The electrochemical behavior of the N-heterocyclic carbene bisphenolate complex of nickel(ii) Ni(L)Py (L – 1,3-bis(3,5-di-tert-butyl-2-phenolato)-5,5-dimethyl-(4,6-dihydropyrimidin-2-ylidene)) was studied using cyclic voltammetry and EPR spectroelectrochemistry. According to the obtained experimental data supplemented by quantum chemical calculations, the electrochemical properties of this complex differ significantly from those of its benzimidazolylidene and imidazolylidene analogs. The oxidation of the Ni(L)Py complex is a ligand-centered process, and the phenoxyl radical group formed is susceptible to decoordination and interaction with the NHC-fragment of the complex to form benzoxazole, the crystal structure of which was determined by X-ray diffraction.

The nickel(II) complex Ni(L)Py (I) (L is 1,3-bis(3,5-di-tert-butyl-2-phenolato)-5,5-dimethyl-(4,6-dihydropyrimidin-2-ylidene)) containing the dianionic bonded N-heterocyclic carbene (NHC) bis(phenolate) ligand is synthesized. In the presence of a stronger base (4-dimethylaminopyridine (DMAP)), the exchange reaction occurs with the replacement of pyridine in complex I by the DMAP molecule to form complex Ni(L)(DMAP) (II), the crystal structure of which is determined by XRD. The synthesized compounds are characterized by elemental analysis, mass spectrometry, and NMR spectroscopy. The spectral characteristics of the compounds are studied.

Our study compares the structural, photophysical, and electrochemical characteristics of 3,4,5- triphenyl-1-neomenthyl-1,2-diphosphole (1) and 3,4,5-triphenyl-1-mesityl-1,2-diphosphole (2). Experimental and optimized geometries of 1-R-1,2-diphospholes are close to each other and imply a significant delocalization within the 1,2-diphosphole ring for both molecules. Both compounds exhibit a green solid-state emission, whereas the DCM solutions are non-emissive. The preliminary electrochemical oxidation followed by electrochemical reduction leads to the anion-radical paramagnetic form, which is stable for 1-aryl-1,2-diphosphole, but unstable for 1-alkyl-1,2-diphosphole. The radical nature of 2(center dot-) was confirmed by in situ EPR-spectroelectrochemistry along with DFT calculations and in situ UV/Vis-spectroelectrochemistry.

The reaction of [NiBr(aryl)(bpy)] organonickel complexes with sodium 1,2-diphospholide leads to unknown 1-aryl-1,2-diphospholes by aryl group transfer.

A novel organonickel sigma-complex [NiBr(Tcpp)(bpy)], where Tcpp is 2,4,6-tricyclopentylphenyl, bpy is 2,2'-bipyridine has been generated in solution by electrochemical macroscale synthesis. The monitoring of the macroscale electrosynthesis and also the cyclic voltammetric measurements have shown that the organonickel sigma-complex is formed at the electrolysis but, in contrast to its analogues with ortho -substituted aromatic fragments, is unstable and decomposes to the homo-coupling product, namely, the earlier unknown sterically hindered biaryl derivative 2,2',4,4',6,6'-hexacyclopentyl-1,1'-biphenyl, the molecular and crystal structure of which are described by NMR spectroscopy and X-ray diffraction techniques.

An Erratum to this paper has been published: https://doi.org/10.1134/S1023193524010087

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The reaction of 3,3',5,5'-tetrabromo-4,4'-bipyridine (BrBipy) with cobalt nitrate and terephthalic acid (H2Bdc) gave 2D and 3D metal-organic frameworks {[Co2(Bdc)2(BrBipy)2(H2O)4] · 4DMF} (I) and {[Co2(Ddc)4(BrDipy)] · · 2MeOH} (II), respectively. The structure of the complexes was studied by X-ray diffraction (CCDC nos. 2259216 (I) and 2259214) (II)).

The electrochemical behavior of tetra-4-[4-(2,4,5-trichlorophenoxy)]phthalocyaninates of cobalt(II) (CoPc) and copper(II) (CuPc) in N,N-dimethylformamide with 0.1 M nBu4NBF4 as a supporting electrolyte is studied by cyclic voltammetry. It is shown experimentally that both metal complexes are capable of irreversible reduction. In this case, the reverse CV-scan for CoPc demonstrates an oxidation peak which is absent in the anodic scan and corresponds to the cathodic reaction product. The metal complexes themselves are not oxidized under these conditions.

