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A bridging monomer with terpyridine moieties at both ends of the insulated conjugated chain was successfully synthesized. The synthesis necessitated a new strategy, in which FeII was employed as a removable water-solubilizing substituent. The monomer was able to coordinate with FeII, CoII, NiII, or RuII to give highly insulated conjugated metallopolymers. The high-coverage insulation suppressed the recombination of charge carriers relative to an uninsulated reference and provided higher charge mobility along the chain than the less insulated metallopolymer.

The hydroallylation of allenes was developed by employing a hydrosilane and allyl chlorides in the presence of a copper catalyst. The reaction provided (E)-1,5-dienes mainly in good to high yields.

We successfully synthesized a hetero face-to-face porphyrin array composed of ZnTPP and RuTPP(DABCO)2 (TPP: 5, 10, 15, 20-tetraphenylporphyrin, DABCO: 1,4-diazabi-cyclo[2.2.2]octane) in 2:1 molar ratio. A cyclic Zn porphyrin dimer (ZnCP) was also used as the host molecule for the Ru porphyrin. In the latter, the Ru-DABCO bonding in RuTPP(DABCO)2 was stabilized by the host-guest complexation. Reaction progress kinetic analysis of the ligand substitution reaction of RuTPP(DABCO)2 and that in ZnCP revealed the stabilization mechanism of the Ru-DABCO bonding. Photoinduced electron transfer (PET) from the Zn porphyrin to the Ru porphyrin was observed in the porphyrin array. The host-guest stabilization of unstable complex for construction of a donor-acceptor-donor structure is expected to be a new method for an artificial photosynthesis.

Triarylalkene-capped conjugated rotaxanes were synthesized via a palladium-catalyzed tandem Sonogashira/hydroaryl reaction between aryl halides and terminal alkynes bearing two permethylated α-cyclodextrins (PM α-CDs) with high regioselectivity because of the insulation effect of the PM α-CDs. Moreover, sequential Sonogashira coupling and hydroarylation reactions using different aryl substrates afforded a regio- and stereoselective trisubstituted alkene as a single product. This new class of rotaxane-forming reactions can be used to increase the diversity of rotaxane skeletons, and thereby the material functionalities of rotaxanes.

The development of new tuning methods for π-conjugated insulated molecular wires with strictly defined axle lengths as well as positions and degrees of macrocycle coverage would provide unprecedented insight into insulation effects in functionalized materials. Herein, iterative reactions of oligo(phenylene ethynylene) (OPE) linked with permethylated α-cyclodextrins were carried out to fabricate insulated molecular wires with a defined length and insulation in desired areas. Insulated OPEs were elongated in a stepwise manner by performing sequential coupling/deprotection reactions. The insulated areas on the OPE units in each expansion step were selectively controlled by means of programmed solvent conditions (high/low polarity). Moreover, a completely insulated OPE (up to a linked [11]rotaxane) with high structural regularity and high covering ratio was synthesized by appropriate tuning of the Pd catalyst and an extension unit bearing a traceless capping unit based on a tert-butyldimethylsilyl group. This strategy may guide the development of the selective synthesis of fully insulated, partially insulated, and uninsulated molecular wires with well-defined lengths and covered/uncovered areas.

The nickel-catalyzed double carboxylation of internal alkynes employing carbon dioxide (CO2) has been developed. The reactions proceed under CO2 (1 atm) at room temperature in the presence of a nickel catalyst, Zn powder as a reducing reagent, and MgBr2 as an indispensable additive. Various internal alkynes could be converted to the corresponding maleic anhydrides in good to high yields. DFT calculations disclosed the indispensable role of MgBr2 in the second CO2 insertion.

Borylative allyl-allyl coupling using allenes, bis(pinacolato)diboron, and allyl phosphates has been developed in the presence of a copper catalyst bearing an N-heterocyclic carbene ligand. The reaction affords boryl-substituted 1, 5-diene derivatives in good to high yields with high regioselectivity and Z selectivity.

Iron-catalyzed reduction of acid chlorides to the corresponding aldehydes with a hydrosilane as a reducing agent has been developed. A simple mixture of a commercially available iron oxide (FeO) and tris(2,4,6-trimethoxyphenyl)phosphine (TMPP) as a catalyst realized the reduction of acid chlorides to the corresponding aldehydes under mild reaction conditions.

This review summarizes the transformation of alkynes using a copper hydride (Cu–H) or boryl copper (Cu–B) species as the active species. The semihydrogenation, hydrocarboxylation, and hydroboration of alkynes have been developed using Cu–H as the active species. The hydroboration, diboration, carboboration and boracarboxylation of alkynes involve the Cu–B species. These transformations afforded multi-substituted alkenes that are potentially good intermediates in organic synthesis. The key to the regioselective transformation is the addition of the Cu–H or Cu–B species to an alkyne, to afford the corresponding alkenylcopper intermediate regioselectively.

