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The reactivity of [PB{EX2}] (X = Cl or Br; PB = 1,2-iPr2C6H4BCy2; E = C, Si, Ge) adducts is described.

Tetrasilabicyclo[1.1.0]but-1(3)-enes, compounds containing an Si=Si double bond with an inverted geometry, have recently emerged as a new class of stable π-electron systems of silicon. Herein, we r...

Complexes that could be switched between two electronic states by external stimuli have attracted much attention for their potential application in molecular devices. However, a realization of such a phenomenon with low-valent main-group element-centered complexes remains challenging. Herein, we report the synthesis of cyclic (alkyl)(amino)silylene (CAASi)-ligated monatomic silicon(0) complexes (silylones). The bis(CAASi)-ligated silylone adopts a π-localized ylidene structure (greenish-black color) in the solid state and a π-delocalized ylidene structure (dark-purple color) in solution that could be reversibly switched upon phase transfer (ylidene [L: → :Si = L ↔ L = Si: ← :L]). The observed remarkable difference in the physical properties of the two isomers is attributed to the balanced steric demand and redox noninnocent character of the CAASi ligand which are altered by the orientation of the two terminal ligands with respect to the Si-Si-Si plane: twisted structure (π-localized ylidene) and planar structure (π-delocalized ylidene). Conversely, the CAASi/CDASi-ligated heteroleptic silylone (CDASi = cyclic dialkylsilylene) only exhibited the twisted π-localized ylidene structure regardless of the phase. The synthesized silylones also proved themselves as monatomic silicon surrogates. Thermolysis of the silylones in the presence of an ethane-1,2-diimine afforded the corresponding diaminosilylenes. Analyses of the products suggested a stepwise mechanism that proceeds via a disilavinylidene intermediate.

Due to an intrinsically polar π-bond with a narrow π-π* gap, silenes (silicon-carbon doubly bonded compounds) should receive remarkable attention as a member of π-conjugation units. We report herei...

Although isolable silicon analogs of acetylene have been extensively studied, the silicon analogs of vinylidene, which is a short-lived isomer of acetylene, remain scarce. Herein, we report isolabl...

A cyclic (alkyl)(amino)bromoborane (CAABBr) was synthesized by a reaction of the corresponding hydroborane with bromine in the presence of triethylamine. Reduction of the resulting CAABBr with Li p...

An isolable three-coordinate dialkylsilanone without substantial electronic stabilization reacts with several ethers resulting in the cleavage of the C–O or C–H and C–O bonds in the ethers which have not been observed for the hitherto-known electronically stabilised isolable SiO species. The formation of the Lewis base (DMAP and MTHP) complexes of the dialkylsilanone and the DFT calculations elucidated that the coordination of the ethereal oxygen atom to the Lewis acidic Si atom of the genuine SiO bond is a key interaction for the reaction.

Overcrowded 1-amino-2-boryldisilenes were isolated as blue crystals by the direct hydro/chloroborylation of a cyclic (alkyl)(amino)silylene-coordinated monatomic silicon complex (silylone) with 9-BBN (BBN = borabicyclo[3.3.1]nonane) hydride/chloride. The extreme twisting and push-pull effect around the SiSi bonds resulted in strong polarization of the SiSi bond. The disilenes exhibit longest-wavelength absorptions above 600 nm due to the charge-transfer-type π → π* transitions and undergo reversible 1,3-hydride/halide migration in solution reflecting the electrophilic terminal silicon atoms.

High performance global exploration of isomers and isomerization channels on the quantum chemical potential energy surface (PES) is performed for H5 C2 NO2 by using the scaled hypersphere search-anharmonic downward distortion following (SHS-ADDF) method. A multi-node operation, NeoGRRM, has achieved high performance exploration calculations for the large system by submitting SHS-ADDF sub-jobs into many cores in parallel and unifying the results of sub-jobs into the total lists of the main-job. Global exploration of equilibrium (EQ) and transition-state structures at the level of B3LYP/6-31G(d) gave 3210 EQs and 23278 TSs. Nine compounds were found in the low energy regions of 0-100 kJ/mol; the lowest energy compound is N-methylcarbamic acid, the second is methyl carbamate, and the third is glycine (the most fundamental amino acid). Interconversion pathways between the conformers of each of the low energy compounds were surveyed. Isomerization channels around glycine were explored in detail. The lowest energy barriers around some of the EQs turned to be negative after zero-point energy corrections. This indicates that those structures cannot exist as independent structures because they spontaneously collapse into more stable structures. The global PES search showed various interesting dissociating channels which indicate synthon reaction pathways in the reverse directions.

