Fully conjugated tetraborylethylene: selenium mediated C-C double bond formation from diborylcarbenoid.

Heteroatom-substituted ethylenes have long been studied owing to their potential application to electronic devices. In contrast to well-studied π-donor substituted ethylene, the π-acceptor substituted one has only been limitedly reported. While boron can be a candidate of π-acceptors, there has still been no example of fully conjugated tetraborylethylene (TBE).

Stability of Medium-Ring Cyclic Unsaturated Carbonyl Compounds: Direct Access to Unsaturated Ketones with C-C Double Bonds at Distal Positions via Transfer Dehydrogenation of Alicyclic Ketones.

Medium-ring cyclic compounds have characteristic distortions. For alicyclic enones, conjugated enones are known to be less stable than unconjugated enones. In this study, the relative stability of cycloalkenones with varied C-C double bond positions with C6-C12 rings was theoretically investigated to reveal that C8-C12 cycloalkenones prefer the unconjugated isomer.

A dinuclear Rh(-i)/Rh(i) complex bridged by biphilic phosphinine ligands.

Bimetallic complexes have enabled precise control of catalysis by accumulating two discrete metal centres. In these complexes, bridging ligands are essential to combine multiple metals into one molecule. Among some bridging modes, an unsymmetric bridging mode will differentiate the electronic structures of the two metal centres.

Boron Polycation Supported by Cyclic Bis(carbodiphosphorane).

A novel cyclic bis(carbodiphosphorane) ligand was prepared and investigated in coordination with group 13 elements, B, Al, and Ga. Al and Ga afforded dinuclear adduct where two metal centers were bridged by the bis(carbodiphosphorane) ligand. In contrast, the reaction with boron trichloride afforded a monomeric dicationic three-coordinate boron species composed of one boron moieties and one ligand.

Synthesis, Characterization, and Trapping of a Cyclic Diborylcarbene, an Electrophilic Carbene.

A carbene bearing two geminal boryl substituents, called diborylcarbene (DBC), has been predicted to be highly Lewis acidic in sharp contrast to the well-studied persistent carbenes stabilized by π-donating substituents. Studies on DBC have been limited to either the base-trapping or theoretical calculations. Herein, we developed chemical equivalents for DBC, namely, K/X-diborylcarbenoids (X = F or Cl).

Pincer-Supported Perfluororhodacyclopentanes: High Nucleophilicity of the M-C Bond.

Perfluororhodacyclopentane supported by PBP pincer ligand PBP-Rh (CF ) (2) was prepared from PBP-Rh -PPh (1) and tetrafluoroethylene (TFE). By scXRD analysis, it was revealed that the Rh-C bond trans to the boryl ligand was largely elongated compared to the one in the apical position. Although M-C bonds of perfluorometallacyclopentanes are known to be very stable, 2 shows high reactivity toward hydrogenolysis, iodinolysis and protonolysis, thanks to the strong trans-effect of the highly σ-donating boryl ligand.

Synthesis and reactivity of PC(sp)P-pincer iridium complexes bearing a diborylmethyl anion.

Novel PCP-pincer iridium complexes bearing a diborylmethyl anion were synthesized. Strong σ-electron-donation to the metal and significant π-backdonation from the metal to boron atoms at the β-position were observed both experimentally and computationally. H/D exchange of the aromatic C-H bond proceeded smoothly and, in addition, the α-methine-hydrogen between boron atoms was found to be replaced with deuterium in benzene- solution possibly through diborylcarbene metal complexes as intermediates.

Atom Swapping on Aromatic Rings: Conversion from Phosphinine Pincer Metal Complexes to Metallabenzenes Triggered by O Oxidation.

Herein, we report a novel method for the synthesis of metallabenzenes by swapping the phosphorus atom in an aromatic phosphinine ring with transition metal fragments. The oxidation of a phosphine-phosphinine-phosphine pincer iridium complex by O triggered the replacement of the phosphorus atom of the phosphinine ring by an iridium fragment to afford iridabenzene. Dianionic rhodabenzene was also synthesized from a phosphinine rhodium complex by oxidation of the phosphorus atom, followed by subsequent reduction using metallic potassium.

Heterolytic Oxidative Addition of sp and sp C-H Bonds by Metal-Ligand Cooperation with an Electron-Deficient Cyclopentadienone Iridium Complex.

Oxidative addition reactions of C-H bonds that generate metal-carbon-bond-containing reactive intermediates have played essential roles in the field of organometallic chemistry. Herein, we prepared a cyclopentadienone iridium(I) complex designed for oxidative C-H bond additions. The complex cleaves the various sp and sp C-H bonds including those in hexane and methane as inferred from their H/D exchange reactions.

