Alkylation of a tetrahedral cobalt(Il)-dichloro complex bearing a sterically demanding and electron-donating diphosphine chelate gave a corresponding dialkyl-cornplex, which is the first coordinatively unsaturated cobalt(II)-(diphosphine)(dialkyl) complex isolated and characterized by X-ray analysis. This complex is expected to serve as a model intermediate in the cobalt(II)-catalyzed Heck-type reactions.