Ru(II) complexes with a N-heterocyclic carbene ligand bearing flexible zeroth-, first-, or second-generation dendritic moieties were synthesized and characterized. The structure of the ruthenium complex with the zeroth-generation dendritic moieties was determined by X-ray crystallography. ONIOM calculations showed that the second generation dendritic moieties surrounded the ruthenium core. These complexes worked as active catalysts for the ring-closing metathesis at 25 °C.

Palladium-catalyzed formal arylacylation of allenes using acid chlorides and arylboronic acids has been achieved. The reaction afforded the corresponding α, β-unsaturated ketones regio- and stereoselectively.

This review summarizes transformations using copper hydride (Cu-H), boryl copper (Cu-B) or silyl copper (Cu-Si) as active catalyst species. Semihydrogenation, hydroboration, and hydrocarboxylation have been developed using Cu-H as active catalyst species. Preferential reduction of sterically hindered ketones is accompanied by Cu-H species bearing a bowl-shaped phosphine as a crucial ligand. Employing Cu-B species, hydroboration of alkynes and allenes, synthesis of 2-boryl-1,3-butadiene, and borylative allyl-allyl coupling are established. Silacarboxylation of alkynes, regiodivergent silacarboxylation of allenes, and silylative allylation of ketones involve Cu-Si species. The key to these selective transformations is regioselective addition of Cu-H, Cu-B, or Cu-Si species to carbon-carbon multiple bonds of alkynes and allenes to afford the corresponding alkenylcopper or allylcopper intermediates.

The copper-catalyzed silylative allylation of ketones with allenes and silylboranes via an in situ generated β-silylallylcopper intermediate has been developed. Various ketones and allenes were con...

Something solid to build on: 2-Boryl 1,3-butadienes with various substitution patterns were formed in good to high yields in a copper-catalyzed borylation of α-alkoxy allenes with bis(pinacolato)diboron (see scheme; Bn=benzyl, pin=pinacolate, L is an N-heterocyclic carbene ligand). The products were found to be useful intermediates for the synthesis of cyclic vinyl boranes, α,β-unsaturated ketones, and functionalized multisubstituted dienes.

Cobalt-catalyzed carboxyzincation reactions employing carbon dioxide and zinc metal powder are developed. By using alkynes as substrates, regio- and stereodefined (Z)-β-zincated acrylates are provided. The corresponding alkenylzinc moiety can be converted to various substituents, affording multisubstituted acrylic acids. Furthermore, by adding electron-deficient alkene to the reaction system, the four-component coupling reactions of alkyne, alkene, CO2, and the Zn atom proceed via carboxyzincation.

N-Heterocyclic carbenes bearing poly(ethylene glycol) chains of different lengths have been designed and employed as ligands in palladium-catalyzed coupling reactions. The catalyst system having longer chains was found to be highly efficient for Suzuki–Miyaura coupling and borylation reactions employing aryl chlorides under mild reaction conditions.

A highly efficient cobalt-catalyzed reductive carboxylation reaction of alkenyl trifluoromethanesulfonates (triflates) has been developed. By employing Mn powder as a reducing reagent under 1 atm pressure of CO2 at room temperature, diverse alkenyl triflates can be converted to the corresponding α,β-unsaturated carboxylic acids. Moreover, the carboxylation of sterically hindered aryl triflates proceeds smoothly in the presence of a nickel or cobalt catalyst.

Reaction and work-up conditions for the regioselective transformation of various 1-substituted, 1,1- and 1,3-disubstituted allenes with carbon dioxide to homoallyl alcohol derivatives are developed which tolerate numerous functional groups.

An efficient synthesis of aldehydes from acid chlorides with hydrosilanes as a reducing agent in the presence of a palladium catalyst has been achieved. A simple mixture of commercially available Pd(dba)2 and Mes3P as a catalyst realized the reduction of various acid chlorides including aliphatic acid chlorides and α,β-­unsaturated acid chlorides to the corresponding aldehydes in good to high yields under mild reaction conditions.

A copper catalyst bearing a suitable Xantphos derivative or NHC ligand was found to be highly efficient for the selective semihydrogenation of non-polar unsaturated compounds using a mixture of a silane and an alcohol as reducing agent. The catalytic system was useful for the selective semihydrogenation of internal alkynes to (Z)-alkenes with suppression of overreduction to the corresponding alkanes. Furthermore, semihydrogenations of terminal alkyne, 1,2-diene, 1,3-diene, 1,3-enyne and 1,3-diyne systems were also achieved selectively.