The stabilization of silicon(II) and germanium(II) dihydrides by an intramolecular Frustrated Lewis Pair (FLP) ligand, PB, i Pr2 P(C6 H4 )BCy2 (Cy=cyclohexyl) is reported. The resulting hydride complexes [PB{SiH2 }] and [PB{GeH2 }] are indefinitely stable at room temperature, yet can deposit films of silicon and germanium, respectively, upon mild thermolysis in solution. Hallmarks of this work include: 1) the ability to recycle the FLP phosphine-borane ligand (PB) after element deposition, and 2) the single-source precursor [PB{SiH2 }] deposits Si films at a record low temperature from solution (110 °C). The dialkylsilicon(II) adduct [PB{SiMe2 }] was also prepared, and shown to release poly(dimethylsilane) [SiMe2 ]n upon heating. Overall, this study introduces a "closed loop" deposition strategy for semiconductors that steers materials science away from the use of harsh reagents or high temperatures.

The catalyst-free hydrosilylation of CO2 under mild conditions remains limited. Herein, we report the synthesis, characterization, and reactivity of 5,10,15,20-tetraphenylporphyrinato(dihydrido)silicon(IV) (1) as a six-coordinate silicon dihydride. The Si-H moiety of 1 reacts with polar double bonds and CO2 in the absence of a catalyst to afford hydrosilylated products. Combining the hydrosilylation with subsequent transformation furnishes formic acid from CO2 . Computational studies indicate that the hydride-donor properties of 1 are exceptionally high for a neutral silicon hydride, and that the direct hydride transfer from silicon to carbon is a pivotal step in the hydrosilylation of CO2 with 1.

Development of efficient bond formation reactions remains important in organic and main-group-element chemistry. Herein, we report the metal-free one-pot condensation reaction of 1-iodo-3-trimethyl...

Bulky phosphines and their redox properties have received increased attention in the view of useful auxiliary ligands for transition metal catalysts and Lewis-base components of frustrated Lewis pairs for chemical transformations. Herein we report the synthesis, structure, and properties of a series of trialkylphosphines 2R (R = methyl, ethyl, isopropyl, tert-butyl, 1-adamantyl) that possess the bulky 2,2,5,5-tetrakis(trimethylsilyl)-1-phosphacyclopentane as a structural backbone. Among these phosphines, 2Ad, which contains an adamantyl moiety, has a very large buried volume (%Vbur) for a trialkylphosphine (62.0) and shows a quasi-reversible oxidative wave at a lower oxidation potential (-0.12 V in CH2Cl2, vs ferrocene/ferrocenium couple) by cyclic voltammetry. The reaction of 2Ad with AgPF6 afforded a cationic silver aquo complex [Ag(2Ad)(H2O)]+[PF6]-, whereas the reaction with NOSbF6 gave a persistent phosphine radical cation [2Ad]•+. Based on the EPR spectra and DFT studies, the spin and positive charge of [2Ad]•+ are localized on the phosphorus atom.

Isolable compounds that contain π bonding without an underlying σ-bond framework (π-type single bonding) remain scarce. Herein we report the synthesis and properties of 1,3-diiodotetrasilabicyclo[1.1.0]butane

Heavy element analogues of bicyclo[1.1.0]butane have attracted much attention as they often exhibit skeletal isomerisations that are not observed for all-carbon bicyclo[1.1.0]butanes. The reaction of a bicyclo[1.1.0]tetrasil-1(3)-ene with CCl4 at low temperature provided orange crystals of a 1,3-dichlorobicyclo[1.1.0]tetrasilane containing a planar Si4 ring with a π-type bridgehead Si-Si bond. The equilibrium between the bicyclotetrasilane and an isomer, 1-chloro-2-(chlorosilyl)cyclotrisilene in solution, which is an unprecedented interconversion mode of Si4R6 isomers, was identified by NMR spectroscopy and also the formation of its 4-(dimethylamino)pyridine (DMAP) complex.