The interaction between (PNP)PdH (1); PNP = bis(2-diisopropylphosphino-4-methylphenyl)amide and different acids (CF3SO3H, HBF4∙Et2O, fluorinated alcohols and formic acid) was studied in benzene or toluene as well as in neat alcohols by IR and NMR spectroscopies. The structures of hydrogen-bonded complexes were also optimized at the DFT/ωB97-XD/def2-TZVP level. The nitrogen atom of the amidophosphine pincer ligand readily accepts proton not only from strong Brønsted acids but from relatively weak fluorinated alcohols. That suggests that binding to palladium(II) increases the diarylamine basicity, making it a strong base. Nevertheless, H+ can be taken from [(PN(H)P)PdH]+ (2) by pyridine or hexamethylphosphoramide (HMPA). These observations confirm the need for a shuttle base to form [(PN(H)P)PdH]+ (2) as the result of the heterolytic splitting of H2 by [(PNP)Pd]+. At that, a stoichiometric amount of formic acid protonates a hydride ligand yielding an unstable η2-H2 complex that rapidly converts into formate (PNP)Pd(OCHO), which loses CO2 to restore (PNP)PdH, whereas the relatively high acid excess hampers this reaction through competitive protonation at nitrogen atom.

New bis-chelate cobalt(II) complex [Co(DPG) 2 (DMF) 2 ] ( 1 ), where DPG is N -(2,5-bis(methoxycarbonyl)phenyl)-α-diphenylphosphorylglycinate, has been prepared and characterized. The complex is the first example of cobalt complex containing phosphorylated derivative of α-amino acid. Octahedral coordination geometry of the cobalt complex 1 has been determined by X-ray diffraction. Electrochemical reduction of the obtained complex has been found to be irreversible two-electron process ( E_p^red = –1.70 V vs Ag/AgNO 3 , 1 × 10 –2 М in CH 3 CN), resulting in formation of cobalt metal adsorbed on the surface of working electrode.

The low-stable organonickel sigma-complex (2,2'-bipyridyl)bromo(2,4,6-tricyclopentylphenyl)nickel(II) [NiBr(Tcpp)(bpy)] was obtained by a modified procedure of preparative electrochemical synthesis and isolation. The crystal structure of the resulting organonickel complex was determined by the X-ray diffraction method. Its structure was compared with that of its more stable analogue [NiBr(Tchp)(bpy)], where Tchp is 2,4,6-tricyclohexylphenyl. It was found that a more efficient network of intermolecular interactions is formed in the [NiBr(Tchp)(bpy)] crystal, which is responsible for its higher stability, whereas [NiBr(Tcpp)(bpy)] is more likely to enter into an equilibrium Schlenk reaction, leading to its decomposition.

An Erratum to this paper has been published: https://doi.org/10.1134/S0022476623010080

The hydride ion transfer and proton transfer are the key steps in the reactions of (de)hydrogenation, dehydrocoupling, production of H 2 , and reduction of CO 2 with the participation of transition metal hydrides; complexes with bifunctional ligands often act as catalysts for these transformations. The aim of this work was to study the hydride-donating properties of pincer palladium(II) hydride (PNP)PdH ( 1 ; PNP is bis(2-diisopropylphosphino-4-methylphenyl)amide). For this purpose, its reaction with Lewis acids (BF 3 ·Et 2 O, B(C 6 F 5 ) 3 ) was studied using IR and NMR spectroscopies combined with quantum chemical calculations (DFT/M06/def2-TZVP). Correlations between electrochemical reduction potentials of the corresponding cations and thermodynamic hydridity of the metal hydrides proposed in the literature were also applied. [(PNP)Pd(MeCN)][BF 4 ] undergoes an irreversible two-electron reduction in acetonitrile ( E_p^ = –1.82 V). The use of the obtained potential in correlations gives an overestimated value of the hydride donating ability Δ G_H^-^^∘. It was found that the reaction of 1 with boron-containing Lewis acids unexpectedly leads to the protonation of the nitrogen atom of the pincer ligand with an impurity of water, rather than the reaction with the hydride ligand. According to DFT calculations, the proton affinity of the nitrogen atom is much higher than that of PdH, which determines its higher activity in protonation processes.

