Double C-H activation of ethane by metal-free SO2*+ radical cations.
The room-temperature C-H activation of ethane by metal-free SO(2)(*+) radical cations has been investigated under different pressure regimes by mass spectrometric techniques. The major reaction channel is the conversion of ethane to ethylene accompanied by the formation of H(2)SO(2)(*+), the radical cation of sulfoxylic acid. The mechanism of the double C-H activation, in the absence of the single activation product HSO(2)(+), is elucidated by kinetic studies and quantum chemical calculations. Under near single-collision conditions the reaction occurs with rate constant k=1.0 x 10(-9) (+/-30%) cm(3) s(-1) molecule(-1), efficiency=90%, kinetic isotope effect k(H)/k(D)=1.1, and partial H/D scrambling. The theoretical analysis shows that the interaction of SO(2)(*+) with ethane through an oxygen atom directly leads to the C-H activation intermediate. The interaction through sulfur leads to an encounter complex that rapidly converts to the same intermediate. The double C-H activation occurs by a reaction path that lies below the reactants and involves intermediates separated by very low energy barriers, which include a complex of the ethyl cation suitable to undergo H/D scrambling. Key issues in the observed reactivity are electron-transfer processes, in which a crucial role is played by geometrical constraints. The work shows how mechanistic details disclosed by the reactions of metal-free electrophiles may contribute to the current understanding of the C-H activation of ethane.
de Petris
Giulia
G
Dipartimento di Chimica e Tecnologie del Farmaco, Università La Sapienza, P. le Aldo Moro 5, 00185 Roma, Italy. giulia.depetris@uniroma1.it
Cartoni
Antonella
A
Troiani
Anna
A
Barone
Vincenzo
V
Cimino
Paola
P
Angelini
Giancarlo
G
Ursini
Ornella
O
D002244:Carbon / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D004980:Ethane / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D008670:Metals / Q000737:chemistry; D011789:Quantum Theory; D013458:Sulfur Dioxide / Q000737:chemistry*; D013696:Temperature
D002412:Cations; D008670:Metals; D013458:Sulfur Dioxide; D002244:Carbon; D006859:Hydrogen; D004980:Ethane