Umpolung of B-H Bonds by Metal-Ligand Cooperation with Cyclopentadienone Iridium Complexes.

In contrast to conventional metal-ligand cooperative cleavage of a B-H bond, which provides a B cation on the ligand and an H anion on the metal, we report herein the umpolung of B-H bonds by novel cyclopentadienone iridium complexes. The B-H bonds of 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (HBpin) and 1,8-naphthalenediaminatoborane (HBdan) were cleaved to give a B anion on the metal and an H cation on the phenolic oxygen atom of the ligand. Mechanistic investigation by DFT calculations revealed that the alkoxycarbonyl-substituted cyclopentadienone ligand facilitated deprotonation from Ir-H after oxidative addition of the B-H bond to give the umpolung product.

Reductive Coupling of Carbon Dioxide and an Aldehyde Mediated by a Copper(I) Complex toward the Synthesis of α-Hydroxycarboxylic Acids.

Copper-mediated reductive coupling between CO and an aldehyde to form α-hydroxycarboxylic acid was achieved using silylborane as a reductant. CO cleanly inserted into a copper-carbon bond that was formed by the reaction between a silylcopper-NHC complex and an aldehyde. A series of reactions that regenerate the silylcopper complex were developed for the synthesis of an α-hydroxycarboxylic acid.

Cleavage of Si-H, B-H, and C-H Bonds by Metal-Ligand Cooperation.

Metal-ligand cooperation, in which metal and ligand participate in bond cleavage and formation, is gathering great attention in recent years. In contrast to the classical bond cleavage by active metal centers with spectator ligands, metal-ligand cooperation has enabled unprecedented reactivities. Especially, metal-ligand cooperative H-H bond cleavage has been extensively studied and applied to various catalysts.

Metal-Ligand Cooperative C-H Bond Formation by Cyclopentadienone Platinum Complexes.

C-H bond cleavage and formation is one of the most essential elementary reactions in organic chemistry. Herein, a heterolytic sp C-H bond reductive elimination from hydroxyCp dimethylplatinum(IV) B is reported. Protonation of cyclopentadienone dimethylplatinum(II) A afforded B via the protonation of the ligand.

The Retro-Hydroformylation Reaction.

Hydroformylation, a reaction that adds carbon monoxide and dihydrogen across an unsaturated carbon-carbon multiple bond, has been widely employed in the chemical industry since its discovery in 1938. In contrast, the reverse reaction, retro-hydroformylation, has seldom been studied. The retro-hydroformylation reaction of an aldehyde into an alkene and synthesis gas (a mixture of carbon monoxide and dihydrogen) in the presence of a cyclopentadienyl iridium catalyst is now reported.

Direct and selective hydrogenolysis of arenols and aryl methyl ethers.

For valorization of biomass, the conversion of lignin to deoxygenated bulk aromatic compounds is an emerging subject of interest. Because aromatic rings are susceptible to metal-catalysed hydrogenation, the selective hydrogenolysis of carbon-oxygen bonds still remains a great challenge. Herein we report direct and selective hydrogenolysis of sp(2) C-OH bonds in substituted phenols and naphthols catalysed by hydroxycyclopentadienyl iridium complexes.

Acceptorless dehydrogenation of C-C single bonds adjacent to functional groups by metal-ligand cooperation.

Unprecedented direct acceptorless dehydrogenation of C-C single bonds adjacent to functional groups to form α,β-unsaturated compounds has been accomplished by using a new class of group 9 metal complexes. Metal-ligand cooperation operated by the hydroxycyclopentadienyl ligand was proposed to play a major role in the catalytic transformation.

Why did incorporation of acrylonitrile to a linear polyethylene become possible? Comparison of phosphine-sulfonate ligand with diphosphine and imine-phenolate ligands in the Pd-catalyzed ethylene/acrylonitrile copolymerization.

Palladium-catalyzed coordination-insertion copolymerization of ethylene with acrylonitrile (AN) proceeded only by using phosphine-sulfonate (P-SO(3)) as a ligand among the neutral and anionic ligands we examined, those are phosphine-sulfonate (P-SO(3)), diphosphine (P-P), and imine-phenolate (N-O). In order to answer a question that is unique for P-SO(3), theoretical and experimental studies were carried out for the three catalyst systems. By comparing P-SO(3) and P-P, it was elucidated that (i) the π-acrylonitrile complex [(L-L')PdPr(π-AN)] is less stable than the corresponding σ-complex [(L-L')PdPr(σ-AN)] in both the phosphine-sulfonato complex (L-L' = P-SO(3)) and the diphosphine complex (L-L' = P-P) and (ii) the energetic difference between the π-complex and the σ-complex is smaller in the P-SO(3) complexes than in the P-P complexes.