 83.14; H, 6.55.
Synthesis of the Dibenzhydryl Methyl Phosphate (5a). The mixture of 2a (100 mg) and MeI (300 mg, 10 eq.) in MeCN (2 mL) was stirred for 24 h at 50 °C. The solid part was then separated by centrifugation and the solvent was evaporated under vacuum, and 78 mg of 5a (82%) as orange oil was obtained. 1H NMR (400.13 MHz, CDCl3): 3.39 (d, 3H, OСН3, 3JР-О-С-Н = 11.6 Hz), 6.34 (d, 2Н, РОСН, 3JР-О-С-Н = 8.4 Hz), 7.15–7.30 (m, 20Н, Нo, Нm, Нp). 13C NMR (100.62 MHz, CDCl3): δ = 54.11 (ОСН3, 2JР-О-С = 5.9 Hz), 81.25 (НС-О-Р, 2JР-О-С = 5.1 Hz), 126.85 and 127.10 (Co), 128.02 and 128.20 (Сp), 128.47 and 128.54 (Cm), 140.27 and 140.45 (Сi, 3JР-O-С-C = 4.9 and 5.4 Hz). 31P NMR (161.98 MHz, CDCl3): δ = 0.10 (qt 3JР-О-СН3 = 11.6 Hz, 3JР-О-С-Н = 8.4 Hz). IR (microlayer): 3090, 3064, 3031, 3008, 2953, 2922, 2852, 1495, 1454, 1267, 1188, 1032, 1007, 990, 741, 697, 604, 558 сm−1. Anal. Calcd for C27H25O4P (m.w. 444.47): C, 72.96; H 5.67. Found: C 72.49; H 5.42.

4. Conclusions

In conclusion, diaryl(hetaryl)ketones are directly phosphorylated (85 °C, 1.5 h) with red phosphorus in the KOH/DMSO(H2O) suspension to give potassium bis(diaryl(hetaryl)methylphosphates in yields up to 45%.
Unlike the previously developed phosphorylation of various electrophiles with elemental phosphorus in strongly basic media proceeding as nucleophilic addition or substitution reactions to form in all of the cases only C-P bonds, the phosphorylation studied here leads to the formation of exclusively C-О-P bond systems.
Despite the modest yield of the diester of phosphoric acid, this synthesis may be rated as practically attractive, because it is based on cheap and available starting materials, is operationally simple and environmentally neutral. A major competitive advantage of this approach is that it allows avoiding toxic and irritating phosphorus chlorides or pentoxide and polyphosphoric acids. Also, this methodology enables the selective synthesis of diesters of phosphoric acid free of admixtures of mono- and triphosphates. Another beneficial feature of this chemistry is the possibility of preparing asymmetrical bis(diarylmethyl)phosphates, including those combining aromatic and heteroaromatic substituents.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/molecules30061367/s1: The synthesis of initial ketones (S4–S6); Table S1: Screening of bases (S7); Control experiments: Radical-probe experiments (S9–S13); 31P NMR spectra of the reaction mixtures (Figures S1–S6); Reactions of (2- or 4-halo)benzophenones with red phosphorus (S13–S14); EPR experiments (S15–S18, Figures S7–S12); Evaluation of 2a stability (S19); Crystal data and details of experiments for 2a (S20, Figures S13–S16); Unsuccessful substrates (S25, Figure S17), Copy of 1H NMR, 13C NMR, 31P NMR, Raman, and FT-IR spectra of compounds 2a–p and 3a (S26–S89). Refs. [90,91,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123] are cited in the Supplementary Materials.

Author Contributions

Supervision (B.A.T.); Conceptualization (B.A.T. and V.A.K.); Methodology and Investigation (S.F.M., V.A.K. and N.A.B.); Resources (R.I.F.); Formal Analysis (A.I.A.). N.I.T. acquired and interpreted ESR data. I.Y.B. carried out X-ray crystallography. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministry of Education and Science of the Russian Federation. (State Registration No. 125020401307-9).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available in the Supplementary Materials.

Acknowledgments

The main results were obtained using the equipment of the Baikal Analytical Center of Collective using SB RAS. The authors would like to acknowledge the Multi-Access Chemical Research Center SB RAS for spectral and analytical measurements. Deposition Number 2366416. The authors would like to acknowledge A. Vakhtel (Melytec Ltd., Moscow, Russia) for recording the Raman spectra.

Conflicts of Interest

The authors declare no conflicts of interest.

