Exploring Catalytic Intermediates in Pd-Catalyzed Aerobic Oxidative Amination of 1,3-Dienes: Multiple Metal Interactions of the Palladium Nanoclusters.

Metal nanoclusters (NCs) have unique properties because of their small size, which makes them useful as catalysts in reactions like cross-coupling. Pd-catalyzed oxidative amination, which involves dehydrogenative C-N bond formation, uses Pd complexes as the active species. It is known that the catalytic conditions involve the formation of Pd(0) species from Pd NCs, but the precise role of Pd NCs in the transformations has not been established. In this study, we investigated the characteristic properties of Pd NCs in oxidative amination of 1,3-dienes. The reaction achieved direct amination of commercially accessible 1,3-dienes with secondary aromatic amines, providing a variety of nitrogen containing 1,3-dienes. The compound was applicable to radical polymerization to provide the nitrogen-fabricated 1,3-diene-based polymer, which exhibited a different thermal stability compared to aliphatic nitrogen-fabricated diene polymers. In addition to the synthetic utility, by combining X-ray absorption fine structure and small-angle X-ray scattering analysis, we revealed amines and 1,3-dienes affected metal leaching from the Pd nanoparticles and stabilization of Pd NCs in the catalytic reaction. Additionally, DFT calculation suggested that the catalytic intermediate contained multiple adjacent Pd atoms and was responsible for formation of an σ-allylic intermediate that is difficult to form with the use of Pd complexes. These results could be used to understand the underlying phenomenon in the oxidative coupling reaction and develop Pd NCs-based dehydrogenation.

Paddle-Wheel Dirhodium Complexes Bearing Bulky Carboxylate Ligands: Synthesis and Catalysis in Carbene Insertion Reactions.

Dirhodium complexes bearing bulky carboxylate ligands are synthesized and characterized. The steric bulk of carboxylate ligands could affect the reaction selectivity in Rh-catalyzed intramolecular reactions: Rh catalysts with bulky carboxylate ligands provided five-membered ring products preferentially via the insertion into a carbon-hydrogen bond. Meanwhile, six-membered ring products were obtained using conventional Rh catalysts via the insertion of a carbon-carbon double bond.

Dimethylacetamide-stabilized ruthenium nanoparticles for catalysing α-alkylations of amides with alcohols.

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 via hydrogen autotransfer with alcohols.

Synthesis of Cyclic Allylborates from 1,3-Dienes and a Diboron Reagent.

The synthesis of cyclic allylborates was achieved by the reaction of 1,3-dienes and B2 pin2 using a copper catalyst. Several 1,3-dienes were converted to the corresponding cyclic allylborates in moderate to high yields. The cyclic allylborate obtained could be used in several organic transformations such as allylation of electrophiles and Suzuki-Miyaura coupling.

Copper-Catalyzed Regioselective Sila-Acylation and Silaformylation of 1,3-Dienes Using Esters.

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

Palladium-Catalyzed Difunctionalization of 1,3-Diene with Amine and Disilane under a Mild Re-oxidation System.

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.

Cu-Catalyzed three-component coupling reactions using nitriles, 1,3-dienes and silylboranes.

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 ß,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.

Pd-Catalyzed intermolecular C-H bond arylation reactions: effect of bulkiness of carboxylate ligands.

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.

Complementary Color Tuning by HCl via Phosphorescence-to-Fluorescence Conversion on Insulated Metallopolymer Film and Its Light-Induced Acceleration.

An insulated metallopolymer that undergoes phosphorescence-to-fluorescence conversion between complementary colors by an acid-stimulus is proposed as a color-tunable material. A Pt-based phosphorescent metallopolymer, where the conjugated polymeric backbone is insulated by a cyclodextrin, is depolymerized by HCl via acidic cleavage of Pt-acetylide bonds to form a fluorescent monomer. The insulation enables phosphorescence-to-fluorescence conversion to take place in the solid film. Rapid color change was achieved by accelerating the reaction between the metallopolymer and HCl by UV irradiation. These approaches are expected to provide new guidelines for the development of next-generation color-tunable materials and printable sensors based on precise molecular engineering.

Insulated conjugated bimetallopolymer with sigmoidal response by dual self-controlling system as a biomimetic material.

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.

Zinc-Catalyzed Synthesis of Acylsilanes Using Carboxylic Acids and a Silylborane in the Presence of Pivalic Anhydride.

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.

Carboxylation Reactions Using Carbon Dioxide as the C1 Source via Catalytically Generated Allyl Metal Intermediates.

The use of carbon dioxide (CO2) is an important issue with regard to current climate research and the Earth's environment. Transition metal-catalyzed carboxylation reactions using CO2 are highly attractive. This review summarizes the transition metal-catalyzed carboxylation reactions of organic substrates with CO2 via allyl metal intermediates. First, carboxylation reactions via transmetalation are reviewed. Second, catalytic carboxylation reactions using allyl electrophiles and suitable reducing agents are summarized. The last section discusses the catalytic carboxylation reactions via addition reactions, affording allyl metal intermediates.

Two-step template method for synthesis of axis-length-controlled porphyrin-containing hollow structures.

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.

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source.

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,ß-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.

Steric Effect of Carboxylate Ligands on Pd-Catalyzed Intramolecular C(sp2 )-H and C(sp3 )-H Arylation Reactions.

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.

Kinetic stabilization of a Ni(ii) bis(dithiobenzoate)-type complex achieved using three-dimensional insulation by a [1]rotaxane structure.

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.

Programmed Synthesis of Molecular Wires with Fixed Insulation and Defined Length Based on Oligo(phenylene ethynylene) and Permethylated α-Cyclodextrins.

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.

Copper-catalyzed hydroallylation of allenes employing hydrosilanes and allyl chlorides.

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.

Hetero Face-to-Face Porphyrin Array with Cooperative Effects of Coordination and Host-Guest Complexation.

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.