Expanding the Library of 2-Phenylbenzotellurazoles: Red-Shifting Effect­ of Ethoxy Functionalities on the UV/Vis Absorption Properties

Dedicated to Prof. A. Krief on the occasion of his 80^th birthday

Abstract

This work describes the high-yield synthesis of a novel series of benzotellurazoles bearing a phenyl ring in 2-position, which is differently functionalized with ethoxy chains. Changing the number and the position of these functional groups determines differences in the self-assembly in the solid state, as well as in the photophysical properties of the targeted molecules. As anticipated by theoretical calculations of the HOMO-LUMO gap of each molecule, the presence of ethoxy chains in o- and p-positions determines up to 20 nm red-shifts in the absorption peaks, when compared to unsubstituted benzotellurazole. Similarly, more significant changes are observed in the chemical shifts of ¹²⁵Te NMR spectra for those derivatives bearing o- and p-ethoxy functionalization.

In the last two decades, the high chemical stability of benzo-1,3-tellurazoles towards light, air, and heat promo­ted their utilization in several research domains.[1] Noteworthy examples deal with their employment as photographic fog inhibitors,[2] room temperature phosphorescent emitters,[3] antioxidants,[4] and pharmaceutical derivatives.[5] Despite their resourceful features, there was a low number of publications focusing on their preparation,[6] which often required harsh conditions[7] and the use of toxic interme­diates.[8] Among the first synthetic protocols in the literature, that of Kambe et al. suggested the reaction between elemental Te⁰ and in situ prepared lithiated secondary amines.[9] Resulting telluride was then added to 2-iodophenyl isocyanide and CuI, leading to the formation of 2-amino-substituted benzotellurazoles in modest yields. A breakthrough contribution was provided by Junk et al. in 2013, who proposed a two-step synthetic sequence first treating commercially available 2-haloanilines with freshly prepared Na₂Te.[10] Bistellurides obtained with this method would then undergo reductive cyclization in the presence of acyl chlorides and H₃PO₂, thus producing benzotellurazoles in good yields (56–74%).

The same research group further contributed with more recent works using bistellurides as starting materials, trea­ted with opportune reducing agent to afford 2-methylmercaptobenzotellurazole,[11] as well as benzotellurazoles bea­ring acylamino and arylamino moieties in 2-position, to further aim at the investigation of their self-assembly in the solid state.[12] A few years ago our research group also contri­buted to the field, providing insight into a novel synthetic protocol to prepare mono- and bis-benzochalcogenazoles.[3] According to this procedure, the cyclization would no longer occur on the bistelluride-based scaffold, but their preliminary reduction to corresponding o-methyltelluro deri­vatives allows to build the molecular backbone by amidation, then performing a POCl₃-induced dehydrative cyclization.[13] This high-yielding methodology[14] was later applied to prepare a wide series of 2-substituted benzotellurazoles,[15] which revealed the ability to self-assemble in wire-like supramolecular polymers in the solid state through directio­nal N∙∙∙Te chalcogen bonds.[16] Particularly crucial was the effect of changing the substituent in 2-position, which played a crucial role in controlling the solid-state assembly, by affecting the σ-hole of the chalcogen atom through electronic and steric effects.[15]

Building on these results, we aimed at expanding the library of 2-phenylbenzo-1,3-tellurazoles, preparing some novel derivatives whose properties would be tuned by modulating the level of substitutions on the 2-phenyl ring. The advantage of this strategy allows to combine effective synthetic protocols previously developed in our group, ha­ving proved to be highly tolerant to differently functiona­lized substituents in 2-position of the benzochalcogenazole unit. In particular, introducing ethoxy groups in different positions of the aromatic ring is expected to intensely affect the optical properties in solution, depending on their direct participation to the π-conjugation of the molecular scaffold (Figure [1]).

Furthermore, increasing the number of ethoxy moieties on the ring would favor the occurrence of additional interactions in the solid-state, expecting chemical affinity among the alkyl chains.[17] This is envisaged to positively affect the molecular packing, developed through the expected N∙∙∙Te chalcogen bond in one direction, and by means of intermolecular C–C bonds among the ethoxy chains in the orthogonal direction.

The synthesis of each ethoxy-functionalized phenyl ring is expected to occur in two steps, using commercially avai­lable phenols as starting materials. Te-containing amine 7 can be prepared according to synthetic protocols previously optimized in our group. The two moieties are, then, assembled via amidation conditions, followed by dehydrative cyclization to afford targeted benzotellurazoles. The synthetic procedure started with commercially available phenols 2, most of them purchased as alkyl benzoates except for 2 _p , being a hydroxybenzaldehyde. They were first treated in the presence of a large excess of K₂CO₃ as base, followed by the quenching of resulting phenates by adding EtI. Notably, three equivalents of base and EtI were respectively employed per hydroxy group, affording compounds 3 _x,y,z in very good to excellent yields. Alkyl benzoates were then hydrolyzed in basic conditions, followed by acidification using aqueous HCl, which led to the formation of corresponding carboxylic acids 4 _x,y,z in yields globally higher than 85%. A different synthetic protocol was instead performed to get 4 _p from the aldehyde 3 _p . The latter underwent oxidizing conditions using KMnO₄ and Na₂HPO₄ in a mixture of CH₃CN and H₂O, which provided carboxylic acid 4 _p in 71% yield. Te-containing amine 7 was prepared starting from commercially available 2-bromoaniline (5), which underwent nucleophi­lic displacement of Br atom by Te, when treated with in situ prepared Na₂Te in boiling NMP, yielding bistelluride 6 in 47% yield.[10] The synthesis of 7 was finally accomplished by reductive cleavage of the ditelluride bond in the presence of NaBH₄, followed by addition of CH₃I to provide 7 in 73% yield. Having prepared the two molecular scaffolds of inte­rest, they were coupled through amide bond formation. Differently from the synthetic protocols previously reported in our group,[3] carboxylic acids 4 _x,y,z were no longer activated by using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC·HCl) as coupling agent. Instead, 4 _x,y,z were in situ converted to the corresponding acyl chlorides by treatment with (COCl)₂ and DMF in anhydrous CH₂Cl₂. Resulting intermediates were added to solutions of Te-containing amine 7 in anhydrous CH₂Cl₂ in the presence of a base, following two different synthetic protocols. To obtain benzamides 8 _p , 8 _m,m′ and 8 _m,p,m′ , respective acyl chlorides were mixed at 0 °C with 7 using NEt₃ as base. Applying this reaction conditions to derivatives 4 _o , 4 _m , and 4 _m,p did not lead to the formation of targeted benzamides, thus pyridine was employed as base and co-solvent to CH₂Cl₂, adding DMAP in 5 mol% as catalyst. This synthetic strategy afforded benzamides 8 _o , 8 _m , and 8 _m,p in 34–57% yields. The whole set of amides finally underwent dehydrative cyclization reaction in the presence of POCl₃ and NEt₃ as a base, to give benzotellurazoles 1 _x,y,z in good to excellent yields (Scheme [1]).