A highly efficient cobalt-catalyzed reductive carboxylation reaction of alkenyl trifluoromethanesulfonates (triflates) has been developed. By employing Mn powder as a reducing reagent under 1 atm pressure of CO2 at room temperature, diverse alkenyl triflates can be converted to the corresponding α,β-unsaturated carboxylic acids. Moreover, the carboxylation of sterically hindered aryl triflates proceeds smoothly in the presence of a nickel or cobalt catalyst.

Magnesium chloride (MgCl2), a stable and cheap salt, works as an active catalyst for the synthesis of cyclic carbonates from epoxides and atmospheric-pressure carbon dioxide (CO2). Various epoxides are converted to the corresponding cyclic carbonates in good to high yields.

Iridium complexes show high catalytic activity in intermolecular additions of acid chlorides to terminal alkynes to afford valuable (Z)-β-chloro-α,β-unsaturated ketones. Ligands in the catalytic system play a crucial role in this reaction. An N-heterocyclic carbene (NHC) is an efficient ligand for the addition of aroyl chlorides, while dicyclohexyl(2-methylphenyl)phosphine (PCy(2)(o-Tol)) is indispensable for the reaction of aliphatic acid chlorides. The addition reactions proceed regio- and stereoselectively with suppression of decarbonylation and β-hydrogen elimination, which have been two major intrinsic problems in transition-metal-catalyzed reactions. Stoichiometric reactions of active iridium catalysts with aroyl chlorides and aliphatic acid chlorides are carried out to gain insights into the reaction mechanisms.

Palladium complexes with a salicylaldiminato ligand bearing a hydroxyl group (1a and 1b) have been synthesized and characterized. The structures of these complexes were confirmed by X-ray crystallography. A reversible deprotonation/protonation of the hydroxyl moiety on 1b was observed, while such behaviour was impossible with a related palladium complex (1c) bearing a methoxyl group in place of the hydroxyl group. The deprotonation affected its catalytic behaviour: the activity for polymerization of methyl acrylate catalyzed by 1b considerably decreased in the presence of 1 equiv. of tBuOK.

A highly efficient hydroesterification of alkynes employing aryl formates has been developed without the use of external carbon monoxide and at ambient pressure. The reaction in the presence of a palladium-xantphos catalyst system selectively affords α,β-unsaturated esters in good to high yields. Use of an aryl formate is crucial and alkyl formates did not react at all. The hydroesterification of norbornene and terminal alkenes also readily proceeded under similar reaction conditions. A mechanistic study showed that conversion of aryl formates to carbon monoxide and phenol derivatives occurred in the hydroesterification. Xantphos is highly effective as a ligand both in the conversion of aryl formates and the hydroesterification reactions.

Transition-metal-catalyzed transformation to produce various kinds of carbonyl compounds is one of the most powerful synthetic methods. Among them, transition-metal-catalyzed addition reactions of carbonyl compounds to carbon-carbon multiple bonds such as alkynes are environmentally friendly because all atoms of the substrates are retained in the products. Although the addition of aldehydes to alkynes, hydroacylation, has been intensively studied, the addition of acid chlorides, formamides, and formates has not been fully developed. One plausible explanation for it is the occurrence of competing decarbonylation reactions. In addition, relatively lower reactivity of formamides or formates limits the application as substrates in these addition reactions. In this paper, we overview recent results on the transition-metal-catalyzed addition reactions of carbonyl functionalities to alkynes.

A new type of molecular wiring method was developed based on the polymerization or copolymerization of an insulated π-conjugated monomer between nanosized electrodes.

We synthesized cyclic host molecules, A, B, and C, based on a rigid π-conjugated system composed of porphyrin and fluorene units. After the transformation of the ester units of cyclic host B to car...

Transition-metal-catalyzed transformations between carbonyl compoundsand carbon-carbon unsaturated bonds are important and attractive.In this account, we describe our recent results on the iridium-and palladium-catalyzed additions of acid chlorides, carbamoyl chlorides,and formamides to alkynes. 1 Introduction 2 Decarbonylation of Aldehydes 3 Addition Reactions 3.1 Addition of Acid Chlorides to Terminal Alkynes 3.2 Addition of Formamides to Alkynes 4 Annulation of N-Arylcarbamoyl Chlorideswith Internal Alkynes 5 Conclusion

Synthesis and characterization of a series of mono-O-(diphenylphosphinobenzyl)calix[6]arenes are presented. The two types of calix[6]arene moieties were prepared: 1 (with tert-butyl groups at the u...

A new phosphine bearing dodeca(ethylene glycol) chains has been synthesized and employed as a ligand in the palladium-catalyzed Suzuki-Miyaura coupling reaction. The system was found to be highly effective using unactivated aryl chlorides as the substrate.

