Annotation of the results obtained in 2021
During the implementation of the second stage of the project, in accordance with the general work plan, studies were carried out in the following areas: - Obtaining polyfunctional nitrogen-containing ligands; - Synthesis of new isocyanide complexes of palladium and platinum containing polyfunctional nitrogen-containing ligands; - Study of the influence of non-covalent interactions in polyfunctional nitrogen-containing ligands and synthesized complexes on their structure and properties. A number of specific tasks were solved: - Synthesis of new polyfunctional nitrogen-containing ligands - N-pyridinyl carbamates and carbene/isocyanide complexes of Pd(II) and Pt(II) based on them. - Determination of the halide ligand influence in binuclear palladium complexes on the structure of the complexes. - Expansion of the line of cyclometallated complexes of palladium(II) and platinum(II) with deprotonated diaminocarbene ligands based on N-hetarylureas. - Study of supramolecular oligmerization of diaminocarbene/isocyanide complexes of platinum(II). - Synthesis of binuclear diaminocarbene/isocyanide complexes of platinum(II). - Assessment of the catalytic activity of the palladium(II) complexes synthesized in the course of the project. - Assessment of the catalytic activity of the platinum(II) complexes synthesized in the course of the project. In the course of the work, the following scientific results were obtained: - Developed safe and environmentally friendly synthesis of pyridin-2-yl- and quinolin-2-yl-substituted alkyl carbamates based on alcoholysis of various pyridin-2-yl- and quinolin-2-yl-substituted ureas with a wide range of primary, secondary and tertiary alcohols. This method compares favorably with the existing protocols for the preparation of hetaryl carbamates in that it does not require the addition of transition metal complexes, avoids the use of chloroformates or gaseous CO, and also uses relatively readily available dialkyl hetaryl ureas. An additional important advantage of the developed method is that the reaction proceeds without a catalyst. In this reaction, alcohols are both reagents and solvents. As a rule, no by-products are formed in the reaction; the selectivity of obtaining most of the studied carbamates is more than 99%. The proposed method is suitable for the synthesis in good or high yield of a wide range of substituted pyridin-2-yl- and quinolin-2-yl-alkyl carbamates with electron-donor or electron-withdrawing groups in any position of the hetaryl ring and containing various primary, secondary and even tertiary alkyl substituents at the atom oxygen. Calculation by the DFT method and experimental study showed that the reaction proceeds through the intermediate formation of hetaryl isocyanates. The data obtained make it possible to consider the hetarylureas studied in this work as "masked" isocyanates. - It has been demonstrated that the resulting azin-2-yl-substituted alkyl carbamates can act as nucleophiles in a metal-promoted reaction with coordinated isocyanides. As a result, depending on the metal center and reaction conditions, both mono- and binuclear complexes of palladium(II) and platinum(II) with carbene and deprotonated carbene ligands can form. - It was found that a change in the nature of halogen strongly affects the position of regioisomeric equilibrium in binuclear palladium complexes B'/A' with annelated metal rings, which include a diaminocarbene fragment. The iodide ligand, which is the weakest acceptor of the chalcogen bond in the chlorine/bromine/iodine series, causes the greatest shift in equilibrium towards the formation of a form in which this bond is replaced by a chalcogen bond with a nitrogen atom. Thus, additional evidence has been obtained that the position of this equilibrium is determined precisely by the energy of the chalcogenic bond. - The boundaries of the method developed during the previous stage of the project for the synthesis of cyclometallic complexes of platinum metals containing condensed azaheterocycle in the composition of the deprotonated diaminocarbene fragment were determined. A platinum complex has been synthesized, exhibiting interesting photophysical properties. This indicates that the deprotonated diaminocarbene linker does not interfere with the possibility of charge transfer from the metal to the ligand (MLCT), which means that it can be used to obtain a new type of luminescent platinum(II) complexes. - The possibility of the formation of macrocyclic tetranuclear metalcycles as a result of association in solution of mononuclear C,S-chelated deprotonated diaminocarbene platinum complexes in the presence of a base was found. - It was shown that the interaction of the bis-(xylylisocyanide) complex of Pt(II) with substituted 1,3-thiazole- and 1,3,4-thiadiazol-2-amines leads to the formation of binuclear platinum complexes, which contain two annelated metal rings. Annelation is carried out by the formation of a diaminocarbene moiety common to the metalcycles. These complexes are formed in the form of regioisomeric mixtures, and the kinetic product is isomerized into the thermodynamic one at an insignificant rate, which in some cases makes it possible to study the regioisomers separately. The relative thermodynamic stability of regioisomers, as in the case of palladium analogs, is due to different energies of chalcogenic bonds. - It has been demonstrated that the palladium(II) complexes 4(M = Pd) and 5(M = Pd) synthesized during this stage exhibit a certain catalytic activity in the Suzuki reaction. It is noteworthy that for both complexes, TON is almost the same and amounts to 102 for the interaction of 4-bromoanisole (2·102 for 4-bromotoluene) and phenylboronic acid in boiling ethanol in the presence of potash. The identical catalytic activity of these two complexes of different structures suggests that, under the reaction conditions, complex 4(M = Pd) quickly transforms into 5(M = Pd), or both of them are precursors of the same true catalyst. At the same time, both studied complexes are practically inactive in the Sonogashira copperless reaction. - It was found that all studied C,N-chelated deprotonated diaminocarbene complexes of platinum with an azine fragment (complex 7 and its analogs) catalyze the hydrosilylation of PDMS-v and PDMS-co-PMGS at temperatures above 80 °C and exhibit similar catalytic activity. The optimal range of catalyst concentrations is 10–3–10–4 mol/L. The use of complex 7 in this case leads to the production of silicone rubbers with significant luminescence (λem = 534 and 574 nm, quantum yield 4%), apparently associated with the presence of platinum catalyst particles in their composition. Heating these silicone rubbers to 120 °C causes this luminescence to disappear. This means that complex 7 can be used to obtain silicone materials with irreversible thermoregulated luminescence. https://dx.doi.org/10.1021/acsapm.0c01190 https://doi.org/10.1039/D1OB00783A https://doi.org/10.1039/d0nj05386d https://doi.org/10.1039/D1DT02823E

