The catalytic activity of the pentamethylcyclopentadienylsilicon­(II) cation Cp*Si:+ was investigated. It was shown that Cp*Si:+ efficiently catalyzes reactions of technical relevance in organosilicon chemistry: Cp*Si:+ proved to be a very efficient nonmetallic catalyst for the hydrosilylation of olefins at low catalyst amounts of <0.01 mol % and for the Piers–Rubinsztajn reaction in order to make controlled silicone topologies. The thermal induction of hydrosilylation which is important for the manufacturing of silicone rubber can be achieved by small amounts of alkoxysilanes.

Aldehydes can be easily prepared from the corresponding alcohols in good to excellent yields by oxidation with technical bleach and catalytic amounts of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (1b, 4-hydroxy TEMPO, "HOT"). Whereas the well-known batch process performed on lab scale is not suitable for the technical synthesis especially of activated -substituted aldehydes, this transformation can be performed continuously in a simple tube reactor. This layout meets all requirements necessary for the process, i.e., turbulent mixing of the biphasic mixture, removal of heat, short contact times, and high output. Thus, a single tube of 3 mm diameter renders about 60 mol of aldehyde per day.

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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