Synthesis and Characterization of Bis(2‐iminopyrrolyl) Iron(II) Complexes by N–H Bond Activation

The reactions of 2‐iminopyrroles 1 – 3 with Fe(PMe₃)₄ afforded the N–H activated bis(2‐iminopyrrolyl) iron(II) complexes 4 – 6 . The structures of compounds 4 – 6 were determined by single‐crystal X‐ray diffraction. The formation mechanism of complexes 4 – 6 was discussed.     

Palladium‐Catalyzed Intramolecular Reductive Cross‐Coupling of Csp2Csp3 Bond Formation

A Pd‐catalyzed efficient reductive cross‐coupling reaction without metallic reductant to construct a Csp²?Csp³ bond has been reported. A Pd^IV complex was proposed to be a key intermediate, which subsequently went through double oxidative addition and double reductive elimination to produce the cross‐coupling products by involving Pd^0/II/IV in one transformation. The oxidative addition from Pd^II to Pd^IV was partially demonstrated to be a radical process by self‐oxidation of substrate without additional oxidants. Furthermore, the solvent was proved to be the reductant for this transformation through XPS analysis.     

Insertion Reactions of Heterocumulenes with Zincocene Cp*2Zn

Zincocene Cp*₂Zn reacts with carbodiimides C(NR)₂ with insertion into the Zn–Cp* bond and formation of [(Cp*C(NR)₂]₂Zn [R = Et ( 1 ), iPr ( 2 ), Cy ( 3 )]. In addition, the reaction of Cp*₂Zn with CS₂ under dry conditions gives (Cp*CS₂)₂Zn ( 4 ), whereas in the presence of a small amount of water [Zn₄(μ₄‐O)(S₂CCp*)₆] ( 5 ) is obtained. Compounds 1 – 4 were characterized by NMR (¹H, ¹³C) and IR spectroscopy as well as elemental analysis and single‐crystal X‐ray diffraction ( 2 – 4 , 5 of poor quality). The solid‐state structure of 5 is comparable to the carboxylate complex previously obtained from the reaction of Cp*₂Zn with CO₂.     

Transformations of Aryl Ketones via Ligand‐Promoted C−C Bond Activation

The coupling of aromatic electrophiles (aryl halides, aryl ethers, aryl acids, aryl nitriles etc.) with nucleophiles is a core methodology for the synthesis of aryl compounds. Transformations of aryl ketones in an analogous manner via carbon–carbon bond activation could greatly expand the toolbox for the synthesis of aryl compounds due to the abundance of aryl ketones. An exploratory study of this approach is typically based on carbon–carbon cleavage triggered by ring‐strain release and chelation assistance, and the products are also limited to a specific structural motif. Here we report a ligand‐promoted β‐carbon elimination strategy to activate the carbon–carbon bonds, which results in a range of transformations of aryl ketones, leading to useful aryl borates, and also to biaryls, aryl nitriles, and aryl alkenes. The use of a pyridine‐oxazoline ligand is crucial for this catalytic transformation. A gram‐scale borylation reaction of an aryl ketone via a simple one‐pot operation is reported. The potential utility of this strategy is also demonstrated by the late‐stage diversification of drug molecules probenecid, adapalene, and desoxyestrone, the fragrance tonalid as well as the natural product apocynin.     

Synthesis,Structures, and Light‐Induced Transformation of Keto‐Functionalized Selenidogermanate Complexes

A double‐decker (DD) type selenidogermanate complex with C=O functionalized organic decoration, [(R¹Ge₄)Se₆] ( 1 , R¹ = CMe₂CH₂COMe), was synthesized by reaction of R¹GeCl₃ with Na₂Se, and subsequently underwent a light‐induced transformation reaction to yield [Na(thf)₂][(RGe^IV)₂(RGe^III)(Ge^IIISe)Se₅] ( 2 ). Similar to the observations reported previously for the Sn/S homologue of 1 , the product comprises a mixed‐valence complex with a newly formed Ge–Ge bond. However, different from the transformation of the tin sulfide complex, the selenidogermanate precursor did not produce a paddle‐wheel‐like dimer of the DD type structure, but led to the formation of a noradamantane (NA) type architecture, which has so far been restricted to the Si/Se and Ge/Te elemental combination.     

A novel C?C bond cleavage reaction of 2, 2′‐pyridil in solution

2,2′‐Pyridil reacted with CuCl₂ to give C–‐C bond cleavage product (picolinate)₂Cu, and its structure has been unambiguously confirmed by an X‐ray structural analysis.     

