The gas-phase chemistry of simple Fe(olefin)(+) complexes with CH(3)X (X = OH, F, Cl, Br, I) has been studied by Fourier-transform ion cyclotron resonance mass spectrometry. C-C bond formation between the alkene and CH(3)X occurs via initial insertion of Fe+ into the C-X bond, followed by a migratory insertion of the olefin into the iron-carbon bond of(X)-Fe(CH3)(+). This step constitutes a gas-phase analog of the initial stage in the Ziegler-Natta type C-C bond formation; a combination of subsequent beta-H shift and reductive elimination of HX completes the reaction. In the case of Fe(propene)(+) a remarkable regioselectivity is observed in that the addition results in the exclusive formation of an unbranched Fe(butene)(+) complex. Starting from Fe(ethene)(+), up to two consecutive methylations occur using CH3-. OH as a reactant; with methyl halides the number of methylations varies from 2 (for X = I) to 4 (for X = F). For alkyl halides RX bearing a beta-hydrogen, Fe+-mediated dehydrohalogenation of RX competes efficiently with the C-C coupling of RX and Fe(olefin)(+).