Computational methods were used to study the surprising 2004 synthesis of decamethyldizincocene, Zn-2(eta(5)-C5Me5)(2), which was the first molecule to have a direct, unbridged bond between two first-row transition metals. The computational results show that the methyl groups of decamethylzincocene, Zn(eta(5)-C5Me5)(eta(1)-C5Me5), affect the transition-state stability of its reaction with ZnEt2 (or ZnPh2) through steric hindrance, and this could possibly allow a counter-reaction, the homolytic dissociation of Zn(eta(5)-C5Me5)(eta(1)-C5Me5) into Zn(eta(5)-C5Me5)(center dot) and (eta(1)-C5Me5)(center dot), to occur, and because no such steric hindrance occurs when zincocene, Zn(eta(5)-C5H5)(eta(1)-C5H5), is used as a reactant, its dissociation never occurs regardless of what ZnR2 reagent is used.