Successive reactions of iron carbonyl cations with dimethyl ether: direct cleavage versus rearrangement
Abstract
The reaction kinetics of electron impact ionization generated Fe(CO)n+ cations with dimethyl ether (DME) is investigated using a triple-cell Fourier Transform Ion Cyclotron Resonance spectrometer. The primary reaction is rapid substitution of CO by DME. One-step substitution of two CO ligands by one DME molecule also occurs for n = 3–4, and for unrelaxed Fe(CO)2+ ions. Successive substitutions in the Fe(CO)4+/DME system lead mainly to Fe(CO)(DME)2+, in which the last CO remains unsubstituted. This ion is slowly converted to Fe(CO)(DME)3+ and Fe(DME)2+. The latter reaction implies formation of neutral CH3COOCH3 resulting from iron-promoted CO insertion reaction. Further reaction of Fe(DME)+ with DME involves the cleavage of a C–O bond according to two channels, either direct CH3˙ loss or more exothermic CH4 loss, implying a molecular rearrangement. The branching ratio is strongly energy-dependent: the latter channel is observed only for Fe(DME)+ ions having a very low energy content.