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The oxidative addition of homo- and heteronuclear molecules XI (X=I, Me, Ph) to the square planar rhodium phosphino enolate complex [Rwh{Ph₂PCHbC(bO^z)Ph}(CO)(PPh₃)]1 afforded the hexacoordinate Rh(iii) complexes [Rwh{Ph₂PCHbC(bO^z)Ph}X(I)(CO)(PPh₃)] (X=Me 2; X=Ph 3; X=I 4). Complex 2 undergoes CO insertion into the Rh–Me bond to afford three isomers of the acetyl species [Rwh{Ph₂PCHbC(bO^z)Ph}- {C(O)Me}(I)(CO)(PPh₃)] 5a–c. Two of these isomers lose acetyl iodide to regenerate 1 and these transformations were followed by NMR and IR spectroscopic methods. The reaction of 1 with acetyl chloride results in rapid formation of the acetyl complex [Rwh{Ph₂PCHbC(bO^z)Ph}{C(O)Me}(Cl)(CO)(PPh₃)] 6. When left in solution, 6 isomerizes to give two additional isomeric acetyl species. All three isomers rapidly decompose to a Rh(i) species. The crystal structures of 1–3 have been determined by X-ray diffraction. The coordination geometry around the rhodium atom of 2 and 3 is distorted octahedral and the alkyl and halide ligands are in a mutually trans position.