Catalytic C-H Borylation Using Iron Complexes Bearing 4,5,6,7-Tetrahydroisoindol-2-ide-Based PNP-Type Pincer Ligand.

Catalytic C-H borylation has been reported using newly designed iron complexes bearing a 4,5,6,7-tetrahydroisoindol-2-ide-based PNP pincer ligand. The reaction tolerated various five-membered heteroarenes, such as pyrrole derivatives, as well as six-membered aromatic compounds, such as toluene. Successful examples of the iron-catalyzed sp3 C-H borylation of anisole derivatives were also presented.

Cross-Coupling Reactions of Alkenyl Halides with 4-Benzyl-1,4- Dihydropyridines Associated with E to Z Isomerization under Nickel and Photoredox Catalysis.

Cross-coupling reactions of alkenyl halides with 4-alkyl-1,4-dihydropyridines as alkylation reagents have been achieved by combination of nickel and photoredox catalysts. Alkenyl halides bearing alkyl and aryl substituents are available. Particularly, in the use of aryl-substituted alkenyl halides, cross-coupling reactions are associated with E to Z isomerization of alkenes. Thus, Z-isomers of the products are obtained as major products. The present strategy provides a novel synthetic method to control the stereochemistry around alkenes.

Preparation and reactivity of iron complexes bearing anionic carbazole-based PNP-type pincer ligands toward catalytic nitrogen fixation.

Iron-chloride, -dinitrogen, and -methyl complexes bearing anionic carbazole-based PNP-type pincer ligands are designed, prepared and characterized by X-ray analysis. Some iron complexes are found to work as catalysts toward nitrogen fixation under mild reaction conditions.

Expression of RSOsPR10 in rice roots is antagonistically regulated by jasmonate/ethylene and salicylic acid via the activator OsERF87 and the repressor OsWRKY76, respectively.

Plant roots play important roles in absorbing water and nutrients, and in tolerance against environmental stresses. Previously, we identified a rice root-specific pathogenesis-related protein (RSOsPR10) induced by drought, salt, and wounding. RSOsPR10 expression is strongly induced by jasmonate (JA)/ethylene (ET), but suppressed by salicylic acid (SA). Here, we analyzed the promoter activity of RSOsPR10. Analyses of transgenic rice lines harboring different-length promoter::ß-glucuronidase (GUS) constructs showed that the 3-kb promoter region is indispensable for JA/ET induction, SA repression, and root-specific expression. In the JA-treated 3K-promoter::GUS line, GUS activity was mainly observed at lateral root primordia. Transient expression in roots using a dual luciferase (LUC) assay with different-length promoter::LUC constructs demonstrated that the novel transcription factor OsERF87 induced 3K-promoter::LUC expression through binding to GCC-cis elements. In contrast, the SA-inducible OsWRKY76 transcription factor strongly repressed the JA-inducible and OsERF87-dependent expression of RSOsPR10. RSOsPR10 was expressed at lower levels in OsWRKY76-overexpressing rice, but at higher levels in OsWRKY76-knockout rice, compared with wild type. These results show that two transcription factors, OsERF87 and OsWRKY76, antagonistically regulate RSOsPR10 expression through binding to the same promoter. This mechanism represents a fine-tuning system to sense the balance between JA/ET and SA signaling in plants under environmental stress.

Synthesis and reactivity of iron-dinitrogen complexes bearing anionic methyl- and phenyl-substituted pyrrole-based PNP-type pincer ligands toward catalytic nitrogen fixation.

Iron-dinitrogen complexes bearing methyl- and phenyl-substituted pyrrole-based anionic PNP-type pincer ligands are prepared and characterized by X-ray analysis. The former complex is found to work as a more effective catalyst than that bearing a non-substituted PNP-type pincer ligand toward the transformation of nitrogen gas into ammonia and hydrazine under mild reaction conditions.

Hydroboration of Alkynes Catalyzed by Pyrrolide-Based PNP Pincer-Iron Complexes.

To utilize iron complexes as catalysts, the application of a well-designed ligand is critical to control the reactivity of the iron center. Recently, our group has succeeded in the synthesis of iron complexes bearing a pyrrolide-based PNP pincer ligand and their application to the catalytic transformation of dinitrogen into ammonia under mild reaction conditions. As an extensive study, we report the iron-catalyzed hydroboration of alkynes with pinacolborane, where the corresponding E-isomers are obtained selectively.

