• A) -alkyl elimination, wherein a metal bound alkyl ligand is fragmented into the corresponding metal alkyl and alkene units. • B) oxidative addition, wherein the C-C bond is cleaved by addition to a low oxidation state metal complex, increasing the metal oxidation state by two and creating two new M-C bonds. • C) A cycloaddition reaction between a hydrocarbon and metal reagent, creating a strained metallocycle which can then undergo C-C bond activation (e.g. through -elimination or an electrocyclic reaction). Scheme 1. Carbon-carbon bond activation mechanisms, via a) -alkyl elimination or migration; b) oxidative addition; c) cycloaddition reaction and subsequent rearrangement.