The coordination step of 1–2 homopolymerization of 4-methyl-1,3-pentadiene in presence of Ziegler-Natta initiators is discussed on the basis of ab initio computations. The results show that, as for 1–4 homopolymerizations, the coordination of the incoming monomer requires a substantial rearrangement of the ending unit, whose coordination mode changes from the η 3 -allylic type to the η 1 - σ one. This step, most probably the rate-determining one, appears to be easier for 4-methyl-1,3-pentadiene than for butadiene or isoprene homopolymerization, in agreement with the observed homopolymerization rates.