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This account summarizes the Cu-catalyzed borylative functionalization of unsaturated hydrocarbons that we have developed over the past decade. First, we focus on the regioselective hydroboration of unsymmetrical internal alkynes and 1,2-dienes. Second, the borylative allyl-allyl coupling using 1,2-dienes, B2pin2, and allyl phosphate is presented. Third, we introduce boro-acylation and boroformylation of 1,2-dienes using an acid anhydride and formate, respectively, as the electrophile. Lastly, we describe the synthesis of 2-boryl-1,3-butadienes and cyclic allylborates. These reactions can offer a versatile method for synthesizing a broad range of useful compounds, and also provide a detailed understanding of the reaction mechanism, which could lead to the development of more efficient and selective catalysts.

Carbon dioxide (CO2) is the final product of hydrocarbon oxidation and is thermodynamically and kinetically stable. Therefore, efforts to find methods to activate and reuse this material under mild reaction conditions are required. To achieve efficient conversion, one solution is the use of transition-metal catalysts. This chapter reviews the process of catalytic carboxylation with carbon dioxide via carbon–carbon bond formation involving base-metal complexes (copper, nickel, and cobalt) as catalysts. These reactions are organized based on the metal used, and the reactions using each metal are classified according to substrate and reaction pattern.

α-Alkylation reactions between amides and alcohols, with dimethylacetamide-stabilized Ru nanoparticles (NPs) as the catalyst, were investigated. The reactions proceeded with low catalyst loadings compared to metal complexes. Characterizations of the Ru NPs were performed by X-ray photoelectron spectroscopy, X-ray absorption fine structure spectroscopy, and various techniques. Control experiments revealed the reaction mechanisms, which proceeded

Carbon dioxide (CO2) is an ideal source of carbon because it is inexpensive, non-toxic, and abundant. In general, the development of carbon–carbon bond forming reactions is not easy because CO2 is thermodynamically and kinetically stable. However, recent progress in the strategies used for CO2 fixation utilizing transition metals is very useful for catalytic carboxylation toward the synthesis of carboxylic acid derivatives. In this chapter, the recent progress in the transition-metal-catalyzed carboxylation of CO2 is reviewed, including the carboxylation of unsaturated hydrocarbons, organometallic reagents, and organic halides, as well as carboxylation via carbon–hydrogen bond activation.

The sila-acylation of allenes is performed in the presence of a copper catalyst using PhMe2Si-B(pin) and esters as the silyl and acyl sources, respectively. β-Silyl-β,γ-unsaturated ketones are obtained regioselectively in good to high yields. The sila-imination of allenes is also achieved using nitriles as electrophiles. Exposure of the reaction mixture to air results in the production of cyclic silyl peroxides.

We have succeeded in the synthesis of various tetrasilatetrathia[8]circulenes with alkyl and aryl groups on the silicon atoms. We also disclosed the effect of phosphine ligands on palladium-catalyzed silylation of tetraiodotetrathienylene and rhodium-catalyzed intramolecular silylation of tetrasilyltetrathienylenes. Experimental and theoretical analysis revealed the effect of the substituents on the silicon atoms on their electronic property.

The synthesis of cyclic allylborates was achieved by the reaction of 1,3-dienes and B

A series of pyridine ligands bearing poly(ethylene glycol) (PEG) chains at the para position was synthesized and characterized by NMR and ESI‐HRMS analysis. 1H NMR analysis showed that pyridines coordinate to Pd(OAc)2 even when a long PEG chain is attached to the pyridine ring. In the Pd‐catalyzed oxidation of alcohols, the pyridines bearing longer PEG chains were found to be efficient ligands.

This paper reports novel Cu-catalyzed three-component coupling reactions using nitriles, 1, 3-dienes and silylboranes. The desired reactions proceed at room temperature and yield β, γ-unsaturated ketones with a (dimethylphenylsilyl)methyl moiety at the α-position. Diverse nitriles participate in the reaction and the corresponding products were obtained in good to high yields with high regioselectivity.

A bulky carboxylic acid bearing one 1-adamantylmethyl and two methyl substituents at the α-position is demonstrated to work as an efficient carboxylate ligand source in Pd-catalyzed intermolecular C(sp2)-H bond arylation reactions. The reactions proceeded smoothly under mild conditions, taking advantage of the steric bulk of the carboxylate ligands.

