Breaking and Making of Carbon–Carbon Bonds by Lanthanides and Third‐Row Transition Metals

Carbon‐atom extrusion from the ipso‐position of a halobenzene ring (C₆H₅X; X=F, Cl, Br, I) and its coupling with a methylene ligand to produce acetylene is not confined to [LaCH₂]⁺; also, the third‐row transition‐metal complexes [MCH₂]⁺, M=Hf, Ta, W, Re, and Os, bring about this unusual transformation. However, substrates with substituents X=CN, NO₂, OCH₃, and CF₃ are either not reactive at all or give rise to different products when reacted with [LaCH₂]⁺. In the thermal gas‐phase processes of atomic Ln⁺ with C₇H₇Cl substrates, only those lanthanides with a promotion energy small enough to attain a 4fⁿ5d¹6s¹ configuration are reactive and form both [LnCl]⁺ and [LnC₅H₅Cl]⁺. Branching ratios and the reaction efficiencies of the various processes seem to correlate with molecular properties, like the bond‐dissociation energies of the C?X or M⁺?X bonds or the promotion energies of lanthanides.     

TBAI‐Catalyzed/Water‐Assisted Double C−S Bond Formations: An Efficient Approach to Sulfides through Metal‐Free Three‐Component Reactions

An aqueous catalytic method for double C?S bond formations that involves alcohol derivatives, organic halides, and sodium thiosulfate has been developed. A diverse range of functionalized sulfides, including pharmaceutical and biological derivatives, can be obtained in an efficient and eco‐friendly manner under air. The mechanistic studies revealed that this tetrabutylammonium‐iodide‐catalyzed/water‐assisted reaction generated a mercaptan species as the key intermediate.     

Is it True That the Normal Valence‐Length Correlation Is Irrelevant for Metal–Metal Bonds?

The most intriguing feature of metal–metal bonds in inorganic compounds is an apparent lack of correlation between the bond order and the bond length. In this study, we combine a variety of literature data obtained by quantum chemistry and our results based on the empirical bond valence model (BVM), to confirm for the first time the existence of a normal exponential correlation between the effective bond order (EBO) and the length of the metal–metal bonds. The difference between the EBO and the formal bond order is attributed to steric conflict between the (TM)_n cluster (TM=transition metal) and its environment. This conflict, affected mainly by structural type, should cause high lattice strains, but electron redistribution around TM atoms, evident from the BVM calculations, results in a full or partial strain relaxation.     

Is PdII‐Promoted σ‐Bond Metathesis Mechanism Operative for the PdPEPPSI Complex‐Catalyzed Amination of Chlorobenzene with Aniline? Experiment and Theory

Reduction of the Pd?PEPPSI precatalyst to a Pd⁰ species is generally thought to be essential to drive Buchwald–Hartwig amination reactions through the well‐ documented Pd⁰/Pd^II catalytic cycle and little attention has been paid to other possible mechanisms. Considered here is the Pd?PEPPSI‐catalyzed aryl amination of chlorobenzene with aniline. A neat reaction system was used in new experiments, from which the potentially reductive roles of the solvent and labile ligand of the PEPPSI complex in leading to Pd⁰ species are ruled out. Computational results demonstrate that anilido‐containing Pd^II intermediates involving σ‐bond metathesis in pathways leading to the diphenylamine product have relatively low barriers. Such pathways are more favorable energetically than the corresponding reductive elimination reactions resulting in Pd⁰ species and other putative routes, such as the Pd^II/Pd^IV mechanism, single electron transfer mechanism, and halide atom transfer mechanism. In some special cases, if reactants/additives are inadequate to reduce a Pd^II precatalyst, a Pd^II‐involved σ‐bond metathesis mechanism might be feasible to drive the Buchwald–Hartwig amination reactions.     

Aromaticity Relocation in Perylene Derivatives upon Two‐Electron Oxidation To Form Anthracene and Phenanthrene

We prepared perylene dications 1 ²⁺ and 2 ²⁺ by using “capped” perylene derivatives, and for the first time, successfully obtained single crystals of a perylene dication 1 ²⁺ that enabled us to perform its structural analysis. We realized that the substituted aryl groups on perylene control the positions of positive charges, thus the remaining electronic system satisfies Clar's sextet rule toward the highest number of localized sextets. Experimental and theoretical evidence proved that Clar's aromatic π‐sextet rule could be applied even for the dicationic perylenes in a very simple way.     

