Laser-ablated iridium atom has been codeposited at 4 K with acetylene in excess argon. The vinylidene IrCCH2, insertion product HIrCCH, and metallacycle complexes Ir-eta(2)-(C2H2) and Ir-eta(2)-(C2H2)(2) are produced in present experiments and identified on the basis of the (C2H2)-C-13, C2D2 and mixed C2HD isotopic substitutions and the comparison with theoretical predictions. The agreement between the experimental and calculated vibrational frequencies supports the identification of these molecules. Two alternative reaction mechanism of formation of Ir=C=CH2 complex has been found on the potential energy surface of the studied system to account for the product formation. The conversion of acetylene to vinylidene on a Ir atom is exothermic by 3.4 kcal/mol based on the B3LYP functional calculations.