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A channel-cut Si(111) crystal with a channel width of 90 µm was developed for achieving reflection self-seeding in hard X-ray free-electron lasers (XFELs). With the crystal a monochromatic seed pulse is produced from a broadband XFEL pulse generated in the first undulator section with an optical delay of 119 fs at 10 keV. The small optical delay allows a temporal overlap between the seed optical pulse and the electron bunch by using a small magnetic chicane for the electron beam placed between two undulator sections. Peak reflectivity reached 67%, which is reasonable compared with the theoretical value of 81%. By using this monochromator, a monochromatic seed pulse without broadband background in the spectrum was obtained at SACLA with a conversion efficiency from a broadband XFEL pulse of 2 × 10 -2 , which is ∼10 times higher than the theoretical efficiency of transmission self-seeding using a thin diamond (400) monochromator.

Most of the chemical and biological processes involving the fixation and transformation of small molecules have long been exclusive for metal complexes. Meanwhile, the last decades have seen a significant advance in main group chemistry that mimics transition-metal complexes, among which various boron-containing systems have been successful in mediating the small molecule activation. In this review, we focus on boron-containing heterocycles enabling the activation of σ- and π-bonds in small molecules, in conjunction with the proposed mechanisms.

Annulated 1,4,2,5-diazadiborinine 3 has been synthesized and fully characterized. Computational studies revealed that compound 3 features a relatively small HOMO-LUMO gap (2.61 eV). When 3 was treated with elemental grey selenium (Se), oxidative addition of Se proceeded regioselectively at the boron centres of 3 to give a bicyclo[2.2.2] molecule 4 involving a B-Se-Se-B unit, which can be deemed a heavier analogue of dibora-peroxide.

Reaction of a 1,2-diboraallene 1 with tetradibromodiborane B 2 Br 4 coordinated by a cyclic (alkyl)(amino)carbene (cAAC) in a 3:1 ratio affords a neutral tetraboron species 2 that possesses a planar tetraatomic boron(0) unit with the average oxidation state of zero. X-ray diffraction analysis and computational studies indicate that 2 features the delocalized electrons in the part of the σ-framework of the B 4 unit, as well as the conjugated π-system over the C-B 3 -C moiety.

The reactions of germylone 1 with one equivalent of [M(COD)Cl]2 (M = Ir, Rh) afforded the germylone-bridged bimetallic complexes 2 and 3, which have been spectroscopically and structurally characterized. Density functional theory (DFT) studies reveal the relatively strong interactions between the Ge atom and these metals. By the reaction of [Rh(COD)Cl]2 with CO followed by addition of 1, a complex 4 involving a Rh-Ge-Rh-Ge-Rh chain was also synthesized.

Research at modern light sources continues to improve our knowledge of the natural world, from the subtle workings of life to matter under extreme conditions. Free-electron lasers, for instance, have enabled the characterization of biomolecular structures with sub-ångström spatial resolution, and paved the way to controlling the molecular functions. On the other hand, attosecond temporal resolution is necessary to broaden our scope of the ultrafast world. Here we discuss attosecond pulse generation beyond present capabilities. Furthermore, we review three recently proposed methods of generating attosecond x-ray pulses. These novel methods exploit the coherent radiation of microbunched electrons in undulators and the tailoring of the emitted wavefronts. The computed pulse energy outperforms pre-existing technologies by three orders of magnitude. Specifically, our simulations of the proposed Soft X-ray Laser at MAX IV (Lund, Sweden) show that a pulse duration of 50-100 as and a pulse energy up to 5 [Formula: see text]J is feasible with the novel methods. In addition, the methods feature pulse shape control, enable the incorporation of orbital angular momentum, and can be used in combination with modern compact free-electron laser setups.

