Valence tautomeric interconversion of bis-dioxolene cobalt complex with imino-pyridine functionalized by TEMPO moiety in solid solutions with isostructural nickel analogue: phase transitions and monocrystal destruction.

Valence tautomeric complexes (VT) are promising systems for creating molecular devices. From this viewpoint, valence tautomeric complexes with a hysteresis loop on the magnetic curve are of special interest as potential memory elements. The hysteresis loop is a consequence of retarded structural rearrangements which investigation is an actual problem. Recently, we have described a new VT transition taking place in a bis-dioxolene cobalt complex with imino-pyridine having a TEMPO substituent (A. A. Zolotukhin, et al., Inorg. Chem., 2017, 56, 14751-14754). Valence tautomeric transformation occurs with a hysteresis loop and is accompanied by a phase transition. The phase transition taking place during cooling is accompanied by crystal destruction. This fact makes it impossible to monitor the structural changes responsible for the hysteresis loop. The current research attempts to resolve this problem. A nickel compound of the same composition (TEMPO-imino-pyridine)Ni(3,6-DBSQ)2 was synthesized and characterized. It was established to be isostructural with the cobalt complex. It was used as an inert matrix for the dilution of the VT cobalt complex. The number of solid solutions with Co/Ni ratios of 1 : 1, 1 : 2, 1 : 4, and 1 : 8 was obtained. Variable temperature magnetic susceptibility measurements show that VT transformation with a hysteresis loop takes place in all solid solutions. The hysteresis loop is shifted to low temperatures primarily due to the shifting of its low-temperature boundary with dilution. The hysteresis width does not change significantly with dilution. DSC detected that transformations are accompanied by phase transitions at different temperatures at cooling and heating. The phase transition at the first cooling occurs at slightly lower temperatures compared with subsequent cycles. These temperatures correspond to the transition temperatures detected from the magnetic curves. The phase transition during the first cooling is accompanied by crystal destruction. Physical destruction takes place in the crystals of all solid solutions. X-ray diffraction powder patterns confirm that phase transition is accompanied by considerable reorganization of the crystal structure typical for the first order transitions. The unit cell volume of solid solutions is larger than that of pure complexes. Especially calculated crystal invariom indicated that the "lattice energy" in a solid solution is the lowest compared with that in "pure" nickel and cobalt complexes.

Photoinitiated Rearrangement of Aromatic Azides to 2-Aminonicotinates.

This study describes a one-pot photoinduced method for azepine synthesis and their subsequent rearrangement into pyridines. The rearrangement of the azepine, formed during photolysis, occurs due to both thermal and photochemical activation of the reaction. This requires an electron-donating substituent at the second position of the azepine and an electron-withdrawing substituent at the third position of the azepine. A reaction mechanism has been proposed to explain the role of water and the nature of the azepine substituents.

Lanthanide Coordination Polymers with Soft-Base Ditopic Bisthiazolate Ligands.

In order to prepare the first lanthanide coordination polymers (CPs) based on ditopic sulfide ligands, benzo[1,2-d:4,5-d']bisthiazole-2,6(3H,7H)-dithione (H2L) was used as a linker. The reactions of lanthanide silylamides Ln[N(SiMe3)2]3 (Ln = Nd, Gd, Er, and Yb) with H2L result in the formation of soluble dimethyl sulfoxide (DMSO) ionic salts [Ln(DMSO)8][L]1.5 [Ln = Nd (1), Gd (2), Er (3), and Yb (4)]. Due to the lack of coordination of anionic ligands, compounds 1, 3, and 4 do not show sensitized metal-centered photoluminescence (PL), while Gd compound 2 shows weak phosphorescence at 77 K. It was found that the heating of 1 in a 1:9 DMSO/1,4-dioxane mixture leads to the formation of large crystals of 2D CP [Nd(DMSO)3L1.5·0.5diox]n (5), where deprotonated dithione H2L plays the role of a ditopic linker. This linker acts as an "antenna" in compound 5, providing an intense near-infrared (NIR) PL of Nd3+ ion upon near-UV and blue-light excitation. The application of a synthetic protocol similar to that of compounds 2-4 led to the formation of amorphous compounds [Ln(DMSO)3L1.5·0.5diox]n [Ln = Gd (6), Er (7), and Yb (8)], whose PL properties significantly differ from those of the parental ionic salts. In the case of Yb polymer 8, the PL excitation spectra are shifted to the red region due to a low-energy ligand-to-metal charge-transfer state. The synthesized compounds 5-8 are the first examples of lanthanide CPs using soft-base ditopic linkers in their structures.

