An Isolable Silicon Analogue of a Ketone that Contains an Unperturbed Si=O Double Bond

Despite tremendous efforts to synthesize isolable compounds with an Si=O bond, silicon analogues of ketones that contain an unperturbed Si=O bond have remained elusive for more than 100 years. Herein, we report the synthesis of an isolable silicon analogue of a ketone that exhibits a three‐coordinate silicon center and an unperturbed Si=O bond, thus representing the first example of a genuine silanone. Most importantly, this silanone does not require coordination by Lewis bases and acids and/or the introduction of electron‐donating groups to stabilize the Si=O bond. The structure and properties of this unperturbed Si=O bond were examined by a single‐crystal X‐ray diffraction analysis, NMR spectroscopy, and theoretical calculations. Bimolecular reactions revealed high electrophilicity on the Si atom and high nucleophilicity on the O atom of this genuine Si=O bond.     

From a Si3‐Cyclopropene to a Si3S‐Bicyclo[1.1.0]butane to a Si3S‐Cyclopropene to a Si3S2‐Bicyclo[1.1.0]butane: Back‐and‐Forth,and In‐Between

Compact and highly reactive bicyclo[1.1.0]butanes constitute one of the most fascinating classes of organic compounds. Furthermore, interplay of bicyclo[1.1.0]butanes with their valence isomers, such as buta‐1,3‐dienes and cyclobutenes, is among the fundamental pericyclic transformations in organic chemistry. Herein we report the back‐and‐forth interconversion between the cyclotrisilenes and thiatrisilabicyclo[1.1.0]butanes, allowing for the synthesis of novel representatives of such classes of highly reactive organometallics. The peculiar structural and bonding features of the newly synthesized compounds, as well as the mechanism of their isomerization, were verified both experimentally and computationally.     

From a Si3‐Cyclopropene to a Si3S‐Bicyclo[1.1.0]butane to a Si3S‐Cyclopropene to a Si3S2‐Bicyclo[1.1.0]butane: Back‐and‐Forth,and In‐Between

Compact and highly reactive bicyclo[1.1.0]butanes constitute one of the most fascinating classes of organic compounds. Furthermore, interplay of bicyclo[1.1.0]butanes with their valence isomers, such as buta‐1,3‐dienes and cyclobutenes, is among the fundamental pericyclic transformations in organic chemistry. Herein we report the back‐and‐forth interconversion between the cyclotrisilenes and thiatrisilabicyclo[1.1.0]butanes, allowing for the synthesis of novel representatives of such classes of highly reactive organometallics. The peculiar structural and bonding features of the newly synthesized compounds, as well as the mechanism of their isomerization, were verified both experimentally and computationally.     

α‐Selective Ring‐Opening Reactions of Bicyclo[1.1.0]butyl Boronic Ester with Nucleophiles

The reaction of bicyclo[1.1.0]butyl pinacol boronic ester (BCB‐Bpin) with nucleophiles has been studied. Unlike BCBs bearing electron‐withdrawing groups, which react with nucleophiles at the β‐position, BCB‐Bpin reacts with a diverse set of heteroatom (O, S, N)‐centred nucleophiles exclusively at the α‐position. Aliphatic alcohols, phenols, carboxylic acids, thiols and sulfonamides were found to be competent nucleophiles, providing ready access to α‐heteroatom‐substituted cyclobutyl boronic esters. In contrast, sterically hindered bis‐sulfonamides and related nucleophiles reacted with BCB‐Bpin at the β′‐position leading to cyclopropanes with high trans‐selectivity. The origin of selectivity is discussed.     

