Hydroalumination of dialkynylgermanes—synthesis of alkenyl–alkynylgermanes with intramolecular aluminium–carbon interactions

Abstract

Reactions of dialkylaluminium hydrides, R 2 AlH [R = CH 2 CMe 3 , CMe 3 , CH(SiMe 3 ) 2 ], with di(phenylethynyl)germanes, R 2 Ge(CRC-C 6 H 5 ) 2 [R = CH 3 (1), C 6 H 5 (2)], afforded mixed alkenyl-alkynylgermanes, R 2 Ge(CRC-C 6 H 5 )[C(AlR 2 )QC(H)-C 6 H 5 ] (3 to 7), by hydroalumination of one of the CRC triple bonds. In all cases the cis-arrangement of the Al and H atoms across the resulting CQC double bond was observed. Crystal structure determinations revealed relatively strong intramolecular bonding interactions between the coordinativelyunsaturated aluminium atoms and the a-carbon atoms of the intact triple bonds bearing a partial negative charge. This interaction is only prevented by application of the very bulky bis(trimethylsilyl)methyl substituent.

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

“…[8] With the exception of the bis(trimethylsilyl)methyl compounds, we observed an interesting close intramolecu-lar interaction between the α-carbon atoms of the alkynyl groups and the aluminium atoms. [9] Similar structures have been observed for corresponding germanium compounds [10] or were derived from NMR spectroscopic data for some products of hydroboration reactions. The p-tolyl derivatives 1 and 2 [Equation (1)] have not been reported previously.…”

“…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.…”

Alkenyl‐Alkynylgermanes Functionalised by Lewis Acids: Intramolecular Aluminium– and Gallium–Alkyne Interactions and Potential Ge–C Bond Activation

“…afforded the dialkynyl derivatives 3 to 8 by salt elimination in high yields (Scheme ). The syntheses of 3 and 6 have been reported by our group previously 9…”

“…They were extremely air sensitive, pyrophoric and difficult to handle. Compounds 19 , 20 and 22 have been published by our group only recently 9…”

“…Compared to the starting dialkynylgermanes (2185 and 2150 cm –1 ) a slight shift to smaller wavenumbers was observed, which may be indicative of the bridging positions of the alkynyl groups and their interaction to aluminium or gallium atoms. Accordingly, absorptions at 2164 and 2151 cm –1 were found in an alkenyl‐alkynylgermanium compound (see the Introduction) in which bulky bis(trimethylsilyl)methyl groups prevented the interaction between Al atoms and the ethynyl groups 7,9…”