Density functional theory calculations were carried out to investigate structures and stabilities of tropone and troponeiron complexes, (tropone)Fe(CO) 3 , (tropone)Fe(CO) 2 (PH 3 ) and (tropone)Fe(PH 3 ) 3 , and their protonated species. The results show that the oxygen-protonated tropone is more stable than the carbon-protonated tropone. On the contrary, in the troponeiron complexes, the carbon protonated species are more stable than the oxygen protonated species. In the neutral and oxygen-protonated complexes, the tropone and oxygen-protonated tropone ligands are η 4 -coordinated. In the carbon-protonated complexes, the carbon-protonated tropone ligand is η 5 -coordinated. The results also show that the metal shift for complexes containing phosphine ligands is more difficult than that for those containing carbonyl ligands. For the neutral methyl-substituted troponeiron complexes, steric effect was found to play a key role in determining the relative stability of the regioisomers. For their protonated species, the electron-donating properties of the methyl substituent(s) were found to be important in determining the relative stability among the different regioiosmers.