Hydroaluminierung von Silicium‐zentrierten Dialkinen – Synthese gemischt‐substituierter Alkenyl‐alkinylsilane

Abstract

Bis(phenylethynyl)silanes reacted with equimolar quantities of various dialkylaluminium hydrides, R2Al–H [R = CH2tBu, tBu, iBu, CH(SiMe3)2], by hydroalumination and addition of a Al–H bond to a C≡C triple bond. Alkenyl‐alkynylsilanes were formed, which had the aluminium atoms in geminal positions with the silicon atoms and adopt a cis arrangement of aluminium and hydrogen at the resulting C=C double bonds in most cases. cis/trans‐Rearrangement with the formation the trans‐addition products was observed only for the two sterically least shielded compounds. Intramolecular interactions of the coordinatively unsaturated aluminium atoms with the α‐carbon atoms of the intact alkynyl groups were detected by crystal structure determinations for the tert‐butyl and neopentyl derivatives, whereas they did not occur with bulky bis(trimethylsilyl)methyl substituents.

Hydroalumination of Bis(alkynyl)silanes: Generation of Chelating Lewis Acids, Their Application in the Coordination of Chloride Ions and a 1,1‐Carbalumination Reaction

“…The cis arrangement of Al and H atoms at the C=C double bond is evident from crystal structure determinations ( Figure 1) and from the characteristic 3 J H-C=C-Si coupling constant of 25.8 Hz (trans positions of H and Si; see below for further discussion). The resonances for the ethenyl carbon atoms are in a narrow range of the 13 C NMR spectrum between δ = 157.7 and 161.8 ppm; signals for ethynyl carbon atoms (δ = 90-120 ppm of 1 and 2 and other mixed alkenyl-alkynyl derivatives [7,10,13] ) are missing, which verifies complete hydroalumination. The relatively short intramolecular Al1-C21 distances [248.2(2) (1) and 255.5(1) pm (2)], the positions of the Al atoms up to 33.3 pm above the planes of the adjacent atoms (C5, C6, C11) and the small torsion angles Al1-C11-Si1-C21 of 4.37(8)°and -17.58 (7)°, respectively, verify the interaction of the Al atoms with the α-carbon atoms of the triple bonds (C21) bearing a relatively high negative charge.…”

“…[7] A relatively clear reaction course was observed in refluxing toluene with the complete consumption of 7 after 48 h and the formation of an oily product, which shows an intensive resonance of tert-butyl groups in the 1 H NMR spectrum in addition to signals of unknown impurities. However, heating of the solutions in toluene or of the neat materials led to decomposition with the formation of inseparable mixtures of several unknown components in most cases.…”

“…[7] A relatively clear reaction course was observed in refluxing toluene with the complete consumption of 7 after 48 h and the formation of an oily product, which shows an intensive resonance of tert-butyl groups in the 1 H NMR spectrum in addition to signals of unknown impurities. and -34.5 ppm [7] ). Addition of THF gave an adduct (8), which could be crystallized from diisopropyl ether and was isolated in 73 % yield [Equation (3)].…”

“…[7] In most cases, the cis addition products were isolated, which have the Al and H atoms on the same side of the resulting C=C double bonds. [7] In most cases, the cis addition products were isolated, which have the Al and H atoms on the same side of the resulting C=C double bonds.…”

“…The resulting compounds were found to coordinate halide, thiolate or benzoate anions. Rearrangement and 1,1-carbalumination was observed upon heating of a mixed alkenyl-alkynylsilane (7). [6] In formation of the dialkenyl species 3-5 with an all-trans configuration of the alkenyl groups.…”