Disilene R*RSi=SiRR* (R* = SitBu3) mit siliciumgebundenen Me‐ und Ph‐Gruppen R: Bildung,Nachweis, Thermolyse,Struktur: Verbindungen des Siliciums. 154 [1]. Ungesättigte Siliciumverbindungen. 61 [1]

Compounds of Silicon. 154 [1]. Unsaturated Silicon Compounds. 61 [1] Disilenes R*RSi=SiRR* (R* = SitBu₃) with Silicon‐Bound Me and Ph Groups R: Formation, Identification, Thermolysis, Structure Dehalogenations of the 1, 2‐disupersilylsilanes R*MeBrSi—SiBrMeR* (gauche : trans 1.15 : 1.00) and R*PhClSi—SiBrPhR* (gauche : trans = 2.7 : 1.0) in THF with equimolar amounts of NaR* (R* = SitBu₃ = Supersilyl) lead at —78 °C under exchange of bromine for sodium to the disilanides R*MeBrSi—SiNaMeR* and R*PhClSi—SiNaPhR* which are identified by protonation and bromination (formation of R*RXSi—SiX′RR* with R = Me, X/X′ = Br/H, Br/Br: gauche : trans = 1.15 : 1.00, and R = Ph, X/X′ = Cl/H, Cl/Br: gauche : trans = 2.7 : 10, respectively). These eliminate at about —55 °C NaHal with formation of non‐isolable trans‐R*MeSi=SiMeR* and isolable trans‐R*PhSi=SiPhR*. The intermediate existence of the disilene R*MeSi=SiMeR* could be proved by trapping it with PhC≡CPh (formation of a [2+2] cycloadduct; X‐ray structure analysis). In the absence of trapping agents, R*MeSi=SiMeR* decomposes into a mixture of substances, the main product of which is R*MeHSi—SiMeR*—SiHMeR*. The light yellow disilene R*PhSi=SiPhR* has been characterized by spectroscopy (Raman: ν(Si=Si) = 592 cm^—1; UV/VIS: λ_max = 398 nm with ∈ = 1560; ²⁹Si‐NMR: δ(>Si=) = 128 ppm) and by X‐ray structure analysis (planar central framework >Si=Si<; Si=Si distance 2.182Å). R*PhSi=SiPhR* is reduced by lithium in THF with formation of a red radical anion which decomposes at room temperature into hitherto non‐identified products. At about 70 °C, R*PhSi=SiPhR* decomposes with intramolecular insertion of the Si=Si group into a C—H bond of a Ph group and with change of configuration of the R* groups, which at first are trans then cis‐positioned (X‐ray structure analysis of the thermolysis product).     

A Gallium‐Substituted Distibene and an Antimony‐Analogue Bicyclo[1.1.0]butane: Synthesis and Solid‐State Structures

RGa {R=HC[C(Me)N(2,6‐iPr₂C₆H₃)]₂} reacts with Sb(NMe₂)₃ with insertion into the Sb? N bond and elimination of RGa(NMe₂)₂ ( 2 ), yielding the Ga‐substituted distibene R(Me₂N)GaSb?SbGa(NMe₂)R ( 1 ). Thermolysis of 1 proceeded with elimination of RGa and 2 and subsequent formation of the bicyclo[1.1.0]butane analogue [R(Me₂N)Ga]₂Sb₄ ( 3 ).     

1,3‐Diazasilabicyclo[1.1.0]butane with a Long Bridging N−N Bond

A 1,3‐diazasilabicyclo[1.1.0]butane ( 1 ) is synthesized as thermally stable crystals by using the cycloaddition reaction of an isolable dialkylsilylene with aziadamantane. The bridge N?N bond length of 1 (1.70 Å) is the longest among those of known N?N singly‐bonded compounds, including side‐on bridged transition‐metal dinitrogen complexes. The compound 1 is intact in air but moisture sensitive. No reaction occurs with hydrogen, even under pressure at 0.5 MPa. Irradiation of 1 with light gives an isomer quantitatively by N?N and adamantyl C?C bond cleavage. The origin of the remarkable N?N bond elongation is ascribed to significant interaction between a Si?C σ* and Ν?Ν π and σ orbitals as determined by DFT calculations of model compounds.