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π-Electron systems of silicon have attracted attention because of their narrow HOMO-LUMO gap and high reactivity, but the structural diversity remains limited. Herein, new dialkylboryl-substituted disilenes were synthesized by the selective desilylation-borylation of the corresponding trimethylsilyl-substituted disilenes. The dialkylboryl-substituted disilenes were fully characterized by a combination of NMR spectroscopy, MS spectrometry, single-crystal X-ray diffraction analysis, and theoretical calculations. The longest-wavelength absorption bands of boryldisilenes were bathochromically shifted compared to the corresponding silyl-substituted disilenes, indicating a substantial conjugation between π(Si=Si) and vacant 2p(B) orbitals. In the presence of 4-(dimethylamino)pyridine (DMAP), the dialkylboryl groups in the boryl-substituted disilenes were easily converted to trimethylsilyl groups, suggesting the dialkylboryl-substituted disilenes in the presence of a base serve as the surrogates of disilenyl anions (disilenides).

Molecular silicon clusters with unsubstituted silicon vertices (siliconoids) have received attention as unsaturated silicon clusters and potential intermediates in the gas-phase deposition of elemental silicon. Investigation of behaviors of the siliconoids could contribute to the greater understanding of the transformation of silicon clusters as found in the chemical vapor deposition of elemental silicon. Herein we reported drastic transformation of a Si8R8 siliconoid to three novel silicon clusters under mild thermal conditions. Molecular structures of the obtained new clusters were determined by XRD analyses. Two clusters are siliconoids that have unsaturated silicon vertices adopting unusual geometries, and another one is a bis(disilene) which has two silicon–silicon double bonds interacted to each other through the central polyhedral silicon skeleton. The observed drastic transformation of silicon frameworks suggests that unsaturated molecular silicon clusters have a great potential to provide various molecular silicon clusters bearing unprecedented structures and properties.

π-Electron compounds that include multiple bonds between silicon atoms have received much attention as novel functional silicon compounds. In the present paper, 1,2-bis(trimethylsilyl)-1,2-disilacyclohexene 1 was successfully synthesized as thermally stable yellow crystals. Disilene 1 was easily converted to the corresponding potassium disilenide 4, which furnished novel functionalized disilenes after the subsequent addition of an electrophile. Interestingly, two trimethylsilyl groups in 1 can be stepwise converted to anthryl groups. The novel disilenes derived from 1 were characterized by a combination of nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS), elemental analyses, and X-ray single crystal diffraction analysis. The present study demonstrates that disilene 1 can serve as a unit of cis-1,2-dialkyldisilene.

We explored coordination chemistry associated with valence isomerization between a methylene(thioxo)phosphorane (MTP) and a thiaphosphirane. For this purpose, we developed the selective synthesis of a MTP by eliminating chlorodimethylphenylsilane from the corresponding chlorophosphine sulfide. Treatment of the MTP with an equivalent amount of pentafluorophenylgold(I) complex resulted in the formation of a thiaphosphirane gold(I) complex, which likely proceeds via an η²-P,C-MTP gold complex. The MTP undergoes a valence isomerization catalyzed by copper(I) chloride to furnish a transition metal-free thiaphosphirane. Computational studies proposed a plausible mechanism involving a Cu-assisted cyclization reaction. [ABSTRACT FROM AUTHOR]

Utility of a thermally stable divalent silicon species (silylene) toward the dehydroaromatization of a dihydropentacene is demonstrated. The reaction of a cyclic (alkyl)(amino)silylene with 6,13-dipropyl-5,14-dihydropentacene afforded the corresponding pentacene-silylene adducts. The reaction likely proceeds through a combination of 1,4-dehydrogenation and (1+ 4) cycloaddition of the silylene towards the dihydropentacene. [ABSTRACT FROM AUTHOR]

Ni(CO)3 complexes ligated by an isolable cyclic (alkyl)(amino)silylene (CAASi) or an isolable cyclic dialkylsilylene (CDASi) were synthesized by the reaction of the corresponding Ni(dvtms) complex (dvtms = 1,1,3,3-tetramethyl-1,3-divinyldisiloxane) with CO to estimate the donor strengths of CAASi and CDASi. The CO stretching frequencies (Tolman electronic parameters, TEP) of the Ni(CO)3 complexes indicate that the net donating ability of CDASi and CAASi to Ni(CO)3 are almost the same and in between PPh3 and P(tBu)3. The DFT calculations suggested that the TEP values are mainly correlated with the energy level of the lone pair orbital of the ligand but not strongly associated with those of the vacant p-accepting orbitals. [ABSTRACT FROM AUTHOR]

