Jun Terao

Copper‐Catalyzed Hydrocarboxylation of Alkynes Using Carbon Dioxide and Hydrosilanes

to the corresponding methyl ester 2aMe.Byemploying [IPrCuCl] + tBuONa (Table 1, entry 1) or[IMesCuCl] + tBuONa (Table 1, entry 2) as a catalyst,2aMe was obtained in only trace amounts and 49% yield,respectively. In the latter case, a considerable amount (19%yield)ofcis-stilbene(3a)wasobservedasaby-product.When[IPrCuF]

Cross-Coupling Reaction of Alkyl Halides with Grignard Reagents Catalyzed by Ni, Pd, or Cu Complexes with π-Carbon Ligand(s)

Transition metal-catalyzed cross-coupling reactions of organic halides and pseudo-halides containing a C-X bond (X = I, Br, Cl, OTf, OTs, etc.) with organometallic reagents are among the most important transformations for carbon-carbon bond formation between a variety of sp, sp(2), and sp(3)-hybridized carbon atoms. In particular, researchers have widely employed Ni- and Pd-catalyzed cross-coupling to synthesize complex organic structures from readily available components. The catalytic cycle of this process comprises oxidative addition, transmetalation, and reductive elimination steps. In these reactions, various organometallic reagents could bear a variety of R groups (alkyl, vinyl, aryl, or allyl), but the coupling partner has been primarily limited to sp and sp(2) carbon compounds: alkynes, alkenes, and arenes. With alkyl coupling partners, these reactions typically run into two problems within the catalytic cycle. First, oxidative addition of alkyl halides to a metal catalyst is generally less efficient than that of aryl or alkenyl compounds. Second, the alkylmetal intermediates formed tend to undergo intramolecular beta-hydrogen elimination. In this Account, we describe our efforts to overcome these problems for Ni and Pd chemistry. We have developed new catalytic systems that do not involve M(0) species but proceed via an anionic complex as the key intermediate. For example, we developed a unique cross-coupling reaction of alkyl halides with organomagnesium or organozinc reagents catalyzed by using a 1,3-butadiene as the additive. This reaction follows a new catalytic pathway: the Ni or Pd catalyst reacts first with R-MgX to form an anionic complex, which then reacts with alkyl halides. Bis-dienes were also effective additives for the Ni-catalyzed cross-coupling reaction of organozinc reagents with alkyl halides. This catalytic system tolerates a wide variety of functional groups, including nitriles, ketones, amides, and esters. In addition, we have extended the utility of Cu-catalyzed cross-coupling reactions. With 1-phenylpropyne as an additive, Cu-catalyzed reactions of alkyl chlorides, fluorides, and mesylates with Grignard reagents proceed efficiently. These new catalytic reactions use pi-carbon ligands such as pi-allyl units or alkynes instead of heteroatom ligands such as phosphines or amines. Overall, these reactions provide new methodology for introducing alkyl moieties into organic molecules.

Nickel-Catalyzed Carboxylation of Aryl and Vinyl Chlorides Employing Carbon Dioxide

Nickel-catalyzed carboxylation of aryl and vinyl chlorides employing carbon dioxide has been developed. The reactions proceeded under a CO(2) pressure of 1 atm at room temperature in the presence of nickel catalysts and Mn powder as a reducing agent. Various aryl chlorides could be converted to the corresponding carboxylic acid in good to high yields. Furthermore, vinyl chlorides were successfully carboxylated with CO(2). Mechanistic study suggests that Ni(I) species is involved in the catalytic cycle.

Highly Selective Copper‐Catalyzed Hydroboration of Allenes and 1,3‐Dienes

The highly selective copper-catalyzed hydroboration of allenes has been developed. Allylboranes and alkenylboranes were selectively prepared by the judicious choice of catalytic species (copper hydride and boryl copper). Furthermore, two types of alkenylboranes could be selectively synthesized by the choice of an appropriate ligand. Mechanistic studies confirmed that the protonation of a (Z)-σ-allyl copper species, which was isolated and structurally characterized by single-crystal X-ray diffraction, was a key step in these reactions. Besides allenes, this method is also applicable to the selective hydroboration of 1,3-diene derivatives to afford allylboranes and homoallylboranes.

