Halogenated organic compounds (HOCs) are attributed as one of the major environmental contaminants. Hydrodehalogenation (HDH) has become an effective approach to degrade HOCs. Therefore, exploring various methods of catalytic HDH has persistently attracted many research concerns in this field. Among these methods, due to its special electronic effect and steric effect, metal complexes (MCs) have also presented the efficient catalytic dehalogenation performance. So the catalytic dehalogenation by MCs is reported as the novel HDH method in many recent studies. In this review, the reaction types and mechanisms are summarized for the catalytic dehalogenation processes of fluorinated, chlorinated, and brominated organic compounds using various MCs. It is indicated that the electron transfer conditions, spatial structure, and the affinity of ligand to halogen in HOCs play the major roles to dehalogenation reaction. Additionally, the influential factors including central metal ions, ligands, types of HOCs, reductants, etc. are discussed and analyzed for their effects on catalytic dehalogenation reaction. Finally, it is proposed about existing problems of the catalytic dehalogenation using MCs. Moreover, the future trends for the development of this method to HOCs degradation are prospected.

Contents
1 Introduction
2 Types and mechanisms of catalytic dehalogenation by MCs
2.1 Dechlorination and debromination
2.2 Defluorination
3 Influential factors
3.1 Effect of central ion and ligand in MCs
3.2 Effect of HOCs categories, substituted position of halogen atoms and functional groups
3.3 Effect of reductant
3.4 Effect of solvent
3.5 Effect of pH
3.6 Effect of catalyst support
4 Conclusion and outlook