Junnian Wei

Aromatic Dicupra[10]annulenes

Metal-containing aromatic systems (metalla-aromatics) are unique and important both experimentally and theoretically. Among metalla-aromatics, six-membered metallabenzenes and metallabenzynes have attracted much attention in recent years. However, reports on their superior homologues are rare. In this work, the first series of aromatic dicupra[10]annulenes were isolated from the reaction of dilithio reagents and copper salts. Single-crystal X-ray structural analysis revealed dicupra[10]annulenes with averaged bond lengths. (7)Li NMR spectra and theoretical calculations revealed considerable aromatic character. XPS data suggested that the oxidation state of Cu atom in dicupra[10]annulenes was more likely to be Cu(I), indicating that the dilithio moieties in dicupra[10]annulenes participated as noninnocent ligands. This work demonstrates a novel approach to construct macrocyclic metalla-aromatics.

Magnesiacyclopentadienes as Alkaline‐Earth Metallacyclopentadienes: Facile Synthesis, Structural Characterization, and Synthetic Application

Metallacyclopentadienes have attracted much attention as building blocks for synthetic chemistry as well as key intermediates in many metal-mediated or metal-catalyzed reactions. However, metallacyclopentadienes of the alkaline-earth metals have not been reported, to say nothing of their structures, reaction chemistry, and synthetic applications. In this work, the first series of magnesiacyclopentadienes, spiro-dilithio magnesiacyclopentadienes, and dimagnesiabutadiene were synthesized from 1,4-dilithio 1,3-butadienes. Single-crystal X-ray structural analysis of these magnesiacycles revealed unique structural characteristics and bonding modes. Their reaction chemistry and synthetic application were preliminarily studied and efficient access to amino cyclopentadienes was established through their reaction with thioformamides. Experimental and DFT calculations demonstrated that these magnesiacyclopentadienes could be regarded as bis(Grignard) reagents wherein the two Mg-C(sp(2)) bonds have a synergetic effect when reacting with substrates.

Dianions as Formal Oxidants: Synthesis and Characterization of Aromatic Dilithionickeloles from 1,4‐Dilithio‐1,3‐butadienes and [Ni(cod)2]

Organolithium compounds can behave as reductants but never as oxidants in redox reactions. Reported herein is that 1,4-dilithio-1,3-butadienes reacted with [Ni(cod)2] (cod = 1,5-cyclooctadiene) to deliver dilithionickeloles. Single-crystal X-ray structural analysis revealed a coplanar structure of dilithionickeloles with an averaging of bond lengths. XPS data confirmed the oxidation state of Ni in dilithionickeloles was Ni(2+). (7)Li NMR spectra of dilithionickeloles and theoretical calculations revealed a considerable aromatic character. In this redox reaction, the dilithio dianionic compounds behaved as formal oxidants, thus oxidizing Ni(0) into Ni(2+). These results demonstrated that organolithium compounds with π-conjugation could be used as oxidants and could continue to accept extra electrons.

1,3‐Butadienyl Dianions as Non‐Innocent Ligands: Synthesis and Characterization of Aromatic Dilithio Rhodacycles

Herein we report that 1,4-dilithio-1,3-butadienes, a type of 1,3-butadienyl dianion, can act as non-innocent ligands, taking electrons from low-valent transition metals. Dilithio reagents reacted with [{RhCl(cod)}2] to give dilithio rhodacycle 3 a. Single-crystal X-ray structural analysis revealed the structure of 3 a with averaged bond lengths. XPS data suggested that the oxidation state of Rh in 3 a was more likely to be Rh(3+). CDA/ECDA confirmed the electron-transfer process. (7)Li NMR spectra of 3 a and theoretical calculations revealed a considerable aromatic character. In this process, the dilithio compounds behaved as non-innocent ligands and formal oxidants. These results demonstrated that organolithium compounds with suitable π-conjugation could be used as electron acceptor.

Isolable and well-defined butadienyl organocopper(I) aggregates: facile synthesis, structural characterization, and reaction chemistry.