Novel Rigidochromic and Anti-Kasha Dual Emission Fluorophores Based on D-π-A Dyads as the Promising Materials for Potential Applications Ranging from Optoelectronics and Optical Sensing to Biophotonics and Medicine.

Today we see an increasing demand for new fluorescent materials exhibiting various sensory abilities due to their broad applicability ranging from the construction of flexible devices to bioimaging. In this paper, we report on the new fluorescent pigments AntTCNE, PyrTCNE, and PerTCNE which consist of 3-5 fused aromatic rings substituted with tricyanoethylene fragments forming D-π-A diad. Our studies reveal that all three compounds exhibit pronounced rigidochromic properties, i.e., strong sensitivity of their fluorescence to the viscosity of the local environment. We also demonstrate that our new pigments belong to a very rare type of organic fluorophores which do not obey the well-known empirical Kasha'rule stating that photoluminescence transition always occurs from the lowest excited state of an emitting molecule. This rare spectral feature of our pigments is accompanied by an even rarer capability of spectrally and temporally well-resolved anti-Kasha dual emission (DE) from both higher and lowest electronic states in non-polar solvents. We show that among three new pigments, PerTCNE has significant potential as the medium-bandgap non-fullerene electron acceptor. Such materials are now highly demanded for indoor low-power electronics and portable devices for the Internet-of-Things. Additionally, we demonstrate that PyrTCNE has been successfully used as a structural unit in template assembling of the new cyanoarylporphyrazine framework with 4 D-π-A dyads framing this macrocycle (Pyr4CN4Pz). Similarly to its structural unit, Pyr4CN4Pz is also the anti-Kasha fluorophore, exhibiting intensive DE in viscous non-polar medium and polymer films, which strongly depends on the polarity of the local environment. Moreover, our studies showed high photodynamic activity of this new tetrapyrrole macrocycle which is combined with its unique sensory capacities (strong sensitivity of its fluorescent properties to the local environmental stimuli such as viscosity and polarity. Thus, Pyr4CN4Pz can be considered the first unique photosensitizer that potentially enables the real-time combination of photodynamic therapy and double-sensory approaches which is very important for modern biomedicine.

Charge Transfer Chromophores Derived from 3d-Row Transition Metal Complexes.

A series of new charge transfer (CT) chromophores of "α-diimine-MII-catecholate" type (where M is 3d-row transition metals-Cu, Ni, Co) were derived from 4,4'-di-tert-butyl-2,2'-bipyridyl and 3,6-di-tert-butyl-o-benzoquinone (3,6-DTBQ) in accordance with three modified synthetic approaches, which provide high yields of products. A square-planar molecular structure is inherent for monomeric [CuII(3,6-Cat)(bipytBu)]∙THF (1) and NiII(3,6-Cat)(bipytBu) (2) chromophores, while dimeric complex [CoII(3,6-Cat)(bipytBu)]2∙toluene (3) units two substantially distorted heteroleptic D-MII-A (where D, M, A are donor, metal and acceptor, respectively) parts through a donation of oxygen atoms from catecholate dianions. Chromophores 1-3 undergo an effective photoinduced intramolecular charge transfer (λ = 500-715 nm, extinction coefficient up to 104 M-1·cm-1) with a concomitant generation of a less polar excited species, the energy of which is a finely sensitive towards solvent polarity, ensuring a pronounced negative solvatochromic effect. Special attention was paid to energetic characteristics for CT and interacting HOMO/LUMO orbitals that were explored by a synergy of UV-vis-NIR spectroscopy, cyclic voltammetry, and DFT study. The current work sheds light on the dependence of CT peculiarities on the nature of metal centers from various groups of the periodic law. Moreover, the "α-diimine-MII-catecholate" CT chromophores on the base of "late" transition elements with differences in d-level's electronic structure were compared for the first time.