A borane B(C 6 F 5 ) 3 -catalyzed metathesis reaction between the Si-C bond in the cyclic (alkyl)(amino)germylene (CAAGe) 1 and the Si-H bond in a silane (R 3 SiH; 2) is reported. Mechanistic studies propose that the initial step of the reaction involves Si-H bond activation to furnish an ionic species [1-SiR 3 ] + [HB(C 6 F 5 ) 3 ] - , from which [Me 3 Si] + [HB(C 6 F 5 ) 3 ] - and an azagermole intermediate are generated. The former yields Me 3 SiH concomitant with the regeneration of B(C 6 F 5 ) 3 whereas the latter undergoes isomerization to afford CAAGes bearing various silyl groups on the carbon atom next to the germylene center. This strategy allows the straightforward synthesis of eight new CAAGes starting from 1., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Activation of dioxygen (O 2 ) by 1,4,2,5-diazadiborinine 1 is reported. Two boron centers in 1 undergo a formal [4 + 2] cycloaddition with O 2 at room temperature affording a bicyclo[2.2.2] molecule 2 featuring a B-O-O-B unit. Treatment of 2 with an additional equivalent of 1 leads to the cleavage of the O-O bond in 2 concomitant with the formation of two B-O bonds to yield 4 involving the extremely rare B 4 C 2 N 2 O 2 ten-membered rings. A series of these reactions demonstrate the stepwise scission of the O[double bond, length as m-dash]O π-bond and the O-O σ-bond of O 2 ., (This journal is © The Royal Society of Chemistry 2019.)

Metal-free activation of homoatomic E-E σ bonds (E=P, B) in white phosphorus (P 4 ) and bis(catecholato)diboron (B 2 cat 2 ) with a 1,2-diboraallene 1 is reported. The 1:1 and 1:2 reactions of P 4 with 1 afford B n P 4 cages (2: n=2, 3: n=4), whereas a stoichiometric mixture of 1 and B 2 cat 2 undergoes homonuclear catenation through the addition of the B-B σ bond of B 2 cat 2 across the B=B double bond of 1 (i.e. diboration), which leads to the formation of a tetraborane (4) featuring a B 4 chain., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Synthesis of a series of cationic coinage metal (Au: 2-4, Ag: 5, and Cu: 6) complexes of asymmetric diborenes (1 a, 1 b) is reported. X-ray diffraction analysis reveals that the metal center interacts unsymmetrically with the B 2 moiety and the terminal boron atom exhibits pronounced pyramidal geometry. A computational study shows that in complexes 2-6, the bonding between the B 2 units and the metal center is dominated by electrostatic interactions concomitant with non-negligible covalent contributions., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Despite the large number of plausible isomers of benzene (C 6 H 6 ), only four valence isomers [(CH) 6 ] have been experimentally detected, all of which are nonionic and possess skeletal frameworks built from localized C-C bonds. Herein, we present the isolation of a diazatetraborabenzene analogue of a hypothetical zwitterionic valence isomer of benzene. Therein, two electrons are delocalized over the four boron atoms in the six-membered B 4 N 2 ring, which is a result of the σ-bonding interaction between two odd-electron B-B π-orbitals. Simple treatment with a crown ether leads to the formation of a paramagnetic potassium-doped radical ion pair that exhibits a thermally populated triplet character.

The undulator is a magnetic device usually consisting of a series of rare-earth permanent magnets (REPMs) arranged to generate a sinusoidal magnetic field, and is installed in synchrotron radiation and free electron laser facilities to periodically deflect high-energy electrons. Because the undulator is operated under a high-radiation environment, it is important to take possible measures to avoid the quality degradation, in particular the radiation damage of REPMs. We present a simple scheme to enhance the radiation resistance of REPMs in undulators, in which the easy axis of each REPM is tilted by 45°. Experimental studies have revealed that the radiation resistance of REPMs in this configuration is enhanced by an order of magnitude compared to that in the conventional undulator.

The synthesis of neutral Mg complexes of asymmetric diborenes is reported. X-ray diffraction analysis reveals that the Mg center is unsymmetrically coordinated to the B2 units of diborenes. Theoretical calculations manifest the donation of electrons from the π-type orbitals of diborenes to an empty orbital of Mg.