Once the synthesis of targeted molecules 1 _x,y,z was accomplished, the investigation of the supramolecular organization in the solid state was performed by X-ray diffraction (XRD) analysis. Compound 1 _m was excluded from the study, being in an oily state at atmospheric conditions. Despite several attempts to crystallize all the molecules, only 1 _m,m′ and 1 _m,p,m′ gave suitable crystals for XRD analysis. Crystals of 1 _m,m′ were obtained by slow evaporation of a CHCl₃/toluene solution. Differently from what was envisaged, the intermolecular bond governing the molecular packing is a Te∙∙∙Te contact (d _{Te∙∙∙Te} = 3.621 Å). Despite its being significantly shorter than the sum of van der Waals (vdW) radii of the atoms involved (4.2 Å), this bond does not display the correct planar geometry among the atoms, which is an important prerequisite for defining it a chalcogen bond (C₇-Te₁∙∙∙Te₁ = 136.7°, Figure [2b]). The molecules further organize in an off-set π-π stacking between phenyl ring of the benzotellurazole moiety and ethoxy-substituted ring of a neighboring molecule (average d _π-π = 3.46 Å, Figure [2c]). Since the Te∙∙∙Te interaction disposes the molecules in a stair-like fashion, the final supramolecular organization assumes a zig-zag conformation (Figure [2d]). By contrast with the cry­stal structure of 1 _m,m′, that of 1 _m,p,m′ is marked by the pre­sence of two molecules in the asymmetric unit, interconnected through a weak hydrogen bond (d _N∙∙∙C = 3.322 Å, Fi­gure [3b]). Each molecule participates to the supramolecular organization through two major intermolecular intera­ctions. On the one hand, the foreseen chalcogen bond takes place among N and Te atoms of proximal molecules (d _N∙∙∙Te = 3.165 Å < Σ_vdw radii = 3.45 Å; C₇-Te₁∙∙∙N₁ = 159.4°, Figure [3c]). Similar to what is observed in the solid-state organization of benzotellurazoles previously published,[15] a rod-like supramolecular polymer is achieved, having each unit di­sposed almost perpendicularly among themselves. On the other hand, the polymeric chains expand along the b axis through several C–C contacts among the ethoxy moieties, with an average length of 3.7 Å (Figure [3d]). This generates a V-shaped supramolecular organization in the solid state, having two polymeric chains interlaced among them through multiple vdW interactions involving the ethoxy substituents (Figure [3e]).

Aiming at understanding how the ethoxy groups would affect the optoelectronic properties, the frontier orbitals of 1 _x,y,z were determined by DFT calculations using Gaussian09, including the D01 revision at B97-D3/Def2TZVP level of theory.[18] Unsubstituted 1 was also included in the inve­stigation to better appreciate the effect embodied by the ethoxy chains when added in different amounts and positions (Figure [4]). When a single ethoxy group is added in o- and p-positions, its electron-donating effect is enhanced, thus both HOMO and LUMO energy levels increase in comparison to 1 (HOMO = –5.08, –5.03, and –5.27 eV; LUMO = –2.25, –2.27, and –2.54 eV, for 1 _o , 1 _p , and 1, respectively). This response is less evident for molecules 1 _m,p and 1 _m,p,m′ , given the presence of the substituent in m-position, which contributes less to the electron-donating effect. Taking into account the m-substitution, lowered theoretical bandgaps are depicted when compared to 1, with derivative 1 _m,m′ notably possessing the lowest ΔE in the series (2.64 vs. 2.73 eV of 1).

Moving to the investigation in solution, solvent-dependent UV/Vis measurements were first performed for the whole set of benzochalcogenazoles 1 _x,y,z . All the experiments were carried out with a concentration of 0.1 mM, aiming at potential solvatochromic effects rising from the change of polarity of the screened solvents (CH₃CN, THF, CH₂Cl₂, benzene, toluene, hexane, and methylcyclohexane, respectively). No significant difference was displayed in the absorption spectra by changing the solvent polarity, which can be due to an intrinsic stability of both ground (S₀) and excited (S₁) states of all the molecules in solution, independently on the dielectric constant of each solvent (see Figure S44 in SI). On the other hand, in accordance with the computational predictions, the presence of the ethoxy chains generated substantial changes in the absorption spectra among the different derivatives in CH₂Cl₂ solutions (Figure [5]). 2-Phenyl-substituted 1 was also included in the investigation as reference molecule (see absorption spectra in Figure [5]). The absorption profile of 1 displays a main intense peak centered at 308 nm and a broader shoulder at 370 nm, being a peculiar n-π* transition, often reported for Te-containing materials.[3] When an ethoxy chain is introduced in p-position of the phenyl ring of 1 _p , the main absorption peak converts into a bimodal absorption, which globally shows a slight red shift of λ_max when compared to the one of unsubstituted 1 (see Table S1 in SI for the λ_max values of each molecule). Furthermore, a weakening in the intensity of the shoulder band is depicted, most likely due to an energy level rearrangement. The same trend is observed for o-substituted derivative 1 _o , which analogously presents an absorption spectrum with a better-defined vibrational structure marked by bimodal features at 323 and 336 nm, as well as a weakened band at 353 nm. Notably, the UV/Vis spectral envelope of 1 _o is the most blue-shifted among the molecules studied. This result is in accordance with the computationally-predicted values of ΔE for 1 _o , being the highest among the series (2.83 eV). In sharp contrast, the presence of ethoxy chains in m-position does not significantly affect the absorption envelope. When the spe­ctrum of 1 _m is compared to the one of unsubstituted 1, a modest red shift is depicted, being the strong signal of the shoulder band located at 375 nm (Figure [5a]). Equivalent results can be depicted from UV/Vis analysis of diethoxy-substituted derivatives 1 _m,p and 1 _m,m′ . In accordance with all spectral observations, the ethoxy functionality in p-position exerts the strongest bathochromic shift. Namely, the spectrum exhibits two main peaks at 324 and 333 nm, whereas the weakened n-π* peak falls at 371 nm.

