Twelve-membered cyclic diethynylphosphine derivatives (R(2)(1)SiCdropC-R(2)PCdropC)(2) (1a: R-1 = R-2 = Ph; 1b: R-1 = Ph, R-2 = t-Bu; 1c: R-1 = i-Pr, R-2 = Ph) have been synthesized as a novel cyclic phosphine ligand including potentially reactive acetylene and silane moieties. Compounds 1a and 1b were formed as a mixture of cis-and trans-isomers, while an only trans-isomer was obtained for 1c. X-ray structural analysis revealed planar skeletal structures of the trans-isomers of 1a-c.