Hydroalumination and hydrogallation of an aryl-chloro-dialkynylsilane: Si–Cl bond activation by intramolecular Al–Cl and Ga–Cl interactions

The chlorine functionalized dialkynylsilane (4-tBu-C6H4)(Cl)Si(C≡C-tBu)2 (3) reacted with equimolar quantities of H–AltBu2 or H–GatBu2 by hydrometallation of a C≡C triple bond and formation of mixed alkenyl-alkynylsilanes (4 and 5) in which the Si and Lewis acidic metal atoms adopt geminal positions at the α-C atoms of the alkenyl groups. Intramolecular M···Cl interactions (M=Al, Ga) afforded four-membered SiCMCl heterocycles which in comparison with 3 had significantly lengthened Si–Cl bonds. Dual hydrometallation of 3 was only observed for H–GatBu2. One Ga atom of the product (6) was coordinated by the silicon-bound Cl atom, while the second one showed an interaction with the aromatic ring of the tert-butyl-phenyl group. Treatment of the aluminium compound 4 with two equivalents of H–GatBu2 afforded a Si–H bond by Cl-H exchange and release of Cl–AltBu2. The resulting silane (7) has the Si atom and two Ga atoms bridged by the α-C atoms of two vinyl groups. The specific functionality of 4 caused a remarkable reactivity. Phenyl isocyanate reacted by the formal insertion into the Al–C(vinyl) and the activated Si–Cl bonds and resulted in the formation of a C–C bond. The product (8) has a SiC2N heterocycle with an Si–N bond and exocyclic C=C and C=O double bonds. The keto group is coordinated to a Cl–AltBu2 molecule, which was formed by the shift of the Cl atom from silicon to aluminium.