Catalytic Activity of Thiolate-Bridged Diruthenium Complexes Bearing Pendent Ether Moieties in the Oxidation of Molecular Dihydrogen.

Thiolate-bridged diruthenium complexes bearing pendent ethers have been found to work as effective catalysts toward the oxidation of molecular dihydrogen into protons and electrons in water. The pendent ether moiety in the complex plays an important role to facilitate the proton transfer between the metal center and the external proton acceptor.

Nickel- and Photoredox-Catalyzed Cross-Coupling Reactions of Aryl Halides with 4-Alkyl-1,4-dihydropyridines as Formal Nucleophilic Alkylation Reagents.

A combination of nickel and photoredox catalysts promoted novel cross-coupling reactions of aryl halides with 4-alkyl-1,4-dihydropyridines. 4-Alkyl-1,4-dihydropyridines act as formal nucleophilic alkylation reagents through a photoredox-catalyzed carbon-carbon (C-C) bond-cleavage process. The present strategy provides an alternative to classical carbon-centered nucleophiles, such as organometallic reagents.

Iron-Catalyzed [2 + 2 + 2] Cycloaddition Reactions of Diynes with Oxyphosphaethynes To Construct 2-Phosphaphenol Derivatives.

Iron-catalyzed [2 + 2 + 2] cycloaddition reactions of diynes with siloxyphosphaethynes have been developed to give 2-phosphaphenol derivatives. The use of electronically neutral siloxyphosphaethynes generated in situ by the reaction of anionic phosphaethynolate with silyl triflates is key to achieving the reactions.

Synthetic Utilization of α-Aminoalkyl Radicals and Related Species in Visible Light Photoredox Catalysis.

Single electron oxidation of amines provides an efficient way to access synthetically useful α-aminoalkyl radicals as reactive intermediates. After the single electron oxidation of amines, fragmentation of the resulting radical cations proceeds to give the α-aminoalkyl radicals along with generation of a proton. In the synthetic utilization of the α-aminoalkyl radicals, precise control of single electron transfer is essential, because further oxidation of the α-aminoalkyl radicals occurs more easily than the starting amines and the α-aminoalkyl radicals are converted into the corresponding iminium ions. As a result, photoinduced single electron transfer is quite attractive in the synthetic utilization of the α-aminoalkyl radicals. Recently, visible light-photoredox catalysis using transition metal-polypyridyl complexes and other dyes as catalysts has attracted considerable attention, where useful molecular transformations can be achieved through the single electron transfer process between the excited catalysts and substrates. In this context, MacMillan et al. ( Science 2011, 334 , 1114 , DOI: 10.1126/science.1213920 ) reported an aromatic substitution reaction of cyanoarenes with amines, where α-aminoalkyl radicals work as key reactive intermediates. Pandey and Reiser et al. ( Org. Lett. 2012 , 14 , 672 , DOI: 10.1021/ol202857t ) and our group ( Nishibayashi et al. J. Am. Chem. Soc. 2012 , 134 , 3338 , DOI: 10.1021/ja211770y ) independently reported reactions of amines with α,ß-unsaturated carbonyl compounds, where addition of α-aminoalkyl radicals to alkenes is a key step. After these earliest examples, nowadays, a variety of transformations using the α-aminoalkyl radicals as reactive intermediates have been reported by many groups. The α-aminoalkyl radicals are usually produced from amines by single electron oxidation and the subsequent deprotonation of the C-H bond adjacent to the nitrogen atom. In addition, the α-aminoalkyl radicals are also produced from α-silylamines and α-amino acids in high efficiency through desilylation or decarboxylation after the single electron oxidation. The generated α-aminoalkyl radicals are utilized in a variety of reaction systems. In fact, reactions based on the addition of α-aminoalkyl radicals to alkenes and other unsaturated bonds have been extensively studied. Aromatic and other types of substitution reactions have also been investigated. Some of these transformations are achieved by combination of photoredox catalysts and other catalysts such as Brønsted and Lewis acids, organocatalysts, and transition metal catalysts. It is also noteworthy that the enantioselective reactions have been accomplished by combination of photoredox catalysts and chiral catalysts. The strategy for the generation of α-aminoalkyl radicals can be applied to utilize other types of alkyl radicals. In the generation of α-aminoalkyl radicals, the bond dissociation of the radical cations occurs at the α-position of amines. In relation to this process, synthetic utilization of other types of alkyl radicals generated by the bond dissociation of the radical cations at a remote position has been also investigated. These alkyl radicals have been applied to molecular transformations in a manner similar to the α-aminoalkyl radicals. Recently, organic synthesis using the α-aminoalkyl radicals and related alkyl radicals has been studied extensively. In this Account, we describe recent advances in photoredox-catalyzed synthetic utilization of these alkyl radicals.

