Reactions of the bulky amidinate and guanidinate salts K[(ArN)2CR] (R = But, NPri2 or N(C6H11)2; Ar = 2,6-diisopropylphenyl) with [{RhCl([small eta]4-COD)}2] (COD = 1,5-cyclooctadiene) lead to KCl elimination and the formation of the complexes, [Rh{([small eta]5-ArN)(ArN)CR}(COD)], in which the anionic ligand coordinates the rhodium centre in an unprecedented [small eta]5-cyclohexadienyl mode. The thermal conversions of these complexes to their N,N[prime or minute]-chelated isomers, [Rh{[small kappa]2-N,N[prime or minute]-(ArN)2CR}(COD)], were carried out and the kinetics of these processes have been shown to be first order. The rates of the isomerisations are inversely proportional to the size of the amidinate or guanidinate backbone substituent. Analogies between the ligating properties of the bulky amidinates and guanidinates used in the study, and those of [small beta]-diketiminates are discussed.