9 research outputs found
Pentasila-1,4-diene: Homoconjugation between Siî—»Si Double Bonds via a SiMe<sub>2</sub> Unit
Although the synthesis of several
bisÂ(disilenes) has already been
reported, the number of reported conjugation modes between the Siî—»Si
double bonds remains limited. Herein, we report the properties of
the stable pentasila-1,4-diene <b>1</b>, which was obtained
from the reaction of two equivalents of disilenide <b>4</b> with
dichlorodimethylsilane. The Ï€Â(Siî—»Si)→π*Â(Siî—»Si)
absorption band of <b>1</b> 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 <b>1</b> should be attributed to the homoconjugation between Siî—»Si
double bonds through the SiMe<sub>2</sub> unit
Redox Reactions of a Stable Dialkylphosphinyl Radical
A stable
dialkylphosphinyl radical, 2,2,5,5-tatrakisÂ(trimethylsilyl)-1-phosphacyclopentan-1-yl (R<sup>H</sup><sub>2</sub>P<sup>•</sup>), showed both irreversible one-electron oxidation
and reduction peaks at −0.24 and −2.29 V vs ferrocene/ferrocenium
couple. One-electron reduction of R<sup>H</sup><sub>2</sub>P<sup>•</sup> with KC<sub>8</sub> in the presence of 18-crown-6 (18-c-6) or [2.2.2]Âcryptand
(crypt-222) gave the corresponding phosphides [KÂ(18-c-6)]<sup>+</sup>[R<sup>H</sup><sub>2</sub>P]<sup>−</sup> and [KÂ(crypt-222)]<sup>+</sup>[R<sup>H</sup><sub>2</sub>P]<sup>−</sup>. Whereas [KÂ(18-c-6)]<sup>+</sup>[R<sup>H</sup><sub>2</sub>P]<sup>−</sup> exists as
a contact ion pair, [KÂ(crypt-222)]<sup>+</sup>[R<sup>H</sup><sub>2</sub>P]<sup>−</sup> exists as a solvent-separated ion pair in the
solid state. Reaction of R<sup>H</sup><sub>2</sub>P<sup>•</sup> with AgOTf afforded an unexpected product, a silverÂ(I) phosphaalkene
complex
New Isolable Dialkylsilylene and Its Isolable Dimer That Equilibrate in Solution
The new isolable dialkylsilylene <b>3</b> bearing
a bidentate
alkyl substituent was synthesized. Recrystallization of silylene <b>3</b> gave yellow crystals of <b>3</b> and orange-red crystals
of tetraalkyldisilene <b>4</b>, a dimer of <b>3</b>. In
the solid state, <b>3</b> exists as a monomer with a closest
distance of 6.745 Ã… between dicoordinate silicon atoms, while
disilene <b>4</b> has a remarkably long Siî—»Si double
bond distance of 2.252 Å. An equilibrium between <b>3</b> and <b>4</b> in solution was observed by NMR and UV–vis
spectroscopies, and the thermodynamic parameters of the equilibrium
were estimated to be Δ<i>H</i> = −36 ±
3 kJ mol<sup>–1</sup> and Δ<i>S</i> = −170
± 15 J mol<sup>–1</sup> K<sup>–1</sup>. Analysis
of the percent buried volume, a measure of the steric demand around
the divalent silicon, showed that the flexible steric bulkiness of
the alkyl substituent of <b>3</b> and <b>4</b> allows
the reversible dimerization of silylene <b>3</b> to disilene <b>4</b> and the isolation of both species
Anthryl-Substituted 3‑Silylene-2-silaaziridine Obtained by Isomerization of Disilacyclopropanimine: An Exocyclic Silene Showing a Distinct Intramolecular Charge Transfer Transition
An anthryl-substituted exocyclic
silene, 3-silylene-2-silaaziridine,
was synthesized by isomerization of the corresponding disilacyclopropanimine.