Binuclear Triphenylantimony(V) Catecholates through N-Donor Linkers: Structural Features and Redox Properties.

A series of binuclear triphenylantimony(V) bis-catecholato complexes 1-11 of the type (Cat)Ph3Sb-linker-SbPh3(Cat) was prepared by a reaction of the corresponding mononuclear catecholates (Cat)SbPh3 with a neutral bidentate donor linker ligands pyrazine (Pyr), 4,4'-dipyridyl (Bipy), bis-(pyridine-4-yl)-disulfide (PySSPy), and diazobicyclo[2,2,2]octane (DABCO) in a dry toluene: Cat = 3,6-di-tert-butyl-catecholate (3,6-DBCat), linker = Pyr (1); PySSPy (2); Bipy (3); DABCO (4); Cat = 3,5-di-tert-butyl-catecholate (3,5-DBCat), linker = Bipy (5); DABCO (9); Cat = 4,5-(piperazine-1,4-diyl)-3,6-di-tert-butylcatecholate (pip-3,6-DBCat), linker = Bipy (6); DABCO (10); Cat = 4,5-dichloro-3,6-di-tert-butylcatecholate (4,5-Cl2-3,6-DBCat), linker = Bipy (7); DABCO (11); and Cat = 4,5-dimethoxy-3,6-di-tert-butylcatecholate (4,5-(MeO)2-3,6-DBCat), linker = Bipy (8). The same reaction of (4,5-Cl2-3,6-DBCat)SbPh3 with DABCO in an open atmosphere results in a formation of 1D coordination polymer {[(4,5-Cl2-3,6-DBCat)SbPh3·H2O]·DABCO}n (12). Bis-catecholate complex Ph3Sb(Cat-Spiro-Cat)SbPh3 reacts with Bipy as 1:1 yielding a rare macrocyclic tetranuclear compound {Ph3Sb(Cat-Spiro-Cat)SbPh3∙(Bipy)}2 (13). The molecular structures of 1, 3, 4, 5, 8, 10, 12, and 13 in crystal state were established by single-crystal X-ray analysis. Complexes demonstrate different types of relative spatial positions of mononuclear moieties. The nature of chemical bonds, charges distribution, and the energy of Sb...N interaction were investigated in the example of complex 5. The electrochemical behavior of the complexes depends on the coordinated N-donor ligand. The coordination of pyrazine, Bipy, and PySSPy at the antimony atom changes their mechanism of electrooxidation: instead of two successive redox stages Cat/SQ and SQ/Cat, one multielectron stage was observed. The coordination of the DABCO ligand is accompanied by a significant shift in the oxidation potentials of the catecholate ligand to the cathodic region (by 0.4 V), compared to the initial complex.

N-Heterocyclic Carbene-Coordinated M(II) (M = Yb, Sm, Ca) Bisamides: Expanding the Limits of Intermolecular Alkene Hydrophosphination.

A series of NHC-stabilized amido compounds (NHC)nM[N(SiMe3)2]2 (M = Yb(II), Sm(II), Ca(II); n = 1, 2) showed remarkable catalytic efficiency in addition of PhPH2 and PH3 to alkenes under mild conditions and low catalyst loading. The effect of σ-donor capacity of NHCs on catalytic activity in hydrophosphination of styrene with PhPH2 and PH3 was revealed. For the series of three-coordinate complexes 1-4M, a tendency to increase the catalytic activity with growth of σ-donating strength of the carbene ligand was clearly demonstrated. The complex (NHC)2Sm[N(SiMe3)2]2 (NHC = 1,3-diisopropyl-2H-imidazole-2-ylidene) (5Sm) proved to be the most efficient catalyst, which enabled hardly realizable transformations such as PhPH2 addition across internal C═C bonds of norbornene and cis- and trans-stilbenes, providing the highest reaction rate for addition of PH3 to styrene. Excellent regio- and chemoselectivities of alkylation of PH3 with styrenes allow for a selective and good-yield synthesis of desired organophosphines─either primary, secondary, or tertiary. Stepwise alkylation of PH3 with various substituted styrenes can be efficiently applied as an approach to nonsymmetric secondary phosphines. The rate equation of the addition of styrene to PH3 promoted by 5Sm was found: rate = k[styrene]1[5Sm]1.

