Deoxygenative Cycloaddition of Aldehydes with Alkynes Mediated by AlCl3 and Zirconium: Formation of Cyclopentadiene Derivatives

Porphyrinatonickel(II)-Cyclopentene and Porphyrinatonickel(II)-Cyclopentadiene Hybrids: Zirconacyclopentadiene-Mediated Syntheses, Structures, and Mechanistic Study

The reaction of meso-formyl Ni(II) porphyrin 1 with zirconacyclopentadiene 2 in the presence of AlCl₃ afforded four products 3, 4, 5, and 6 with a total yield of over 85%. The structures of these compounds are well-characterized by ¹H NMR an d¹³C NMR spectroscopy, HRMS, and X-ray single-crystal diffraction. The mechanism is proposed mainly on the basis of isotopic labeling experiments, which showed that a Friedel-Crafts-type reaction and β-H shift may be critical during the formation of 5 and 6.

An Unusual and Facile Synthetic Route to Alumoles

Reaction of the aluminum dialkynyl LAl(CCR)₂ (L=N,N‐chelate ligand and R=organic group) with B(C₆F₅)₃ proceeds through an intermediate with Al⋅⋅⋅η²‐C≡C side‐on coordination to form the alumoles (2, 4, 6). A distinctive reaction pattern indicates a new facile synthetic route to aluminum‐containing heterocycles. The synthetic process is described, and the characterization of compounds and computational calculations were carried out. Furthermore, alumoles 2 and 4 exhibit an aggregation‐induced emission (AIE) of the bright yellow fluorescence.

Ring expansion of alumoles with organic azides: selective formation of six-membered aluminum-nitrogen heterocycles

A cyclopentadienyl-substituted alumole is shown to undergo ring expansions with a series of organic azides, affording 1,2-azaaluminabenzenes either with or without an azo group.

Aside from simple Lewis acid–base chemistry, the reaction chemistry of aluminacyclopentadienes, which are commonly referred to as aluminoles or simply alumoles, remains relatively underdeveloped. To date, few attempts to extend their inherent insertion and cycloaddition reactivity to the construction of stable aluminum-containing heterocycles have been reported. Herein, we demonstrate the selective ring expansion of a cyclopentadienyl-substituted alumole with a series of organic azides to form unsaturated six-membered AlN heterocycles. Depending on the substituent on the azide, the reaction proceeds either with or without loss of dinitrogen, leading to incorporation of only the “NR” unit of the azide or the entire azo substituent into the periphery of the heterocycle. A deeper understanding of these ring expansion reactions is reached through computational studies, illustrating deviations in the mechanism as a function of the organic azide employed.

Synthesis and characterization of manganese(ii) complexes supported by cyclopentadienyl-phosphine ligands

A series of manganese(ii) complexes supported by cyclopentadienyl-phosphine ligands have been synthesized and characterized. [LMn(μ-Cl)]₂ served as a precursor to organomanganese(ii) derivatives.

Synthesis and reactivity of asymmetric Cr(i) dinitrogen complexes supported by cyclopentadienyl–phosphine ligands

Trinuclear and dinuclear Cr(i) dinitrogen complexes and mixed-valence dinuclear Cr–N₂ complex, with novel asymmetric N₂ coordination modes, are realized.

Cyclopentadiene Construction via Rh-Catalyzed Carbene/Alkyne Metathesis Terminated with Intramolecular Formal [3 + 2] Cycloaddition

A new type of intramolecular carbene cascade reaction of alkynyl-tethered styryl diazoesters is presented, which is terminated with a formal [3 + 2] cycloaddition to give the bicyclic cyclopentadiene derivatives in high yields and selectivity. Additionally, it was found that the β-H shift is the dominating process in the case of alkyl alkyne-tethered substrates.

