Reactions of laser-ablated Be and Mg atoms with C2H2, (C2H2)-C-13, and C2D2 upon condensation in excess argon at 10 K give new infrared absorptions that are assigned to the insertion and decomposition products HBeCCH, BeCCH, and MgCCH with the help of density functional theory isotopic frequency calculations. The 2819-cm(-1) C=C stretching fundamental for BeCCH is between values for BCCH and AlCCH, which are all slightly blue shifted from acetylene itself.