Hydroalumination of bis(alkynyl)germanes and -silanes: Generation of a chelating Lewis-acid and observation of a dismutation reaction

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

“…Therefore, it was particularly important to test their acceptor properties in a simple experiment prior to the beginning of systematic investigations. [13,15] In accordance with the higher coordination numbers of the aluminium atoms, the Al-C bonds of 6 show the usual lengthening relative to those in 4 (203.0 pm vs. 198.7 pm, on average). A suspension was obtained, which, after evaporation of the solvent and treatment of the residue with n-hexane, gave a colourless amorphous solid.…”

“…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.…”

“…Their 13 C NMR spectra show the resonances characteristic of ethynyl (δ = 92.5 and 117.4 ppm, on average) and ethenyl carbon atoms (δ = 146.5 and 157.9 ppm). [13] The central silicon atoms of the dialkenyl compounds 3-5 ( Figure 2) have a slightly distorted tetrahedral coordination sphere and are bound to two phenyl and two alkenyl groups. The C=C and CϵC bond lengths (134.9 and 121.1 pm, on average) are in accord with standard values.…”

The Methylene-bridged Dialuminium Compound R2Al-CH2-AlR2 [R=CH(SiMe3)2] as an Effective Chelating Lewis Acid – Adducts with Halides, Perchlorate and Isopropylamide

“…The solid-state structure revealed a unique molecular arrangement with one of the two lithium cations being sandwiched between two alkynide groups and showing close Li-C contacts to the ethynyl α-C atoms and the bridging CH 2 group. Similar chelating Lewis acids have been obtained by the dual hydrogallation of an alkyne [21,22] or the hydroalumination of silicon-or germanium-centered bis-alkynes [23,24]. In the latter case the acceptor atoms are separated by three bridging atoms (SiC 2 or GeC 2 ).…”

Hydroalumination versus Deprotonation of Alkynes with Sterically Demanding Substituents

“…Compounds 5 follow the expected trend with E-C(sp 2 ) bond lengths being shorter than the corresponding E-C(sp 3 ) distances. Surprisingly this trend is reversed in case of compound 6 probably caused by the increased steric bulk in these compound (c. f. [31,32]). Other bond lengths and an- Table 3.…”