σ-Type 3-electron-2-center (3e-2c) bonds have been extensively studied as one of the key bonding motifs in radical chemistry and some biological systems. "π-Type 3e-2c-bonded species" that contain a 3e-2c π-bond without an underlying σ-bond framework, however, have been unexplored so far both theoretically and experimentally. Herein, we report the synthesis of the first stable π-type 3e-2c-bonded species, a silicon analogue of a bicyclo[1.1.0]butane radical anion. This compound exhibits an extremely long bridgehead Si-Si bond (3.0638(8) Å) and a strong near-IR absorption at 922 nm in solution which arises from a HOMO→SOMO [π(Si-Si)→π*(Si-Si)] transition. DFT calculations revealed a π-type bonding interaction between the two bridgehead silicon atoms with an unpaired electron mainly delocalized across the corresponding π*-type orbital, which introduces a novel bonding motif for constructing π-electron systems.

We examined a virtual simulation scheme for reaction condition optimization using machine learning for a small number of experiments with nine reaction conditions, consisting of five continuous and...

Cyclic (alkyl)(amino)silylene (CAASi) 1 has been found to successfully dehydrogenate 1,4-dihydroaromatic compounds containing various substituents to afford the corresponding aromatic compounds. The observed high substrate generality proves 1 to be a potential 1,4-dehydrogenation reagent for organic compounds. For the reaction with 9,10-dimethyl-9,10-dihydroanthracene, silylene 1 activated not only benzylic C-H bonds but also aromatic C-H bonds to yield a silaacenaphthene derivative, which is an unprecedented reaction of silylenes. The results of the experimental and computational study of the reaction of CAASi 1 with 9,10-dihydroanthracene and 1,4-cyclohexadiene are consistent with the notion that 1,4-dehydrogenation with CAASi 1 proceeds mainly through a stepwise hydrogen-abstraction mechanism.

We have found capsule-formed dimers of polycyclic aromatic hydrocarbons (cap-di-PAH) for coronene, ovalene, and circumcoronene by quantum chemical calculations. Two monomers are connected at the edge that gives a capsule form, holding the aromatic characters in the inner six-membered rings. The aromatic π-electron networks at the upper and lower parts of the dimers are not merged each other. Those cap-di-PAHs are located in sufficiently deep potential wells surrounded by high energy barriers, indicating the high possibility of existence.

Bicyclo[1.1.0]tetrasil-1(3)-ene 1, a tetrasilicon analogue of bicyclo[1.1.0]but-1(3)-ene that contains a formal double bond between bridgehead silicon atoms in an inverted geometry, was synthesized and isolated in the form of thermally stable orange crystals. The distance between the bridgehead Si atoms in 1 is much longer than those in typical Si=Si bonds, but still shorter than that of a previously reported pentasila[1.1.1]propellane. DFT calculations suggest that the bridgehead bond in 1 comprises a σ bond with an inverted geometry and a π bond. This notion is supported by the UV/Vis spectrum of 1, which exhibits several absorption bands in the UV/Vis region. While 1 is stable toward typical trapping agents for Si=Si double bonds, 1 reacts with carbon tetrachloride to furnish a hexachlorotetrasilane.

Spiroconjugation, that is, through-space orbital interactions between two perpendicular π orbitals, is a key concept in the contemporary molecular design of spirocyclic π-electron systems. We synthesized spiropentasiladiene radical cation salt 1 as a dark-green solid via the one-electron oxidation of the stable spiropentasiladiene 2. Characterization of the molecular structure combined with theoretical studies indicated that the spin and positive charge are delocalized across the two perpendicular Si═Si double bonds of 1. Two π(Si═Si) orbitals are split into HOMO and SOMO with a small energy gap owing to the second-order Jahn-Teller distortion and steric repulsion between bulky alkyl groups upon one-electron oxidation. In the UV-vis-NIR spectrum, the longest-wavelength absorption band of 1 (λmax = 1972 nm) covers the IR-B region (1400-3000 nm; 0.89-0.41 eV) despite having the smallest possible spiroconjugation motif. The unprecedented absorption band in the IR region was assigned to the HOMO → SOMO transition that arises from the delocalized π-orbitals in the spirocyclic Si5 skeleton.

An isolable three-coordinate dialkylsilanone without substantial electronic stabilization reacts with several ethers resulting in the cleavage of the C-O or C-H and C-O bonds in the ethers which have not been observed for the hitherto-known electronically stabilised isolable Si[double bond, length as m-dash]O species. The formation of the Lewis base (DMAP and MTHP) complexes of the dialkylsilanone and the DFT calculations elucidated that the coordination of the ethereal oxygen atom to the Lewis acidic Si atom of the genuine Si[double bond, length as m-dash]O bond is a key interaction for the reaction.