Synthesis and Antioxidant Activity of New Catechol Thioethers with the Methylene Linker.

Novel catechol thio-ethers with different heterocyclic substituents at sulfur atom were prepared by reacting 3,5-di-tert-butyl-6-methoxymethylcatechol with functionalized thiols under acidic conditions. A common feature of compounds is a methylene bridge between the catechol ring and thioether group. Two catechols with the thio-ether group, bound directly to the catechol ring, were also considered to assess the effect of the methylene linker on the antioxidant properties. The crystal structures of thio-ethers with benzo-thiazole moieties were established by single-crystal X-ray analysis. The radical scavenging and antioxidant activities were determined using 2,2'-diphenyl-1-picrylhydrazyl radical test, ABTS∙+, CUPRAC (TEAC) assays, the reaction with superoxide radical anion generated by xanthine oxidase (NBT assay), the oxidative damage of the DNA, and the process of lipid peroxidation of rat liver (Wistar) homogenates in vitro. Most catechol-thioethers exhibit the antioxidant effect, which varies from mild to moderate depending on the model system. The dual anti/prooxidant activity characterizes compounds with adamantyl or thio-phenol substituent at the sulfur atom. Catechol thio-ethers containing heterocyclic groups (thiazole, thiazoline, benzo-thiazole, benzo-xazole) can be considered effective antioxidants with cytoprotective properties. These compounds can protect molecules of DNA and lipids from the different radical species.

Sc and Y bis(alkyl) complexes supported by bidentate and tridentate amidinate ligands. Synthesis, structure and catalytic activity in polymerization of isoprene and 1-heptene.

A series of bis(alkyl) complexes {(tBu)C[N(2,6-Me2C6H3)]2}Ln(CH2SiMe3)2(THF)n (Ln = Y, n = 1 (1); Ln = Sc, n = 1 (2)), {2-[Ph2P(O)]C6H4NC(tBu)N(2,6-Me2C6H3)}Sc(CH2SiMe3)2 (3), {2-[Ph2P(NPh)]C6H4NC(tBu)N(2,6-Me2C6H3)}Sc(CH2SiMe3)2 (4) coordinated by bidentate (N,N) and tridentate (N,N,O; N,N,N) amidinate ligands are synthesized using an alkane elimination approach. Yttrium complex 1 demonstrated a half-life of ∼2.5 days at room temperature in benzene-D6 (C6D6) solution, whereas scandium complexes proved to be much more stable (25 d (2), 30 d (3) and 42 d (4)). Complexes 1-4 as a part of ternary catalytic systems 1-4/TB, HNB/AlR3 (AlR3 = AliBu3, AliBu2H; TB = [Ph3C][B(C6F5)4], HNB = [PhNHMe2][B(C6F5)4]) demonstrated high catalytic activity in isoprene polymerization and enable 80%-100% conversion of 1000 equivalents of monomer into polymer at 25 °C within 3-180 min. The isolated polyisoprenes feature predominantly cis-1,4-regularity (69.2%-87.3%) and polydispersities Mw/Mn = 2.26-8.92. Moreover, the binary (2/TB) and ternary (1-4/TB/10 AliBu3) systems initiate 1-heptene polymerization providing 40%-100% conversion of 500 equivalents of monomer in 24 h at 25 °C giving polymer samples with Mn = 1.55-190.2 × 103 and Mw/Mn = 1.55-3.87.

2-Imino-2,3-dihydrobenzoxazole-a useful platform for designing rare- and alkaline earth complexes with variable di- and trianionic O,N,N, ligands.