Reactivity of a N-Coordinated Germylene-Borane Complex: From Ge→B to Ge→Ga Coordination

Reactivity studies of the Ge^II→B complex L(Cl)Ge⋅BH₃ ( 1 ; L=2-Et₂NCH₂-4,6-tBu₂-C₆H₂) were performed to determine the effect on the Ge^II→B donation. N-coordinated compounds L(OtBu)Ge⋅BH₃ ( 2 ) and [LGe⋅BH₃]₂ ( 3 ) were prepared. The possible tuning of the Ge^II→B interaction was proved experimentally, yielding compounds 1-PPh₂-8-(LGe)-C₁₀H₆ ( 4 ) and L(Cl)Ge⋅GaCl₃ ( 5 ) without a Ge^II→B interaction. In 5 , an unprecedented Ge^II→Ga coordination was revealed. The experimental results were complemented by a theoretical study focusing on the bonding in 1 − 5 . The different strength of the Ge^II→E (E=B, Ga) donation was evaluated by using energy decomposition analysis. The basicity of different L(X)Ge groups through proton affinity is also assessed.     

An Isolable Gallium-Substituted Nitrilimine and its Reactivity with B−H,Si−H and B−B Bonds

Reaction of the Ga(I) compound NacNacGa ( 9 ) with the diazo compound N₂CHSiMe₃ affords the nitrilimine compound NacNacGa(N-NCSiMe₃)(CH₂SiMe₃) ( 10 ). Carrying out this reaction in the presence of pyridine does not lead to C−H activation on the transient alkylidene NacNacGa=CHSiMe₃ but generates a metallated diazo species NacNacGa(NHN=CHSiMe₃)(CN₂SiMe₃) ( 13 ) that further rearranges into the isonitrile compound NacNacGa(NHN=CHSiMe₃)(N(NC)SiMe₃) ( 15 ). Reactions of 10 with the silane H₃SiPh and the borane HBcat furnished products of 1,3 addition to the nitrilimine moiety NacNacGa{N(ER_n)NCSiMe₃}(CH₂SiMe₃), whereas reaction with the diborane B₂cat₂ gave the product of formal nitrene insertion into the B−B bond. DFT calculations suggest that the interaction of 9 with N₂CHSiMe₃ proceeds through intermediate formation of an alkylidene compound that undergoes CH activation with a second molecule of N₂CHSiMe₃. Insertion into the B−B bond likely proceeds through an initial 1,3-addition of the diborane, followed by boryl migration to the former nitrene center.     

A convenient synthesis of 3-aryl-5-methylidene-2-thiohydantoins

3-Aryl-5-methylidene-2-thiohydantoins were constructed in one-pot reaction of aryl isothiocyanates and 3-morpholino- alanine in alkaline medium with the subsequent treatment with boiling hydrochloric acid.     

Real-Space Interpretation of Interatomic Charge Transfer and Electron Exchange Effects by Combining Static and Kinetic Potentials and Associated Vector Fields**

Intricate behaviour of one-electron potentials from the Euler equation for electron density and corresponding gradient force fields in crystals was studied. Channels of locally enhanced kinetic potential and corresponding saddle Lagrange points were found between chemically bonded atoms. Superposition of electrostatic and kinetic potentials and electron density allowed partitioning any molecules and crystals into atomic - and potential-based -basins; -basins explicitly account for the electron exchange effect, which is missed for -ones. Phenomena of interatomic charge transfer and related electron exchange were explained in terms of space gaps between zero-flux surfaces of - and -basins. The gap between - and -basins represents the charge transfer, while the gap between - and -basins is a real-space manifestation of sharing the transferred electrons caused by the static exchange and kinetic effects as a response against the electron transfer. The regularity describing relative positions of -, -, and - basin boundaries between interacting atoms was proposed. The position of -boundary between - and -ones within an electron occupier atom determines the extent of transferred electron sharing. The stronger an H⋅⋅⋅O hydrogen bond is, the deeper hydrogen atom's -basin penetrates oxygen atom's -basin, while for covalent bonds a -boundary closely approaches a -one indicating almost complete sharing of the transferred electrons. In the case of ionic bonds, the same region corresponds to electron pairing within the -basin of an electron occupier atom.     

Hetaryl- and heteroarylvinyl-substituted nitrofurans identified as non-cytotoxic selective antitubercular agents

New (E)-5-[2-(5-nitrofuran-2-yl)vinyl]-1,2,4-oxadiazoles and 5-(5-nitrofuran-2-yl)-1,2,4-oxadiazoles were synthesized via the base-promoted condensation of nitrofuran-containing acyl chlorides with amidoximes. Testing these compounds against Gram-negative E. coli, Gram-positive B. subtilis and S. aureus as well as M. tuberculosis HRv37 strain revealed three compounds being selectively antimycobacterial. None of these compounds displayed any cytotoxicity towards human pancreatic epithelioid carcinoma cell line, PANC-1.