Conversion of zirconacyclopentadienes into metalloles: Fagan-Nugent reaction and beyond

Metalloles are derivatives of cyclopentadiene in which the methylene unit is replaced by a heteroatom, such as S, Se, Te, N, P, As, Sb, Bi, Si, Ge, Sn, B, Al, Ga, and so on. Many metallole derivatives have been widely used as photovoltaic cells, organic light emitting diodes (OLEDs), chemical sensors, electrochromic devices, microelectronic actuators, and organic field effect transistors (OFETs). In the meantime, many of them showed promising biological actives. Due to the similarity to cyclopentadiene, the anionic forms of metalloles were also widely explored in coordination chemistry. As a result, development of a general method for the formation of metalloles from available starting materials is highly desired. In this Account, we outline formation of various p-block element metalloles from zirconacyclopentadienes. The zirconacyclopentadienes can be easily prepared from two molecules of alkynes and a low-valent zirconocene species "Cp2Zr(II)" (Cp = cyclopentadienyl). Fagan and Nugent first reported the formation of main group metalloles from zirconacyclopentadiene, which provided a versatile approach for the construction of metalloles, especially for the formation of metalloles in heavier p-block elements. To further expand the substrate scope, a number of stepwise conversions were developed, which involve 1,4-dimetallo- or dihalo-1,3-butadiene as intermediates from zirconacyclopentadienes. Here, four processes are classified based on direct and indirect conversion of zirconacyclopentadienes into metalloles. Direct reaction of zirconacyclopentadienes with element halides afforded heterocycles of main group elements, which provided a versatile method for the synthesis of metalloles. Nonetheless, the reaction scope was restricted to heavier p-block elements such as S, Se, P, As, Sb, Bi, Ge, Sn, Ga, and In. And these reactions usually suffered low yields and long reaction time. Transmetalation of zirconacyclopentadiene with copper chloride greatly enriched the zirconacyclopentadiene chemistry. The synthesis of stannoles and pyrroles from zirconacyclopentadienes has been developed in the presence of CuCl. The direct reaction of the zirconacyclopentadienes with SiCl4 or R2SiCl2 does not give the desired silacyclopendadiene derivatives, even in the presence of CuCl. It can be circumvented by using dilithiated dienes from diiododienes, which are easily prepared by the iodination of zirconacyclopentadienes using CuCl as an additive. Finally, an umpolung strategy, reaction of electrophilic 1,4-diiodo-1,3-butadiene with nucleophilic amine or sulfide reagents, was successfully used in the formation of pyrroles and thiophenes.

The first lutetacyclopentadienes: synthesis, structure, and diversified insertion/C-H 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.

1,2,3,4-Tetrasubstituted cyclopentadienes and their applications for metallocenes: efficient synthesis through zirconocene- and CuCl-mediated intermolecular coupling of two alkynes and one diiodomethane

1,2,3,4-Tetrasubstituted cyclopentadienes and indene derivatives with identical or different substituents were obtained in good to excellent isolated yields through a zirconocene- and CuCl-mediated intermolecular coupling process. This synthetic procedure involved three organic partners, including one CH2 I2 , and two different or identical alkynes. Two alkynes or one diyne undergo Cp2Zr(II)-mediated (Cp = η(5)-C5H5) pair-selective reductive coupling to afford the corresponding zirconacyclopentadiene derivatives, which react, in the presence of CuCl and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1 H)-pyrimidinone (DMPU), with CH2I2 through intermolecular followed by intramolecular coupling to afford the cyclopentadiene derivatives. An application of the prepared tetrasubstituted cyclopentadiene derivatives was demonstrated by the facile synthesis of the corresponding zirconocene complexes [((4R)Cp)2ZrCl2] and [((4R)Cp)2ZrR'2] (R' = Me, Et, or nBu). The unique 1,2,3,4-tetrasubstituted cyclopentadiene ligands and the corresponding metallocenes are expected to have further applications in organometallic chemistry and organic synthesis.

Access to quinolines through gold-catalyzed intermolecular cycloaddition of 2-aminoaryl carbonyls and internal alkynes

A facile and general method leading to polyfunctionalized quinolines was developed. In the presence of a highly efficient combination encompassing (PPh)(3)AuCl and AgOTf, the reactions between 2-aminocarbonyls and an array of internal alkynes proceeded smoothly to afford quinoline derivatives in good to excellent yields (up to 93%).