Diphosphene with a phosphineborane tether and its rhodium complex.

A diphosphene ligand possessing a PP bond and a phosphineborane moiety in its molecule was synthesized. The reaction of the new bidentate diphosphene-phosphineborane ligand with [Rh(cod)]BF provided a cationic diphosphene-rhodium complex with -coordination through the η-PP and η-BH moieties. The complex was applied to the coupling reaction of benzimidazole with cyclohexylallene.

Rh(I)-Catalyzed Enantioselective Arylation of Cyclic -Sulfonyl Diketimines Using Planar-Chiral Phosphine-Olefin Ligands Based on a (Cyclopentadienyl)manganese(I) Scaffold with a Highly Fluorinated Aryl Phosphino Group.

Catalytic enantioselective 1,2-addition reactions of arylboronic acids with 1,2,5-thiadiazoline 1,1-dioxide derivatives were achieved using planar-chiral phosphine-olefin ligand with a bis[(2,3,4,5,6-pentafluoro)phenyl]phosphino group, showing ≤98% ee. The enantioselectivities of the addition products were improved by increasing the number of fluoro substituents on the aromatic ring of the ligand. X-ray crystallographic studies of and [RhCl/] revealed the absolute configuration of the enantioenriched addition product and the mode of phosphine-olefin bidentate coordination of to a rhodium(I) cation.

Synthesis, Structures, and Properties of π-Extended Phosphindolizine Derivatives.

Dibenzo[b,g]phosphindolizine oxide and three types of benzo[e]naphthophosphindolizine oxides have been synthesized by the ring-closing metathesis of benzo[b]phosphole oxide and naphthophosphole oxides with two olefin tethers. Their molecular structures and properties were revealed by X-ray crystallographic analysis, UV-vis spectroscopy, and electrochemical analysis. The number and position of the benzene rings were found to alter the structural geometry and the HOMO/LUMO energy levels, and their effects were investigated by theoretical calculations.

Palladium(II) complexes of bis(diphosphene) with different coordination behaviors.

Organophosphorus compounds possessing a P-P double-bond character are intriguing materials in coordination chemistry because it is possible to form a variety of coordination modes from the π-bond in addition to the lone pairs. We report herein the complexation of a new bidentate ligand, ethylene-tethered bis(binaphthyldiphosphene) (,)-2, with palladium(II) species. The reaction of (,)-2 with [Pd(π-allyl)(cod)](SbF) and PdCl(cod) afforded η/η-bis(diphosphene) complex 7 and η-diphosphene/η-phosphanylphosphide complex 8, respectively.

Transformation from triple helicene to double helicene embedding adjacent stereogenic carbon atoms and axial stereogenicity.

Transformation of triple helicene (TH) to double helicene (DH) with adjacent stereogenic carbon atoms and axial stereogenicity was achieved by the unexpected conjugate addition to the central aromatic ring of TH-1. We also studied the boundary at which different reactivities to addition reactions occur in some helicenes with different π-extension.

Metal-metal multiple bond formation induced by σ-acceptor Lewis acid ligands.

The reaction of [Cp*Ru(μ-NHPh)]2 (Cp* = η5-C5Me5) with Lewis acids of the type MX2 (M = Zn, Sn, Pb; X = Cl, OTf) affords Ru2 → M donor-acceptor adducts characterized as π complexes of a Ru[double bond, length as m-dash]Ru double bond with M(ii) Lewis acids. The results illustrate for the first time the ability of σ-acceptor Lewis acid ligands to induce the formation of a metal-metal multiple bond via stabilizing dative interactions.

Synthesis, Structure, and Complexation of an S-Shaped Double Azahelicene with Inner-Edge Nitrogen Atoms.

Invited for the cover of this issue is Ken Kamikawa and co-workers at Osaka Prefecture University and RIKEN Center for Sustainable Resource Science. The image depicts an S-shaped double azahelicene capturing the palladium in a trans-chelating fashion. Read the full text of the article at 10.

Synthesis, Structure, and Complexation of an S-Shaped Double Azahelicene with Inner-Edge Nitrogen Atoms.

An S-shaped double azahelicene (1) was synthesized in excellent yield by a palladium-catalyzed double dehydrogenative C-H coupling reaction. The stereochemistry of 1 was confirmed to be dl by single-crystal X-ray diffraction analysis. Selective formation of dl-1 was attributed to the isomerization of the kinetically controlled product (meso-1) into the more thermodynamically stable dl-1 under the applied reaction conditions.

Enantioselective Synthesis of Triple Helicenes by Cross-Cyclotrimerization of a Helicenyl Aryne and Alkynes via Dynamic Kinetic Resolution.

Optically active triple helicenes () were prepared via a palladium-catalyzed enantioselective cross-cyclotrimerization of two helicenyl arynes , which are generated from , with dialkyl acetylenedicarboxylate . Enantiomeric ratios of up to 98:2 were obtained when using and ()-QUINAP as the alkyne and chiral ligand, respectively. The absolute stereochemistry of was revealed to be (,,) by a single-crystal X-ray diffraction analysis.

