The paramagnetic tetrahydride cluster, Cp*3-Co3(μ2-H)3(μ 3-H) (1) reacts with acetylene to ultimately form the bis(ethylidyne) cluster Cp*3Co3(μ3-CCH3) 2 (2). Two intermediates were detected during the course of the reaction: the diamagnetic Cp*3Co3(μ2-H)3(μ 3-CCH3 (3) and the paramagnetic Cp*3Co3(μ3-H)(μ3-CCH3) (4). Cluster 3 loses H2 in refluxing toluene to generate 4, and 4 reacts with H2 at 80°C to generate 3. Kinetic analysis indicates 3 and 4 are both formed directly from cluster 1. © 1993 American Chemical Society.