The reactions of 2-imino-2,3-dihydrobenzoxazole LH with M[N(SiMe3)2]2(THF)2 (M = Yb and Ca) and Y(CH2SiMe3)3(THF)2 proceed with the opening of the dihydrobenzoxazole ring and the elimination of HN(SiMe3)2 or SiMe4. Besides, in the case of Yb[N(SiMe3)2]2(THF)2, an electron transfer from Yb(II) to L takes place and Yb(III) complex 1 is coordinated by a dianionic phenolate ligand containing a pendant radical-anionic diazabutadiene fragment form. When LH is reacted with Ca[N(SiMe3)2]2(THF)2, C-H bond activation of a methyl fragment by imino nitrogen occurs and affords a dimeric calcium complex 2. In 2, the phenolate ligand is dianionic due to the presence of the amido-imino fragment [R-NC(CH3)-C(CH2)-NR']- (R = 2,4-tBu2-C6H2O; R' = 2,6-iPr2C6H3). In situ generated ate-complex {Na(Et2O)n}{Ca[N(SiMe3)2]3} also enables C-H bond activation, however the dianionic phenolate ligand in the resulting complex 3 contains an amido-imino fragment [R-N-C(CH2)-C(CH3)NR']- featuring the sequence of N-C and NC bonds opposite to that in 2. The reaction of Y(CH2SiMe3)3(THF)2 with LH affords mono(alkyl) yttrium complex 4. 4 contains a dianionic amido-imino phenolate ligand resulting from the migration of one alkyl group to the CN bond [R-N-C(Me)(CH2SiMe3)-C(Me)NR']. 4 undergoes slow intramolecular C-H bond activation of the residual CH3 group to afford a yttrium complex coordinated by a trianionic diamido-phenolate ligand [R-N-C(Me)(CH2SiMe3)-C(CH2)NR'].

Luminescence thermochromism in novel mixed Eu(II)-Cu(I) iodide.

A new mixed Eu(II)-Cu(I) iodide [Eu(DME)4][Cu2I4] (1) was synthesized by the reaction of an organosulphide salt of Eu(II) and CuI in DME media. X-ray analysis revealed that 1 is an ate-complex consisting of Eu(DME)4 dications and tetraiododicuprate dianions. Upon UV light excitation (λ = 365 nm), the compound exhibits intense double-peaked photoluminescence (PL) at 445 and 500 nm. The relative intensity of these peaks changes dramatically when the temperature changes in the range of 180-250 K. To understand the nature of the found PL thermochromism, the structure and time-resolved PL of 1 were studied at various temperatures. The time-resolved PL studies of 1 at various temperatures revealed the presence of two luminescent centers which are excited by the capture of an electron from the conduction band. The ratio of intensities at 445 and 500 nm (R = I445/I500) in the PL spectra of 1 changes by almost two orders of magnitude and the relative sensitivity S (S = (∂R/∂T)/R) exceeds 5% per K in the range of 190-245 K that makes this compound a promising luminescent thermometer for the range where ammonia exists in a liquid state.

Novel Oxidovanadium Complexes with Redox-Active R-Mian and R-Bian Ligands: Synthesis, Structure, Redox and Catalytic Properties.

A new monoiminoacenaphthenone 3,5-(CF3)2C6H3-mian (complex 2) was synthesized and further exploited, along with the already known monoiminoacenaphthenone dpp-mian, to obtain oxidovanadium(IV) complexes [VOCl2(dpp-mian)(CH3CN)] (3) and [VOCl(3,5-(CF3)2C6H3-bian)(H2O)][VOCl3(3,5-(CF3)2C6H3-bian)]·2.85DME (4) from [VOCl2(CH3CN)2(H2O)] (1) or [VCl3(THF)3]. The structure of all compounds was determined using X-ray structural analysis. The vanadium atom in these structures has an octahedral coordination environment. Complex 4 has an unexpected structure. Firstly, it contains 3,5-(CF3)2C6H3-bian instead of 3,5-(CF3)2C6H3-mian. Secondly, it has a binuclear structure, in contrast to 3, in which two oxovanadium parts are linked to each other through V=O···V interaction. This interaction is non-covalent in origin, according to DFT calculations. In structures 2 and 3, non-covalent π-π staking interactions between acenaphthene moieties of the neighboring molecules (distances are 3.36-3.40 Å) with an estimated energy of 3 kcal/mol were also found. The redox properties of the obtained compounds were studied using cyclic voltammetry in solution. In all cases, the reduction processes initiated by the redox-active nature of the mian or bian ligand were identified. The paramagnetic nature of complexes 3 and 4 has been proven by EPR spectroscopy. Complexes 3 and 4 exhibited high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The yields of products of cyclohexane oxidation were 43% (complex 3) and 27% (complex 4). Based on the data regarding the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play the most crucial role in the reaction. The initial products in the reactions with alkanes are alkyl hydroperoxides, which are easily reduced to their corresponding alcohols by the action of triphenylphosphine (PPh3). According to the DFT calculations, the difference in the catalytic activity of 3 and 4 is most likely associated with a different mechanism for the generation of ●OH radicals. For complex 4 with electron-withdrawing CF3 substituents at the diimine ligand, an alternative mechanism, different from Fenton's and involving a redox-active ligand, is assumed.

