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)3Ge:+]B(SiCl3)4
–.
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