Substituted Tetraaza‐ and Hexaazahexacenes and their N,N′‐Dihydro Derivatives: Syntheses,Properties, and Structures

The palladium‐catalyzed coupling of a substituted o‐diaminoanthracene and a substituted o‐diaminophenazine to substituted 2,3‐dichloroquinoxalines furnishes 10 differently substituted N,N′‐dihydrotetraaza‐ or ‐hexaazahexacenes with the quinoxaline group of the azaacenes carrying fluorine, chlorine, or nitro groups. The N,N′‐dihydrotetraazahexacenes with hydrogen, chlorine, and fluorine subtituents are oxidized to azaacenes, whereas only the parent N,N′‐dihydrohexaazahexacenes, with hydrogen substituents, are oxidized by MnO₂. The resultant azaacenes are characterized by their optical and spectroscopic data. In addition, single‐crystal X‐ray structures have been obtained for the parent tetraazahexacenes and their difluoro‐substituted derivatives. The di‐ and tetrachloro derivatives of the N,N′‐dihydrohexaazahexacene have also been structurally characterized.     

New stable germylenes,stannylenes, and related compounds 7. Synthesis and structures of compounds Hal—Sn—OCH<Subscript>2</Subscript>CH<Subscript>2</Subscript>NMe<Subscript>2</Subscript> (Hal = Cl or F)

New stable divalent tin derivatives containing no bulky substituents at the metal atom, Hal—Sn— OCH₂CH₂NMe₂ (Hal = Cl or F), were synthesized, and their crystal structures were studied by X-ray diffraction. Unlike the analogous monomeric divalent germanium derivative Cl—Ge—OCH₂CH₂NMe₂, the new compounds are centrosymmetric dimers formed via two intermolecular Sn←CO coordination bonds. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 259–262, February, 2007.     

Trinuclear Cyanido-Bridged [Cr2Fe] Complexes: To Be or not to Be a Single-Molecule Magnet,a Matter of Straightness

Trinuclear systems of formula [{Cr(L^N3O2Ph)(CN)₂}₂M(H₂L^N3O2R)] (M=Mn^II and Fe^II, L^N3O2R stands for pentadentate ligands) were prepared in order to assess the influence of the bending of the apical M−N≡C linkages on the magnetic anisotropy of the Fe^II derivatives and in turn on their Single-Molecule Magnet (SMM) behaviors. The cyanido-bridged [Cr₂M] derivatives were obtained by assembling trans-dicyanido Cr^III complex [Cr(L^N3O2Ph)(CN)₂]⁻ and divalent pentagonal bipyramid complexes [M^II(H₂L^N3O2R)]²⁺ with various R substituents (R=NH₂, cyclohexyl, S,S-mandelic) imparting different steric demand to the central moiety of the complexes. A comparative examination of the structural and magnetic properties showed an obvious effect of the deviation from straightness of the M−N≡C alignment on the slow relaxation of the magnetization exhibited by the [Cr₂Fe] complexes. Theoretical calculations have highlighted important effects of the bending of the apical C−N−Fe linkages on both the magnetic anisotropy of the Fe^II center and the exchange interactions with the Cr^III units.     

Probing the Effects of the Number and Positions of −OCH3 and −CN Substituents on Color Tuning of Ir(III) Complex Derivatives through a Joint Computational and Experimental Study

We performed a joint theoretical and experimental study on sixteen Ir(III) complexes bearing a similar molecular platform of bis(2-phenylbenzothiozolato-N,C^2’) iridium(III) (acetylacetonate) by grafting −OCH₃ group and/or −CN group on different positions of the C-related arene moiety of the ligand (C-ring). Our results reveal that the introduction of −CN renders an overall drop in the FMO energy levels while a reverse increase is observed for −OCH₃. The ortho- and para-sites of the C-ring are more effective substitution positions to modulate the HOMO energy level due to the fact that the electronic density of HOMO mainly locates at them while the meta-site would induce a stronger impact on LUMO since the electronic density of LUMO mainly distributes over the position. Utilizing the synergistic effects of the substituents and the substituted positions, a wide color-tuning range from 479 nm to 637 nm was achieved, which covers nearly the whole window of visible spectrum. In particular, the tri-substituted Ir35mo4cn complex (λ_{em max}=637 nm) may be a potential candidate for high efficiency red OLEDs materials due to its greatly enhanced absorption processes, relatively higher ³MLCT (%), lower ΔE_S1–T1, enlarged separation between ³MLCT/π–π* and ³MC d–d states, and good hole and particle-transporting performances. Finally, six representative complexes were synthesized and their spectra were determined, which confirm the reliability of our computational strategy.     

