Abstract The reaction of (η 5-C 5H 5)Mo(CO)(dppe)Cl with LiCCCCSiMe 3 yielded (η 5-C 5H 5)(CO)(dppe)MoCCCCSiMe 3 ( 1b) and, as a by-product (η 5-C 5H 5)Mo(CO)(dppe)Br ( 1a). Treatment of 1b with 0.2 equivalents of tetrabutylammonium fluoride or (η 5-C 5H 5)Mo(CO)(dppe)Cl with HCCCCH gave the terminal butadiyne complex (η 5-C 5H 5)(CO)(dppe)MoCCCCH ( 2). Complex 2 was deprotonated with sec-BuLi or lithium diisopropylamide, and the resulting anion (η 5-C 5H 5)(CO)(dppe)MoCCCCLi ( 3) was trapped with Me 3SiCl to regenerate 1b. The synthesis of Co 2(CO) 4L 2(μ-η 2-Me 3SiC 2CCSiMe 3) (L 2=dppa 4, 2PPh 2Me 5) compounds can be achieved by two methods: from Co 2(CO) 6(μ-dppa) by reaction with Me 3SiCCCCSiMe 3 in 1:1 ratio to yield 4, or from Co 2(CO) 6(μ-η 2-Me 3SiC 2CCSiMe 3) by reaction with dppa (1:1 ratio) and PPh 2Me (1:2 ratio) to yield 4 and 5, respectively. When the Co 2(CO) 4(μ-dppa)(μ-η 2-Me 3SiC 2CCSiMe 3) complex was treated with more Co 2(CO) 6(μ-dppa) the green di-substituted complex [Co 2(CO) 4(μ-dppa)] 2(μ-η 2:μ-η 2-Me 3SiC 2C 2SiMe 3) ( 6) was obtained. Desilylation of 4 with Bu 4NF gave Co 2(CO) 4(μ-dppa)(μ-η 2-Me 3SiC 2CCH) ( 7). All compounds synthesized have been characterized by analytical and spectroscopic data (IR, 1H-, 31P-, 13C-NMR, MS). In addition, compounds 1a and 4 were characterized by X-ray structure analysis.