Differently from 1 _m,p , the presence of two ethoxy groups in 1 _m,m′ does not induce a significant change in the spe­ctrum but, similarly to what was observed with 1 _m , a slight red shift of the π-π* transition can be detected in comparison to the λ_max in unsubstituted 1 (312 vs 308 nm, respe­ctively, Figure [5b]). Finally, triethoxy-substituted 1 _m,p,m′ is marked by absorption properties analogous to those described for 1 _p and 1 _m,p , showing bimodal features and a lowered shoulder peak at 374 nm (Figure [5c]). Variable-temperature (VT) UV/Vis spectra were also performed for triethoxy-substituted 1 _m,p,m′ , to evaluate if the presence of the substituents would favor supramolecular self-assembly in solution. Two different solutions at different concentrations were screened, namely at 200 μM and 2 mM. Unfortunately, no significant change in the absorption envelop could be detected by recording the spectra from 90 to –6 °C, which excludes any associative role triggering the self-assembly of these molecules (Figure S45 in SI). Finally, steady state fluorescence and phosphorescence emissive properties were additionally investigated in deaerated CH₂Cl₂ solutions, but no emission was detected both at room temperature and at 77 K.

Additional ¹²⁵Te NMR inquiries were completed for 10 mM solutions in CD₂Cl₂ of monoethoxy-substituted 1 _p , diethoxy 1 _m,m′ , and triethoxy 1 _m,p,m′ , in comparison with non-functionalized molecular reference 1. ¹²⁵Te spectroscopy provides, indeed, narrow lines over a significantly wide chemical shift range, thus constituting a suitable technique to fingerprint the substitutional effect played by the pre­sence of the ethoxy moieties in different positions of the 2-aryl ring. Similarly to the outcome achieved with the UV/Vis analysis, varying the positions of the ethoxy group among the compounds determines significant shifts in the ¹²⁵Te NMR peaks. Notably, a shielding effect is observed comparing the peaks of 1 and 1 _p (846.42 and 828.76 ppm, respectively), which can be explained with the electron-donating effect of the ethoxy group on Te atom. In contrast, a substantial deshielding emerges by looking at the ¹²⁵Te NMR spectrum of 1 _m,m′ . Finally, a mediated effect among p- and m-substituents is illustrated by the peak of triethoxy-substituted 1 _m,p,m′ , falling at a chemical shift quite similar to the one of unsubstituted 1 (840.42 vs 846.42 ppm, respe­ctively, see Figure S46 in SI). The investigation of the effect of the ethoxy chains in solution was ultimately evaluated by VT ¹²⁵Te NMR experiments of 100 mM solutions containing 1, 1 _p , 1 _m,m′ , and 1 _m,p,m′ in CD₂Cl₂. Specifically, the spectra were recorded at room temperature and at –40 °C, with the lowest temperature expected to favor the self-assembly. Unfortunately, negligible differences among the chemical shifts at the two working temperatures could be observed for all the derivatives (Figure S47 in SI), leading us to exclude­ the development of any supramolecular organization in solution.

In conclusion, we have designed and synthesized a novel class of 2-phenylbenzo-1,3-tellurazoles using a high-yiel­ding synthetic procedure, to introduce ethoxy functional groups on the phenyl ring in 2-position. Varying their number and their position on the aromatic ring significantly affected the absorption properties, with the strongest effects manifested by o- and p-substituted derivatives. These results were in total agreement with what could be envisaged by calculating the theoretical frontier orbitals. The effect of the ethoxy chain in the supramolecular self-assembly in solution was also tested through variable temperature UV/Vis and ¹²⁵Te NMR measurements, but negligible variations could be detected. The effect of the ethoxy groups was also estimated in the solid-state arrangements of highly substituted derivatives 1 _m,m′ and 1 _m,p,m′ , whose molecular packing could expand through several C···C contacts among the aliphatic chains. These results highlight the significant effect of modulating both molecular (photophysical) and supramolecular (solid-state organization) properties of benzotellurazoles by changing the functionalities on their molecular scaffold. Additional studies dealing with the implementation of longer alkyl chains are currently ongoing, finally aiming at inducing and strengthening the supramolecular association of these chalcogenide molecules in solution.

Chemicals were purchased from Sigma Aldrich, Acros Organics, TCI, Apollo Scientific, ABCR, Alfa Aesar, Carbosynth, and Fluorochem and were used as received. Solvents were purchased from Fluorochem, Fisher Chemical, and Sigma Aldrich, while deuterated solvents from Eurisotop and Sigma Aldrich. THF and CH₂Cl₂ were dried on a M Braun MB SPS-800 solvent purification system. NMP, MeOH, CHCl₃, and acetone were purchased as reagent-grade and used without further purification. Et₃N was distilled from CaH₂ and then stored over KOH. Anhydrous­ 1,4-dioxane and pyridine were purchased from Sigma Aldrich. Low temperature baths were prepared using different solvent mixtures depending on the desired temperature: 0 °C with ice/H₂O. Anhydrous conditions were achieved by heating two-necked flasks with a heat gun under vacuum and purging with argon. The inert atmosphere­ was maintained using argon-filled balloons equipped with a syringe and needle that were used to penetrate the silicon stoppers closing the flask’s necks. Additions of liquid reagents were performed using dried plastic or glass syringes. All reactions were performed in dry conditions and under inert atmosphere, unless otherwise stated.

Preparation of compounds 3 and 4 is provided in the Supporting Information. For the alphabetical numbering of the H atoms for assigning chemical shifts in ¹H NMR spectra, see the Supporting Information.

Benzamides 8; General Procedure

Method A, for 8_p , 8_m,m′ and 8_{m,p,m′ :} To a suspension of carboxylic acid 4 _p , 4 _m,m′ , or 4 _m,p,m′ (0.4 mmol) in anhyd CH₂Cl₂ under anhydrous condition were added (COCl)₂ (57 mg, 0.45 mmol) and one drop of DMF at 0 °C and then the reaction mixture was stirred at r.t. overnight. Once the solvents were removed under reduced pressure, the resulting acyl chloride derivative was dissolved in anhyd CH₂Cl₂, followed by the addition of a solution of 7 (0.48 mmol) and NEt₃ (0.50 mmol) in anhyd CH₂Cl₂ at 0 °C. The resulting system was stirred at r.t. overnight, then quenched with H₂O (20 mL) and extracted with CH₂Cl₂ (3 × 30 mL). The combined organic extracts were washed with brine, dried (MgSO₄), filtered and the solvents removed under reduced pressure. The crude materials were purified by silica gel chromatography.

Method B, for 8_o , 8_m , and 8_m,p : To a suspension of carboxylic acid 4 _o , 4 _m , or 4 _m,p (0.4 mmol) in anhyd CH₂Cl₂ under anhydrous condition were added (COCl)₂ (57 mg, 0.45 mmol) and one drop of DMF at 0 °C and then the reaction mixture was stirred at r.t. overnight. Once the solvents were removed under reduced pressure, the resulting acyl chloride derivative was dissolved in anhyd CH₂Cl₂, followed by the addition of a solution of 7 (0.48 mmol) and DMAP (2 mg, 0.02 mmol) in anhyd CH₂Cl₂ and pyridine at 0 °C. The resulting system was stirred at 50 °C overnight, then quenched with H₂O (20 mL) and extracted with CH₂Cl₂ (3 × 30 mL). The combined organic extracts were washed with brine, dried (MgSO₄), filtered and the solvents removed under reduced pressure. The crude materials were purified by silica gel chromatography.

