Reaction of [Rh(μ-OtBu)(diene)]2 [diene = 1,5-cyclooctadiene (COD) or bicyclo[2.2.1]hepta-2,5-diene (NBD)] with the oxazolinylcarbene ligand precursor 2-(4,4-dimethyl)oxazolinylimidazolium bromide (“Me2carboxH+Br−”, 2) yielded the five-coordinate complexes [RhBr(Me2carbox)(diene)] [diene = COD (3), NBD (4)]. Single-crystal X-ray structure analyses established a distorted trigonal bipyramidal configuration for 3, whereas the molecular structure of 4 is distorted square pyramidal. The dynamic properties of these five-coordinate complexes have been investigated by variable temperature 1H NMR spectroscopy, indicating polytopal rearrangements of the five-coordinate complexes. The two compounds were converted into the square-planar cationic complexes [Rh(Me2carbox)(diene)]+ (5 and 6, respectively), which have been isolated and fully characterised. The rhodium complex [RhBr(Me2carbox)(CO)] (7) was obtained in high yield in a one-step reaction of the ligand precursor 2 and [Rh(acac)(CO)2] (acac = acetylacetonate).