AbstractReaction of MoCo(CO)5(PPh3)2(η5‐C5H5) (1a) with trimethylsilylacetylene in tetrahydrofuran at 58° C yielded two acetylene bridged heterobimetallic compounds, MoCo(CO)4(PPh3){μ‐HCCSiMe3}(η5‐C5H5) (4) and MoCo (CO)5{μ‐HCCSiMe3}(η5‐C5H5)(5). (4) was characterized by mass, infrared,1H,13C and31P NMR spectra. The X‐ray crystal structure of (4) was determined:triclinic, P‐1, a=8.821(1) Å, b=11.315(3) Å, c=17.029(2) Å, α=70.73(1)°, β=78 .72(1)°, γ=86.10(2)°,V =1573.4(6) Å3, Z=2, R = 3.92%,Rw= 6.06% for 4285 (F>4σ (F)) observed reflections. The core of this molecule is a quasi‐tetrahedron containing Mo, Co and two carbons of acetylene. The triphenylphosphine ligand is attached to