Cata-Annulated Azaacene Bisimides

Ultra-electron-deficient azaacenes were synthesized via Buchwald-Hartwig coupling of ortho-diaminoarenes with chlorinated mellophanic diimide followed by oxidation of the intermediate N,N’-dihydro compounds with MnO₂ or PbO₂. The resulting cata-annulated bisimide azaacenes have ultrahigh electron affinities with first reduction potentials as low as −0.35 V recorded for a tetraazapentacene. Attempts to prepare a tetrakis(dicarboximide)tetraazaheptacene resulted in the formation of a symmetric butterfly dimer.     

Effect of substituents on the chemical shift of the ring protons in the PMR spectra of monosubstituted sym-triazines

A correlation equation that links the relative chemical shift of the protons of the triazine ring with the F and R constants of the substituents was obtained on the basis of data from the PMR spectra of solutions of sym-triazine and its monosubstituted derivatives [OCH₃, N(CH₃)₂, CH₃, C₆H₅, COOC₂H₅, and CN] in dimethyl sulfoxide (DMSO). The equation was analyzed by comparison with the corresponding equations for monosubstituted benzenes and pyrimidines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 410–414, March, 1982.     

Ylide-Functionalization via Metalated Ylides: Synthesis and Structural Properties

The α-metallated ylides [Ph₃P−C−Z]⁻M⁺ (with Z=SO₂Tol or CN and M=Na or K) were used as versatile nucleophiles for the facile access to ylide-substituted compounds. Halogenations, alkylations, carbonylations and functionalization reactions with main group element halides were easily accomplished by simple trapping reactions with the appropriate electrophiles. X-ray crystallographic studies of all compounds – including the first structures of α-fluorinated P-ylides – showed remarkable differences in the ylide backbone depending on the substituents. In the fluorinated compounds, a change from a fully planar to a pyramidalized ylidic carbon centre was observed despite the strongly anion-stabilizing ability of the yldiide substituent. π-Donation from the ylide substituent also resulted in geometric restrictions depending on the steric and electronic properties of the introduced substituents.     

Liquid crystalline properties of dissymmetric molecules IV. The substituent effect on thermal properties of nematic and smectic A phases in three aromatic ring systems with ester linkages

This paper describes the effect of substituent and ester linkage on smectic properties for some derivatives of 4-R -phenyl 4-(4-octyloxybenzoyloxy)benzoates (1), 4-octyloxyphenyl 4-(4-R-benzyloxy)benzoates (2), 4-(4-octyloxybenzoyloxy)phenyl 4- R -benzoates (3), and 4-R-phenyl 4-octyloxyphenyl terephthalates (4) where R = OCH₃, CH₃, OC₈H₁₇, C8H17, halogens, CF₃, OCF₃, CN, NO2, etc. The thermal properties are discussed in terms of the electrostatic nature of the substituents and the relative orientation of the ester groups with respect to both terminal substituents. The substituent effect on the layer structure of the smectic A phase is also examined by means of a small angle X-ray analysis.     

