BARE IRON METHOXIDE CATION - A SIMPLE-MODEL TO PROBE THE MECHANISM OFBETA-HYDROGEN TRANSFER IN ORGANOMETALLIC COMPOUNDS

Iron methoxide cation, Fe(OCH3)(+) (1), and its tautomer, the formalde hyde complex of the iron hydride cation, HFe(OCH2)(+) (2), have been e xamined in combined mass spectrometric and computational studies. Alth ough the experimental methods used for ion generation yield two isomer s, largely because intermolecular isomerization is facile, differentia tion of them is straightforward. Fe(OCH3)(+) corresponds to the global minimum of the [Fe,C,H-3,O](+) potential-energy hypersurface with an experimentally determined bond-dissociation energy of 69 +/- 2 kcal/mo l for the Fe+-OCH3 bond. In the gas phase, Fe(OCH3)(+) can isomerize v ia a B-hydrogen transfer to HFe(OCH2)(+), which is experimentally foun d to be 15 +/- 4 kcal/mol less stable than Fe(OCH3)(+). The experiment s suggest and the calculations predict that the two isomers are separa ted by a significant activation barrier. According to the calculations both species exhibit quintet ground states and the transition structu re associated with their interconversion on the quintet potential-ener gy hypersurface is 37 kcal/mol above Fe(OCH3)(+). Consideration of the excited triplet surface indicates that the barrier for the beta-hydro gen transfer connecting both isomers may be lowered substantially by a dditional ligands. Moreover, in the complexes Fe(L)(OCH3)(+) (L = C2H4 , CH2O) direct H-transfer from the OCH3 ligand to L may occur without involving an iron hydride as an intermediate.