Ключевыми стадиями реакций (де)гидрирования, дегидросочетания, получения H 2 , восстановления CO 2 с участием гидридов переходных металлов являются перенос гидрид-иона и перенос протона, а катализаторами данных превращений часто выступают комплексы с бифункциональными лигандами. Целью настоящей работы было исследование гидридодонорных свойств пинцетного гидрида палладия(II) (PNP)PdH ( 1 ; PNP = бис (2-диизопропилфосфино-4-метилфенил)амид). Для этого методами ИК- и ЯМР-спектроскопии исследовано его взаимодействие с кислотами Льюиса (BF 3 · Et 2 O, B(C 6 F 5 ) 3 ) с привлечением квантово-химических расчетов (DFT/M06/def2-TZVP), а также использованы предложенные в литературе корреляции потенциалов электрохимического восстановления соответствующих катионов с термодинамической гидридностью. [(PNP)Pd(MeCN)][BF 4 ] претерпевает необратимое двухэлектронное восстановление в ацетонитриле ( \(E_{p}^{{{\text{red}}}}\) = –1.82 В). Для полученного потенциала корреляции дают завышенное значение гидридодонорной способности \(\Delta G_{{{{{\text{H}}}^{--}}}}^{^\circ }.\) Установлено, что реакция 1 с борсодержащими кислотами Льюиса неожиданно приводит к протонированию атома азота пинцетного лиганда примесью воды, а не к взаимодействию с гидридным лигандом. По данным DFT-расчетов, сродство к протону атома азота значительно выше, чем PdH, что обусловливает его более высокую активность в процессах протонирования.

Получен и охарактеризован новый бисхелатный комплекс кобальта (II) [Co(DPG) 2 (DMF) 2 ] ( 1 ), где DPG – N -(2,5- бис (метоксикарбонил)фенил)-α-дифенилфосфорилглицинат, являющийся первым примером комплекса кобальта, содержащего в своей структуре фосфорилированное производное α-аминокислоты. Методом рентгеновской дифракции определена октаэдрическая координационная геометрия комплекса кобальта 1 . Установлено, что электрохимическое восстановление полученного комплекса кобальта является необратимым двухэлектронным процессом ( E p red = –1.70 В отн. Ag/AgNO 3 , 1 × 10 –2 М в CH 3 CN), приводящим к образованию металлического кобальта, адсорбированного на поверхности рабочего электрода.

The organonickel σ-complex 2,3,4,5,6-pentamethylphenyl-nickel(II)-bromide-2,2′-bipyridine is synthesized electrochemically. This is the first example from a series of [NiBr(Aryl)(bpy)] complexes containing a meta-substituted aromatic moiety (Pmp is 2,3,4,5,6-pentamethylphenyl). The obtained compound is characterized in solution by 1H, 13С{1H}, and 1H13С{1H}–HSQC NMR and UV spectroscopy and ESI mass spectrometry. The crystal structure is determined by X-ray diffraction. The electrochemical properties of the complex are studied by cyclic voltammetry. It is found that in the DMF solution, a ligand exchange reaction occurs, resulting in the formation of a [Ni(Pmp)(bpy)(DMF)]+ derivative with elimination of the bromide anion. Similar cationic derivatives are active in catalytic processes of oligo- and polymerization of olefins, which indicates the importance of data obtained in this work for the development of the chemistry of nickel(II) organometallic complexes.

Электрохимически синтезирован никельорганический сигма-комплекс 2,3,4,5,6-пентаметилфенил-никель(II)-бромид-2,2'-бипиридил, являющийся первым примером из серии комплексов [NiBr(Aryl)(bpy)], содержащим мета-замещенный ароматический фрагмент (Pmp - 2,3,4,5,6-пентаметилфенил). Полученное соединение охарактеризовано в растворе методами 1H, 13С{1H} и 1H13С{1H}–HSQC ЯМР и УФ–спектроскопии и ИЭР масс-спектрометрии. Кристаллическая структура определена методом рентгеновской дифракции. Электрохимические свойства комплекса исследованы с помощью циклической вольтамперометрии. Обнаружено, что в растворе ДМФА происходит реакция лигандного обмена, приводящая к образованию производного [Ni(Pmp)(bpy)(DMF)]+ с элиминированием бромид-аниона. Подобные катионные производные являются активными в каталитических процессах олиго- и полимеризации олефинов, что свидетельствует о важности полученных в настоящей работе данных для развития химии металлоорганических комплексов никеля (II).

The ability of a series of 20 halogen-substituted aromatic di-, tri-, and tetracarboxylic acids and 14 halogenated derivatives of 4,4′-bipyridyl to form a halogen bond is estimated by quantum chemical calculations. The comparison of surface electrostatic potentials provides the rational selection of building blocks to obtain the respective porous materials, in particular, metal-organic frameworks and porous organic salts.