 

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Annotation of the results obtained in 2019
During the implementation of the first phase of the project, in accordance with the general work plan, studies were carried out in the following areas: - Obtaining multifunctional nitrogen-containing ligands; - Synthesis of new isocyanide complexes of palladium and platinum, containing polyfunctional nitrogen-containing ligands; - Study of the effect of non-covalent interactions in the synthesized complexes on their structure and properties. A number of specific tasks were solved: Task 1. Obtaining bis-(isocyanide) ligands. Task 2. Obtaining bis-hydrazide ligands. Task 3. Synthesis of new multifunctional nitrogen-containing ligands with a pharmaceutically privileged periphery — N-pyridinylureas containing an oxadiazole fragment — and palladium carbene complexes based on them. Task 4. Synthesis and study of the structural features of the palladium(II) complex with a substituted terpyridine ligand as a precursor in the reaction of obtaining binuclear complexes with bis(isocyanide) linkers. Task 5. Obtaining C,N-chelated palladium(II) carbene complexes with a 2-aminobenzo[d]thiazole fragment and studying their catalytic properties and biological activity. In the course of the work, the following scientific results were obtained: - Experimental testing of possible approaches to the preparation of bridged bis-isocyanide ligands was carried out. It is shown that the best approach is based on the functional conversion of aromatic diamines to diisocyanides. A 1,4-diisocyanobenzene sample has been accumulated for further research; - The methodology for the synthesis of bis-carbohydrazides was developed and samples of 5 different bis-carbohydrazides were synthesised for use as polynucleophiles in the preparation of bridged bis-carbene ligands. - It was shown that pyridine-N-oxides bearing a pharmacophore oxadiazole group can be C–H functionalized by an acid-catalyzed reaction with dialkyl cyanamides, allowing the synthesis of previously undescribed 2-aminopyridines: N-(pyridin-2-yl) ureas containing an oxadiazole moiety. Atom economy, environmental friendliness, ease of processing, as well as scalability are the main advantages of the applied procedure. The possibility of using such compounds as polynucleophiles for the synthesis of chelated deprotonated carbene complexes of palladium has been demonstrated. - Using the example of a model compound — a palladium (II) complex with a substituted terpyridine ligand — a technique was developed for producing mononuclear complexes of platinum metals with a tridentate ligand. Unfortunately, this complex did not exhibit luminescent properties. However, a study of its crystalline structure revealed a number of interesting patterns. According to single crystal X-ray diffraction data Pd(II)-terpyridine complex [4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine]chloridopalladium(II) chloride crystallizes as double columns. Inside the columns planar complex species packed in layers located at a distance of 3.332(6) Å one from other and accomplished by lp−π and π−π interactions. Hydrogen bonds do not participate in the layer-to-layer interactions, but are responsible only for the horizontal binding of the columns. DFT calculations and topological analysis of the electron density distribution within the formalism of Bader’s theory (QTAIM method) confirmed that the layers are interconnected by lp−π and π−π interactions. The Pd, O, and Cl atoms provide their pairs of electrons for formation of lp−π contacts whose energy lies in the range 0.9–1.6 kcal/mol. Short contacts between some of the carbon and nitrogen atoms are the result of π−π interactions. The energy of each of these contacts (0.6 kcal/mol) is a bit lower than the one for lp−π interactions, but their greater number leads to a significant contribution of π−π interactions to the total binding energy. The fact that the metal atoms in the layers are shifted relative to each other, indicates dz2−π noncovalent bonds are more preferable than the Pd···Pd metal−metal interactions for this compound structure. - It was shown that the interaction of the bis-(cyclohexylisocyanide) complex of Pd(II) with substituted benzo[d]thiazole-2-amines in the presence of triethanolamine as the base leads to the formation of deprotonated C,N-chelate carbene complexes with a structure similar to that described previously for the reaction with unsubstituted benzo[d]thiazole-2-amine. The obtained complexes exhibit some catalytic activity in the Suzuki reaction (TON lies in the range 103–104 for the interaction of 4-bromoanisole and phenylboronic acid in boiling ethanol in the presence of K2CO3) and moderate antibacterial activity against the following microorganisms: bacteria E. coli, S. aureus, P. fluorescens, B. subtillis, and C. albicans fungi. One of the compounds (R1 / R2 = benzo, Scheme 7) showed selective ability to inhibit the growth of the studied strains of gram-positive bacteria, especially S. aureus (BMD 25 μg / ml), and can be recommended for further study and medical-chemical modification. https://doi.org/10.1016/j.molstruc.2019.126957 https://doi.org/10.1016/j.tetlet.2019.151108 https://link.springer.com/article/10.1134/S1070363219100128 http://mendeleev2019.ru/index.php/ru/

