A New Disilene with π-Accepting Groups from the Reaction of Disilyne RSiSiR (R = Si^<i>i</i>Pr[CH(SiMe₃)₂]) with Isocyanides

The reaction of 1,1,4,4-tetrakis­[bis­(trimethylsilyl)­methyl]-1,4-diisopropyltetrasila-2-yne (<b>1</b>) with <i>tert</i>-butylisocyanide or <i>tert</i>-octylisocyanide produced the corresponding disilyne–isocyanide adducts [RSiSiR­(CNR′)₂] (R = Si^<i>i</i>Pr­[CH­(SiMe₃)₂]₂, R′ = ^<i>t</i>Bu (<b>2a</b>) or CMe₂CH₂^<i>t</i>Bu (<b>2b</b>)), which are stable below −30 °C and were characterized by spectroscopic data and, in the case of <b>2a</b>, X-ray crystallography. Upon warming to room temperature, <b>2</b> underwent thermal decomposition to produce 1,2-dicyanodisilene R­(NC)­SiSi­(CN)­R (<b>3</b>) and 1,2-dicyanodisilane R­(NC)­HSiSiH­(CN)­R (<b>4</b>) via C–N bond cleavage and elimination of an alkane and an alkene. The 1,2-dicyanodisilene derivative <b>3</b> was characterized by X-ray crystallography

A New Disilene with π-Accepting Groups from the Reaction of Disilyne RSiSiR (R = Si^<i>i</i>Pr[CH(SiMe₃)₂]) with Isocyanides

The reaction of 1,1,4,4-tetrakis­[bis­(trimethylsilyl)­methyl]-1,4-diisopropyltetrasila-2-yne (<b>1</b>) with <i>tert</i>-butylisocyanide or <i>tert</i>-octylisocyanide produced the corresponding disilyne–isocyanide adducts [RSiSiR­(CNR′)₂] (R = Si^<i>i</i>Pr­[CH­(SiMe₃)₂]₂, R′ = ^<i>t</i>Bu (<b>2a</b>) or CMe₂CH₂^<i>t</i>Bu (<b>2b</b>)), which are stable below −30 °C and were characterized by spectroscopic data and, in the case of <b>2a</b>, X-ray crystallography. Upon warming to room temperature, <b>2</b> underwent thermal decomposition to produce 1,2-dicyanodisilene R­(NC)­SiSi­(CN)­R (<b>3</b>) and 1,2-dicyanodisilane R­(NC)­HSiSiH­(CN)­R (<b>4</b>) via C–N bond cleavage and elimination of an alkane and an alkene. The 1,2-dicyanodisilene derivative <b>3</b> was characterized by X-ray crystallography

An Isolable NHC-Stabilized Silylene Radical Cation: Synthesis and Structural Characterization

The silyl-substituted silylene–NHC complex bis­(tri-<i>tert</i>-butylsilyl)­silylene–(1,3,4,5-tetramethylimidazol-2-ylidene) [(^<i>t</i>Bu₃Si)₂Si:←NHC^Me, <b>2</b>] was synthesized and isolated as air- and moisture-sensitive orange crystals by reductive debromination of the dibromosilane (^<i>t</i>Bu₃Si)₂SiBr₂ (<b>1</b>) with 2.0 equiv of KC₈ in the presence of NHC^Me. In addition, the silylene–NHC complex <b>2</b> cleanly underwent one-electron oxidation with 1.0 equiv of Ph₃C⁺·Ar₄B^– (Ar₄B^– = tetrakis­[4-(<i>tert</i>-butyldimethylsilyl)-2,3,5,6-tetrafluorophenyl]­borate) in benzene to afford the NHC-stabilized silylene radical cation [(^<i>t</i>Bu₃Si)₂Si←NHC^Me]^•+·Ar₄B^– (<b>3</b>). The radical cation <b>3</b> was isolated as air- and moisture-sensitive yellow crystals and structurally characterized by X-ray crystallography and electron paramagnetic resonance spectroscopy, which showed that <b>3</b> has a planar structure with a π-radical nature

An Isolable NHC-Stabilized Silylene Radical Cation: Synthesis and Structural Characterization

The silyl-substituted silylene–NHC complex bis­(tri-<i>tert</i>-butylsilyl)­silylene–(1,3,4,5-tetramethylimidazol-2-ylidene) [(^<i>t</i>Bu₃Si)₂Si:←NHC^Me, <b>2</b>] was synthesized and isolated as air- and moisture-sensitive orange crystals by reductive debromination of the dibromosilane (^<i>t</i>Bu₃Si)₂SiBr₂ (<b>1</b>) with 2.0 equiv of KC₈ in the presence of NHC^Me. In addition, the silylene–NHC complex <b>2</b> cleanly underwent one-electron oxidation with 1.0 equiv of Ph₃C⁺·Ar₄B^– (Ar₄B^– = tetrakis­[4-(<i>tert</i>-butyldimethylsilyl)-2,3,5,6-tetrafluorophenyl]­borate) in benzene to afford the NHC-stabilized silylene radical cation [(^<i>t</i>Bu₃Si)₂Si←NHC^Me]^•+·Ar₄B^– (<b>3</b>). The radical cation <b>3</b> was isolated as air- and moisture-sensitive yellow crystals and structurally characterized by X-ray crystallography and electron paramagnetic resonance spectroscopy, which showed that <b>3</b> has a planar structure with a π-radical nature