Naphthodislacyclobutadiene 3 and anthradisilacyclobutadiene 4 were synthesized and characterized. In these compounds, the diatropic ring current on the benzene ring adjacent to the disilacyclobutadiene moiety decreases while that on the other benzene rings remains intact. The longest-wavelength absorption bands of 3 and 4 were hypsochromically shifted compared to those of benzodisilacyclobutadiene 1a despite the extended π-electron systems.

High performance global exploration of isomers and isomerization channels on the quantum chemical potential energy surface (PES) is performed for H

Direct activation of inert C(sp3 )-H bonds by main group element species is yet a formidable challenge. Herein, the dehydrogenation of cyclohexene and 1,2,3,4-tetrahydronaphthalene through the allylic/benzylic and homoallylic/homobenzylic C-H bond activation by cyclic (alkyl)(amino)silylene 1 in neat conditions is reported to yield the corresponding aromatic compounds. As for the reaction of cyclohexene, allylsilane 3 and 7-silanorbornene 4 were also observed, which could be interpreted as a direct dehydrogenative silylation reaction of monoalkenes at the allylic positions. Experimental and computational studies suggest that the dehydrogenation of cyclohexene at the homoallylic position was accomplished by a combination of silylene 1 and radical intermediates such as hydrosilyl radical INT1 or cyclohexenyl radical H, which are generated in the initial step of the reaction.

The catalyst-free hydrosilylation of CO

The existence of a new carbon allotrope family with four-membered rings as a key unit has been recently predicted with quantum chemical calculations. This family includes carbon allotropes in prism-, polymerized prism-, sheet-, tube-, and wavy-forms. An atypical bond property has been observed in this series of carbon structures, which differs from the typical sp3 , sp2 , and sp hybridizations. The lowest energy barrier from some of the equilibrium states of the carbon structures has been determined with the SHS-ADDF (scaled-hypersphere-search combined with the anharmonic downward distortion following) method within the GRRM software program package. The height of the barriers indicates that the well is deep enough for the carbon structures to exist. This class of carbon allotropes is expected to be energy-reservoirs with extra energy of 100-350 kJ mol-1 per one carbon atom. This article presents the structures, energies and reactivity of the carbon allotropes with four-membered ring structures as well as the background of the findings in the context of the global exploration of potential energy surfaces. © 2018 Wiley Periodicals, Inc.

Two-coordinate group-15 element centered radicals that bear a lone pair and an unpaired electron on the same group-15 atoms have received much attention in group-15 element chemistry. We previously synthesized an isolable dialkylphosphinyl radical, 2,2,5,5-tetrakis(trimethylsilyl)-1-phosphacyclopentane-1-yl (1P) and its antimony and bismuth analogues (stibinyl radical 1Sb and bismuthinyl radical 1Bi) as persistent radicals. We report herein (1) synthesis of an isolable cyclic dialkylarsinyl radical 1As that exists in the radical form both in solution and in the solid state and (2) comprehensive study of a series of neutral two-coordinate pnictogen-centered radicals (1P, 1As, 1Sb, 1Bi) including UV-vis spectra, redox properties, and reactions.

The unexpected formations of fused polycyclic disilenes 2 a and (E),(Z)-3 b by the reduction of the 1,2-dibromodisilanes 5 a (R=Me) and 5 b (R=iPr) bearing bicyclo[1.1.1]pentasilanyl (BPS) groups is reported. The disilenes 2 a and (E),(Z)-3 b were characterized by a combination of NMR spectroscopy and X-ray diffraction analysis (XRD). The reduction of 5 b in the presence of 2,3-dimethyl-1,3-butadiene provided an ene adduct of the disilene 1 b bearing BPS groups, which suggested that an initial product of the reduction of 5 b was the disilene 1 b. Thermal reactions of 2 a and (E),(Z)-3 b afforded the highly strained saturated silicon clusters 4 a and 4 b. A computational study suggested that the transformation of 1 to 2, 3, or 4 can involve silyldisilene-disilanylsilylene rearrangement reactions and insertion reactions of a silylene into a Si-Si bond.