We investigated the metalation reaction between Fe atom and two porphyrin derivatives,5,10,15,20-tetra(4-pyridyl)porphyrin(2HTPyP)and 5,10,15,20-tetraphenylporphyrin(2HTPP),on Au(111)substrate by a combined study of cryogenic scanning tunneling microscopy and density functional theory(DFT)calculations.With excess Fe,at room temperature all the 2HTPP molecules are metalated,i.e.with Fe atom incorporated into the porphyrin macrocycle,in agreement with previous reports [1].In contrast,only a proportion of 2HTPyP molecules are metalated at room temperature even in the excess of Fe,forming FeTPyP,and we also observed an Fe-2HTPyP complex at the initial stage of metalation reaction in STM image,whose structure was further confirmed by DFT calculations.Both the proportions of FeTPyP and Fe-2HTPyP increase at elevated annealing temperatures,but the non-metalated 2HTPyP molecules always remain on the surface even at the annealing temperature of 516 K.By comparing the metalation reaction and the structural difference of the two porphyrin derivatives,we infer that the metalation reaction between Fe and 2HTPyP is hindered by the peripheral pyridyl groups,which coordinate with Fe atoms and reduced the reaction probability between Fe atom and central porphyrin macrocycle,resulting in a lowered metalation reaction rate.Our results demonstrate the kinetic process on-surface metalation reaction between transition metal atoms and porphyrin derivatives can be influenced by side reactions at peripheral groups.