Abstract
AbstractHydroalumination or hydrogallation of tri(ethynyl)silanes, RSi(C≡C‐Ar)3 (1a, R = Ph, Ar = Ph; 1b, R = Me, Ar = Ph; 1c, R = Me, Ar = C6H4Me), with the element hydrides H‐EtBu2 (E = Al, Ga) in stoichiometric ratios of 1:1 to 1:3 at ambient temperature yielded the addition products (PhC≡C)2(R)Si[(tBu2E)C=C(H)Ph] (2, R = Ph, E = Ga; 3a, R = Me, E = Al; 3b, R = Me, E = Ga), (PhC≡C)(Me)Si[(tBu2E)C=C(H)Ph]2 (4a, E = Al, 4b, E = Ga) and (Me)Si[(tBu2Al)C=C(H)Ar]3 (5, Ar = Ph; 6, Ar = C6H4Me). Compounds 2–4 show a relatively close interaction between the coordinatively unsaturated aluminium or gallium atoms and one of the Cα(≡C) atoms of unreacted alkyne substituents [245 (E = Al) and 266 pm (E = Ga)] that stabilises the kinetically favoured cis addition products with E and hydrogen on the same side of the resulting C=C double bonds. In the absence of these stabilising effects the compounds were found to isomerise to the thermodynamically favoured trans isomers.
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