Catalytic transformation of dinitrogen into ammonia and hydrazine by iron-dinitrogen complexes bearing pincer ligand.

Synthesis and reactivity of iron-dinitrogen complexes have been extensively studied, because the iron atom plays an important role in the industrial and biological nitrogen fixation. As a result, iron-catalyzed reduction of molecular dinitrogen into ammonia has recently been achieved. Here we show that an iron-dinitrogen complex bearing an anionic PNP-pincer ligand works as an effective catalyst towards the catalytic nitrogen fixation, where a mixture of ammonia and hydrazine is produced. In the present reaction system, molecular dinitrogen is catalytically and directly converted into hydrazine by using transition metal-dinitrogen complexes as catalysts. Because hydrazine is considered as a key intermediate in the nitrogen fixation in nitrogenase, the findings described in this paper provide an opportunity to elucidate the reaction mechanism in nitrogenase.

Synthesis of phosphabenzenes by an iron-catalyzed [2+2+2] cycloaddition reaction of diynes with phosphaalkynes.

A method for the synthesis of phosphabenzenes under iron catalysis is described. Thus, the FeI2 -catalyzed [2+2+2] cycloaddition of diynes with phosphaalkynes in m-xylene gave a variety of phosphabenzenes in good to high yields (up to 87 % yield).

Thiolate-bridged dinuclear ruthenium and iron complexes as robust and efficient catalysts toward oxidation of molecular dihydrogen in protic solvents.

Thiolate-bridged dinuclear ruthenium and iron complexes are found to work as efficient catalysts toward oxidation of molecular dihydrogen in protic solvents such as water and methanol under ambient reaction conditions. Heterolytic cleavage of the coordinated molecular dihydrogen at the dinuclear complexes and the sequential oxidation of the produced hydride complexes are involved as key steps to promote the present catalytic reaction. The catalytic activity of the dinuclear complexes toward the chemical oxidation of molecular dihydrogen achieves up to 10000 TON (turnover number), and electrooxidation of molecular dihydrogen proceeds quite rapidly. The result of the density functional theory (DFT) calculation on the reaction pathway indicates that a synergistic effect between the two ruthenium atoms plays an important role to realize the catalytic oxidation of molecular dihydrogen efficiently. The present dinuclear ruthenium complex is found to work as an efficient organometallic anode catalyst for the fuel cell. It is noteworthy that the present dinuclear complex worked not only as an effective catalyst toward chemical and electrochemical oxidation of molecular dihydrogen but also as a good anode catalyst for the fuel cell. We consider that the result described in this paper provides useful and valuable information to develop highly efficient and low-cost transition metal complexes as anode catalysts in the fuel cell.

Visible light-mediated oxidative decarboxylation of arylacetic acids into benzyl radicals: addition to electron-deficient alkenes by using photoredox catalysts.

Reactions of arylacetic acids bearing an amino group at the para-position in the benzene ring with alkenes in the presence of a catalytic amount of transition metal polypyridyl complexes as photocatalysts under visible light illumination proceed smoothly to give the corresponding benzylated products via oxidative decarboxylation in good to high yields.

Visible-light-mediated utilization of α-aminoalkyl radicals: addition to electron-deficient alkenes using photoredox catalysts.

Synthetic use of α-aminoalkyl radicals formed by single electron oxidation of amines is quite limited. Here we demonstrate addition of α-aminoalkyl radicals to electron-deficient alkenes by visible-light-mediated electron transfer using transition metal polypyridyl complexes as photocatalysts, via a sequential redox pathway.