Mechanisms for C-H activations by metal centers can be classified into three general categories: 
*(i) Oxidative addition, in which a low-valent metal center inserts into a carbon-hydrogen bond, which cleaves the bond and oxidizes the metal:
:LM  + RH  →  LMR(H)
*(ii) Electrophilic activation in which an electrophilic metal attacks the hydrocarbon, displacing a proton:
:LM  + RH  →  LMR  +  H
*(iii) Sigma-bond metathesis, which proceeds through a "four-centered" transition state in which bonds break and form in a single step:
:LMX  + RH  →  LMR  +  XH