The push−pull effect has been widely used to effectively tune Ï€-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 Ï€ → Ï€* 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. [ABSTRACT FROM AUTHOR]

In the last decade, several stablesilicon compounds with nonclassicalinverted geometry around silicon atoms have been synthesized. Their unusual structures, bonding, and reactivity have been investigated extensively by X-ray analysis, spectroscopy, and theoretical calculations. In thishighlight review, recent progress on chemistry of silicon compounds with inverted geometry around silicon atoms is summarized. [ABSTRACT FROM AUTHOR]

Ferrocenyl-substituted bicyclo[1.1.1]pentasilanes 1, 2, and 3 were synthesized by the reactions of bromo-substituted bicyclo[1.1.1]pentasilanes with lithioferrocene. Significant interactions between bicyclo[1.1.1]pentasilane and ferrocenyl units were suggested by cyclic voltammetry, UV-vis absorption spectrum, and theoretical calculations. [ABSTRACT FROM AUTHOR]

Hexakis( tert-butyldimethylsilyl)bicyclo[1.1.0]tetrasilane ( 3), which is known to isomerize to the corresponding cyclotetrasilene 4above 0 °C, was synthesized via an alternative synthetic route and isolated at low temperatures as air-sensitive yellow crystals. The short-bond structure of 3was disclosed by X-ray analysis and DFT calculations, and facile ring flipping of 3below 0 °C with the activation parameters of Δ H‡= 6.67 ± 0.18 kcal mol −1and Δ S‡= −22.7 ± 0.8 cal mol −1K −1was observed. [ABSTRACT FROM AUTHOR]

A new carbon family with a prism structure has been found by quantum chemical calculations. The prism-C20 has a D10h structure with double-layered decagonal rings connected each other by ten vertical CC bonds. The CC bond lengths are 0.144 nm on the decagonal rings and 0.148 nm on the side faces. The diameter of the ring is 0.465 nm. The prism-C20 is expected to be stable, since the lowest energy barrier from it was estimated to be 158.0 kJ mo1-1. [ABSTRACT FROM AUTHOR]

Reaction of stable phosphinyl radical 1a with AZADO gave aminoxyphosphine 3 as the primary product by selective radical coupling at -40 °C. Compound 3 decomposed to phosphorane 4, silyl phosphinate 5, and aminophosphine 6 at room temperature. The molecular structures of 4-6 were determined by X-ray structural analysis. The homolytic N-O bond cleavage of 3 and the subsequent silyl migration of the resulting phosphinoyl radical 7 would be key steps in the reaction. [ABSTRACT FROM AUTHOR]

Two-coordinate dialkylsilylene-coinage metal complexes 3+-TPFPB- (Cu) and 4+·TPFPB (Ag) were synthesized as the first dialkylsilylene-copper complex and the first silylene-silver complex, respectively, by the reaction of dialkylsilylene 1 with the corresponding metal borate. X-ray analysis showed that both the complexes adopted a linear structure with two perpendicular dialkylsilylene units. Theoretical study indicated that weak π back-donation of the copper and silver complexes compared to that of the corresponding isoelectronic neutral palladium complex would be due to low-lying d orbitals of Cu+ and Ag+ centers and responsible for the linear structures. [ABSTRACT FROM AUTHOR]

A kinetic study of the thermal irreversible isomerization of an isolable dialkylsilylene into the corresponding cyclic silene revealed that the activation enthalpy (ΔH‡) and entropy (ΔS‡) are 18.49 ± 0.43 kcal mol−1and −20.32 ± 1.35 cal mol−1K−1, respectively. The relatively low ΔH‡and negative ΔS‡values are in accord with the concerted 1,2-silyl migration via a cyclic transition state as previously proposed. The cyclic silene in benzene-d6isomerized photochemically into the corresponding alkenylsilane via 1,3-hydrogen shift. [ABSTRACT FROM AUTHOR]