Above −40°C, 3a,b decompose in solution, which coupling of the butadiene ligands to afford Ni(η3,η3,η2-C12H18), which was shown to be an intermediate of the nickel-catalyzed cyclotrimerisation reaction of butadiene. Thus 3a,b are the first butadienecomplexes of nickel that are catalytically active despite the presence of stabilizing ligands.