The UV–vis spectrum of the silene shows a distinct intramolecular
charge transfer (ICT) transition from the π orbital of the SiC
double bond to the π* orbital of the anthryl moiety. The relatively
high-lying Ï€Â(Siî—»C) orbital of the 3-silylene-2-silaaziridine
moiety and the low-lying π* orbital of the anthryl group would
be responsible for the distinct ICT band
Anthryl-Substituted 3‑Silylene-2-silaaziridine Obtained by Isomerization of Disilacyclopropanimine: An Exocyclic Silene Showing a Distinct Intramolecular Charge Transfer Transition
An anthryl-substituted exocyclic
silene, 3-silylene-2-silaaziridine,
was synthesized by isomerization of the corresponding disilacyclopropanimine.
The UV–vis spectrum of the silene shows a distinct intramolecular
charge transfer (ICT) transition from the π orbital of the SiC
double bond to the π* orbital of the anthryl moiety. The relatively
high-lying Ï€Â(Siî—»C) orbital of the 3-silylene-2-silaaziridine
moiety and the low-lying π* orbital of the anthryl group would
be responsible for the distinct ICT band
New Isolable Dialkylsilylene and Its Isolable Dimer That Equilibrate in Solution
The new isolable dialkylsilylene <b>3</b> bearing
a bidentate
alkyl substituent was synthesized. Recrystallization of silylene <b>3</b> gave yellow crystals of <b>3</b> and orange-red crystals
of tetraalkyldisilene <b>4</b>, a dimer of <b>3</b>. In
the solid state, <b>3</b> exists as a monomer with a closest
distance of 6.745 Ã… between dicoordinate silicon atoms, while
disilene <b>4</b> has a remarkably long Siî—»Si double
bond distance of 2.252 Å. An equilibrium between <b>3</b> and <b>4</b> in solution was observed by NMR and UV–vis
spectroscopies, and the thermodynamic parameters of the equilibrium
were estimated to be Δ<i>H</i> = −36 ±
3 kJ mol<sup>–1</sup> and Δ<i>S</i> = −170
± 15 J mol<sup>–1</sup> K<sup>–1</sup>. Analysis
of the percent buried volume, a measure of the steric demand around
the divalent silicon, showed that the flexible steric bulkiness of
the alkyl substituent of <b>3</b> and <b>4</b> allows
the reversible dimerization of silylene <b>3</b> to disilene <b>4</b> and the isolation of both species
Siloxy-Substituted Cyclopentadiene Showing Aggregation-Enhanced Emission: An Application of Cycloaddition of Isolable Dialkylsilylene
Cycloaddition of an isolable dialkylsilylene converted
nonemissive 2,3,4,5-tetraphenylcyclopentadienone to an emissive siloxycyclopentadiene,
which shows aggregation-enhanced emission behavior with a light blue
fluorescence (λ<sub>em</sub> = 474 nm, Φ<sub>F</sub> =
0.11) in the solid state rather than in solution
Siloxy-Substituted Cyclopentadiene Showing Aggregation-Enhanced Emission: An Application of Cycloaddition of Isolable Dialkylsilylene
Cycloaddition of an isolable dialkylsilylene converted
nonemissive 2,3,4,5-tetraphenylcyclopentadienone to an emissive siloxycyclopentadiene,
which shows aggregation-enhanced emission behavior with a light blue
fluorescence (λ<sub>em</sub> = 474 nm, Φ<sub>F</sub> =
0.11) in the solid state rather than in solution
Hydrogen Bonds-Enabled Design of a <i>C</i><sub>1</sub>‑Symmetric Chiral Brønsted Acid Catalyst
We have developed new <i>C</i><sub>1</sub>-symmetric,
chiral bis-phosphoric acids with an electron-withdrawing group as
one of the two substituents. This <i>C</i><sub>1</sub>-symmetric,
chiral bis-phosphoric acid with a pentafluorophenyl group performs
exceptionally well in the asymmetric Diels–Alder reaction of
acrolein, methacrolein, and α-haloacroleins with substituted
amidodienes. Control over the atropisomeric catalyst structure, enhancement
of the catalytic activity, and differentiation of the asymmetric reaction
space is possible by the remote control of the pentafluorophenyl group.
Furthermore, we have conducted theoretical studies to clarify the
roles of both intra- and intermolecular hydrogen bonds in the <i>C</i><sub>1</sub>-symmetric chiral environment of chiral bis-phosphoric
acid catalysts. The developed strategy, <i>C</i><sub>1</sub>-symmetric catalyst design through hydrogen bonding, is potentially
applicable to the development of other chiral Brønsted acid catalysts