Biological systems are known to spontaneously adjust the functioning of neurotransmitters, ion channels, and the immune system, being promoted or regulated through allosteric effects or inhibitors, affording non-linear responses to external stimuli. Here we report that an insulated conjugated bimetallopolymer, in which Ru(II) and Pt(II) complexes are mutually connected with insulated conjugations, exhibits phosphorescence in response to CO gas. The net profile corresponds to a sigmoidal response with a dual self-controlling system, where drastic changes were exhibited at two threshold concentrations. The first threshold for activation of the system is triggered by the depolymerization of the non-radiative conjugated polymer to luminescent monomers, while the second one for regulation is triggered by the switch in the rate-determining step of the Ru complex. Such a molecular design with cooperative multiple transition metals would provide routes for the development of higher-ordered artificial molecular systems bearing bioinspired responses with autonomous modulation., Molecules can serve as biomimetic sensors, but dual self-controlling systems that involve self-activation and self-regulation are difficult to mimic. Here the authors report an insulated conjugated bimetallopolymer with cooperative multiple transition metals that phosphoresces in response to carbon monoxide.

Zinc-catalyzed synthesis of acylsilanes using carboxylic acids and a silylborane has been achieved in the presence of pivalic anhydride. Various carboxylic acids were converted to the corresponding acylsilanes. The in situ formation of mixed anhydrides was essential in the present reaction.

The regioselective sila-acylation and silaformylation of 1,3-dienes was achieved over a copper catalyst using a silylborane as a silyl source. β,γ-Unsaturated ketones with a (dimethylphenylsilyl)methyl moiety at the α-position were obtained using esters, while β,γ-unsaturated aldehydes were obtained using formate esters.

π-Conjugated porphyrin-containing hollow structures with defined axis-length were successfully synthesized by a two-step template method, i.e., template-assisted cyclization and oligomerization. During the oligomerization, templates played important roles in controlling the reaction rates and the axis lengths. The hollow structures exhibited an extended effective π-conjugation because of the high coplanarity between porphyrins.

A highly regioselective and stereoselective difunctionalization reaction of 1,3-diene with amine and disilane to form C-N and C-Si bonds via a one-step Pd/Cu/O2 system is disclosed. The difunctionalization reaction affords allylic silanes, including the allylic amine moiety, in up to 92 % yield in the absence of any acid, base, or external ligand. The developed synthetic methodology can be scaled to 100 g in high yield with high Z-selectivity, which demonstrates the feasibility of the reaction for industrial applications.

Carbon dioxide (CO2) is one of the most important materials as renewable chemical feedstock. In this review, the Co- and Rh-catalyzed transformation of CO2 via carbon–carbon bond-forming reactions is summarized. Combinations of metals (cobalt or rhodium), substrates, and reducing agents realize efficient carboxylation reactions using CO2. The carboxylation of propargyl acetates and alkenyl triflates using cobalt complexes as well as the cobalt-catalyzed reductive carboxylation of α,β-unsaturated nitriles and carboxyamides in the presence of Et2Zn proceed. A Co complex has been demonstrated to act as an efficient catalyst in the carboxylation of allylic C(sp3)–H bonds. Employing zinc as the reductant, carboxyzincation and the four-component coupling reaction between alkyne, acrylates, CO2, and zinc occur efficiently. Rh complexes also catalyze the carboxylation of arylboronic esters, C(sp2)–H carboxylation of aromatic compounds, and hydrocarboxylation of styrene derivatives. The Rh-catalyzed [2 + 2 + 2] cycloaddition of diynes and CO2 proceeds to afford pyrones.

A bulky carboxylic acid bearing three cyclohexylmethyl substituents at the α-position, namely, tri(cyclohexylmethyl)acetic acid, is demonstrated to act as an efficient ligand source in Pd-catalyzed intramolecular C(sp2 )-H and C(sp3 )-H arylation reactions. The reactions proceed smoothly under mild reaction conditions, even at room temperature due to the steric bulk of the carboxylate ligands, which accelerates the rate-determining C-H bond activation step in the catalytic cycle.

Herein, copper-catalyzed borylative and silylative transformations of allenes using borylcopper or silylcopper as the active catalytic species are described. First, the synthesis and characterization of borylcopper and silylcopper complexes are briefly introduced. Next, the borylative transformations of allenes are summarized including hydro­boration, carboboration, and borylative allylation of carbonyl compounds. We next deal with the silylative transformations of allenes such as hydrosilylation, carbosilylation, and silylative allylation of carbonyl compounds.1 Introduction2 Synthesis of Borylcopper and Silylcopper Complexes3 Borylative Transformations4 Silylative Transformations5 Conclusions and Future Outlook

Carboxylic acids 1a and 1b bearing three poly(ethylene glycol) (PEG) chains and carboxylic acid 1c bearing one PEG chain were designed and synthesized. The carboxylic acids 1a–c were fully characterized by NMR and ESI-HRMS analyses. In a Pd-catalyzed aerobic oxidation of 1-phenylethanol, 1a and 1b worked well as carboxylate ligands.

