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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.

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.

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.

Recently, there has been a progressive development of insulated π-conjugated metallopolymers with accumulated features of π-conjugated bridging units, transition metal complexes, and encapsulating moieties, as higher-order functionalized materials. A number of insulated conjugated metallopolymers have been successfully synthesized and their fascinating properties have been reported. In addition to the conventional features derived from π-conjugation and transition metals, their insulated structures can compensate for solubility, a disadvantage in conventional metallopolymers, and enhance their functionalities, such as sensing, luminescence, and conduction. In this review, we summarize the synthetic methodologies, structural characteristics, and functionalities of one-dimensional insulated π-conjugated metallopolymers, while focusing on the effect of transition metals and insulation on their properties.

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.

A palladium catalyst system that allows the reduction of carboxylic acids to the corresponding aldehydes with hydrosilanes as reducing agent and pivalic anhydride as an indispensable reagent is developed.

The reaction products can be used for Suzuki—Miyaura coupling reactions or Diels—Alder and hetero—Diels—Alder reactions.

Formation of allylboranes or alkenylboranes depends on the borylating agent and conditions used.

The reaction proceeds with excellent regio- and stereoselectivities without any directing groups in the acyl chlorides.

The reaction proceeds regioselectively, the major isomers (IV) are isolated in good to high yields.

A mixture of a palladium precursor and a phosphine ligand shows high catalytic activity in the reduction of acid chlorides to aldehydes with hydrosilanes.

Recent carbon–carbon bond forming reactions of carbon dioxide with alkenes, alkynes, dienes, aryl zinc compounds, aryl boronic esters, aryl halides, and arenes having acidic C–H bonds are reviewed in which transition-metal catalysts play an important role.

Aryl formates are efficient carbon monoxide sources in palladium-catalyzed esterification of aryl halides. The carbonylation readily proceeds at ambient pressure without the use of external carbon monoxide to afford the corresponding esters in high yields.

Nickel-catalyzed carboxylation of aryl and vinyl chlorides employing carbon dioxide has been developed. The reactions proceeded under a CO2 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 CO2. Mechanistic study suggests that Ni(I) species is involved in the catalytic cycle.

The optimized conditions are applied to a wide range of internal and terminal alkynes to provide the products with complete (Z)-selectivity.

The ligands in the iridium catalytic system play a crucial role for the success of the 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.

Two highly active ruthenium-based metathesis catalysts with N-heterocyclic carbene ligands bearing 2,3,4,5-tetraarylphenyl moieties are developed.

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.

Copper complexes (I) bearing an N-heterocyclic carbene ligand are efficient catalysts for the hydrocarboxylation of unsymmetrical or symmetrical alkynes using SiH(OEt)3 as reducing agent to give α,β-unsaturated carboxylic acids as (E)-isomers.

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

Silylation of allylic acetates (1) using organodisilanes (2) was carried out in the presence of a catalytic amount of Pd(DBA)2−LiCl at 100 °C. The silylation proceeded smoothly without β-hydrogen elimination of a resulting (π-allyl)palladium intermediate. The added chloride salt such as LiCl or NaCl was indispensable for the catalytic activity. On the other hand, remarkable improvement of the silylation was realized by employing allylic trifluoroacetates (4) in place of the acetates (1) as the substrates. The silylation proceeded even at room temperature, and the added chloride salts was not necessary as the catalyst component. In the silylation, transmetalation of the disilanes (2) with (η3-allyl)palladium intermediate (7) might be a critical step in the catalytic cycle. Model reactions for the transmetalation were carried out.

Triisopropoxymethyltitanium (1a) or diisopropoxydimethyltitanium (1b) was treated with carbon monoxide (1 atm, balloon) at room temperature overnight (16–18 h), and then the reaction mixture was added to various allyl derivatives in the presence of palladium catalyst (5 mob% based on the allylic derivatives) at room temperature. From 1b and cinnamyl acetate in the presence of tetrakis(triphenylphosphine)palladium, (E)-3,3-dimethyl-6-phenyl-5-hexen-2-one (5a) was afforded in 57% yield. A similar reaction with trans-2-hexenyl acetate also gave the corresponding γ,δ-unsaturated ketone in 57% yield. The formation of the products would be rationalized by titanium η2-acyl and oxicarbenoid intermediates.

Various allylic acetates (1a-j) are silylated with hexamethyldisilane (Me 3 SiSiMe 3 , 2) in the presence of a catalytic amount of Pd(DBA) 2 and LiCl at 100 o C to afford the corresponding allylic silanes in high yields. In addition, (trimethylsilyl)tributylstannane (Me 3 SiSnBu 3 , 3) can be used for the silylation of aromatic allylic acetates 1g-j at room temperature

Allylic carbonates and acetates are cyanated with trimethylsilyl cyanide in the presence of a catalytic amount (5 mol % based on the allylic substrates) of Pd-(PPh 3 ) 4 or Pd(CO)(PPh 3 ) 3 in THF under reflux to afford β,γ-unsaturated nitriles in high yields

Co2(CO)8-catalyzed ring-opening carbonylation of oxiranes and oxetane smoothly proceeds with high regioselectivity under 1 atm of carbon monoxide at room temperature to give the corresponding β- and γ-siloxy amides in high yields, respectively. [(R3Si)2NR1R2]+[Co(CO)4]− is thought to be an active catalyst species and directs the high regioselectivity of the carbonylation.

Various N,N‘-disubstituted and trisubstituted ureas were obtained in high yields by the ruthenium-complex-catalyzed dehydrogenation of N-substituted formamides and amines under reflux in mesitylene for 12 h under an argon atmosphere. From formanilide (1a) and aniline (2a), N,N ‘-diphenylurea (3a) was obtained in 92% yield. During this reaction, a stoichiometric amount of gaseous hydrogen was spontaneously evolved; thus, the addition of a hydrogen acceptor was not required. Formamide itself, i.e., HCONH2 (4), can also be used as a versatile carbonyl source. From HCONH2 (4) and primary amines, the corresponding N,N‘-disubstituted ureas were obtained in high yields together with the evolution of hydrogen and ammonia. To identify a catalytically active species, the stoichiometric reaction of RuCl2(PPh3)3 with formanilide (1a) was carried out in CH2Cl2 at room temperature to give a novel oxygen-atom-bridged dinuclear ruthenium complex, Ru2(μ-Cl)2Cl2(μ-PhNHCHO-O,O)(PPh3)4 (5), in 87% yield. Complex 5 showed a h...

Allylic carbonates are cyanated in high yields to β,γ-unsaturated carbonitriles using trimethylsilyl cyanide in the presence of a catalytic amount (5 mol %) of Pd(PPh3)4 in THF under reflux. In the reaction, cinnnamyl methyl carbonate affords cinnamyl cyanide in 98% yield. Allylic acetates also provide the corresponding carbonitriles, but often in lower yields. The cyanations of several cis- and trans-alicyclic substrates proceed cleanly (stereoselectivity > 99%) with overall retention. Characterization and reaction of palladium complexes relevant to the present catalysis indicate that transmetalation of an η3-allyl palladium complex with trimethylsilyl cyanide is facile, while the resulting cyano(η3-allyl)palladium complexes afford the corresponding allylic cyanides only when excess trimethylsilyl cyanide is present. Stereochemistry of the product indicates that the CN attacks the η3-allyl moieties from the palladium side.

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)-α,β-unsaturated amides regio- and stereoselectively. The same catalyst system realized the first example of the addition of formamides to terminal alkynes giving the corresponding α,β-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.