Synthesis and Oligomerization of CpM(CO)2

We showcase efficient synthetic protocols of cyclopentadienyl metal dicarbonyl, CpM­(CO)2 (M = Rh and Ir). Reflecting the relativistic effect, the 1H and 13C 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.