Macrocyclic dinuclear complexes have been gaining popularity in the design of homogeneous catalysts. Herein, we report the design of such a complex featuring catalytically active sites fixed inside the ring and its synthesis using a cross-coupling reaction.

The boraformylation of allenes with B2 (pin)2 and a formate ester as boron and formyl source, respectively, proceeds in the presence of a copper catalyst. The reaction selectively affords the corresponding β-boryl β,γ-unsaturated aldehydes in good to high yields. Furthermore, the silaformylation of allenes was achieved with a formate ester and PhMe2 Si-B(pin) as the silicon source.

Various carboxylic acids with different substitution patterns were used as ligands in intra- and intermolecular Pd-catalyzed C–H activation reactions to investigate steric effect of the ligands. Bulky carboxylic acids suppress deactivation of Pd catalysts.

We report the synthesis of an insulated π-conjugated polymer containing 2,2'-bipyridine moieties as metal coordination sites. Metal coordination to the polymer enabled easy and reversible tuning of the luminescent color without changes to the main chain skeleton. The permethylated α-cyclodextrin (PM α-CD)-based insulation structure allowed the metalated polymers to demonstrate efficient emission even in the solid state, with identical spectral shapes to the dilute solutions. In addition, the coordination ability of the metal-free polymer was maintained in the solid state, resulting in reversible changes in the luminescent color in response to the metal ions. The synthesized polymer is expected to be suitable for application in recyclable luminescent sensors to distinguish different metal ions.

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.

We describe a new concept for rotaxane synthesis through intramolecular slippage using π-conjugated molecules as rigid axles linked with organic soluble and flexible permethylated α-cyclodextrins (PM α-CDs) as macrocycles. Through hydrophilic-hydrophobic interactions and flipping of PM α-CDs, successful quantitative conversion into rotaxanes was achieved without covalent bond formation. The rotaxanes had high activation barrier for their de-threading, so that they were kinetically isolated and derivatized even under conditions unfavorable for maintaining the rotaxane structures. (1) H NMR spectroscopy experiments clearly revealed that the restricted motion of the linked macrocycle with the rigid axle made it possible to control the kinetic stability by adjusting the length of the rigid axle in the precursor structure rather than the steric bulkiness of the stopper unit.

A bulky carboxylic acid bearing three cyclohexylmethyl substituents at the α-position, namely, tri(cyclohexylmethyl)acetic acid, is demonstrated to act as an efficient ligand source in Pd-catalyzed intramolecular C(sp

We describe herein the synthesis of a Ni(II) bis(dithiobenzoate)-type complex three-dimensionally insulated by a [1]rotaxane structure to reveal the importance of the insulation. Under cyclic voltammetry conditions, the complex showed a stable and reversible redox behavior in contrast to a non-insulated reference complex, clearly demonstrating the effectiveness of the rotaxane-type insulation as a new method of kinetic metal complex stabilization.

In this study, π-conjugated molecular wires strapped by cyclic π-conjugated side chains were efficiently synthesized by the integration of dehydrobenzo[20]annulene units by intramolecular Glaser-type cyclization under high dilution conditions.

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.

A highly selective carbon-carbon bond-forming transformation of carbon dioxide (CO2) to alcohol oxidation level has been disclosed. By employing a copper/bisphosphine catalyst system and hydrosilanes as mild and easy-to-handle reducing agents, various allenes can be reacted with CO2 to regioselectively obtain homoallylic alcohols. Esters and other reducible functionalities on the allenes remain intact during the reaction, whereas CO2 is reduced to alcohol oxidation level.

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.

We synthesized symmetrically insulated oligo(para-phenylene) and oligothiophene with a pseudo-linked [3]rotaxane structure by full rotation of glucopyranose units via a flipping (tumbling) mechanism in the π-conjugated guest having two permethylated β-cyclodextrin units at both ends. We also succeeded in the synthesis of an organic-soluble fixed [3]rotaxane by a cross-coupling or complexation reaction of thus formed pseudo linked [3]rotaxane. Oligo(para-phenylene), oligothiophene, and porphyrin derivatives were used as π-conjugated guests with stopper groups.