A New Disilene with π-Accepting Groups from the Reaction of Disilyne RSiSiR (R = Si^<i>i</i>Pr[CH(SiMe₃)₂]) with Isocyanides

The reaction of 1,1,4,4-tetrakis­[bis­(trimethylsilyl)­methyl]-1,4-diisopropyltetrasila-2-yne (<b>1</b>) with <i>tert</i>-butylisocyanide or <i>tert</i>-octylisocyanide produced the corresponding disilyne–isocyanide adducts [RSiSiR­(CNR′)₂] (R = Si^<i>i</i>Pr­[CH­(SiMe₃)₂]₂, R′ = ^<i>t</i>Bu (<b>2a</b>) or CMe₂CH₂^<i>t</i>Bu (<b>2b</b>)), which are stable below −30 °C and were characterized by spectroscopic data and, in the case of <b>2a</b>, X-ray crystallography. Upon warming to room temperature, <b>2</b> underwent thermal decomposition to produce 1,2-dicyanodisilene R­(NC)­SiSi­(CN)­R (<b>3</b>) and 1,2-dicyanodisilane R­(NC)­HSiSiH­(CN)­R (<b>4</b>) via C–N bond cleavage and elimination of an alkane and an alkene. The 1,2-dicyanodisilene derivative <b>3</b> was characterized by X-ray crystallography

Functionalized Cyclic Disilenes via Ring Expansion of Cyclotrisilenes with Isocyanides

The reaction of cyclotrisilenes <b>1</b> with 1 equiv of alkyl and aryl isocyanides at 25 °C affords the four-membered trisilacyclobutenes <b>2</b> with an exocyclic imine functionality as the major products of formal insertion into one of the Si–Si single bonds of <b>1</b>. Minor quantities of the iminotrisilabicyclo[1.1.0]­butanes <b>3</b> are obtained as side products, formally resulting from [1 + 2] cycloaddition of the isocyanides to the Si–Si double bond of <b>1</b>. The bicyclo[1.1.0]­butanes <b>3</b> become dominant at lower temperatures and may react with an additional 1 equiv of isonitriles to give the diiminotrisilabicyclo[1.1.1]­pentanes <b>4</b>

Functionalized Cyclic Disilenes via Ring Expansion of Cyclotrisilenes with Isocyanides

The reaction of cyclotrisilenes <b>1</b> with 1 equiv of alkyl and aryl isocyanides at 25 °C affords the four-membered trisilacyclobutenes <b>2</b> with an exocyclic imine functionality as the major products of formal insertion into one of the Si–Si single bonds of <b>1</b>. Minor quantities of the iminotrisilabicyclo[1.1.0]­butanes <b>3</b> are obtained as side products, formally resulting from [1 + 2] cycloaddition of the isocyanides to the Si–Si double bond of <b>1</b>. The bicyclo[1.1.0]­butanes <b>3</b> become dominant at lower temperatures and may react with an additional 1 equiv of isonitriles to give the diiminotrisilabicyclo[1.1.1]­pentanes <b>4</b>

Theoretical Study on the Enhancement of the Second Hyperpolarizabilities of Si‑, Ge-Disubstituted Quinodimethanes: Synergy Effects of Open-Shell Nature and Intramolecular Charge Transfer

We have investigated the second hyperpolarizabilities (γ), that is, the third-order nonlinear optical (NLO) properties at the molecular scale, of the realistic Si- and Ge-disubstituted <i>para</i>- and <i>meta</i>-quinodimethanes from the viewpoint of synergy effect of the open-shell singlet nature and the donor (D)−π–donor (D) intramolecular charge transfer (ICT). It has been revealed that the disubstituted <i>para</i> isomers exhibit strong D−π–D nature together with the intermediate open-shell singlet nature, which leads to their significantly enhanced γ values. These results well demonstrate the validity of our recent result of the theoretical model study on <i>para</i>-quinodimethane with point charges, and also present a new design strategy based on the concept of open-shell NLO that the replacement of the radical site of the π-conjugated carbon framework with the heavier main group elements induces both the larger open-shell singlet nature and the D−π–D type strong ICT, both of which synergetically contribute to the further enhancement of the γ values