Reactions of laser-ablated Group 3 metal atoms with ethylene isotopomers have been carried out, and the primary products have been identified in the matrix IR spectra. The insertion and dihydrido cyclic products (HM-C2H3 and H2M-C2H2) are identified from the matrix IR spectra of Sc and Y, whereas only the insertion product is observed in the La spectra along with many lanthanium hydride absorptions. The observed metal hydride absorptions suggest that the H-2-elimination reaction becomes faster upon going down the group column, and the trend is also consistent with the energies of the H-2-elimination products relative to those of the dihydrido cyclic products. The present results support the conclusion that C-H insertion and following H migration from C to M are in fact general phenomena in reactions of early transition metals (Groups 3-6) and actinides with ethylene. The back-donation of electron-deficient Group 3 metals to the pi-cyclic system of H2M-C2H2 is evidently much weaker than that of the previously studied systems.