An annulated 1,3,2,5-diazadiborinine with 14 π electrons has been synthesized and fully characterized. Experimental and computational studies revealed that this compound features a rather small HOMO-LUMO gap, which leads to enhanced reactivity towards small molecules. Thus, the 1,3,2,5-diazadiborinine readily cleaves the H-H bond of dihydrogen and an N-H bond of ammonia under mild conditions. Moreover, it reacts with 2,6-dimethylphenylisonitrile in a [4+1] cycloaddition at room temperature., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

One-electron oxidation of 1,4,2,5-diazadiborinine 1 has been studied. While the reaction of 1 a bearing phenyl groups on the B atoms with AgAl{OC(CF 3 ) 3 } 4 afforded a complex mixture, the same oxidation reaction with 1 b featuring bulky mesityl substituents on the B atoms rendered the corresponding cation radical 2 b as an isolable species. X-ray diffraction analysis, EPR spectroscopy, and DFT calculations of 2 b revealed the delocalization of the unpaired electron over the entire π-system of 2 b, as well as a large spin density (0.76 in total) on the two equivalent boron atoms. The chemical trapping reaction of 2 b with p-benzoquinone and triphenyltin hydride afforded the dicationic species 3 containing two newly formed B-O bonds and the monocationic product 2b-H containing a B-H bond, respectively, thus confirming the boron-centered radical reactivity of 2 b., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Because the construction of the C-C bond is one of the most significant reactions in organic chemistry, the development of an efficient strategy has attracted much attention throughout the synthetic community. Among various protocols to form C-C bonds, organoboron compounds are not just limited to stoichiometric reagents, but have also made great achievements as catalysts because of the easy modification of the electronic and steric impacts on the boron center. This review presents recent developments of boron-based catalysts applied in the field of C-C bond-formation reactions, which are classified into four kinds on the basis of the type of boron catalyst: 1) highly Lewis acidic borane, B(C 6 F 5 ) 3 ; 2) organoboron acids, RB(OH) 2 , and their ester derivatives; 3) borenium ions, (R 2 BL)X; and 4) other miscellaneous kinds., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In the presence of a catalytic amount of heavier tetrylene dichlorides, an allenic diborene 1 undergoes a 1,3-hydrogen shift to afford a terminal diborene 2, which can be deemed a boron analogue of vinylidene dication stabilized by Lewis bases. X-ray diffraction analysis and computational studies revealed that 2 involves a conjugative interaction between the C═C and B═B π-orbitals. The reaction of 2 with ZnBr 2 afforded the corresponding isolable complex 3, in which two boon centers coordinate to the Zn atom asymmetrically.

N-Heterocyclic phosphenium triflates (NHP-OTf) 1 serve as efficient catalysts for the regio- and chemoselective hydroboration of pyridines under ambient condition with good functional group tolerance. Mechanistic studies indicate that a boronium salt, [(Py) 2 ·Bpin]OTf 4, is generated concomitant with NHP-H 5 via hydride abstraction from HBpin by 1 in the initial reaction step. Hydride reduction of the activated pyridine in [(Py) 2 ·Bpin]OTf 4 by NHP-H 5 affords the 1,4-hydroboration product selectively. Thus, the phosphenium species act as a hydrogen transfer reagent in the catalytic cycle.

The addition of phenyl lithium (PhLi) to an aromatic 1,3,2,5-diazadiborinine (1) afforded isolable ionic species 2, which can be deemed as an inorganic analogue of a Janovsky complex. X-ray diffraction analysis and DFT studies of 2 indicate the delocalization of π-type electrons mainly over the C-B-C unit in the central B 2 C 2 N 2 six-membered ring. The reactions of 2 with methyl iodide (MeI) and chloro(tricyclohexylphosphine)gold(i) (Cy 3 PAuCl) gave 3 bearing a B-Me bond and 4 featuring a B-Au bond, respectively, demonstrating the nucleophilic properties of the tricoordinate boron center in 2.

