FE(I)-MEDIATED REGIOSELECTIVE AND STEREOSELECTIVE C-C C-H BOND ACTIVATION OF INTERNAL METHYLENE GROUPS OF ALPHA-OMEGA-DIPHENYLALKANES/

For three a,omega-diphenylalkanes the mechanistic details of the Fe+-m ediated activation of C-H and C-C bonds in the gasphase have been eluc idated by isotopic labelling experiments. The unimolecular reactions, i.e. dehydrogenation of the alkane chain, formation of ethylene from i nternal methylene groups, and generation of toluene, proceed largely w ith high selectivity. Particularly interesting are the results for the dehydrogenation of the Fe+ complex 3-Fe+ of 1, 8-diphenyl-octane whic h involves to 93% the internal methylene groups C-4/C-5. In addition, the study of the stereoisotopomers 3c-d provides evidence for the oper ation of isotopically sensitive branching (''metabolic switching'') in the reaction, and the analysis of the data suggests that the selectiv ity of the reaction is, most likely, due to a sandwich-type structure.