Kinetics and mechanism of halogen-atom-transfer reactions between haloalkanes and several 17-electron transition-metal complex negative ions in the gas phase

Reactivity of Negative Ions with Trifluoromethyl Halides

“…i. Halogen Atom Transfer . A major and sometimes dominant pathway in most of the reactions of both Fe - and FeCO - is halogen atom transfer, a channel found previously in work involving other transition metal complex anions. , The relative contribution from the halogen transfer channel diminishes with heavier CF 3 X. This same trend is found in the reactions of o- , m- , and p- CF 3 C 6 H 4 CN - , for which halogen atom transfer dominates for CF 3 Cl and CF 3 Br but is a minor pathway for CF 3 I, where the main channel is association.…”

“…Thus, while energetically-allowed NDET generally implies a fast overall reaction, endothermic NDET should not be seen as an indication that the reaction will be slow, since highly exothermic pathways may exist which do not involve electron transfer per se , e.g., nucleophilic attack at carbon by O - . Jones et al have pointed out that, even in some cases where NDET is endothermic, electron transfer may occur within the collision complex, since the attractive ion−dipole and ion−induced dipole interactions supply additional energy with which to overcome the endothermicity of electron transfer. In that model, a subsequent step, halide transfer from CF 3 X - , would then take place within the collision complex, leading to the observed exothermic products.…”

“…We have previously shown that the rates of the reactions of O 2 - with fully halogenated methanes correlate with both the electron affinities and the electron attachment rates of the halomethanes, supporting the above mechanism. Earlier, McDonald et al suggested an initial electron transfer mechanism to explain the reactivity of (CH 3 O) 2 PO - with CF 3 X. Jones et al showed a correlation between haloalkane electron attachment rates and the rates for reactions of 17-electron transition-metal anions and concluded that the reactivity of these systems is governed by initial electron transfer. Knighton and Grimsrud 8 also concluded that initial electron transfer controls the reactivity of a series of reactions of substituted benzene anions and haloalkanes.…”

“…Bunnett named this mechanism “S RN 1” and studied its applicability to aromatic substitution. Initial electron transfer in the gas phase was proposed by McDonald et al to explain the reactivity of (CH 3 O) 2 PO - with CF 3 X and by Jones et al to explain the reactivity of 17-electron transition-metal complex anions with a variety of haloalkanes. Knighton and Grimsrud also attributed anion reactivity trends in haloalkanes to an initial electron transfer mechanism.…”

Organometallic Chemistry in the Flowing Afterglow: A Review

“…A more comprehensive look at the reactions of 17-electron transition-metal anions and haloalkanes by McDonald in 1989 considered the metal carbonyl anions Mn(CO) 4 X - (X = Br, Cl), Re(CO) 4 X - (X = Br, Cl), (η-C 3 H 5 )Mn(CO) 3 - , (η-C 3 H 5 )Re(CO) 3 - , Cr(CO) 5 - , Fe(CO) 4 - , and Ni(CO) 3 - . Two others studied, Mn(CO) 3 X - (X = Br, Cl), although formally 15-electron anions, behaved in both rate and reactivity studies in a manner similar to the 17-electron anions, suggesting to the authors that Cl and Br are 3-electron donors in Mn(CO) 3 X - . The rates of these reactions vary widely but do not correlate with C−X BDEs.…”