Transition‐Metal‐Mediated and ‐Catalyzed C−F Bond Activation by Fluorine Elimination

The activation of carbon–fluorine (C?F) bonds is an important topic in synthetic organic chemistry. Metal‐mediated and ‐catalyzed elimination of β‐ or α‐fluorine proceeds under milder conditions than oxidative addition to C?F bonds. The β‐ or α‐fluorine elimination is initiated from organometallic intermediates having fluorine substituents on carbon atoms β or α to metal centers, respectively. Transformations through these elimination processes (C?F bond cleavage), which are typically preceded by carbon–carbon (or carbon–heteroatom) bond formation, have been increasingly developed in the past five years as C?F bond activation methods. In this Minireview, we summarize the applications of transition‐metal‐mediated and ‐catalyzed fluorine elimination to synthetic organic chemistry from a historical perspective with early studies and from a systematic perspective with recent studies.     

Copper‐Catalyzed N−F Bond Activation for Uniform Intramolecular C−H Amination Yielding Pyrrolidines and Piperidines

The dual function of the N?F bond as an effective oxidant and subsequent nitrogen source in intramolecular aliphatic C?H functionalization reactions is explored. Copper catalysis is demonstrated to exercise full regio‐ and chemoselectivity control, which opens new synthetic avenues to nitrogenated heterocycles with predictable ring sizes. For the first time, a uniform catalysis manifold has been identified for the construction of both pyrrolidine and piperidine cores. The individual steps of this new copper oxidation catalysis were elucidated by control experiments and computational studies, clarifying the singularity of the N?F function and characterizing the catalytic cycle to be based on a copper(I/II) manifold.     

Regioselective Hydrohydroxyalkylation of Styrene with Primary Alcohols or Aldehydes via Ruthenium‐Catalyzed C−C Bond Forming Transfer Hydrogenation

Transfer hydrogenative coupling of styrene with primary alcohols using the precatalyst HClRu(CO)(PCy₃)₂ modified by AgOTf or HBF₄ delivers branched or linear adducts from benzylic or aliphatic alcohols, respectively. Related 2‐propanol mediated reductive couplings also are described.     

Iron‐Catalyzed Radical Cleavage/C−C Bond Formation of Acetal‐Derived Alkylsilyl Peroxides

A novel radical‐based approach for the iron‐catalyzed selective cleavage of acetal‐derived alkylsilyl peroxides, followed by the formation of a carbon–carbon bond is reported. The reaction proceeds under mild reaction conditions and exhibits a broad substrate scope with respect to the acetal moiety and the carbon electrophile. Mechanistic studies suggest that the present reaction proceeds through a free‐radical process involving carbon radicals generated by the homolytic cleavage of a carbon–carbon bond within the acetal moiety. A synthetic application of this method to sugar‐derived alkylsilyl peroxides is also described.     

Direct Transformation of Arenols Based on C—O Activation

In the view of substrate availability, atomic efficiency and cost, directly using arenols as coupling partners in cross‐coupling, would be one of the most attractive goals. Up to date, many efforts have been made to activate the C—O bond of phenols with different strategies, for example, through in‐situ formed intermediates, through a catalytic reductive dearomatization‐condensation‐rearomatization sequence or catalytic deoxygenation. In this review, we summarized recent advances in cross‐couplings of arenols as the electrophiles via C—O activation.     

Asymmetric Desymmetrization via Metal‐Free C−F Bond Activation: Synthesis of 3,5‐Diaryl‐5‐fluoromethyloxazolidin‐2‐ones with Quaternary Carbon Centers

We disclose the first asymmetric activation of a non‐activated aliphatic C?F bond in which a conceptually new desymmetrization of 1,3‐difluorides by silicon‐induced selective C?F bond scission is a key step. The combination of a cinchona alkaloid based chiral ammonium bifluoride catalyst and N,O‐bis(trimethylsilyl)acetoamide (BSA) as the silicon reagent enabled the efficient catalytic cycle of asymmetric C_sp3?F bond cleavage under mild conditions with high enantioselectivities. The ortho effect of the aryl group at the prostereogenic center is remarkable. This concept was applied for the asymmetric synthesis of promising agrochemical compounds, 3,5‐diaryl‐5‐fluoromethyloxazolidin‐2‐ones bearing a quaternary carbon center.     

Synthesis of four series of quinoline‐based heterocycles by reacting 2‐chloroquinoline‐3‐carbonitriles with various types of isocyanides

Four distinct sets of functionalized quinolines were synthesized by reacting 2‐chloroquinoline‐3‐carbonitriles with various types of isocyanides under appropriate conditions. The palladium‐catalysed reaction of less hindered aliphatic and aromatic isocyanides with 2‐chloroquinoline‐3‐carbonitriles yielded 2‐alkyl(aryl)‐1‐imino‐1H‐pyrrolo[3,4‐b]quinolin‐3(2H)‐one derivatives; however, the catalysed reaction of more hindered isocyanides such as tert‐butyl isocyanide produced the corresponding 3‐cyanoquinoline‐2‐carboxamides. Interestingly, chloroquinoline‐3‐carbonitriles reacted with ethyl isocyanoacetate in the presence of Cs₂CO₃ to generate imidazo[1,5‐a]quinoline derivatives; notably, tosylmethyl isocyanide under the same conditions formed unprecedented 2‐tosyl‐3‐cyanoquinolines.     