Benzo-1,3-tellurazoles 1 _x,y,z ; General Procedure

To a suspension of amide 8 (1 mmol) in anhyd 1,4-dioxane (10 mL) under anhydrous condition, were added sequentially POCl₃ (306 mg, 2 mmol) and NEt₃ (607 mg, 6 mmol). The reaction mixture was heated to reflux and stirred overnight, diluted with CHCl₃ (30 mL), and washed with sat. aq NaHCO₃ (30 mL). The aqueous phase was extracted with CHCl₃ (3 × 30 mL), then the combined organic extracts were washed with brine (30 mL), dried (MgSO₄), filtered and the solvents removed under reduced pressure. The crude materials were purified by silica gel chromatography.

2-Ethoxy-N-[2-(methyltellanyl)phenyl]benzamide (8 _o )

Yield: 200 mg (50%); dark yellowish oil.

IR (ATR): 3306, 3052, 2977, 2926, 1656, 1597, 1572, 1511, 1480, 1448, 1432, 1390, 1367, 1295, 1212, 1161, 1131, 1115, 1091, 1032, 925, 888, 839, 751, 712, 670, 647, 610, 587, 527, 441 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 10.13–10.01 (br s, 1 H, H _f ), 8.29 (dd, J _H,H = 7.9, 1.7 Hz, 1 H, H _e ), 8.07 (d, J _H,H = 7.8 Hz, 1 H, H _g ), 7.78 (dd, J _H,H = 7.8, 0.9 Hz, 1 H, H _j ), 7.48 (td, J _H,H = 7.9, 1.7 Hz, 1 H, H _c ), 7.36 (td, J _H,H = 7.9, 1.2 Hz, 1 H, H_d), 7.11 (td, J _H,H = 7.8, 0.9 Hz, 1 H, H _h ), 7.06–6.98 (m, 2 H, H _b,i ), 4.39 (q, J _H,H = 7.0 Hz, 2 H, H _k ), 2.08 (s, 3 H, H _a ), 1.57 (t, J _H,H = 7.0 Hz, 3 H, H _l ).

¹³C NMR (100 MHz, CDCl₃): δ = 164.2, 156.8, 141.3, 138.9, 133.4, 132.9, 129.1, 125.8, 123.8, 122.0, 121.4, 112.5, 108.6, 65.0, 15.1, –15.7.

HRMS (ESI): m/z [M + H]⁺ calcd for C₁₆H₁₇NO₂Te + H⁺: 386.0395; found: 386.0393.

3-Ethoxy-N-[2-(methyltellanyl)phenyl]benzamide (8 _m )

Yield: 132 mg (34%); yellowish oil.

IR (ATR): 3307, 3054, 2977, 2924, 1657, 1575, 1515, 1485, 1434, 1391, 1301, 1262, 1209, 1158, 1114, 1089, 1045, 997, 963, 894, 850, 797, 748, 713, 884, 602, 551, 523 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 9.14–8.97 (br s, 1 H, H _f ), 8.47 (d, J _H,H = 8.2 Hz, 1 H, H _g ), 7.92 (dd, J _H,H = 7.6, 1.3 Hz, 1 H, H _e ), 7.57–7.50 (m, 2 H, H _b,l ), 7.45–7.38 (m, 2 H, H _c,h ), 7.10 (dd, J _H,H = 8.2, 1.8 Hz, 1 H, H _i ), 6.99 (td, J _H,H = 7.6, 1.1 Hz, 1 H, H _d ), 4.13 (q, J _H,H = 7.0 Hz, 2 H, H _j ), 2.07 (s, 3 H, H _a ), 1.46 (t, J _H,H = 7.0 Hz, 3 H, H _k ).

¹³C NMR (100 MHz, CDCl₃): δ = 165.2, 159.4, 141.5, 140.8, 136.1, 130.5, 129.9, 125.2, 120.2, 118.9, 118.7, 113.0, 106.3, 63.7, 14.8, –14.8.

HRMS (ESI): m/z [M + H]⁺ calcd for C₁₆H₁₇NO₂Te + H⁺: 386.0395; found: 386.0489.

4-Ethoxy-N-[2-(methyltellanyl)phenyl]benzamide (8 _p )

Yield: 210 mg (23%); yellow oil.

IR (ATR): 3315, 3053, 2979, 2928, 1667, 1604, 1575, 1525, 1501, 1475, 1432, 1393, 1298, 1247, 1176, 1114, 1042, 922, 847, 800, 761, 697, 643, 585, 531, 441 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 8.96 (br s, 1 H, H _f ), 8.46 (d, J _H,H = 7.7 Hz, 1 H, H _e ), 7.96 (d, J _H,H = 8.2 Hz, 2 H, H _g ), 7.92 (d, J _H,H = 7.7 Hz, 1 H, H _b ), 7.41 (t, J _H,H = 7.7 Hz, 1 H, H _c ), 7.03–6.92 (m, 3 H, H _h,d ), 4.12 (q, J _H,H = 7.0 Hz, 2 H, H _i ), 2.06 (s, 3 H, H _a ), 1.46 (t, J _H,H = 7.0 Hz, 3 H, H _j ).

¹³C NMR (100 MHz, CDCl₃): δ = 164.9, 162.1, 141.4, 141.0, 130.5, 129.1, 126.7, 125.0, 120.2, 114.6, 106.2, 63.8, 14.7, –14.9.

HRMS (ESI): m/z [M + H]⁺ calcd for C₁₆H₁₇NO₂Te + H⁺: 384.0292; found: 384.0377.

3,4-Diethoxy-N-[(2-methyltellanyl)phenyl]benzamide (8 _m,p )

Yield: 120 mg (57%); dark yellow solid; mp 78–83 °C.

IR (ATR): 2052, 1980, 1967, 1925, 1642, 1572, 1510, 1476, 1464, 1434, 1418, 1394, 1315, 1265, 1212, 1154, 1134, 1121, 1104, 1091, 1069, 1058, 1039, 1020, 920, 893, 875, 834, 818, 800, 790, 772, 757, 711, 700, 685, 668, 642, 622, 611, 600, 575, 561, 536, 527, 517, 495, 467, 448, 438, 419, 414 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 8.99 (br s, 1 H, H _f ), 8.47 (d, J _H,H = 7.5 Hz, 1 H, H _e ), 7.91 (dd, J _H,H = 7.5, 1.1 Hz, 1 H, H _b ), 7.59 (d, J _H,H = 1.9 Hz, 1 H, H _g ), 7.53 (dd, J _H,H = 8.3, 1.9 Hz, 1 H, H _m ), 7.41 (t, J _H,H = 7.5 Hz, 1 H, H _c ), 7.00–6.90 (m, 2 H, H _d,l ), 4.25–4.13 (m, 2 H, H _h,j ), 2.06 (s, 3 H, H _a ), 1.50 (t, J _H,H = 6.9 Hz, 6 H, H _i,k ).