Four types of alkenyl organocopper(I) aggregates linked by 1,3-butadienyl and/or 1,3,5,7-octatetraenyl moieties were selectively realized in good isolated yields. All these organocopper(I) aggregates were structurally characterized by single-crystal X-ray structural analysis. These unprecedented aggregates, stabilized by multiple Cu-Cu interactions and the conjugated 1,3-butadienyl or 1,3,5,7-octatetraenyl bridges, could undergo controlled structural transformations. The 1,4-dicopper 1,3-butadienyl aggregate 3 could be efficiently transformed to aggregate 2, while LiI could disaggregate the 1,3-butadienyl-1,3,5,7-octatetraenyl aggregate 4 to 1,3,5,7-octatetraenyl aggregate 5 and 1,3-butadienyl aggregate 2. Preliminary reaction chemistry and synthetic applications of these organocopper(I) aggregates were also investigated.

Transfer of aryl halide to alkyl halide: reductive elimination of alkylhalide from alkylpalladium halides containing syn-β-hydrogen atoms.

β-Hydride abstraction is a well-accepted elementary step for catalytic cycles in organometallic chemistry. It is usually anticipated that alkylpalladium halides containing syn-β-hydrogen atoms will undergo β-hydride abstraction to afford the Heck-type products. However, this study discloses that the above general knowledge is only conditionally correct. Our experimental results demonstrate that the reductive elimination of alkylhalides from alkylpalladium halides containing syn-β-hydrogen atoms may surpass the β-hydride abstraction or even become exclusive in certain cases.

Spiro Metalla-aromatics of Pd, Pt, and Rh: Synthesis and Characterization

Since the concept of aromaticity represents one of the most fundamental principles in chemistry, the search for unprecedented and exciting aromatic systems, therefore, continues to drive research in this area. Herein we report the synthesis and characterization of spiro metalla-aromatics, in which the transition metal (Pd, Pt, or Rh) is the spiro atom, that cross-conjugates two aromatic five-membered metallacycles. These spiro metalla-aromatics tend to take square planar geometries, with the dihedral angle being influenced by the steric repulsion between the α-positioned substituents. Rationalized and classified via both experimental measurements (X-ray structural analysis, NMR spectroscopy, XPS, etc.) and theoretical analysis (DFT calculation, ISE, AICD, NICS, and CMOs), all these fundamental observations extend the concept of aromaticity and organometallic chemistry.

The First Lutetacyclopentadienes: Synthesis, Structure, and Diversified Insertion/CH Activation Reactivity

The first well-defined lutetacyclopentadienes are synthesised from pentamethylcyclopentadienyl lithium (Cp*Li), 1,4-dilithio-1,3-butadienes, and LuCl3. The lutetacyclopentadiene shows excellent reactivity towards some small molecules, such as pivalaldehyde, Se, carbon dioxide, and isonitrile to efficiently construct 3-, 5-, 7-, 8-, and 9-membered rare-earth metallacycles. Both monoinsertion and double-insertion of two Lu-Csp2 bonds are observed. Specially, the reaction between lutetacyclopentadiene and isonitrile afforded [3,5,5]-fused metallacycles. The distinguished reactivity can be attributed to the highly ionic character and the cooperative reactivity of two Lu-Csp2 bonds.

Construction of octaalkyl-substituted and decasubstituted all-cis-octatetraenes via linear dimerization of 1,4-dicopper-1,3-butadienes and subsequent cross-coupling with halides.

Lithium iodide-assisted linear dimerization of 1,4-dicopper-1,3-butadienes and subsequent Pd-catalyzed cross-coupling reaction with halides provide an efficient way to construct octaalkyl-substituted and decasubstituted all-cis octatetraenes.

Lithium Aluminate Complexes and Alumoles from 1,4-Dilithio-1,3-Butadienes and AlEt2Cl

A series of lithium aluminate complexes and alumoles were synthesized from 1,4-dilithio-1,3-butadienes 1 and AlEt2Cl. Their structures were characterized using single-crystal X-ray structural analysis and NMR spectroscopy. The structure of the lithium aluminate complex 2-TMEDA showed that the Al atom adopted a tetra-coordinated mode bonded with two butadienyl Csp2 atoms and two ethyl Csp3 atoms. The lithium cation was located above the alumole ring. The structure of 3a revealed a dimeric 1-ethylalumole in the solid state. Diffusion ordered spectroscopy NMR spectra showed that 3a was also a dimer in C6D6 solvent. However, in tetrahydrofuran (THF) solution, the dimeric 3a dissociated into the 1-ethylalumole-THF adduct. The lithium aluminate complex 2 transformed into 3a-THF when treated with 1.0 equiv of AlEt2Cl. Preliminary reaction chemistry and synthetic applications of the lithium aluminate complex were also investigated.