SEQUENTIAL IRON(I)-MEDIATED HOMOLOGIZATION OF OLEFINS BY METHANOL ANDMETHYL HALIDES IN THE GAS-PHASE

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 cyclo tron resonance mass spectrometry. C-C bond formation between the alken e and CH(3)X occurs via initial insertion of Fe+ into the C-X bond, fo llowed by a migratory insertion of the olefin into the iron-carbon bon d of(X)-Fe(CH3)(+). This step constitutes a gas-phase analog of the in itial stage in the Ziegler-Natta type C-C bond formation; a combinatio n of subsequent beta-H shift and reductive elimination of HX completes the reaction. In the case of Fe(propene)(+) a remarkable regioselecti vity is observed in that the addition results in the exclusive formati on of an unbranched Fe(butene)(+) complex. Starting from Fe(ethene)(+) , up to two consecutive methylations occur using CH3-. OH as a reactan t; 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)(+).