Triphenylantimony(V) Catecholates of the Type (3-RS-4,6-DBCat)SbPh3-Catechol Thioether Derivatives: Structure, Electrochemical Properties, and Antiradical Activity.

A new series of triphenylantimony(V) 3-alkylthio/arylthio-substituted 4,6-di-tert-butylcatecholates of the type (3-RS-4,6-DBCat)SbPh3, where R = n-butyl (1), n-hexyl (2), n-octyl (3), cyclopentyl (4), cyclohexyl (5), benzyl (6), phenyl (7), and naphthyl-2 (8), were synthesized from the corresponding catechol thioethers and Ph3SbBr2 in the presence of a base. The crystal structures of 1, 2, 3, and 5 were determined by single-crystal X-ray analysis. The coordination polyhedron of 1-3 is better described as a tetragonal pyramid with a different degree of distortion, while that for 5- was a distorted trigonal bipyramid (τ = 0.014, 0.177, 0.26, 0.56, respectively). Complexes demonstrated different crystal packing of molecules. The electrochemical oxidation of the complexes involved the catecholate group as well as the thioether linker. The introduction of a thioether fragment into the aromatic ring of catechol ligand led to a shift in the potential of the "catechol/o-semiquinone" redox transition to the anodic region, which indicated the electron-withdrawing nature of the RS group. The radical scavenging activity of the complexes was determined in the reaction with DPPH radical.

Heteroleptic LaIII Anilate/Dicarboxylate Based Neutral 3D-Coordination Polymers.

Three new 3D metal-organic frameworks of lanthanum based on mixed anionic ligands, [(La2(pQ)2(BDC)4)·4DMF]n, [(La2(pQ)2(DHBDC)4)·4DMF]n, [(La2(CA)2(BDC)4)·4DMF]n (pQ-dianion of 2,5-dihydroxy-3,6-di-tert-butyl-para-quinone, CA-dianion of chloranilic acid, BDC-1,4-benzenedicarboxylate, DHBDC-2,5-dihydroxy-1,4-benzenedicarboxylate and DMF-N,N'-dimethylformamide), were synthesized using solvothermal methodology. Coordination polymers demonstrate the rare xah or 4,6T187 topology of a 3D framework. The homoleptic 2D-coordination polymer [(La2(pQ)3)·4DMF]n was obtained as a by-product in the course of synthetic procedure optimization. The thermal stability, spectral characteristics and porosity of coordination polymers were investigated.

Single Crystal X-ray Diffraction Studies of Two Polymorphic Modifications of the Dicarbonyl-o-Semiquinonato Rhodium Complex at Different Temperatures. Destruction Stimulated by Cooling Versus Stability.

It was found that the dicarbonyl-rhodium-o-semiquinonate complex (which thread-like crystals can bend reversibly under light/warm activation) can form two polymorphic modifications: isometric prisms (1) and sticks (2). Some thin sticks can bend as mentioned above. X-ray diffraction studies of polymorphic modifications at different temperatures were carried out. It was found that crystals 1 are destructed after cooling to 110 K as opposed to crystals 2. In turn, the reversible phase transition is detected in 2. In both polymorphic modifications, stack packaging motifs through the direct Rh-Rh bond are observed. The principal difference between packages of polymorphic modifications is that molecules 1 in the adjacent stacks are shifted relative to each other along the stack, in contrast to crystal 2. It was found that different packing of stacks leads to different anisotropic compression of crystals 1 and 2 during cooling, which is a key factor of their stability. Using the molecular invariom approach, the nature of the chemical bonds and charge distribution was investigated; the energy of the Rh-Rh bonds was estimated.

Imine-Based Catechols and o-Benzoquinones: Synthesis, Structure, and Features of Redox Behavior.