¹³C NMR (100 MHz, CDCl₃): δ = 165.1, 152.1, 148.9, 141.6, 141.1, 130.7, 127.2, 125.1, 120.1, 119.9, 112.5, 112.2, 106.2, 64.7, 64.7, 14.9, 14.8, –14.8.

HRMS (ESI): m/z [M + H]⁺ calcd for C₁₈H₂₁NO₃Te + H⁺: 430.0657; found: 430.0746.

3,5-Diethoxy-N-[2-(methyltellanyl)phenyl]benzamide (8 _m,m′)

Yield: 358 mg (55%); white solid; mp 109–114 °C.

IR (ATR): 3256, 2976, 2923, 1643, 1597, 1577, 1519, 1463, 1438, 1393, 1373, 1329, 1263, 1248, 1224, 1164, 1112, 1057, 998, 908, 861, 782, 753, 706, 681, 646, 633, 586, 545, 523, 501, 476, 446, 420, 410 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 8.97 (br s, 1 H, H _f ), 8.44 (d, J _H,H = 7.6 Hz, 1 H, H _e ), 7.91 (d, J _H,H = 7.6 Hz, 1 H, H _b ), 7.41 (t, J _H,H = 7.6 Hz, 1 H, H _d ), 7.09 (s, 2 H, H _g ), 6.98 (t, J _H,H = 7.6 Hz, 1 H, H _c ), 6.63 (s, 1 H, H _j ), 4.09 (q, J _H,H = 6.8 Hz, 4 H, H _h ), 2.06 (s, 3 H, H _a ), 1.44 (t, J _H,H = 6.8 Hz, 6 H, H _i ).

¹³C NMR (100 MHz, CDCl₃): δ = 165.4, 160.5, 141.5, 140.9, 136.9, 130.6, 125.3, 120.3, 106.5, 105.6, 105.3, 64.0, 14.9, –14.7.

HRMS (ESI): m/z [M + H]⁺ calcd for C₁₈H₂₁NO₃Te + H⁺: 430.0657; found: 430.0657.

3,4,5-Triethoxy-N-[2-(methyltellanyl)phenyl]benzamide (8 _m,p,m′)

Yield: 281 mg (66%); orange solid; mp 116–122 °C.

IR (ATR): 3212, 3177, 2970, 2926, 2885, 2850, 2110, 2018, 1622, 1577, 1520, 1496, 1479, 1463, 1432, 1385, 1371, 1336, 1261, 1233, 1156, 1124, 1101, 1054, 1030, 902, 882, 859, 840, 825, 802, 777, 757, 734, 718, 699, 681, 668, 647, 628, 619, 611, 598, 587, 577, 565, 556, 544, 527, 514, 496, 478, 468, 455, 441, 430, 420, 414, 405 cm^–1.

¹H NMR (400 MHz, CD₂Cl₂): δ = 8.95 (br s, 1 H, H _f ), 8.39 (dd, J _H,H = 8.0, 1.1 Hz, 1 H, H _e ), 7.93 (dd, J _H,H = 8.0, 1.1 Hz, 1 H, H _b ) 7.40 (td, J _H,H = 8.0, 1.1 Hz, 1 H, H _d ), 7.20 (s, 2 H, H _g ) 6.99 (td, J _H,H = 8.0, 1.1 Hz, 1 H, H _c ), 4.20–4.06 (m, 6 H, H _h,j ), 2.08 (s, 3 H, H _a ), 1.46 (t, J _H,H = 7.0 Hz, 6 H, H _i ), 1.34 (t, J _H,H = 7.0 Hz, 3 H, H _k ).

¹³C NMR (100 MHz, CD₂Cl₂): δ = 165.2, 153.5, 141.8, 141.4, 141.4, 130.6, 130.1, 125.4, 120.2, 107.1, 105.9, 69.3, 65.2, 15.8, 15.1, –14.8.

HRMS (ESI): m/z [M + H]⁺ calcd for C₂₀H₂₅NO₄Te + H⁺: 474.0920; found: 474.1029.

2-(2-Ethoxyphenyl)benzo[d][1,3]tellurazole (1 _o )

Yield: 134 mg (95%); pale yellow solid; mp 73–76 °C.

IR (ATR): 2885, 2579, 2374, 2336, 2244, 2209, 2187, 2127, 2049, 2037, 1975, 1894, 1779, 1596, 1474, 1451, 1425, 1390, 1294, 1236, 1203, 1162, 1120, 1036, 935, 757, 734, 717, 658, 620, 603, 592, 572, 562, 539, 483, 461, 439, 414 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 8.56 (dd, J _H,H = 7.7, 1.7 Hz, 1 H, H _d ), 8.26 (d, J _H,H = 7.7 Hz, 1 H, H _e ), 8.01 (d, J _H,H = 7.7 Hz, 1 H, H _h ), 7.49 (t, J _H,H = 7.7 Hz, 1 H, H _f ), 7.45 (t, J _H,H = 7.7 Hz, 1 H, H _b ), 7.17 (t, J _H,H = 7.7 Hz, 1 H, H _g ), 7.12 (t, J _H,H = 7.7 Hz, 1 H, H _c ), 7.04 (d, J _H,H = 7.7 Hz, 1 H, H _a ), 4.35 (q, J _H,H = 7.0 Hz, 2 H, H _i ), 1.71 (t, J _H,H = 7.0 Hz, 3 H, H _j ).

¹³C NMR (100 MHz, CDCl₃): δ = 161.7, 159.8, 155.9, 135.7, 131.4, 130.9, 128.5, 127.3, 126.7, 126.5, 124.4, 121.2, 112.2, 65.3, 15.4.

HRMS (ESI): m/z [M + H]⁺ calcd for C₁₅H₁₃NOTe + H⁺: 354.0133; found: 354.0135.

UV/Vis (CH₂Cl₂): λ_max (ε) = 353 (3600), 336 (17800), 323 nm (dm³ mol^–1 cm^–1 15800).

2-(3-Ethoxyphenyl)benzo[d][1,3]tellurazole (1 _m )

Yield: 98 mg (92%); brownish oil.