Synthesis,Structure, and Solution Study of a Mercury(II) Complex with the Ligand [1‐(2‐Methoxyphenyl)‐3‐(4‐chlorophenyl)]triazene

The title ligand, [1‐(2‐methoxyphenyl)‐3‐(4‐chlorophenyl)]triazene, H L ( 1 ), was prepared. In a reaction with Hg(NO₃)₂ it forms the complex [Hg(C₂₆H₂₂Cl₂N₆O₂)], [Hg L ₂] ( 2 ). Both compounds were characterized by means of X‐ray crystallography, CHN analysis, FT‐IR, ¹H NMR, and ¹³C NMR spectroscopy. In the structure of compound 1 , two independent fragments are present in the unit cell. They exhibit trans arrangement about the –N=N– double bond. The dihedral angles between two benzene rings in both fragments are 4.36 and 18.79 Å, respectively. Non‐classic C–H ··· N hydrogen bonding and C–H ··· π interactions form a layer structure along the crystallographic ab plane [110]. In compound 2 , the Hg^II atom is hexacoordinated by two tridentate [1‐(2‐methoxyphenyl)‐3‐(4‐chlorophenyl)]triazenide ligands through a N₂O₂ set. In addition, in the structure of 2 , monomeric complexes are connected to each other by C–H ··· π stacking interactions, resulting in a 2D architecture. These C–H ··· π edge‐to‐face interactions are present with H ··· π distances of 3.156 and 3.027 Å. The results of studies of the stoichiometry and formation of complex 2 in methanol solution were found to support its solid state stoichiometry.     

Pressure‐Induced Bond Rearrangement and Reversible Phase Transformation in a Metal–Organic Framework

Pressure‐induced phase transformations (PIPTs) occur in a wide range of materials. In general, the bonding characteristics, before and after the PIPT, remain invariant in most materials, and the bond rearrangement is usually irreversible due to the strain induced under pressure. A reversible PIPT associated with a substantial bond rearrangement has been found in a metal–organic framework material, namely [tmenH₂][Er(HCOO)₄]₂ (tmenH₂²⁺=N,N,N′,N′‐tetramethylethylenediammonium). The transition is first‐order and is accompanied by a unit cell volume change of about 10 %. High‐pressure single‐crystal X‐ray diffraction studies reveal the complex bond rearrangement through the transition. The reversible nature of the transition is confirmed by means of independent nanoindentation measurements on single crystals.     

Synthesis,Structure and High Thermal Stability of a Novel Three‐dimensional Zinc(II) Complex with an Unsymmetrical Rigid‐flexible Ligand

A novel metal‐organic framework, [Zn(C₁₀H₈O₅)]_n ( 1 ) (C₁₀H₈O₅ = 2‐(4‐carboxylatophenoxy)propionate), was synthesized and characterized by elemental analysis, IR spectroscopy, X‐ray crystallography and thermogravimetric analysis. The crystal structure study reveals that each zinc atom is coordinated by four oxygen atoms from four different ligands to obtain a distorted tetrahedron. The rigid carboxyl group bridges two adjacent zinc atoms to form a dimer of eight‐membered rings, whereas the flexible carboxyl group bridges two adjacent dimers to form 1D chains along the a axis. Two adjacent 1D chains are interconnected by the ligands to produce 2D layers. These layers are further stabilized by intermolecular hydrogen bonds to construct a 3D framework showing high thermal stability (445 °C).     

Synthesis of New Tetrazole Derivatives of Spiro‐ and Bis‐barbiturates

This work described the synthesis of the first and unprecedented examples of 5‐aryl‐1H‐tetrazoles including spiro‐ and bis‐(thio)barbiturates, generated from the reaction between 4‐(1H‐tetrazol‐5‐yl)benzaldehyde with (thio)barbituric acids and cyanogen bromide (BrCN) in the presence of triethylamine, providing good overall yields. Tetrazoles based on bis‐(thio) barbiturates were also obtained in the absence of BrCN under the same conditions. The structures were characterized by IR, ¹H NMR, ¹³C NMR, X‐ray crystallography and mass analysis techniques. The reaction mechanism was proposed. The hydrogen bond strength (E_HB) versus d (O1?????O7 (w)) distance (kcal.mol^?1) and corresponding pKa value for the proton of H_3A (in water molecule) in 4b.H₂O were estimated to be 13.8 kcal.mol^?1 and 8.2, respectively.