Quantum chemistry calculations are used to provide insight into the cycloaddition of two dialkyne chains in initially monocyclic organoplatinum dimers of the type (PtX2)(2)(mu-R2PC4PR2)(2), where X = Cl or Me and R = Ph or Me. Previous experimental studies showed that the cycloaddition occurs with {X, RI = {Cl, Ph} but not {Me, Ph}. Two concerted pericyclic paths, a D-2h-symmetry double-[pi 4s+pi 4s] "Huckel path" and a D-2-symmetry double-[pi 4s+pi 4a] "Mobius path", were explored via orbital energy correlation diagrams (OECDs) computed using a singly occupied molecular orbital technique developed earlier. In accord with pericyclic reaction theory, the 16e(-) rearrangement is forbidden along the D-2h Huckel path; four electrons would need to change their orbital symmetries. The D-2 Mobius path, afforded by the natural twist in the reactant structure which allows the desired Mobius orbital connectivity for a 4n rearrangement, is concluded to be a borderline forbidden pathway. This Mobius path creates avoided crossings in the OECD, which allows consistent orbital populations throughout the reaction, but it does not cause a change in intended orbital correlation, and the predicted activation barrier is rather high (similar to 50 kcal mol(-1)). The avoided crossings show strong coupling, but a clear HOMO-LUMO gap for the reaction is not produced. A stepwise path is also presented, with evidence of its diradical character.