A series of novel imidazolium salts bearing hydrophilic tetraethylene glycol (TEG) and/or hydrophobic long-chain alkyl (n-C12) functionalities, which are precursors for desired N-heterocyclic carbene (NHC) ligands, were synthesized and characterized. Rh(I)-NHC complexes were prepared in good yields by the silver carbene transfer method with NHC-Ag species derived from the imidazolium salts. The molecular structure of the Rh(I)-NHC complex having n-C12 chains has been determined by a single-crystal X-ray diffraction study and the complex is found to possess extended alkyl chains with anti conformations in the solid state. Hydrosilylation with the Rh(I) complexes and Suzuki-Miyaura coupling reactions with the Pd(II) complexes with these NHC ligands were carried out. In the latter case, the TEG moiety enhances catalytic activity considerably.

Expanding catalytic environment to a nanosize is one of the most promising ways to improve performance of homogeneous catalysts. In this highlight review, recent development in homogeneous transiti...

Expanding the catalytic environment to a nanosize must be one of the most promising ways to improve the performance of homogeneous catalysts. In this Forum Article, recent developments in homogeneous nanosize palladium catalysts are reviewed. It contains solubilized palladium nanoparticles, metalated dendrimers, and complexes with well-defined nanosized ligands. These systems realize efficient catalyst recycling, unique selectivity, suppression of metal aggregation, and remarkable enhancement of the catalytic activity.

The formal hydroacylation reaction of allenes has been developed employing carboxylic anhydrides as acyl sources and hydrosilanes as reducing reagents in the presence of a commercially available palladium complex as a catalyst. The reaction affords α,β-unsaturated ketones regio- and stereoselectively. The similar catalyst system is also effective for the reduction of carboxylic anhydrides to the corresponding aldehydes employing hydrosilanes.

The copper-catalyzed silylative allylation of ketones with allenes and silylboranes via an in situ generated β-silylallylcopper intermediate is presented.

A regiodivergent silacarboxylation of allenes under a CO2 atmosphere with PhMe2Si–B(pin) as a silicon source in the presence of a copper catalyst at 70 °C has been developed. The regioselectivity of the reaction is successfully reversed by the proper choice of ligand; carboxylated vinylsilanes are obtained with rac-Me-DuPhos as the ligand, whereas the use of PCy3 affords carboxylated allylsilanes. Thus, two different carboxylated silanes can be selectively and regiodivergently synthesized from a single allene substrate.

The Ni-catalyzed double carboxylation of internal alkynes with CO2, affording highly versatile maleic anhydrides as products is reported.

Alkynyl group-containing α-monosubstituted and α,α-disubstituted carboxylic acids are obtained with moderate to good yields.

The title reaction affords the corresponding α,β-unsaturated ketones (IV), (VI), and (VIII) regio- and stereoselectively.

Copper is one of the ubiquitous and inexpensive metals. In classical methodology, a stoichiometric amount of copper species has been utilised for organic synthesis. However, the development of copper-catalysed reactions is most important from the viewpoint of sustainability and green chemistry. This chapter summarises valuable homogeneous copper-catalysed reactions such as crosscouplings, oxidation, fixation of carbon dioxide, and others.

Three new triarylphosphines were prepared that have a 2,3,4,5-tetraphenylphenyl (TPPh) moiety on one of the phenyl rings (at the ortho, meta, or para position) of triphenylphosphine. Among them, the ortho derivative is particularly effective to utilize unactivated aryl chlorides in three different palladium-catalyzed reactions, i.e., Suzuki−Miyaura coupling, Mizoroki−Heck reaction, and silylation with Me3SiSiMe3. On the other hand, the corresponding meta and para derivatives are not effective as ligands at all in these catalytic reactions. X-ray crystal structures of Pd(0) complexes having the effective phosphines (ortho derivatives) as ligands show that η2-coordination on the TPPh moiety is general and operative to realize a highly active catalyst system.

A platinum(II) complex bearing 1,10-phenanthroline-5,6-dione (phenO2), [PtCl(phenO2-N,N′)(PPh3)]+ ([2]+) was newly prepared and characterized. An X-ray crystallographic study of [2](PF6) revealed t...

A regiodivergent silacarboxylation of allenes under a CO2 atmosphere with PhMe2Si–B(pin) as a silicon source in the presence of a copper catalyst at 70 °C has been developed. The regioselectivity of the reaction is successfully reversed by the proper choice of ligand; carboxylated vinylsilanes are obtained with rac-Me-DuPhos as the ligand, whereas the use of PCy3 affords carboxylated allylsilanes. Thus, two different carboxylated silanes can be selectively and regiodivergently synthesized from a single allene substrate.