Novel Si(II)+ and Ge(II)+ Compounds as Efficient Catalysts in Organosilicon Chemistry: Siloxane Coupling Reaction

Novel catalytically active cationic Si(II) and Ge(II) compounds were synthesized and isolated in pure form. The Ge(II)(+)-based compounds proved to be stable against air and moisture and therefore can be handled very easily. All compounds efficiently catalyze the oxidative coupling of hydrosil(ox)anes with aldehydes and ketones as oxidation reagents and simultaneously the reductive ether coupling at very low amounts of <0.01 mol %. Because the catalysts also catalyze the reversible cyclotrimerization of aldehydes, paraldehyde can be used as a convenient source for acetaldehyde in siloxane coupling. It is shown that the reaction is especially suitable to make siloxane copolymers. Moreover, a new fluorine-free weakly coordinating boronate anion, B(SiCl3)(4)(-), was successfully combined with the Si(II) and Ge(II) cations to give the stable catalytically active ion pairs Cp*Si:B+(SiCl3)(4)(-), Cp*Ge:B+(SiCl3)(4)(-), and [Cp(SiMe3)(3)Ge:(+)]B(SiCl3)(4)(-).