Diverse skeletal transformations of 1,4,2-diazaboroles through ring expansion, photoisomerization, and retrocyclization led to the isolation of various B,N-dihydroindole (compounds 3 and 6), 1,3-azaborolidin-2-imine (compound 7), and 1,4,2-diazaborol-3-imine derivatives (compound 11)., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Single-electron oxidation of neutral boryl-linked tetraaminoethylene derivatives 4 led to the formation of radical cations 4˙ + , which have been isolated and fully characterized. X-ray diffraction analysis, EPR spectroscopy, and computational studies revealed that the unpaired electron is delocalized over the B 2 N 4 C 2 skeleton and the spin density mainly resides on the carbon and boron atoms.

A zwitterionic boraalkenyl boronium 3 was synthesized by reduction of cyclic (alkyl)(amino)carbene (cAAC) and trimethylphosphine (PMe 3 )-coordinated tetrabromodiborane 2 with KC 8 in the presence of PMe 3 . Further reduction of 3 led to the formation of neutral allenic diborene 4. X-ray diffraction and computational studies revealed that 4 features the cumulated C=B and B=B double bonds. The reaction of 4 with four isonitrile molecules afforded a heterocycle 5 with the B 2 C 3 five-membered ring, via a complete scission of the B=B bond of 4., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We have developed bis(N-heterocyclic olefin) derivatives 2 and demonstrated that 2 can be utilized as precursors for the synthesis of isophosphindolylium species 3. X-ray diffraction and density functional theory studies indicate the aromatic property of the PC 4 five-membered ring in 3. Despite its cationic nature, the P center in 3b exhibits nucleophilic character and thus readily forms a bond with CuCl to afford a copper phosphenium complex 4, demonstrating the potential utility of 3 as a σ-donor ligand.

A lightweight-compact variable-gap undulator (LCVGU) having the force-cancellation system based on the multipole monolithic magnets (MMMs) has been developed. The LCVGU is free from the heavy mechanical frames, which is a fundamental element specific to conventional variable-gap undulators (VGUs) because of a strong attractive force, and thus the cost and time for construction and installation are expected to be significantly reduced; the MMMs counteract the strong attractive force in a cost-effective manner. Results of mechanical tests and magnetic-field measurements of two prototype LCVGUs equipped with the proposed force cancellation system have revealed the comparable performance with the conventional VGUs.

The reactivity of L 2 PhB: (1; L = oxazol-2-ylidene) as well as its transition-metal (chromium and iron) complexes toward main-group substrates have been systematically examined, which led to the construction of B-E (E = C, Ga, Cl, H, F, N) bonds. The combination of 1 and triethylborane smoothly captured carbon dioxide concomitant with the formation of B-C and B-O bonds. The soft basic boron center in 1 readily reacted with soft acidic gallium trichloride (GaCl 3 ) to afford the extremely stable adduct 4 involving a B-Ga dative bond. Electrophilic alkylation of a neutral tricoordinate organoboron was first achieved by the treatment of 1 with dichloromethane and methyl trifluoromethanesulfonate (MeOTf), both of which afforded ionic species featuring an additional B-C bond. Comparatively, redox reactions took place when halides of heavier elements such as germanium dichloride, dichlorophenylphosphine, and chlorodiphenylbismuth were employed as substrates, from which cationic species 7 bearing a B-Cl bond was obtained. In addition, reactions of metal complexes [2, Cr(1)(CO) 5 ; 8, Fe(1)(CO) 4 ] with cationic electrophiles were investigated. With HOTf and FN(SO 2 Ph) 2 , the corresponding ionic species featuring a B-H bond (9) and a B-F bond (10) were formed via a formal electrophilic substitution reaction, whereas the reaction of 1 with F·Py-BF 4 resulted in the formation of a dicationic boron species 11 with a newly formed B-N bond.