IR (ATR): 3051, 2981, 2927, 1589, 1511, 1473, 1431, 1392, 1293, 1263, 1255, 1227, 1178, 1158, 1114, 1089, 1047, 1022, 982, 911, 858, 785, 761, 733, 715, 703, 684, 658, 610, 593, 497, 438, 423 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 8.19 (d, J _H,H = 7.9 Hz, 1 H, H _d ), 7.93 (d, J _H,H = 7.9 Hz, 1 H, H _a ), 7.51–7.44 (m, 2 H, H _c,j ), 7.40 (d, J _H,H = 7.8 Hz, 1 H, H _e ), 7.34 (t, J _H,H = 7.8 Hz, 1 H, H_f), 7.18 (td, J _H,H = 7.9, 1.2 Hz, 1 H, H _b ), 7.03 (dt, J _H,H = 8.0, 2.4 Hz, 1 H, H _g ), 4.15 (q, J _H,H = 7.0 Hz, 2 H, H_h), 1.46 (t, J _H,H = 7.0 Hz, 3 H, H _i ).

¹³C NMR (100 MHz, CDCl₃): δ = 173.0, 162.0, 159.5, 142.4, 134.3, 131.6, 130.0, 127.0, 126.6, 125.0, 121.6, 117.6, 113.3, 63.8, 14.8.

HRMS (ESI): m/z [M + H]⁺ calcd for C₁₅H₁₃NOTe + H⁺: 354.0133; found: 354.0140.

UV/Vis (CH₂Cl₂): λ_max (ε) = 374 (3700), 311 nm (dm³ mol^–1 cm^–1 16800).

2-(4-Ethoxyphenyl)benzo[d][1,3]tellurazole (1 _p )

Yield: 102 mg (74%); yellow solid; mp 88–94 °C.

IR (ATR): 2952, 2922, 2853, 1739, 1700, 1602, 1576, 1511, 1488, 1463, 1435, 1427, 1418, 1377, 1304, 1289, 1275, 1243, 1212, 1174, 1114, 1041, 1018, 937, 918, 857, 828, 802, 750, 713, 650, 634, 595, 577, 547, 520, 490, 470, 446, 430 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 8.13 (d, J _H,H = 7.8 Hz, 1 H, H _d ), 7.90 (d, J _H,H = 7.8 Hz, 1 H, H _a ), 7.80 (d, J _H,H = 8.6 Hz, 1 H, H _e ), 7.46 (t, J _H,H = 7.8 Hz, 1 H, H _c ), 7.14 (t, J = 7.8 Hz, 1 H, H _b ), 6.94 (d, J _H,H = 8.6 Hz, 1 H, H _f ), 4.11 (q, J _H,H = 7.0 Hz, 2 H, H _g ), 1.45 (t, J _H,H = 7.0 Hz, 3 H, H _h ).

¹³C NMR (100 MHz, CDCl₃): δ = 172.5, 162.3, 161.6, 134.1, 133.9, 131.7, 130.2, 127.1, 126.1, 124.8, 115.0, 63.9, 14.9.

HRMS (ESI): m/z [M + H]⁺ calcd for C₁₅H₁₃NOTe + H⁺: 354.0133; found: 354.0125.

UV/Vis (CH₂Cl₂): λ_max (ε) = 368 (2700), 330 (16000), 318 nm (dm³ mol^–1 cm^–1 17300).

2-(3,4-Diethoxyphenyl)benzo[d][1,3]tellurazole (1 _m,p )

Yield: 77 mg (84%); yellow solid; mp 78–84 °C.

IR (ATR): 2954, 2921, 2852, 1741, 1598, 1520, 1492, 1461, 1415, 1376, 1292, 1257, 1221, 1140, 1096, 1036, 1022, 917, 868, 797, 754, 729, 709, 684, 663, 649, 620, 602, 592, 572, 561, 513, 500, 483, 459, 422, 410 cm^–1.

¹H NMR (400 MHz, CD₂Cl₂): δ = 8.09 (d, J _H,H = 7.7 Hz, 1 H, H _d ), 7.91 (d, J _H,H = 7.7 Hz, 1 H, H _a ), 7.55 (d, J _H,H = 1.8 Hz, 1 H, H _e ), 7.45 (t, J _H,H = 7.7 Hz, 1 H, H _c ), 7.29 (dd, J _H,H = 8.3, 1.8 Hz, 1 H, H _k ), 7.14 (t, J _H,H = 7.7 Hz, 1 H, H _b ), 6.90 (d, J _H,H = 8.3 Hz, 1 H, H _j ), 4.17 (q, J _H,H = 7.05 Hz, 2 H, H _f or H _g ), 4.12 (q, J _H,H = 7.05 Hz, 2 H, H _f or H _g ), 1.47–1.38 (m, 6 H, H _g,i ).

¹³C NMR (100 MHz, CD₂Cl₂): δ = 172.7, 162.6, 152.0, 149.3, 134.5, 134.1, 132.0, 127.4, 126.2, 125.0, 123.6, 113.0, 111.8, 65.1, 64.9, 15.0, 14.9.

HRMS (ESI): m/z [M + H]⁺ calcd for C₁₇H₁₇NO₂Te + H⁺: 398.0395; found: 398.0379.

UV/Vis (CH₂Cl₂): λ_max (ε) = 371 (6800), 333 (17700), 324 nm (dm³ mol^–1 cm^–1 17200).

2-(3,5-Diethoxyphenyl)benzo[d][1,3]tellurazole (1 _m,m′)

Yield: 255 mg (92%); yellow solid; mp 74–75 °C.

IR (ATR): 2967, 2919, 2869, 1586, 1509, 1458, 1433, 1386, 1371, 1349, 1303, 1261, 1223, 1176, 1113, 1059, 1030, 1010, 988, 940, 905, 857, 842, 823, 797, 757, 716, 679, 655, 646, 615, 597, 588, 576, 566, 553, 534, 526, 509, 498, 466, 457, 433, 422, 406 cm^–1.

¹H NMR (400 MHz, CDCl₃): δ = 8.18 (dd, J _H,H = 7.8, 1.1 Hz, 1 H, H _d ), 7.92 (dd, J _H,H = 7.8, 1.1 Hz, 1 H, H _a ), 7.48 (td, J _H,H = 7.8, 1.1 Hz, 1 H, H _b ), 7.17 (td, J _H,H = 7.8, 1.1 Hz, 1 H, H _c ), 7.04 (d, J _H,H = 2.2 Hz, 2 H, H _e ), 6.58 (t, J _H,H = 2.2 Hz, 1 H, H _h ), 4.11 (q, J _H,H = 7.0 Hz, 4 H, H _f ), 1.45 (t, J _H,H = 7.0 Hz, 6 H, H _g ).

¹³C NMR (100 MHz, CDCl₃): δ = 173.3, 162.0, 160.6, 143.0, 134.5, 131.7, 127.1, 126.7, 125.2, 107.1, 104.1, 64.0, 15.0.

HRMS (ESI): m/z [M + H]⁺ calcd for C₁₇H₁₇NO₂Te + H⁺: 398.0395; found: 398.0396.

