This review is concerned with data on the composition and structure of intermediate paramagnetic cobalt and nickel compounds in Ziegler-type metal complex catalysts. The problem of reactivity of the intermediate compounds is briefly outlined. General regularities are revealed for the mechanism of formation of the metal complex catalysts. Particular emphasis is made on the structure of intermediates whose EPR spectra explicitly exhibit the effects of vibronic interactions. Vibronic effects are shown to play an important role in the realization of geometric configuration for structures with the pseudodegenerate electronic state.