A 2,3-dihydro-1H-1,2-azaborole derivative 2 was converted to a cyclic (alkyl) (amino)carbene (cAAC) via 1,2-hydrogen migration triggered by boranes to afford cAAC-borane adducts. This procedure allowed us to develop an asymmetrical diborene cAAC·(Br)B═B(Br)·IDip 6, which was isolated and fully characterized. The 11 B NMR spectrum, X-ray diffraction analysis and computational studies indicate that π-electrons on the central B 2 moiety in 6 are unequivalently distributed, and thus polarized. A complete scission of the B═B double bond in 6 was achieved by the treatment with an isonitrile, which led to the formation of a base-stabilized B,N-containing methylenecyclopropane 7.

We report an unexpectedly large flux loss observed in permanent magnets in one of the undulators operated in SACLA, the x-ray free electron laser facility in Japan. Characterizations of individual magnets extracted from the relevant undulator have revealed that the flux loss was caused by a homogeneous magnetization reversal extending over a wide area, but not by demagnetization of individual magnets damaged by radiation. We show that the estimated flux-loss rate is much higher than what is reported in previous papers, and its distribution is much more localized to the upstream side. Results of numerical and experimental studies carried out to validate the magnetization reversal and quantify the flux loss are presented, together with possible countermeasures against rapid degradation of the undulator performance.

Metal-free regioselective carboboration of arylnitriles with L 2 PhB: (1: L=oxazol-2-ylidene) catalyzed by Et 3 B afforded the unprecedented acyclic 2-aza-4-borabutadienes 2, thus demonstrating a new strategy to construct a B,C,N-mixed π-system involving B=C and C=N bonds. Thermal isomerization of 2 gave C-borylimines (3), and diverse reactivity of 2 a towards several substrates, such as H + , F + , O 2 , S, Se, and isonitriles, allowed construction of boron-containing heterocycles with various ring sizes, thus illustrating the utility of 2 as a synthetic building block., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A method is proposed to generate an isolated attosecond X-ray pulse in free-electron lasers, using irregularly spaced current peaks induced in an electron beam through interaction with an intense short-pulse optical laser. In comparison with a similar scheme proposed in a previous paper, the irregular arrangement of current peaks significantly improves the contrast between the main and satellite pulses, enhances the attainable peak power and simplifies the accelerator layout. Three different methods are proposed for this purpose and achievable performances are computed under realistic conditions. Numerical simulations carried out with the best configuration show that an isolated 7.7 keV X-ray pulse with a peak power of 1.7 TW and pulse length of 70 as can be generated. In this particular example, the contrast is improved by two orders of magnitude and the peak power is enhanced by a factor of three, when compared with the previous scheme.

A 1,4-addition of a dichlorogermylene dioxane complex with α,β-unsaturated imine 1 gave a dichlorogermane derivative 2 bearing a GeC₃N five-membered ring skeleton. By reducing 2 with KC₈, cyclic (alkyl)(amino)germylene 3 was synthesized and fully characterized. Germylene 3 readily reacted with TEMPO, N₂O and S₈, producing the 1:2 adduct 4, the oxo-bridged dimer 5 and the sulfido-bridged dimer 6, respectively.

One-electron oxidation of organoboron L2PhB: 1 (L = oxazol-2-ylidene) afforded a dicationic diborane(6) species [L2PhB-BPhL2]·2X (X = OTf, BF4, AlCl4) 3, representing a new strategy to construct a B(sp(3))-B(sp(3)) covalent bond. Each boron atom in 3 is in the formal oxidation state +II, and tetracoordinate with a Ph group and two oxazol-2-ylidenes. The cyclic voltammetry of 3 shows irreversible reduction and oxidation. Indeed, two-electron reduction of 3 with potassium graphite (KC8) afforded 1, making a fully reversible 1 ↔ 3 redox system, whereas two-electron oxidation with AuCl produced a boronium [L2PhBCl]OTf 4. Moreover, the reactions of 3 with isonitrile derivatives RNC: under heating conditions gave a cyano-substituted boronium [L2PhBCN]BF4 5 and a 2-boranyl-indole derivative 6, depending on the substituent R. The proposed reaction mechanism involves a borinylium radical 1(•+) which is generated via a homolytic cleavage of the B-B bond of 3.

