Carbonium ion stabilization by (η5-cyclopentadienyl)dicarbonylnitrosylchromium; a 1H and 13C NMR study

Transition-metal mediated heteroatom removal by reactions of FeL(+) [L=O, C 4H 6, c-C 5H 6, c-C 5H 5, C 6H 6, C 5H 4(=CH 2)] with furan, thiophene, and pyrrole in the gas phase

Reactions of Fe(+) and FeL(+) [L=O, C4H6, c-C5H6, C5H5, C6H6, C5H4(=CH2)] with thiophene, furan, and pyrrole in the gas phase by using Fourier transform mass spectrometry are described. Fe(+), Fe(C5H5)(+), and FeC6H 6 (+) yield exclusive rapid adduct formation with thiophene, furan, and pyrrole. In addition, the iron-diene complexes [FeC4H 6 (+) and Fe(c-C5H6)(+)], as well as FeC5H4(=CH2)(+) and FeO(+), are quite reactive. The most intriguing reaction is the predominant direct extrusion of CO from furan by FeC4H6 (+), Fe(c-C5H6)(+), and FeC5H4(=CH2)(+). In addition, FeC4H 6 (+) and Fe(c-C5H6)(+) cause minor amounts of HCN extrusion from pyrrole. Mechanisms are presented for these CO and HCN extrusion reactions. The absence of CS elimination from thiophene may be due to the higher energy requirements than those for CO extrusion from furan or HCN extrusion from pyrrole. The dominant reaction channel for reaction of Fe(c-C5H6)(+) with pyrrole and thiophene is hydrogen-atom displacement, which implies D(O)(Fa(N5H5)(+)-C4H4X)>D(O)(Fe(C5H5)(+)-H)=46±5 kcal mol(-1). D(O)(Fe(+)-C4H4S) and D(O)(Fe(+)-C4H5N)=D(O)(Fe(+)-C4H6)=48±5 kcal mol(-1). Finally, 55±5 kcal mol(-1)=D(O)(Fe(+)-C6H6)>D(O)(Fe(+)-C4H4O)>D(O)(Fe(+)-C2H4)=39.9±1.4 kcal mol(-1). FeO(+) reacts rapidly with thiophene, furan, and pyrrole to yield initial loss of CO followed by additional neutral losses. D(O)(Fe(+)-CS)>D(O)(Fe(+)-C4H4S)≈48±5 kcal mol(-1) and D(O)(Fe(+)-C4H5N)≈48±5 kcal mol(-1)>D(O)(Fe(+)-HCN)>D(O)(Fe(+)-C2H4)=39.9±1.4 kcal mil(-1).