Copolymerization of carbon monoxide and norbornene derivatives with ester groups by palladium catalyst

In this article we will discuss the synthesis of the new copolymers of norbornene derivatives with an ester group and carbon monoxide, using Pd(CH₃CN)₄(BF₄)₂ as a catalyst and 2,2′-bipyridine as a ligand in nitromethane/methanol at 60°C. Elementary analysis, infrared spectra, and NMR spectra indicated that copolymers contain ketone, ester, and bicyclic structures. Methanol functions as the coinitiator and chain transfer agent in copolymerization. A decrease in the molar ratio of [CH₃OH]/[Pd] caused an increase in molecular weight and a decrease in yield of the copolymer. The number-average molecular weight of copolymers (M _n) ranged from 3800 to 5300, and the glass transition temperature (T_g) ranged from −32 to 117°C. Thermal analysis revealed that both T and T exceeded 180 and 230°C, respectively. Linear long-chain substituents such as n-C₁₁H₂₃C(O) O CH₂ drastically reduced T_g to a value of −32°C. In general, copolymers having a longer linear side-chain substituents of ester on norbornene have a more desirable solubility. Moreover, X-ray diffraction demonstrated that the degree of crystallinity decreases with an increasing length of side chain substituents. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1785–1790, 1998     

Tailoring the Solid‐State Fluorescence Emission of BODIPY Dyes by meso Substitution

4,4‐Difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) derivatives bearing varied substituents at the meso position (i.e., CF₃, CH₃, COOR, CHO, CN, Cl, iPr) were synthesized to elucidate the structure–property relationships that give rise to emissive J‐aggregates. Several new BODIPY derivatives can be added to the previously reported 1,3,5,7‐tetramethyl‐8‐trifluoromethyl derivative to the list of those forming J‐aggregates, in addition to other dyes that are emissive in the solid state without forming J‐aggregates.     

Cyano Derivatives of 7-Aminoquinoline That Are Highly Emissive in Water: Potential for Sensing Applications

6-Cyano-7-aminoquinoline (6CN−7AQ ) and 3-cyano-7-aminoquinoline ( 3CN−7AQ ) were synthesized and found to exhibit intense emission with quantum yield as high as 63 % and 85 %, respectively, in water. Conversely, their derivatives 6-cyano-7-azidoquinoline (6CN−7N₃Q ) and 3-cyano-7-azidoquinoline ( 3CN−7N₃Q ) show virtually no emission, which makes them suitable to be used as recognition agents in azide reactions based on fluorescence recovery. Moreover, conjugation of 6CN−7AQ with a hydrophobic biomembrane-penetration peptide PFVYLI renders a nearly non-emissive 6CN−7AQ-PFVYLI composite, which can be digested by proteinase K, recovering the highly emissive 6CN−7AQ with ∼200-fold enhancement. The result provides an effective early confirmation for RT-qPCR in viral detection.     

Role of donor-acceptor functional groups in N3P3 cyclic-triphosphazene backbone. Unraveling bonding characteristics from natural orbitals within an extended transition state-natural orbital for the chemical valence scheme

The formation of cyclophosphazenes containing several ligands or substituent groups gives rise to an attractive derivative set, for development of novel applications, with variable properties. Here, it is possible to unravel the role of different functional groups attached to the N₃P₃ backbone, to reach a better understanding of the bonding character in the cyclic [─P─N─] skeleton. We employed the extended transition state-natural orbital for the chemical valence scheme to unravel the σ and π orbital kernels that are involved in the assembling of such structures, by varying the acceptor-donor characteristics of the ─CF₃, ─NO₂, ─COOH, ─CN, ─NH₂, ─OH, and ─OCH₃ groups, where ─NO₂ behaves as a stronger electron-withdrawing substituent rather than ─CF₃, ─COOH, and ─CN, denoting that the nature of the ligand-phosphazene interaction contributes to some degree to the bond strength of the cyclic [─P─N─] backbone. Our results reveal that the electron-withdrawing ─NO₂ group leads to higher σ and π [─P─N─] orbital-energy contributions, which is reflected in a shortening of the [─P─N─] distance, contrasting with the case of electron-donating groups such as ─NH₂, ─OH, and ─OCH₃ within the phosphazene set. These insights allow further variation and modulation of the bonding in the [─P─N─] ring.     

