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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]

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]

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]

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 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]

Although the synthesis of several bis(disilenes) has already been reported, the number of reported conjugation modes between the Si-Si double bonds remains limited. Herein, we report the properties of the stable pentasila-1,4-diene 1, which was obtained from the reaction of two equivalents of disilenide 4 with dichlorodimethylsilane. The π(Si-Si)→π*(Si-Si) absorption band of 1 is considerably broadened and red-shifted compared to those of the corresponding monodisilene and hexasila-1,5-diene, but blue-shifted relative to those of typical tetrasila-1,3-dienes. The bathochromic shift and the broadening of the absorption band in 1 should be attributed to the homoconjugation between Si-Si double bonds through the SiMe2 unit. [ABSTRACT FROM AUTHOR]

A platinum(0) complex, bearing a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (DVTMS) and an isolable dialkylsilylene ligand, was successfully synthesized by the reaction between the dialkylsilylene and Karstedt's catalyst. The downfield-shifted 29Si NMR resonance, the smaller ¹JSi,Pt value, and the longer Si-Pt distance in this complex relative to the corresponding parameters in related bis(phosphine)-coordinated silylene-platinum complexes suggest weaker π-back-donation from the Pt center to the silylene, which is, however, still significant when compared to related DVTMS-ligated Pt complexes bearing N-heterocyclic carbenes, N-heterocyclic two-coordinate silylenes, or base-stabilized three-coordinate silylenes. The title complex displays excellent catalytic activity in the hydrosilylation of terminal olefins that contain functional groups such as epoxide and amine moieties. [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]

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. [ABSTRACT FROM AUTHOR]

Ethynylsilyllithiums R1R2(R3CC)SiLi:  R1R2t-BuMe2Si, R3Me3Si (5a); R1R2t-BuMe2Si, R3Ph (5b); R1R2R3Me3Si (5c); R1t-BuMe2Si, R2Ph, R3Me3Si (5d); R1t-BuMe2Si, R2Me3SiCC, R3Me3Si (5e) were prepared by the sila-metalation reactions of the corresponding hydrosilanes using tert-butyllithium in THF and trapped by MeI, Me3SiCl, and i-Pr3SiCl in high yields. X-ray structural analysis of a single crystal of 5ahas revealed that 5aadopts a dimer form (7a) containing one THF molecule per dimer. Dimer 7ais a syn dimer with a planar four-membered ring made by two lithium atoms and two anionic silicon atoms; one lithium atom is coordinated by two ethynyl groups and the other by a THF molecule, indicative of the importance of the coordination of ethynyl groups for the stabilization of the silyllithium. 7Li NMR analysis indicates that the dimeric structure of 5a(7a) is maintained in toluene, but 5ais monomeric in THF. Rates and activation parameters of facile intramolecular exchange of the two lithium atoms in 7aobserved in toluene-d8were determined by the dynamic 7Li NMR. The DFT calculations of a model ethynylsilyllithium (H3Si)2(H3SiCC)SiLi, 12have shown that dimer 13, with a similar geometry to 7a, is more stable than the monomeric form. The optimized monomeric form of 12(12‘) has an ethynylsilyllithium-type structure with a largely bent Si−CC skeleton, suggesting significant intramolecular coordination to Li. [ABSTRACT FROM AUTHOR]

A concise synthesis of halogenated chrysene derivatives from 2,2,2-trifluoroethyl tosylate and halostyrene was established. Friedel−Crafts type cyclization of a 1,1-difluoro-1-alkene bearing halogenated phenyl moieties involved skeletal rearrangement and dehydrogenation to afford the title compound in good to moderate yield. X-ray analysis revealed that the halogen substituents induce π-stack packing of the molecules in the crystals. [ABSTRACT FROM AUTHOR]