Dibenzo[b,e]phosphindolizines synthesized by a ring-closing metathesis of benzo[b]phospholes with two vinyl tethers.

Dibenzo[b,e]phosphindolizines 1 were successfully synthesized by a ring-closing metathesis of benzo[b]phosphole chalcogenides 2a-2c with two vinyl tethers (for chalcogen analogs 1a-1c), and by a deselenization reaction (for lone-pair analog 1d). The structures, properties, and bowl inversion derived from a phosphorus atom were fully investigated.

1,1'-Binaphthyl-substituted diphosphene: synthesis, structures, and chiral optical properties.

1,1'-Binaphthyl-substituted diphosphene 1 possessing a P[double bond, length as m-dash]P double bond and an axially chiral 1,1'-binaphthyl group was synthesized and fully characterized. Diphosphene 1 was prepared as an optically active form and thus is the first example of a chiral diphosphene. The CD spectra of 1 showed apparent circular dichroism in the longer wavelength region, caused by the P[double bond, length as m-dash]P moiety.

Synthesis, Structures, and Properties of Hexapole Helicenes: Assembling Six [5]Helicene Substructures into Highly Twisted Aromatic Systems.

Hexapole helicenes 1, which contain six [5]helicene substructures, were synthesized by Pd-catalyzed [2+2+2]cycloadditions of aryne precursor 6. Among the possible 20 stereoisomers, which include ten pairs of enantiomers, HH-1 was obtained selectively. Density functional theory (DFT) calculations identified HH-1 as the second most stable isomer that quantitatively isomerizes under thermal conditions into the most stable isomer (HH-2).

Synthesis and structures of lithium alkoxytris(dimethylphenylsilyl)borates.

The reactions of trialkyl borates B(OR) (R = Me, i-Pr) with dimethylphenylsilyllithium gave lithium alkoxytris(dimethylphenylsilyl)borates 1a,b. X-ray crystallographic analysis showed that 1a,b were obtained as a contact ion pair and a solvent-separated ion pair, respectively. The B and Si chemical shifts as well as the Si-B and B-O bond lengths of 1a,b and related compounds largely change, depending on the numbers of silyl and alkoxy substituents.

Decasilahexahydrotriquinacene and Decasilaisotwistane: σ Conjugation on a Bowl Surface.

The first bowl-shaped oligosilane, hexadecamethyldecasilahexahydrotriquinacene (1), and a related oligosilane, hexadecamethyldecasilaisotwistane (2), were synthesized, and their structures and properties were studied. The results revealed importance of σ conjugation on a bowl surface: the HOMOs of 1 are σ orbitals delocalized on the bowl surface, whereas the LUMO is a pseudo π* orbital on the convex and concave sides of the bowl surface.

Carbon Dioxide to Methanol: The Aqueous Catalytic Way at Room Temperature.

Carbon dioxide may constitute a source of chemicals and fuels if efficient and renewable processes are developed that directly utilize it as feedstock. Two of its reduction products are formic acid and methanol, which have also been proposed as liquid organic chemical carriers in sustainable hydrogen storage. Here we report that both the hydrogenation of carbon dioxide to formic acid and the disproportionation of formic acid into methanol can be realized at ambient temperature and in aqueous, acidic solution, with an iridium catalyst.

The Radical Anion of Cyclopentasilane-Fused Hexasilabenzvalene.

The radical anion of cyclopentasilane-fused hexasilabenzvalene was synthesized by the reduction of the corresponding neutral compound. X-ray crystallographic analysis showed a more trans-bent structure of the disilene moiety than the neutral compound. Theoretical calculations showed that the highly trans-bent structure is attributed to the hexasilabenzvalene structure.

Tetrasilane-bridged bicyclo[4.1.0]heptasil-1(6)-ene.

Tetrasilane-bridged bicyclo[4.1.0]heptasil-1(6)-ene 1 was synthesized by the reduction of 1,1,2,2-tetrachlorocyclohexasilane 2 in 12% yield as red-orange crystals.

Synthesis and structure of a 1-phospha-2-boraacenaphthene derivative and its chalcogenation reactions.

The first stable 1-phospha-2-boraacenaphthene 1 was synthesized by the reduction of 1-dimesitylboryl-8-dichlorophosphinonaphthalene (2a) with elemental magnesium, and it was fully characterized. The chalcogenation reaction of 1 with elemental sulfur or selenium afforded the unique heterocycles, 2-thia- and 2-selena-1-phospha-3-boraphenalenes 9S and 9Se, respectively, through the insertion of the chalcogen atom into a P-B bond of 1. Further chalcogenation of 9 afforded the corresponding phosphine chalcogenides.

Cyclopentasilane-fused hexasilabenzvalene.

Cyclopentasilane-fused hexasilabenzvalene 1 was synthesized by the reduction of tetrachlorocyclopentasilane 6 in 19% yield as a green powder. The molecular structure and properties of 1 were studied by spectroscopic and X-ray crystallographic analyses. Theoretical calculations of the model and real molecules of 1 and their structural isomers 12–16 suggest that the linkage of the central hexasilabenzvalene moiety with trisilane chains and the introduction of tert-butyl groups affect their relative energies.