The reactivity of diazadiphosphapentalene 1 towards various substrates was investigated. Reaction of 1 with ammonia-borane resulted in transfer hydrogenolysis concomitantly with the cleavage of a P-N bond. By treatment of 1 with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), oxidation took place at one of the phosphorus atoms of 1, and a P(V) /P(III) mixed-valence derivative was isolated. At the same time, it was demonstrated that only one of the phosphorus atoms in 1 behaves as an electron donor for electrophiles and Lewis acids. The former afforded an intramolecularly coordinated phosphine-phosphenium species, whereas the latter demonstrates the ligand property of 1. UV irradiation induced rearrangement of 1 into another example of another diazadiphosphapentalene., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Boranes have long been known as the archetypal Lewis acids owing to an empty p-orbital on the boron centre. Meanwhile, Lewis basic tricoordinate boranes have been developed in recent years. Here we report the synthesis of an annulated 1,4,2,5-diazadiborinine derivative featuring boron atoms that exhibit both Lewis acidic and basic properties. Experimental and computational studies confirmed that two boron atoms in this molecule are spectroscopically equivalent. Nevertheless, this molecule cleaves C-O, B-H, Si-H and P-H bonds heterolytically, and readily undergoes [4+2] cycloaddition reaction with non-activated unsaturated bonds such as C=O, C=C, C≡C and C≡N bonds. The result, thus, indicates that the indistinguishable boron atoms in 1,4,2,5-diazadiborinine act as both nucleophilic and electrophilic centres, demonstrating ambiphilic nature.

3,4-dihydro-2H-1,2,4,3-triazaborol-3-yl-lithium 3 was synthesized and fully characterized. The (11)B NMR spectrum, X-ray diffraction analysis, and computational studies revealed the ionic nature of the B-Li bond, and indeed 3 displays nucleophilic property which allowed preparation of a series of 1,2,4,3-triazaborol-3-yl-metal complexes (Al; 5, Au; 6, Zn; 7, Mg; 8, Sb; 9, and Bi; 10). 3 reacted with CO (1 atm) and various isonitriles under ambient condition, and mechanistic study suggests that the reactions with CO and aryl isonitriles proceed via an insertion of CO and isonitrile carbon into the B-Li bond followed by isomerization to yield transient carbene species, one of which was confirmed by trapping with S8. With PhNC, compounds 5 and 7·(thf) underwent exchange of THF molecule coordinating to the metal center with isonitrile, whereas insertion of isonitrile carbon occurred at the B-Bi bond in 10 which afforded stable bismuth (boryl)iminomethane 20.

A simple scheme to quickly switch the polarity of circular radiation is proposed, which is based on spectrum splitting of undulator radiation. In this scheme, two helical undulators with opposite helicities are placed tandem in one straight section, both of which are divided into several segments. The optical phases between segments are tuned so that light waves from one of the two undulators are out of phase, while those from the other are in phase. Then the radiation spectrum of the former is split and the intensity at the fundamental photon energy vanishes. As a consequence, the monochromated photon beam at the fundamental energy is circularly polarized with the helicity specified by the in-phase undulator, which can be quickly flipped by tuning the optical phase. Numerical calculations carried out to demonstrate the feasibility of the proposed scheme show that a relatively high degree of circular polarization is expected if the angular acceptance of the beamline is not too large.

Oxidative addition of the C-O bond in L 2 PhB: (L=oxazol-2-ylidene) to an Al I center induced ring expansion of an oxazol-2-ylidene ring, affording a unique organoboron species formally involving either an Al, N, O mixed heterocyclic carbene or anionic (amino)(boryl)carbene fragment., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The reaction of germylone (L)Ge (1) [L = 3-Ad-1-{C((t)Bu) = N(Mes)}C3H4N2] with 1 equivalent of MeOTf afforded a germyliumylidene ion [(L)GeMe](+)OTf(-) (2), while reactions with M(CO)5(thf) (M = Cr, Mo, W) gave the corresponding germylone-metal complexes [(L)Ge]M(CO)5 (3-5). The former possesses a pyramidal Ge center, whereas the latter display a planar geometry around the Ge atom. Computational studies showed a unique bonding interaction between 1 and the M(CO)5 unit, which involves a σ-donation as well as a weak π-back-donation.