Novel sterically hindered catechols of the type 3-(RN=CH)-4,6-DBCatH2 with iminoalkyl or iminoaryl groups in the third position of the aromatic ring have been synthesized and characterized in detail. The o-benzoquinones 3-(RN=CH)-4,6-DBBQ have been synthesized by the oxidation of the corresponding catechols. The oxidation of methylimino-substituted catechol with K3[Fe(CN)6] in alkaline medium leads to the formation of two products: o-quinone and diene-dione, the product of the water addition to the corresponding o-quinone. Some o-benzoquinones react with water or methanol to yield products of water or methanol addition. A prototropic tautomerism is characteristic of catecholaldimines: a quinomethide form is observed in the case of aliphatic amine derivatives, while aryl-substituted catecholaldimines can exist both in the catechol and quinomethide forms in the crystalline state. The formation of dimeric structures motifs is observed in crystals. The electrochemical oxidation of imino-based catechols proceeds via two one-electron processes; the second wave is quasi-reversible, which is unusual for catechols.

Dual Reactivity of 3a,6a-Diaza-1,4-diphosphapentalene: π-Donor versus n-Donor.

Herein, we present the synthesis, single-crystal X-ray structures, and spectroscopic properties for the 1:1 donor-acceptor complexes of 1,2,4,5-tetracyanobenzene (TCNB) with annelated 3a,6a-diaza-1,4-diphosphapentalenes (DDPs) based on cyclohexanone azine (2) and tetralone azine (4). These are the first complexes of an organic π-acceptor with donor phosphorus heterocycles. According to the X-ray study, the DDPs and TCNB molecules are alternately stacked with interplanar distances of 3.335 and 3.404 Å for 2 and 4, respectively, which are suitable for intermolecular π···π interactions. The bond lengths and angles in the component molecules agree with values for neutral species, and the infrared spectra indicate a very slight degree of ionicity. The estimated HOMO-LUMO gap from the onset of optical absorption (1.40 eV) is in agreement with the band gap estimated from the density functional theory calculations for 2 (1.47 eV). By contrast, in a reaction with the related electron acceptor, tetrachloroterephthalonitrile, the DDPs proved to be donors of lone electron pairs in a nucleophilic aromatic substitution reaction of chlorine atoms demonstrating the duality of their electronic nature.

Polyfunctional Sterically Hindered Catechols with Additional Phenolic Group and Their Triphenylantimony(V) Catecholates: Synthesis, Structure, and Redox Properties.

New polyfunctional sterically hindered 3,5-di-tert-butylcatechols with an additional phenolic group in the sixth position connected by a bridging sulfur atom-(6-(CH2-S-tBu2Phenol)-3,5-DBCat)H2 (L1), (6-(S-tBu2Phenol)-3,5-DBCat)H2 (L2), and (6-(S-Phenol)-3,5-DBCat)H2 (L3) (3,5-DBCat is dianion 3,5-di-tert-butylcatecolate)-were synthesized and characterized in detail. The exchange reaction between catechols L1 and L3 with triphenylantimony(V) dibromide in the presence of triethylamine leads to the corresponding triphenylantimony(V) catecholates (6-(CH2-S-tBu2Phenol)-3,5-DBCat)SbPh3 (1) and (6-(S-Phenol)-3,5-DBCat)SbPh3 (2). The electrochemical properties of catechols L1-L3 and catecholates 1 and 2 were investigated using cyclic voltammetry. The electrochemical oxidation of L1-L3 at the first stage proceeds with the formation of the corresponding o-benzoquinones. The second process is the oxidation of the phenolic moiety. Complexes 1 and 2 significantly expand their redox capabilities, owing to the fact that they can act as the electron donors due to the catecholate metallocycle capable of sequential oxidations, and as donors of the hydrogen atoms, thus forming a stable phenoxyl radical. The molecular structures of the free ligand L1 and complex 1 in the crystal state were determined by single-crystal X-ray analysis.

Ferrocene-Containing Tin(IV) Complexes Based on o-Benzoquinone and o-Iminobenzoquinone Ligands. Synthesis, Molecular Structure, and Electrochemical Properties.