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Molecules 30 01367 sch001
Scheme 1. The reaction of diaryl(hetaryl)ketones with red phosphorus.
Scheme 1. The reaction of diaryl(hetaryl)ketones with red phosphorus.
Molecules 30 01367 sch001
Molecules 30 01367 g001
Figure 1. ESR spectra. (a) Experimental spectrum of the reaction mixture Pred/1a/KOH/DMSO/H2O 5–30 min after the reaction begins. (b) Experimental spectrum of the benzophenone anion-radical. (c) Experimental spectrum of polyphosphinyl radical. (d) Simulated spectrum of the benzophenone anion-radical.
Figure 1. ESR spectra. (a) Experimental spectrum of the reaction mixture Pred/1a/KOH/DMSO/H2O 5–30 min after the reaction begins. (b) Experimental spectrum of the benzophenone anion-radical. (c) Experimental spectrum of polyphosphinyl radical. (d) Simulated spectrum of the benzophenone anion-radical.
Molecules 30 01367 g001
Molecules 30 01367 sch002
Scheme 2. Substrate scope of phosphorylation of diaryl(hetaryl)ketones 1a–o with red phosphorus. Reagents and conditions: Pred (73 mmol), 1 (24 mmol), KOH (154 mmol), H2O (21 mmol), Ar, 85 °C, 1.5 h.
Scheme 2. Substrate scope of phosphorylation of diaryl(hetaryl)ketones 1a–o with red phosphorus. Reagents and conditions: Pred (73 mmol), 1 (24 mmol), KOH (154 mmol), H2O (21 mmol), Ar, 85 °C, 1.5 h.
Molecules 30 01367 sch002
Molecules 30 01367 g002
Figure 2. Molecular structure of 2a (50% thermal ellipsoids are shown), from n-hexane-DMF 1:1, CCDC 2366416.
Figure 2. Molecular structure of 2a (50% thermal ellipsoids are shown), from n-hexane-DMF 1:1, CCDC 2366416.
Molecules 30 01367 g002
Molecules 30 01367 sch003
Scheme 3. Proposed mechanism. (a) The first stage of the reaction is the P-P bond cleavage of the 3D-polymer Pred by the superbasic hydroxide-anion; (b) the second stage is phosphorylation of benzophenone with polyphosphide anion A.
Scheme 3. Proposed mechanism. (a) The first stage of the reaction is the P-P bond cleavage of the 3D-polymer Pred by the superbasic hydroxide-anion; (b) the second stage is phosphorylation of benzophenone with polyphosphide anion A.
Molecules 30 01367 sch003
Molecules 30 01367 sch004
Scheme 4. An example of alkylation of potassium phosphates 2.
Scheme 4. An example of alkylation of potassium phosphates 2.
Molecules 30 01367 sch004
Table 1. Influence of the phosphorylation conditions on the conversion of 1a, the ratio, and yields of products 2a, 3a, and 4a a.
Table 1. Influence of the phosphorylation conditions on the conversion of 1a, the ratio, and yields of products 2a, 3a, and 4a a.
Molecules 30 01367 i001
Entry1a:Pred:H2
OMolar Ratio		BaseSolvent bT, °Ct, hConversion of 1a, %Yield of, (%)
2a c3a d4a d
11:1:3.5KOHDMSO853.0742497
21:1:1.7KOHDMSO853.0863123e
31:1:0.9KOHDMSO853.086341911
41:1:1.7KOHDMSO603.087292712
51:1.5:1.7KOHDMSO753.098334814
61:1:1.7KOHDMSO966.0~10032362
71:2:3.5KOHDMSO853.08136445
81:4:3.5KOHDMSO851.51003149 ce
91:2:1.7KOHDMSO851.51003837 ce
101:3:0.9KOHDMSO851.510045184
11 f1:3:0.9KOHDMSO851.51001184 ce
121:3:0.5KOHDMSO851.510041157
131:3:0KOHDMSO851.51003997
141:3:0KOHDMSO g851.5100312612
151:3:0.9KOHHMPA851.510030 dh29 ce
161:3:0.9KOHNMP851.510014 68 ce
171:3:0.9KOHSulfolane851.510020 dh29 ce
181:3:0.9KOHDMF851.542452
a Reagents and conditions: red phosphorus (50–100 mmol), benzophenone (24–48 mmol), base (154 mmol), water (0–167 mmol), and Ar. b Commercial solvent (50 mL) without further purification was used. с Isolated yield. d Yield determined by 1H NMR using durene as an internal standard. e Traces. f 1a was added dropwise for 1.5 h. g Dry DMSO (over MS 3 Å) was used instead of commercial DMSO. h Contaminated with the solvent.
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Kuimov, V.A.; Malysheva, S.F.; Belogorlova, N.A.; Fattakhov, R.I.; Albanov, A.I.; Bagryanskaya, I.Y.; Tikhonov, N.I.; Trofimov, B.A. Straightforward Superbase-Mediated Reductive O-Phosphorylation of Aromatic and Heteroaromatic Ketones with Red Phosphorus in the Superbase Suspension KOH/DMSO(H2O). Molecules 2025, 30, 1367. https://doi.org/10.3390/molecules30061367

AMA Style

Kuimov VA, Malysheva SF, Belogorlova NA, Fattakhov RI, Albanov AI, Bagryanskaya IY, Tikhonov NI, Trofimov BA. Straightforward Superbase-Mediated Reductive O-Phosphorylation of Aromatic and Heteroaromatic Ketones with Red Phosphorus in the Superbase Suspension KOH/DMSO(H2O). Molecules. 2025; 30(6):1367. https://doi.org/10.3390/molecules30061367

Chicago/Turabian Style

Kuimov, Vladimir A., Svetlana F. Malysheva, Natalia A. Belogorlova, Ruslan I. Fattakhov, Alexander I. Albanov, Irina Yu. Bagryanskaya, Nikolay I. Tikhonov, and Boris A. Trofimov. 2025. "Straightforward Superbase-Mediated Reductive O-Phosphorylation of Aromatic and Heteroaromatic Ketones with Red Phosphorus in the Superbase Suspension KOH/DMSO(H2O)" Molecules 30, no. 6: 1367. https://doi.org/10.3390/molecules30061367

APA Style

Kuimov, V. A., Malysheva, S. F., Belogorlova, N. A., Fattakhov, R. I., Albanov, A. I., Bagryanskaya, I. Y., Tikhonov, N. I., & Trofimov, B. A. (2025). Straightforward Superbase-Mediated Reductive O-Phosphorylation of Aromatic and Heteroaromatic Ketones with Red Phosphorus in the Superbase Suspension KOH/DMSO(H2O). Molecules, 30(6), 1367. https://doi.org/10.3390/molecules30061367

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