Synthesis of Organic-Soluble Conjugated Polyrotaxanes by Polymerization of Linked Rotaxanes

Extensive research on the use of cyclodextrin for insulating pi-conjugated polymer chains has been carried out. However, the resulting polyrotaxanes do not exhibit high and constant covering ratios and are generally insoluble in organic solvents. Here we demonstrate a new method of synthesizing permethylated cyclodextrin-based polyrotaxanes involving the polymerization of linked rotaxane monomers. The insulated molecular wires obtained by this method are highly soluble in organic solvents and have a high covering ratio, rigidity, and photoluminescence efficiency. A cholesteric liquid-crystal phase was observed for these highly rigid polyrotaxanes, in which threading of a pi-conjugated polymer chain through chiral macrocycles occurs.

Insulated Molecular Wire with Highly Conductive π-Conjugated Polymer Core

We have recently developed a new method for synthesizing polyrotaxanes with a high covering ratio, rigidity, photoluminescence efficiency, and solubility in a variety of organic solvents through the polymerization of structurally defined rotaxane monomers. The rigid rodlike structure of the pi-conjugated core polymers in these polyrotaxanes is thought to facilitate the effective transport of charge carriers. Here we applied this method to the synthesis of a polyrotaxane having a poly(phenylene ethynylene) backbone by the Sonogashira copolymerization of a structurally defined rotaxane with a linker molecule. According to time-resolved microwave conductivity and transient absorption spectroscopy measurements, the hole mobility along the pi-conjugated polymer chain of the polyrotaxane thus formed was extremely high and comparable to that in amorphous silicon.

Palladium-catalyzed intermolecular addition of formamides to alkynes.

A novel palladium system for an intermolecular addition of formamides to alkynes has been developed. The reaction of formamides with internal alkynes in the presence of a palladium catalyst with acid chloride as an additive afforded (E)-alpha,beta-unsaturated amides regio- and stereoselectively. The same catalyst system realized the first example of the addition of formamides to terminal alkynes giving the corresponding alpha,beta-unsaturated amides bearing a terminal methylene moiety as major products. The present reaction was widely applicable to substrates with various functionalities. This method also could be applied to the reaction of N,N-disubstituted formamides with norbornene. A hydridopalladium species would be formed as a key intermediate with in situ generated HCl under the reaction conditions.

Iridium-Catalyzed Addition of Acid Chlorides to Terminal Alkynes

An iridium N-heterocyclic carbene (NHC) complex, IrCl(cod)(IPr), successfully catalyzed an addition of common aromatic acid chlorides to terminal alkynes to afford (Z)-beta-chloro-alpha,beta-unsaturated ketones regio- and stereoselectively. When the NHC ligand (IPr) was changed to a phosphine (RuPhos), the addition occurred with decarbonylation to give the corresponding (Z)-vinyl chlorides. Furthermore, the former reaction using IrCl(cod)(IPr) can be applied to the catalytic synthesis of 2,5-disubstituted furans.

Design principle for increasing charge mobility of π-conjugated polymers using regularly localized molecular orbitals

The feasibility of using π-conjugated polymers as next-generation electronic materials is extensively studied; however, their charge mobilities are lower than those of inorganic materials. Here we demonstrate a new design principle for increasing the intramolecular charge mobility of π-conjugated polymers by covering the π-conjugated chain with macrocycles and regularly localizing π-molecular orbitals to realize an ideal orbital alignment for charge hopping. Based on theoretical predictions, insulated wires containing meta-junctioned poly(phenylene–ethynylene) as the backbone units were designed and synthesized. The zigzag wires exhibited higher intramolecular charge mobility than the corresponding linear wires. When the length of the linear region of the zigzag wires was increased to 10 phenylene–ethynylene units, the intramolecular charge mobility increased to 8.5 cm2 V−1 s−1. Theoretical analysis confirmed that this design principle is suitable for obtaining ideal charge mobilities in π-conjugated polymer chains and that it provides the most effective pathways for inter-site hopping processes.

Conversion of a (sp3)C–F bond of alkyl fluorides to (sp3)C–X (X = Cl, C, H, O, S, Se, Te, N) bonds using organoaluminium reagents

A simple method for the conversion of (sp(3))C-F bonds of alkyl fluorides to (sp(3))C-X (X = Cl, C, H, O, S, Se, Te, N) bonds has been achieved by the use of a hexane solution of organoaluminum reagents having Al-X bonds.