Under ambient conditions, a [4 + 2] cycloaddition reaction of 1,3,2,5-diazadiborinine 1 with ethylene afforded a bicyclo[2.2.2] derivative 2 , which was structurally characterized. The cyclization process was found to be reversible, and thus retro-[4 + 2] cycloaddition reproduced 1 quantitatively, concomitant with the release of ethylene. Compound 1 reacted regio-selectively and stereo-selectively with styrene derivatives and norbornene, respectively, and these processes were found to be reversible too. Computational studies determined the reaction pathways which were consistent with the regio-selectivity observed in the reaction of styrene, and the reaction was suggested to be essentially concerted but highly asynchronous.

Hydrophosphination of CO2 with 1,3,2-Diazaphospholene (NHP-H; 1) afforded phosphorus formate (NHP-OCOH; 2) through the formation of a bond between the electrophilic phosphorus atom in 1 and the oxygen atom from CO2 , along with hydride transfer to the carbon atom of CO2 . Transfer of the formate from 2 to Ph2 SiH2 produced Ph2 Si(OCHO)2 (3) in a reaction that could be carried out in a catalytic manner by using 5 mol % of 1. These elementary reactions were applied to the metal-free catalytic N-formylation of amine derivatives with CO2 in one pot under ambient conditions., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An isolable 1,4,2-diazaborole derivative was synthesized and structurally characterized. X-ray diffraction analysis and computational studies revealed a delocalization of 6π-electrons over the BC2N2 five-membered ring, which thus indicates the aromatic property. The reactivity toward electrophiles such as MeOTf and selectfluor was also investigated.

Gold-catalyzed hydroimination of terminal alkynes, giving rise to anti-Markovnikov adducts concomitant with unstable Markovnikov adducts is described. The elementary step can be applied for the construction of pyridine derivatives from ammonia and alkynes.

The seminal discovery in 1865 by Kekulé that benzene nucleus exists with cyclic skeleton is considered to be the beginning of aromatic chemistry. Since then, a myriad of cyclic molecules displaying aromatic property have been synthesized. Meanwhile, borazine (B3N3H6), despite the isostructural and isoelectronic relationships with benzene, exhibits little aromaticity. Herein, we report the synthesis of a 1,3,2,5-diazadiborinine (B2C2N2R6) derivative, a hybrid inorganic/organic benzene, and we present experimental and computational evidence for its aromaticity. In marked contrast to the reactivity of benzene, borazine, and even azaborinines previously reported, 1,3,2,5-diazadiborinine readily forms the adducts with methyl trifluoromethanesulfonate and phenylacetylene without any catalysts. Moreover, 1,3,2,5-diazadiborine activates carbon dioxide giving rise to a bicycle[2,2,2] product, and the binding process was found to be reversible. These results, thus, demonstrate that 1,3,2,5-diazadiborinine features both nucleophilic and electrophilic boron centres, with a formal B(+I)/B(+III) mixed valence system, in the aromatic six-membered B2C2N2 ring.