Mass spectra of monosubstituted trans-stilbenes

The mass spectra of twenty-eight monosubstituted trans-stilbenes in ortho, meta, para and alpha positions with ? N(CH₃)₂, ? NH₂, ? OCH₃, ? OH, ? Br, ? Cl, ? F, ? CH₃, ? COOH, ? CN and ? NO₂ groups as substituents have been studied. A detailed fragmentation pathway is given for stilbene. This fragmentation, characteristic for most of the substituted stilbenes, takes place either from the molecular or from the [M - Substituent] ion. In o-nitro-, o-methoxy-,α-carboxyl- and α-methylstilbene, however, rearrangement reactions prior to fragmentation influence the fragmentation pattern.     

meta-Nitration of Arenes Bearing ortho/para Directing Group(s) Using C−H Borylation

Herein, we report the meta-nitration of arenes bearing ortho/para directing group(s) using the iridium-catalyzed C−H borylation reaction followed by a newly developed copper(II)-catalyzed transformation of the crude aryl pinacol boronate esters into the corresponding nitroarenes in a one-pot fashion. This protocol allows the synthesis of meta-nitrated arenes that are tedious to prepare or require multistep synthesis using the existing methods. The reaction tolerates a wide array of ortho/para-directing groups, such as −F, −Cl, −Br, −CH₃, −Et, −iPr −OCH₃, and −OCF₃. It also provides regioselective access to the nitro derivatives of π-electron-deficient heterocycles, such as pyridine and quinoline derivatives. The application of this method is demonstrated in the late-stage modification of complex molecules and also in the gram-scale preparation of an intermediate en route to the FDA-approved drug Nilotinib. Finally, we have shown that the nitro product obtained by this strategy can also be directly converted to the aniline or hindered amine through Baran's amination protocol.     

The Hexacyanodiborane(6) Dianion [B2(CN)6]2−

Diborane(6) dianions with substituents that are bonded to boron via carbon are very reactive and therefore only a few examples are known. Diborane(6) derivatives are the simplest catenated boron compounds with an electron‐precise B–B σ‐bond that are of fundamental interest and of relevance for material applications. The homoleptic hexacyanodiborane(6) dianion [B₂(CN)₆]²⁻ that is chemically very robust is reported. The dianion is air‐stable and resistant against boiling water and anhydrous hydrogen fluoride. Its salts are thermally highly stable, for example, decomposition of (H₃O)₂[B₂(CN)₆] starts at 200 °C. The [B₂(CN)₆]²⁻ dianion is readily accessible starting from 1) B(CN)₃²⁻ and an oxidant, 2) [BF(CN)₃]⁻ and a reductant, or 3) by the reaction of B(CN)₃²⁻ with [BHal(CN)₃]⁻ (Hal=F, Br). The latter reaction was found to proceed via a triply negatively charged transition state according to an S_N2 mechanism.     

Attempted Abstraction of the Halogenides in (HNEt3)[Re(CH3CN)2Cl4] and Crystal Structures of cis‐[Re(CH3CN)2Cl4]·CH3CN and cis‐[Re(NHC(OCH3)CH3)2Cl4]

The abstraction of the halogenide ligands in [Re(CH₃CN)₂Cl₄]^? should result in a solvent‐only stabilized Re^III complex. The reactions of salts of [Re(CH₃CN)₂Cl₄]^? with silver(I) and thallium(I) salts were investigated and the solid‐state structures of cis‐[Re(CH₃CN)₂Cl₄]·CH₃CN and cis‐[Re(NHC(OCH₃)CH₃)₂Cl₄] are described.     

