Cycloaddition reactions with metallacyclic complexes are critical steps in many stoichiometric and catalytic reactions. 1-11 These reactions are generally assumed to occur on mononuclear metal centers in solution. Recently, we reported the synthesis and alkyne cycloaddition chemistry of platinacycles 1 and 2 (Scheme 1). 12 A full study of these reactions, including TEM and kinetic investigations, provided strong evidence that these cycloaddition reactions do not occur ...