Photodissociation spectra of the classic pi complexes Au+(C2H4) and Pt+(C2H4) in the gas phase are reported, providing upper limits to metal-ligand bond strengths of 28 800 cm(-1) (344 kJ mol(-1)) and 19 200 cm(-1) (230 kJ mol(-1)), respectively. The spectrum of Au'(C2H4) features an extended progression in the metal-ligand stretch with a frequency of 176 cm(-1), which drops to 160 cm-1 in Au+(C2D4). Hybrid density functional theory (DFT) calculations at the B3LYP level indicate that both complexes adopt a metallocyclopropane structure. The effect of basis set size and flexibility on the metal-ligand dissociation energy is explored. In addition, excited electronic states of both complexes have been investigated by using TD-DFT calculations.