The design of new catalytic systems is generally based on the modification of the catalyst structure. Often this leads to more and more complicated structures which require multi-step synthesis and restricts widespread use among different research groups. It would be beneficial for academic research and industry to develop methods for the activation of catalysts by using some simple and commercially available additives. In this thesis fluoride additives, such as [Bu4N]Ph3SiF2] or CsF were studied as such activating additives for different organometallic complexes. The use of the fluoride additives results in the in situ formation of active metal fluoride complexes. We successfully applied this tactic to five different reactions, namely, the aluminum-catalyzed cycloaddition of CO2 to epoxides, vanadium-catalyzed asymmetric trimethylsilylcyanation of aldehydes, nickel-catalyzed asymmetric Michael addition of dimethyl malonate to nitroalkenes, rhodium- and cobalt-catalyzed reductive opening of tetrahydrofuran with amines, and ruthenium-catalyzed reductive alkylation of ketones by aldehydes. Depending on the type of transformation the use of the fluoride additive resulted in an increase in activity, selectivity, milder reaction conditions or even achieving new reactivity. For example, in the case of the vanadium-catalyzed asymmetric trimethylsilylcyanation of aldehydes use of [Bu4N]Ph3SiF2] resulted in a twentyfold increase in catalytic activity with turnover numbers of the catalyst reaching 20000. This resulted in one of the most active catalytic systems for this type of transformation and it is based on a commercially available chiral salen ligand and an inexpensive vanadium source.