UV/Vis (CH₂Cl₂): λ_max (ε) = 375 (1500), 312 nm (dm³ mol^–1 cm^–1 15600).

2-(3,4,5-Triethoxyphenyl)benzo[d][1,3]tellurazole (1 _m,p,m′)

Yield: 190 mg (86%); yellow solid; mp 100–106 °C.

IR (ATR): 2922, 2852, 1729, 1574, 1509, 1483, 1469, 1419, 1382, 1369, 1325, 1288, 1263, 1244, 1228, 1160, 1118, 1094, 1019, 898, 873, 851, 820, 797, 772, 753, 712, 677, 655, 636, 590, 561, 538, 498, 469, 457, 442, 417 cm^–1.

¹H NMR (400 MHz, CD₂Cl₂): δ = 8.28 (d, J _H,H = 7.6 Hz, 1 H, H _d ), 8.09 (d, J _H,H = 7.6 Hz, 1 H, H _a ), 7.63 (t, J _H,H = 7.6 Hz, 1 H, H _c ), 7.32 (t, J _H,H = 7.6 Hz, 1 H, H _b ), 7.26 (s, 2 H, H _e ), 4.36–4.21 (m, 6 H, H _f,h ), 1.62 (t, J _H,H = 7.0 Hz, 6 H, H _g ), 1.50 (t, J _H,H = 7.0 Hz, 3 H, H _i ).

¹³C NMR (100 MHz, CD₂Cl₂): δ = 173.0, 162.5, 153.8, 140.9, 136.7, 134.6, 132.1, 127.4, 126.5, 125.2, 107.2, 69.3, 65.3, 15.8, 15.1.

HRMS (ESI): m/z [M + Na]⁺ calcd for C₁₉H₂₁NO₃Te + Na⁺: 464.0477; found: 464.0480.

UV/Vis (CH₂Cl₂): λ_max (ε) = 374 (3700), 333 (14800), 322 nm (dm³ mol^–1 cm^–1 16100).

Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

D.B. gratefully acknowledges the University of Vienna for the financial support and the use of the Vienna Scientific Cluster (VSC) for the computational results. D.R. thanks the University of Vienna for her Ph.D. fellowship. L.A. thanks the Global Thesis Fellowship program sponsored by the University of Bari Aldo Moro for supporting his master’s thesis work at the University of Vienna.

• References

• 1a Guenther W, Mee J. Patent 4 575 483, 1986 ; Chem. Abstr. 1986, 104, 216429.
  PubMed
• 1b Luo X.-H, Liu X.-F, Xu H.-S. Chin. J. Org. Chem. 1996; 16: 552
  Search in Google Scholar
• 1c Ke W.-J, Liu X.-F, Xu H.-S. Chem. Res. Chin. Univ. 1997; 12: 478
  Search in Google Scholar
• 2 Usagawa Y, Sakamoto H, Yamashita K. Kokai Tokyo Koho 1987; 18 ; Chem. Abstr. 1987, 109, 29967
• 3 Kremer A, Aurisicchio C, De Leo F, Ventura B, Wouters J, Armaroli N, Barbieri A, Bonifazi D. Chem. Eur. J. 2015; 21: 15377
  CrossrefPubMedSearch in Google Scholar
• 4 Jacob C, Arteel GE, Kanda T, Engman L, Sies H. Chem. Res. Toxicol. 2000; 13: 3
  CrossrefPubMedSearch in Google Scholar
• 5 Okun E, Arumugam TV, Tang SC, Gleichmann M, Albeck M, Sredni B, Mattson MP. J. Neurochem. 2007; 102: 1232
  CrossrefPubMedSearch in Google Scholar
• 6 Sadekov ID, Minkin VI. Adv. Heterocycl. Chem. 1993; 58: 47
  CrossrefPubMedSearch in Google Scholar
• 7 Wiriyachitra P, Falcone SJ, Cava MP. J. Org. Chem. 1979; 44: 3957
  CrossrefPubMedSearch in Google Scholar
• 8a Junk T, Irgolic KJ. Phosphorus Sulfur Relat. Elem. 1988; 38: 121
  CrossrefSearch in Google Scholar
• 8b Al-Rubaie AZ, Fingan A.-AM, Al-Salim NI, Al-Jadaan SA. Polyhedron 1995; 14: 2575
  CrossrefSearch in Google Scholar
• 9 Fujiwara S.-i, Asanuma Y, Shin-ike T, Kambe N. J. Org. Chem. 2007; 72: 8087
  CrossrefPubMedSearch in Google Scholar
• 10 McMullen NC, Fronczek FR, Junk T. J. Heterocycl. Chem. 2013; 50: 120
  CrossrefSearch in Google Scholar
• 11 Sanford G, Walker KE, Fronczek FR, Junk T. J. Heterocycl. Chem. 2017; 54: 575
  CrossrefPubMedSearch in Google Scholar
• 12 Smith WE, Franklin DV, Goutierrez KL, Fronczek FR, Mautner FA, Junk T. Am. J. Heterocycl. Chem. 2019; 5: 49
  CrossrefPubMedSearch in Google Scholar
• 13a Abakarov G, Shabson A, Sadekov I, Garnovskii A, Minkin V. Chem. Heterocycl. Compd. 1988; 24: 232
  CrossrefSearch in Google Scholar
• 13b Mbuyi M, Evers M, Tihange G, Luxen A, Christiaens L. Tetrahedron Lett. 1983; 24: 5873
  CrossrefSearch in Google Scholar
• 14a Biot N, Bonifazi D. Chem. Eur. J. 2018; 24: 5439
  CrossrefPubMedSearch in Google Scholar
• 14b Romito D, Biot N, Babudri F, Bonifazi D. New J. Chem. 2020; 44: 6732
  CrossrefSearch in Google Scholar
• 14c Biot N, Romito D, Bonifazi D. Cryst. Growth Des. 2021; 21: 536
  CrossrefPubMedSearch in Google Scholar
• 15 Kremer A, Fermi A, Biot N, Wouters J, Bonifazi D. Chem. Eur. J. 2016; 22: 5665
  CrossrefPubMedSearch in Google Scholar
• 16a Cozzolino AF, Elder PJ. W, Vargas-Baca I. Coord. Chem. Rev. 2011; 255: 1426
  CrossrefSearch in Google Scholar
• 16b Mahmudov KT, Kopylovich MN, da Silva MF. C. G, Pombeiro AJ. Dalton Trans. 2017; 46: 10121
  CrossrefPubMedSearch in Google Scholar
• 16c Benz S, López-Andarias J, Mareda J, Sakai N, Matile S. Angew. Chem. Int. Ed. 2017; 56: 812
  CrossrefPubMedSearch in Google Scholar
• 16d Vogel L, Wonner P, Huber SM. Angew. Chem. Int. Ed. 2019; 58: 1880
  CrossrefPubMedSearch in Google Scholar
• 16e Scilabra P, Terraneo G, Resnati G. Acc. Chem. Res. 2019; 52: 1313
  CrossrefPubMedSearch in Google Scholar
• 16f Ho PC, Wang JZ, Meloni F, Vargas-Baca I. Coord. Chem. Rev. 2020; 422: 213464
  CrossrefSearch in Google Scholar
• 16g Biot N, Bonifazi D. Coord. Chem. Rev. 2020; 413: 213243
  CrossrefSearch in Google Scholar
• 17 Davis R, Saleesh Kumar N, Abraham S, Suresh C, Rath NP, Tamaoki N, Das S. J. Phys. Chem. C 2008; 112: 2137
  CrossrefSearch in Google Scholar
• 18 Garrett GE, Gibson GL, Straus RN, Seferos DS, Taylor MS. J. Am. Chem. Soc. 2015; 137: 4126
  CrossrefPubMedSearch in Google Scholar

