A study of the coordination chemistry of bis(diphenylphosphino)acetylene, Ph2P-C=C-PPh2, with selected group 4 metallocenes is presented. By substitution of the alkyne in complexes of the type Cp'M-2(L)(eta(2)-Me3SiC2SiMe3) (M = Ti, no L; M = Zr, L = pyridine; Cp' = substituted or unsubstituted bridged or unbridged eta(5)-cyclopentadienyl), the expected mononuclear complexes Cp-2*Ti(eta(2)-Ph2PC2PPh2) (4Ti), (rac-ebthi)Ti(eta(2)-Ph2PC2PPh2) (5Ti), and (rac-ebthi)Zr(eta(2)-Ph2PC2PPh2) (5Zr) [ebthi = ethylenebis(tetrahydroindenyl)] were obtained. When [Cp2Zr] was used in the reaction of Cp2Zr(py)(eta(2)-Me3SiC2SiMe3) with Ph2P-C C-PPh2, the dinuclear complex [Cp2Zr(eta(2)-Ph2PC2PPh2)](2) (6) was formed and isolated in the solid state. In solution, this complex is in equilibrium with the very spectacular structure of complex 7b as the first example of such a highly strained four-membered heterometallacycle of a group 4 metal, involving the rare R2PCCR' fragment in the cyclic unit. Both the stability and reactivity of heterodisubstituted alkynes X-C C-X (X = NR2, PR2, SR, SiR3, etc.) themselves and also of their complexes are of general interest. Complex 6 did not react with a second [Cp2Zr] fragment to form a homobimetallic complex. In contrast, for (rac-ebthi)Zr(eta(2)-Ph2PC2PPh2) (5Zr) this reaction occurs. In the reaction of complex 4Ti with the Ni(0) complex (Cy3P)(2)Ni(eta(2)-C2H4) (Cy = cyclohexyl), C-P bond cleavage of the alkyne ligand resulted in the formation of the isolated complex [(Cy3P)Ni(mu-PPh2)](2) (11). The structure and bonding of the complexes were investigated by DFT analysis to compare the different possible coordination modes of the R2P-C C-PR2 ligand. For compound 7h, a flip-flop coordination of the phosphorus atoms was proposed. Complexes 4Ti, 5Ti, 5Zr, 6, and 11 were characterized by X-ray crystallography.