Abstract: The invention relates to the reaction of cyclopentadienyl-transition metal compounds, (C.sub.5 H.sub.5).sub.2 M or C.sub.5 H.sub.5 --M(L).sub.n (M=transition metal, L=olefin), with alkali metal in the presence of olefins, with detachment of the C.sub.5 H.sub.5 rings from the transition metal atom to form alkali metal cyclopentadienide, leads, to transition metal-olefin complex compounds free of alkali metal or also containing alkali metal, in yields of greater than 65%, the latter compounds being able to contain one or even several alkali metal atoms per transition metal atom.It is moreover possible, depending on the selection of the stoichiometry or of the reaction compounds, and depending on the nature of the transition metal, to detach only one or also both cyclopentadienyl rings from the transition metal atom, so that by this method the most various transition metal-olefin complex compounds can be prepared, namely transition metal-olefin complex compounds containing C.sub.5 H.sub.