Crystalline Diradical Dianions of Pyrene-Fused Azaacenes

Although diradicals and azaacenes have been greatly attractive in fundamental chemistry and functional materials, the isolable diradical dianions of azaacenes are still unknown. Herein, we describe the first isolation of pyrene-fused azaacene diradical dianion salts [(18-c-6)K(THF)₂]⁺[(18-c-6)K]⁺⋅ 1 ^2−.. and [(18-c-6)K(THF)]²⁺⋅ 2 ^2−.. by reduction of the neutral pyrene-fused azaacene derivatives 1 and 2 with excess potassium graphite in THF in the presence of 18-crown-6. Their electronic structures were investigated by various experiments, in conjunction with theoretical calculations. It was found that both dianions are open-shell singlets in the ground state and their triplet states are thermally readily accessible owing to the small singlet–triplet energy gap. This work provides the first examples of crystalline diradical dianions of azaacenes with considerable diradical character.     

Reactivity of Hydroxy and Amino Derivatives of 2‐Phenyl‐1H‐imidazoline and 2‐Phenyl‐1H‐imidazole toward Isocyanates: Synthesis of Appropriate Carbamates and Ureas

Reactivity of 2‐(4‐hydroxyphenyl)‐1H‐imidazoline and 2‐(4‐hydroxyphenyl)‐1H‐imidazole toward substituted phenyl isocyanates was studied. When mentioned imidazoline was treated with 2.5 equiv of substituted phenyl isocyanate, three N,O‐dicarboxamides were prepared (substituents are H, 4‐NO₂, and 4‐CH₃). Subsequently, N,O‐diacetylated 2‐(4‐hydroxyphenyl)‐1H‐imidazoline was prepared and selective deprotection method was developed for preparation of 1‐acetyl‐2‐(4‐hydroxyphenyl)‐1H‐imidazoline using diethylamine in acetone. Six carbamates derived from this imidazoline were then prepared using 1.1 equiv of substituted phenyl isocyanates (substituents are H, 4‐CH₃, 4‐OCH₃, 4‐NO₂, 4‐CN, and 3‐CF₃). Finally, two carbamates were prepared from 2‐(4‐hydroxyphenyl)‐1H‐imidazole (substituents are 4‐NO₂ and 4‐CN). No reactivity to imidazole ring was observed in this case. Eight derivatives were subjected to antimycobacterial screening. Concurrently, reactivity of 2‐(2‐aminophenyl)‐ and 2‐(2‐hydroxyphenyl)‐1H‐imidazole toward aliphatic and aromatic isocyanates was studied. Eight ureas were prepared using equivalent mixture of 2‐(2‐aminophenyl)‐1H‐imidazole and isocyanate (Et, Pr, isoPr, terc‐Bu, Cy, Ph, 4‐CH₃C₆H₄, 4‐CNC₆H₄). Similar attempts to obtain related carbamates from 2‐(2‐hydroxyphenyl)‐1H‐imidazole lead only to three substituted phenyl carbamates (substituents are 4‐CH₃, 4‐NO₂, and 4‐CN). In both cases, no reactivity to imidazole ring was observed again.     

Efficient structural modification of electron-withdrawing substituents on Pt(II) complexes for red emitters: A theoretical study

In this study, the electronic structures and optical properties of a cyclometalated Pt(II) complex (M1) and a series of derivatives (M1–F, M1–CF₃, and M1–CN) with electron-withdrawing substituents (–F, –CF₃, and –CN) at the carbazole moiety were theoretically investigated by density functional theory and time-dependent density functional theory. The calculation results reveal that these Pt complexes display deep red phosphorescence emission above Λ = 640 nm. When the ³MLCT/π → π* to triplet metal-centered ³MC/d–d state decay mechanism is taken into consideration, the nonradiative decay rate constant (k_nr) decreased in the order M1 > M1–CF₃ > M1–F > M1–CN. The <T₁|H_SOC|S_m> and kr values of M1-F are similar with those of M1, however the Knr rate ofM1-F is larger than that of M1. M1–F is expected to have improved quantum yields. Moreover, through the analyses of the HOMO/LUMO level and triplet energy, it is found that the introduction of –F and –CN substituents in M1 results in efficient energy transfer from the host material 4,4′-N,N′-dicarbazole-biphenyl to these complexes. In view of the electroluminescent applications in organic light-emitting diodes, M1–F can serve as efficient deep-red guest materials with improved electron injection and transport ability.