The present invention relates to a single-stage process for preparing dienyl-ruthenium complexes of the formula Ru(+II)(dienyl)2, wherein an Ru(II) starting compound of the formula Ru(X)p(Y)q is reacted with a diene ligand in the presence of an inorganic and/or organic base in a single-stage process. Here, polar organic solvents, preferably mixtures of polar organic solvents with water, are used. The dienyl-ruthenium complexes prepared according to the invention are used as precursors for homogeneous catalysts, for producing functional coatings and for therapeutic applications.