SELECTIVE chemical transformations involving hydrocarbons are a major goal in synthetic chemistry. Transition-metal complexes are capable of promoting a range of selective transformations of organic molecules under mild conditions(1,2), and much effort has been devoted to studying their reactivity towards hydrocarbons(3-7). Here we report a reaction promoted by a rhodium complex in which a methylene (CH2) group can be abstracted from a methyl (CH3) group and inserted into a variety of bonds, such as Si-H, Si-Si and C-H. Our approach presently requires a certain coordination geometry in the metal complex, involving chelation of the metal centre, but we believe that it can be extended to other substrates capable of metal coordination and may eventually lead to a general strategy for CH2 transfer from hydrocarbons to other molecules under mild conditions.