Hydrogallation of Trimethylsilylethynylbenzenes:  Generation of Potential Di- and Tripodal Chelating Lewis Acids

Abstract

Hydrogallation of 1,4-bis(trimethylsilylethynyl)benzene and 1,3,5-tris(trimethylsilylethynyl)benzene with dialkylgallium hydrides R2GaH (R = Et, nPr, iPr, neopentyl, tBu) afforded the corresponding addition products with intact GaR2 groups and two or three alkenyl substituents. In all products the gallium atoms attacked those carbon atoms that are attached to the trimethylsilyl groups. The expected cis arrangement of gallium and hydrogen atoms at the CC double bonds was detected only with di(tert-butyl)gallium residues. Smaller alkyl groups gave the spontaneous formation of the trans-addition products. Cis/trans isomerization is an inevitable step for the formation of effective chelating Lewis acids, and in particular the trisalkene derivatives form interesting chalice-like hollows containing three Lewis-acidic centers at their inner surfaces.

Mirror Helices and Helicity Switch at Surfaces Based on Chiral Triangular‐Shape Oligo(phenylene ethynylenes)

“…The S N 2 mechanism of the Mitsunobus reaction completely inverts the R absolute configuration of the stereogenic center of commercial (R)-decan-2-ol ((R)-5) and ensures the same stereoconfiguration for the chiral peripheral chains of both compounds (S)-6 a and (S)-7. Finally, compounds (S)-6 a, (R)-6 b and (S)-7 were reacted with 1,3,5-triethynylbenzene (8) [19] by following a CÀC cross-coupling Sonogashira-type reaction catalyzed by palladium [20] to yield the target OPEs (S)-1 a, (R)-1 b and (S)-2 in 82, 68 and 55 %, respectively. All new compounds reported in this study ((R)-6 b, (S)-7, (S)-1 a, (R)-1 b and (S)-2) have been fully characterized by using NMR and FTIR spectroscopy, and mass spectrometry (see the Supporting Information).…”

Synthesis of 1‐silacyclopent‐2‐ene derivatives using 1,2‐hydroboration, 1,1‐organoboration and protodeborylation

“…Dichloro(methyl)vinylsilane, dichloro(phenyl)vinylsilane, 1-hexyne, ethynylbenzene, 3,3-dimethylbutyne, n BuLi in hexane (1.6 M) and 9-borabicyclo[3.3.1]nonane (9-BBN) were used as commercial products (Aldrich) without further purification. NMR spectra were recorded at 23°C using Varian Inova 300 MHz and 400 MHz spectrometers, both equipped with multinuclear units, using C 6 D 6 solutions (~5-10% v/v) in 5 [19] Optimized geometries at the B3LYP/6-311+G(d,p) level of theory [20] were found to be minima by the absence of imaginary frequencies. NMR parameters were calculated at the same level of theory.…”

“…[2] These silanes are attractive starting materials for application of hydroboration, [3] hydroalumination, [4] hydrogalation [5] and carboboration reactions, [6] leading to numerous novel cyclic and non-cyclic silicon compounds. [7,8] Among cyclic compounds, 1-silacyclopent-2-ene derivatives are of particular importance as the selective synthesis of these compounds in high yield has been a challenging goal.…”

Vinylgallium and Alkyllithium Compounds: Transmetalation and Generation of Oligolithium Cages

“…The respective 3 JA C H T U N G T R E N N U N G (Si,H) coupling constants of the corresponding cis isomers were typically found to be around 20 Hz. [15][16][17] Solid-state structure determinations of 2 a and 2 c revealed the presence of dimeric molecules with four-coordinate gallium atoms and one terminal and two bridging chlorine atoms and confirmed the trans configuration of the vinyl substituent. [12] The alkylation of the Ga À Cl functionalities of 2 a and 2 b with two equivalents of tert-butyl lithium proceeded smoothly at À78 8C to give the alkyl derivatives 3 a and 3 b in moderate yields of 52 and 61 % (Scheme 1).…”