The cluster [Os₃(µ-H)₃(CO)₉(µ₃-CCl)] reacted with excess of butyldiphenylphosphine, in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu), to give the complex [Os₃(µ-H)₂(CO)₉(µ₃-CPBuⁿPh₂)]1. The optically active diphosphine (R)-Ph₂PCH(Me)CH₂PPh₂ reacted similarly to give two isomers, (R)-[Os₃(µ-H)₂(CO)₉{µ₃-CPPh₂CH(Me)CH₂PPh₂}]2a and (R)-[Os₃(µ-H)₂(CO)₉{µ₃-CPPh₂CH₂CH(Me)PPh₂}]2b, which have been spectroscopically characterised. Complex 2a readily undergoes decarbonylation, followed by the formation of Os–P bond, to afford an octacarbonyl chiral cluster complex (R)-[Os₃(µ-H₂)(CO)₈{µ₃-CPPh₂CH(Me)CH₂PPh₂}]3. The molecular structures of 1 and 3 have been established by X-ray crystallography. Complex 1 contains a triosmium alkylidyne metal core with the BuⁿPh₂P moiety bonded to the apical carbon atom through the phosphorus atom. On the other hand, the structure of 3, which also contains a phosphine-substituted µ₃-C ligand bonded to three osmium atoms at the base, is characterised by the formation of a six-membered osmacycle with the centre of chirality being retained in the phosphine ligand of the complex.