Treatment of Pb[N(SiMe₃)₂]₂ with [Mo(R)(CO)₃H] in tetrahydrofuran (thf) affords the green complexes [Pb{Mo(R)(CO)₃}₂(thf)][R =η-C₅Me₅(1a), η-C₅H₃(SiMe₃)₂-1,3 (1b), or η-C₅H₅(1c)]. The brown thf-free analogues [Pb{Mo(R)(CO)₃}₃](2) are obtained from (1) at 25 °C and 10^–2 Torr for R =η-C₅H₃(SiMe₃)₂(2b) or η-C₅H₅(2c), but slightly more forcing conditions (40 °C, 10^–2 Torr) are required to convert complex (1a) to [Pb{Mo(η-C₅Me₅)(CO)₃}₂](2a). The dimeric green bis(isocarbonyl)-bridged complex {Pb[Mo(η-C₅Me₅)(CO)₃][Mo(η-C₅Me₅)(CO)₂(µ-CO)]}₂(3), containing a pair of MoCO–Pb linkages, was obtained from Pb[N(SiMe₃)₂]₂ and [Mo(η-C₅Me₅)(CO)₃H] in a hydrocarbon solvent. The brown toluene solution of complex (3) shows i.r. characteristics similar to those of complexes (2b) or (2c), and is thus believed to contain an isoleptic complex of structure (2a). Addition of triethylphosphine to the brown (2b) yields a green transient believed to be [Pb{Mo[η-C₅H₃(SiMe₃)₂](CO)₃}₂(PEt₃)], which is rapidly converted to the brown [Pb{Mo[η-C₅H₃(SiMe₃)₂](CO)₂(PEt₃)}₂]. The complexes (2) are thermally labile, decomposing to Pb +[{Mo(R)(CO)₃}₂], with decreasing facility in the sequence R =η-C₅H₅ > η-C₅Me₅ > η-C₅H₃(SiMe₃)₂, which is attributed to steric considerations. Complex (3) has three co-ordinate Pb^II, whereas complexes (1) and (2) are assigned as monomers having three- or two-co-ordinate Pb^II environments, respectively; all are diamagnetic, whence it is inferred that complexes (2) are V-shaped, having ground-state singlet structures. These structural conclusions are supported by the i.r. and n.m.r. spectra, and by single-crystal X-ray data on the pentamethylcyclopentadienyl complexes (1a) and (3). Complexes (1a) and (3) crystallise in space groups P2₁/c and P, respectively. Both show a pyramidal three-co-ordinate Pb^II environment, with Mo–Pb 2.989(2) and 3.019(2)Å[(1a)][or for (3): 2.935(1) and 2.989(1)Å] and Pb–O 2.75(2)Å[(1a)][2.918(8)Å in (3)], and Mo–Pb–Mo 118.33(5)°[(1a)][120.71(2)° in (3)].