 

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Annotation of the results obtained in 2020
During the implementation of the second stage of the project, in accordance with the general work plan, studies were carried out in the following areas: - Obtaining polyfunctional nitrogen-containing ligands; - Synthesis of new isocyanide complexes of palladium and platinum containing polyfunctional nitrogen-containing ligands; - Study of the influence of non-covalent interactions in polyfunctional nitrogen-containing ligands and synthesized complexes on their structure and properties. A number of specific tasks were solved: Task 1. Study of methods for the synthesis of bis-(isocyanide) ligands; Task 2. Obtaining complexes of palladium(II) and platinum(II) with new polyfunctional nitrogen-containing ligands – N-pyridinylureas; Task 3. Synthesis of palladium(II) and platinum(II) complexes with diaminocarbene ligands based on N-pyridinylureas; Task 4. Study of the mechanism of binuclear palladium(II) complexes isomerization; Task 5. Study of the coupling of mercaptoazoles with isocyanide complexes of palladium(II) and platinum(II); Task 6. Synthesis of new polyfunctional ligands based on oxalic acid dithioamides; Task 7. Investigation of the influence of non-covalent interactions in isocyanides on their properties and crystal structure. In the course of the work, the following scientific results were obtained: - The study of possible approaches to the preparation of bridged bis-(isocyanide) ligands was continued. The possibility of obtaining bis-(isocyanide) containing a 1,2,4-oxadiazole bridge has been studied. It was found that for the successful completion of the last stage of the synthesis, the development of a new synthetic procedure for the dehydration of bis-(formamide) is required; - The method for the synthesis of palladium(II) complexes with new polyfunctional nitrogen-containing ligands (N-pyridinylureas) has been successfully tested and a sample of one of these complexes has been developed for further research; - The principal possibility of obtaining luminescent cyclometallated platinum(II) complexes containing N,N-dialkyl N'-(6-phenylpyridin-2-yl) urea fragment has been shown; - A procedure was developed for the synthesis of carbene complexes of platinum(II) with diaminocarbene ligands based on N-quinolinylureas and a sample of one of these complexes was developed for further research; - The mechanism of Pd(II) binuclear diaminocarbene complexes regioisomerization has been studied. It is shown that the regioisomerization is a first-order reaction, that is, it occurs intramolecularly. Based on kinetic studies, studying of the polar effect of substituents, the effect of a solvent, determination of activation parameters, and theoretical calculation, it was concluded that the rate-determining stage of the isomerization is the breaking of the carbon–nitrogen bond in the carbene fragment of the binuclear complex. Thus, a rare example of a dissociatively activated process of square planar complexes isomerization has been found; - Using the example of Pd(II)- and Pt(II)-mediated reaction of xylyl and mesityl isocyanides with N-methylimidazole- and N-methyltriazole-2-thiones, the addition of the endocyclic center of an ambident nucleophile to a coordinated isocyanide was first discovered. This reactivity of N-heterocyclic thiones opens a convenient way to obtain acyclic carbene and deprotonated carbene ligands with additional chelation with a thiolate sulfur atom; - The conditions of the modified Willgerodt–Kindler reaction were optimized. Using the developed technique, polyfunctional ligands were synthesized containing both N- and S-nucleophilic centers – dithiooxamides; - For the first time, halogen bonds were discovered with the participation of a carbon atom of the isocyano group, which acts as an acceptor of an XB in the solid state in co-crystals with perfluoroiodoarenes. The DFT calculations performed in combination with the topological analysis of the electron density distribution within the framework of the Bader theory (QTAIM method) showed an almost linear relationship between the distance I•••C and the energy of the XB with isocyanides, which ranges from 1.3–2.5 kcal/mol to 2.8–5.5 kcal/mol. According to the experimental and theoretical results, the formation of XBs with isocyanides is similar to coordination of an isocyanide to a metal center, which can be illustrated by a shift of the ν(C≡N) band in the IR spectra, a strong field shift of the isocyanocarbon signal in the 13C CP/MAS spectra, and the presence of the π-back bonding. It is important to note that co-crystallization or grinding of mesityl isocyanide with XB donors leads to a strong decrease in its specific odor. https://doi.org/10.1038/s41467-020-16748-x https://link.springer.com/article/10.1007/s10593-020-02737-x https://doi.org/10.1021/acs.cgd.9b01334 https://doi.org/10.1016/j.ica.2020.120012 https://doi.org/10.1134/S1070428020050097

 

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