Corresponding Author

Publication History

Received: 15 November 2021

Accepted after revision: 17 December 2021

Article published online:
10 May 2022

© 2022. Thieme. All rights reserved

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany

• References

• 1a Guenther W, Mee J. Patent 4 575 483, 1986 ; Chem. Abstr. 1986, 104, 216429.
  PubMed
• 1b Luo X.-H, Liu X.-F, Xu H.-S. Chin. J. Org. Chem. 1996; 16: 552
  Search in Google Scholar
• 1c Ke W.-J, Liu X.-F, Xu H.-S. Chem. Res. Chin. Univ. 1997; 12: 478
  Search in Google Scholar
• 2 Usagawa Y, Sakamoto H, Yamashita K. Kokai Tokyo Koho 1987; 18 ; Chem. Abstr. 1987, 109, 29967
• 3 Kremer A, Aurisicchio C, De Leo F, Ventura B, Wouters J, Armaroli N, Barbieri A, Bonifazi D. Chem. Eur. J. 2015; 21: 15377
  CrossrefPubMedSearch in Google Scholar
• 4 Jacob C, Arteel GE, Kanda T, Engman L, Sies H. Chem. Res. Toxicol. 2000; 13: 3
  CrossrefPubMedSearch in Google Scholar
• 5 Okun E, Arumugam TV, Tang SC, Gleichmann M, Albeck M, Sredni B, Mattson MP. J. Neurochem. 2007; 102: 1232
  CrossrefPubMedSearch in Google Scholar
• 6 Sadekov ID, Minkin VI. Adv. Heterocycl. Chem. 1993; 58: 47
  CrossrefPubMedSearch in Google Scholar
• 7 Wiriyachitra P, Falcone SJ, Cava MP. J. Org. Chem. 1979; 44: 3957
  CrossrefPubMedSearch in Google Scholar
• 8a Junk T, Irgolic KJ. Phosphorus Sulfur Relat. Elem. 1988; 38: 121
  CrossrefSearch in Google Scholar
• 8b Al-Rubaie AZ, Fingan A.-AM, Al-Salim NI, Al-Jadaan SA. Polyhedron 1995; 14: 2575
  CrossrefSearch in Google Scholar
• 9 Fujiwara S.-i, Asanuma Y, Shin-ike T, Kambe N. J. Org. Chem. 2007; 72: 8087
  CrossrefPubMedSearch in Google Scholar
• 10 McMullen NC, Fronczek FR, Junk T. J. Heterocycl. Chem. 2013; 50: 120
  CrossrefSearch in Google Scholar
• 11 Sanford G, Walker KE, Fronczek FR, Junk T. J. Heterocycl. Chem. 2017; 54: 575
  CrossrefPubMedSearch in Google Scholar
• 12 Smith WE, Franklin DV, Goutierrez KL, Fronczek FR, Mautner FA, Junk T. Am. J. Heterocycl. Chem. 2019; 5: 49
  CrossrefPubMedSearch in Google Scholar
• 13a Abakarov G, Shabson A, Sadekov I, Garnovskii A, Minkin V. Chem. Heterocycl. Compd. 1988; 24: 232
  CrossrefSearch in Google Scholar
• 13b Mbuyi M, Evers M, Tihange G, Luxen A, Christiaens L. Tetrahedron Lett. 1983; 24: 5873
  CrossrefSearch in Google Scholar
• 14a Biot N, Bonifazi D. Chem. Eur. J. 2018; 24: 5439
  CrossrefPubMedSearch in Google Scholar
• 14b Romito D, Biot N, Babudri F, Bonifazi D. New J. Chem. 2020; 44: 6732
  CrossrefSearch in Google Scholar
• 14c Biot N, Romito D, Bonifazi D. Cryst. Growth Des. 2021; 21: 536
  CrossrefPubMedSearch in Google Scholar
• 15 Kremer A, Fermi A, Biot N, Wouters J, Bonifazi D. Chem. Eur. J. 2016; 22: 5665
  CrossrefPubMedSearch in Google Scholar
• 16a Cozzolino AF, Elder PJ. W, Vargas-Baca I. Coord. Chem. Rev. 2011; 255: 1426
  CrossrefSearch in Google Scholar
• 16b Mahmudov KT, Kopylovich MN, da Silva MF. C. G, Pombeiro AJ. Dalton Trans. 2017; 46: 10121
  CrossrefPubMedSearch in Google Scholar
• 16c Benz S, López-Andarias J, Mareda J, Sakai N, Matile S. Angew. Chem. Int. Ed. 2017; 56: 812
  CrossrefPubMedSearch in Google Scholar
• 16d Vogel L, Wonner P, Huber SM. Angew. Chem. Int. Ed. 2019; 58: 1880
  CrossrefPubMedSearch in Google Scholar
• 16e Scilabra P, Terraneo G, Resnati G. Acc. Chem. Res. 2019; 52: 1313
  CrossrefPubMedSearch in Google Scholar
• 16f Ho PC, Wang JZ, Meloni F, Vargas-Baca I. Coord. Chem. Rev. 2020; 422: 213464
  CrossrefSearch in Google Scholar
• 16g Biot N, Bonifazi D. Coord. Chem. Rev. 2020; 413: 213243
  CrossrefSearch in Google Scholar
• 17 Davis R, Saleesh Kumar N, Abraham S, Suresh C, Rath NP, Tamaoki N, Das S. J. Phys. Chem. C 2008; 112: 2137
  CrossrefSearch in Google Scholar
• 18 Garrett GE, Gibson GL, Straus RN, Seferos DS, Taylor MS. J. Am. Chem. Soc. 2015; 137: 4126
  CrossrefPubMedSearch in Google Scholar

• Supplementary Material