The reactivity of a tricoordinate organoboron L 2 PhB: (L = oxazol-2-ylidene) 1 towards metal precursors and its coordination chemistry were comprehensively studied. While the boron center in 1 is reluctant to coordinate to the alkali metals in their trifluoromethanesulfonate salts (MOTf) (M = Li, Na, K), the unprecedented compound 2 containing two L 2 PhB: units linked by a cyclic Li(OTf) 2 Li spacer was obtained from the reaction of 1 with LiOTf. Treatment of 1 with group 9 metal complexes [MCl(COD)] 2 (M = Rh, Ir) afforded the first zwitterionic rhodium(i)-boronium complex 3 and the iridium(iii)-borane complex 4 , respectively. The reaction pathway may involve C-H activation followed by proton migration from the metals to the boron center, demonstrating the first example of the deprotonation of metal hydrides by a basic boron. In the reactions with coinage metals, 1 could act as a two-electron reducing agent towards the metal chlorides MCl (M = Cu, Ag, Au). Meanwhile, the reaction of 1 with gold chloride supported by a N-heterocyclic carbene (NHC) produced a heteroleptic cationic gold complex [(L 2 PhB)Au(NHC)]Cl ( 6 ) featuring both carbene and L 2 PhB: ligands on the gold atom. In contrast, an isolable gold chloride complex (L 2 PhB)AuCl ( 8 ) was obtained by direct complexation between 1 and triphenylphosphine-gold chloride via ligand exchange. X-ray diffraction analysis and computational studies revealed the nature of the B:→Au bonding interaction in complexes 6 and 8 . Natural Population Analysis (NPA) and Natural Bond Orbital (NBO) analysis support the strong σ-donating property of the L 2 PhB: ligand. Moreover, preliminary studies showed that complex 8 can serve as an efficient precatalyst for the addition of X-H (X = N, O, C) to alkynes under ambient conditions, demonstrating the first application of a metal complex featuring a neutral boron-based ligand in catalysis.

The first metal-free catalytic hydroboration of carbonyl derivatives has been developed in which a catalytic amount of 1,3,2-diazaphospholene effectively promotes a hydroboration reaction of aliphatic and aromatic aldehydes and ketones. The reaction mechanism involves the cleavage of both the PO bond of the alkoxyphosphine intermediate and the BH bond of pinacolborane as well as the formation of PH and BO bonds. Thus, the reaction proceeds through a non-metal σ-bond metathesis. Kinetic and computational studies suggest that the σ-bond metathesis occurred in a stepwise but nearly concerted manner., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A diazadiphosphapentalene derivative 5 featuring a bent geometry with two phosphorus atoms at the bridgehead has been synthesized. Under mild conditions, compound 5 readily activated ammonia to afford 1-aza-2,3-diphospholene derivative 6 bearing an enamine group. The reaction is therefore viewed as a formal σ-bond metathesis between an N-H bond of ammonia and an endocyclic P-N bond of 5. Details of the reaction mechanism for ammonia activation as well as subsequent isomerization were explored by density functional theory calculations.

An autoionization of germanium dichloride/dioxane complex with an imino-N-heterocyclic carbene ligand (L) afforded a novel germyliumylidene ion, [(L)GeCl](+)[GeCl3](-), which was fully characterized. Reduction of the germyliumylidene ion with potassium graphite produced a cyclic species [(L)Ge], which can be viewed as both a Ge(0) species and a mesoionic germylene. X-ray diffraction analysis and computational studies revealed one of the lone pairs on the Ge atom is involved in the π system on the GeC2N2 five-membered ring. It was also confirmed that the nucleophilic behavior of [(L)Ge] as a two lone-pair donor., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel type of C4 cumulene derivative featuring 4-pyridylidene units has been synthesized. X-ray diffraction analysis revealed the presence of consecutive C=C double bonds in the C4 backbone as well as the quinoidal pyridylidene structure. This C4 cumulene derivative readily reacted with ammonia-borane, which resulted in transfer hydrogenation of the central C=C double bond.

An isolable phenylborylene species supported by two oxazol-2-ylidene ligands was synthesized and structurally characterized. Computational studies revealed the presence of lone-pair electrons on the boron atom in this molecule; therefore, there are eight electrons around the three-coordinate boron center. The nucleophilic property was confirmed by the reactions with trifluoromethanesulfonic acid and [(thf)Cr(CO)5], which gave the corresponding conjugate acid and a chromium-borylene complex, respectively., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The first example of 1,2,4,3-triazaborole-based oxoborane has been synthesized via hydrogen migration upon the coordination of AlCl3 to the corresponding borinic acid. X-ray diffraction analysis and computational study disclosed the partial B[double bond, length as m-dash]O double-bond property.