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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.

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.

Activation of H2 by compounds of main-group elements has received considerable attention. Herein, we report synthesis of novel monoboryl- and monoamino-substituted disilenes and their characterization by a combination of NMR spectroscopy and single-crystal X-ray diffraction analysis. The monoboryldisilene reacts with two molecules of H2 to provide the corresponding trihydridodisilane and hydroborane, whereas the aminodisilene does not react with H2 under the same conditions. The present results together with our previous results indicate that the presence of the boryl-substituent on the Si=Si double bond is essential to activate the H2 molecule. The low lying empty 2p orbital on the boron atom that interacts effectively with the π*(Si=Si) orbital could be responsible for the activation of H2 .

Although the oxidative coupling of disilenides, i.e., the disilicon analogues of vinyl anions, represents a promising route to extend the conjugation between Si═Si double bonds, previously reported synthetic routes to disilenides involve strongly reducing conditions. Herein, we report a novel synthetic route to disilenides from stable disilenes via the selective cleavage of Si(sp2)–Si(sp3) bonds under milder reaction conditions. Using this method, a 1,4-bis(trimethylsilyl)tetrasila-1,3-diene (5) was synthesized from the corresponding silyl-substituted disilene. Moreover, Et3Si-substituted tetrasila-1,3-diene 7 was synthesized via tetrasila-1,3-dien-1-ide 6, which is the first example of a functionalized tetrasila-1,3-diene.

A spiro-type cyclotrisilene was synthesized by the novel Si–Si coupling reaction of a disilenide and a base-adduct of bromosilylene and characterized by a combination of spectroscopic and crystallo...

The push–pull effect has been widely used to effectively tune π-electron systems. Herein, we report the synthesis and properties of 1-amino-2-boryldisilene 1 as the first push–pull disilene. Its spectroscopic and structural features show substantial interactions between the Si═Si double bond and the amino and boryl substituents. The π → π* absorption band of 1 is remarkably red-shifted compared to that of the corresponding alkyl-substituted disilene 2. Treatment of 1 with H2 resulted in the cleavage of two molecules of H2 under concomitant formation of the corresponding trihydridodisilane and hydroborane.

Benzodisilacyclobutadienes 2a-2c were isolated as blue to green crystalline solids from the reaction of stable disilyne 1 and 1,2-dibromobenzenes in the presence of potassium graphite. In the solid state, substantial bond alternation was observed within the benzene rings of 2a-2c. In hexane, 2a-2c showed remarkable bathochromic shifts for the π -> π* (HOMO -> LUMO) absorption bands at 625-670 nm. NMR spectra and theoretical calculations indicated that the diamagnetic ring currents on the benzene rings of 2a-2c are considerably reduced by the contributions from the antiaromatic 1,2-disilacyclobutadienes. In their entirety, the obtained results indicate that 2a-2c represent 8π-electron systems that contain an antiaromatic 1,2-disilacyclobutadiene.

5- to 6-member ring enlargements of 3-oxa-2-silacyclopentylmethyl to 4-oxa-3-silacyclohexyl radicals were investigated by EPR spectroscopy and QM computations of model indano-oxasilacyclopentane and oxasilinanyl compounds. Both experimental and computational evidence favored a mechanism via a concerted 1,2-migration of the "tethered" Si-group. Thus, the "forbidden" 1,2-Si-group migration from carbon to carbon becomes allowed when the Si-group is "tethered". The EPR data from 3-oxa-2-silacyclopentylmethyl radicals disclosed ground state conformations having semioccupied p-orbitals close to antiperiplanar with respect to their β-Si-C bonds, but indicated Si-hyperconjugation (β-silicon effect) was insignificant in radicals. Kinetic data was obtained by the steady state EPR method for ring enlargement of indano-3-oxa-2-silacyclopentylmethyl radicals. The scope of the novel rearrangement in terms of other ring types and sizes, as well as the analogous 1,2-migration of "tethered" C-centered groups, was explored computationally.

Among the variety of isolable compounds with multiple bonds involving silicon, examples of compounds that contain silicon–boron double bonds (borasilenes) still remain relatively rare. Herein, we report the synthesis of the potassium salt of a chloride adduct of borasilene 1 ([2]−), which was obtained as an orange crystalline solid. Single-crystal X-ray diffraction analysis and reactivity studies on [2]− confirmed the double-bond character of the Si=B bond as well as the reduced Lewis acidity, which is due to the coordination of Cl− to the boron center. A thermal reaction of [2]− afforded a bicyclic product by formal intramolecular C−H insertion across the Si=B bond of 1, which was corroborated by a theoretical study.

Radical anions of a diphosphene with two boryl substituents were isolated and characterized by single-crystal X-ray diffraction, electron spin resonance (ESR), and UV/Vis absorption spectroscopy as well as DFT calculations. Structural analysis of the radical anions revealed an elongation of the P=P bond and a contraction of the B-P bonds relative to the neutral diphosphene. The UV/Vis spectra of these radical anions showed a strong absorption in the visible region, which was assigned to SOMO-related transitions on the basis of DFT calculations. The ESR spectra revealed that the hyperfine coupling constant with the phosphorus nuclei is the smallest that has been reported thus far. The results of the DFT calculations furthermore suggest that this should be attributed to a soaking of electron spin to the vacant p orbitals of the boryl substituents.

Global exploration of isomers and isomerization channels on the quantum chemical potential energy surface (PES) is performed for H3 CNO3 using the Scaled Hypersphere Search-Anharmonic Downward Distortion Following (SHS-ADDF) method. The molecular formula of H3 CNO3 includes functional groups of CH3 , OH, NH2 , COOH, NO, NO2 , and NO3 , which are very important in connection with amino acids and NOx. Geometrical structures and interconversion pathways are disclosed after 18719781 force calculations and 534726 Hessian calculations at the level of B3LYP/6-31G(d). The explored results are confirmed to be valid, especially for the important lower energy regions, by re-optimization at the higher level of B3LYP/6-311++G(d,p). A global reaction route-mapping using SHS-ADDF demonstrates the entire view and undeveloped landscapes on PES of H3 CNO3 . Typical compounds of H3 CNO3 , aminoxy formic acid, hydroxycarbamic acid, aminoperformic acid, hydroxymethyl nitrite, nitromethanol, methyl nitrate, methyl peroxynitrite, and dioxaziridine, are well separated from others by very high energy-barriers. The stable-most conformer of H3 CNO3 is difficult to be determined, because of seven structures existing with nearly the same energies within 5.7 kJ/mol at the level of CCSD(T)/aug-cc-pVTZ.