The addition of different substituted o-benzoquinones and o-iminobenzoquinones to tin(II) bis(o-iminophenolates) of the types (Fc-IP)2SnII and (Fc-4,6-IP)2SnII (where Fc-IP is anion 2-(ferrocenylmethyleneamino)phenolate [Fc-C(H)═N(C6H4)O-] and Fc-4,6-IP is anion 2-(ferrocenylmethyleneamino)-4,6-di-tert-butylphenolate [Fc-C(H)═N(4,6-tBu-C6H2)O-]) in tetrahydrofuran leads to the oxidation of Sn(II) to Sn(IV) with formation of the corresponding tin(IV) catecholates (Fc-4,6-IP)2SnIV(3,6-Cat) (1), (Fc-IP)2SnIV(3,6-Cat) (2), (Fc-4,6-IP)2SnIV(4-Cl-3,6-Cat) (3), (Fc-IP)2SnIV(4-Cl-3,6-Cat) (4), (Fc-4,6-IP)2SnIV(4,5-Cl2-3,6-Cat) (5), and (Fc-IP)2SnIV(4,5-Cl2-3,6-Cat) (6) or the o-amidophenolates (Fc-4,6-IP)2SnIV(AP-Me) (7), (Fc-IP)2SnIV(AP-iPr) (8), and (Fc-4,6-IP)2SnIV(AP-iPr) (9). Here ligands 3,6-Cat, 4-Cl-3,6-Cat, and 4,5-Cl2-3,6-Cat are dianions 3,6-di-tert-butyl-, 4-chloro-3,6-di-tert-butyl-, and 4,5-dichloro-3,6-di-tert-butylcatecholates, respectively, and AP-Me and AP-iPr are dianions 4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-amidophenolate and 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolate, respectively. Complexes 1-9 have been characterized in detail by IR spectroscopy, cyclic voltammetry, and 1H, 13C, and 119Sn NMR spectroscopy. The molecular structures of tin(IV) complexes 5, 7, and 9 in the crystalline state were determined by single-crystal X-ray diffraction analysis. Complexes demonstrate a series of successive oxidations involving alternately catecholato/o-amidophenolato centers and ferrocenyl moieties. The relative oxidation potentials of these redox centers depend on the acceptor properties of the redox-active chelating O,O' or O,N ligand. An increase in the acceptor properties of redox-active o-quinonato-type ligands leads to an increase in the oxidation potentials of redox ligands as well as the following oxidation of ferrocenyl group(s). In two series of complexes, (Fc-4,6-L)2SnL' and (Fc-L)2SnL', where L' is AP-iPr, AP-Me, 3,6-Cat, 4-Cl-3,6-Cat, and 4,5-Cl2-3,6-Cat, a more pronounced convergence of the oxidation potentials of the redox-active o-quinonato ligand and ferrocenyl group occurs in the series (Fc-L)2SnL'.

The Nature of P(σ2λ3↔σ2λ1) Dualism: 3a,6a-Diaza-1,4-diphosphapentalene as a Form of Stabilized Singlet Phosphinidene.

The current study provides a clear understanding of the chemical properties of annelated 3a,6a-diaza-1,4-diphosphapentalenes (DDPs), which are best viewed as stabilized singlet phosphinidenes. It was found that DDPs undergo reversible oligomerization in solution, which provides 1,2,3-diazaphosphole-substituted cyclotetraphosphines, isolated and characterized by X-ray crystal structure analysis. Transformation of the 10-π-electron heteropentalene system into a stabilized phosphinidene occurs when the P-N bond is lengthened, which is facilitated by weak Lewis acids and bases. DFT calculations show that the lowest unoccupied molecular orbital of DDP has a high localization at the phosphorus atom when the N-P bond distance reaches the value of 2.53 Å. Oligomerization is a concentration-dependent process. Increasing the concentration of the monomer solution promotes tetramer formation, and vice versa: a strong dilution leads to a monomer. Tetramer solutions are photosensitive and yield monomers upon irradiation. The new annelated DDP 2 and its dichloro precursor 4 based on tetralone azine were synthesized. 4 exists in the solid state as a 1,4-dichloro isomer, while in solution it gives an equilibrium mixture of 1,1- and 1,4-isomers. Cyclohexanone-annelated diazadiphosphapentalene 1 forms a weak complex (1:1) with Ph3B, showing an elongated P-B bond (2.114(12) Å), which is noticeably larger than the sum of the covalent radii of the elements.