Synthesis and Oligomerization of CpM(CO)(2)

[Image: see text] We showcase efficient synthetic protocols of cyclopentadienyl metal dicarbonyl, CpM(CO)(2) (M = Rh and Ir). Reflecting the relativistic effect, the (1)H and (13)C signals of the Cp ring in CpIr(CO)(2) were upfield shifted when compared with the Rh analogue. A missing dinuclear complex, (CpIr)(2)(μ-CO)(CO)(2), was spontaneously generated together with [CpIr(CO)](3) by the loss of CO. The crystallographic analyses unambiguously determined their unique structures with one and three Ir–Ir bonds, respectively.