Hydroalumination and Hydrogallation Reactions with Tri(ethynyl)silanes – Generation of Compounds with up to Three Coordinatively Unsaturated Aluminium Atoms

Abstract

Abstract Hydroalumination or hydrogallation of tri(ethynyl)silanes, R Si(C≡C‐Ar) 3 ( 1a , R = Ph, Ar = Ph; 1b , R = Me, Ar = Ph; 1c , R = Me, Ar = C 6 H 4 Me), with the element hydrides H‐ Et Bu 2 ( E = Al, Ga) in stoichiometric ratios of 1:1 to 1:3 at ambient temperature yielded the addition products (PhC≡C) 2 ( R )Si[( t Bu 2 E )C=C(H)Ph] ( 2 , R = Ph, E = Ga; 3a , R = Me, E = Al; 3b , R = Me, E = Ga), (PhC≡C)(Me)Si[( t Bu 2 E )C=C(H)Ph] 2 ( 4a , E = Al, 4b , E = Ga) and (Me)Si[( t Bu 2 Al)C=C(H)Ar] 3 ( 5 , Ar = Ph; 6 , Ar = C 6 H 4 Me). Compounds 2 – 4 show a relatively close interaction between the coordinatively unsaturated aluminium or gallium atoms and one of the C α (≡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.