Distinct Demonstration of Methylene Insertion into the Metal−Carbon Bond on Ag(111)

Abstract

We provide a clear demonstration of the migratory insertion of methylene into the metal−carbon bond on a silver single-crystal surface. The insertion reaction is characterized by the interaction between methylene and perfluoromethyl groups coadsorbed on Ag(111). The CH2 insertion into the Ag−CF3 bond followed by β-fluoride elimination produces CH2CF2, which is our experimental evidence for the insertion mechanism. Our observations confirm the step concerning the propagation of the carbon chain in the Fischer−Tropsch processes.

Surface Reactions of CH3I and CF3I with Coadsorbed CH2I2 on Ag(111) as Mechanistic Probes for Carbon−Carbon Bond Formation via Methylene Insertion

“…Briefly, trifluoromethyl (CF 3 ) and methylene- d 2 (CD 2 ) moieties are generated on Ag(111) by the dissociative adsorption of CF 3 I and CD 2 I 2 . The CD 2(ad) group is inserted into the Ag−CF 3 bond to form CF 3 CD 2(ad) , which then undergoes β -fluoride elimination to evolve CF 2 CD 2 at 262 K. Paul and Gellman found that the adsorbed CF 3 CH 2(ad) , generated directly on the Ag(111) surface by thermally rupturing the C−I bond in adsorbed CF 3 CH 2 I, indeed loses one fluorine at the β carbon position, to afford CF 2 CH 2 at ∼250 K. Since the situations of CF 3(ad) + CH 2(ad) (CF 3(ad) + CD 2(ad) ) and CF 3 CH 2(ad) lead to identical end products, the insertion of methylene into the Ag−CF 3 bond is strongly inferred . To test this argument further, Figure (top panel) shows the evolution of CF 2 CH 2 in TPR as a result of CH 2(ad) + Ag−CF 3 → Ag−CH 2 CF 3 → CH 2 CF 2(g) + F (ad) (methylene insertion/ β -elimination) after the coadsorption of 1.0 L CH 2 I 2 and 0.3 L CF 3 I.…”

“…Besides, extended Hückel calculations by Hoffmann and co-workers also indicate an increase of the coupling rate (decrease of the reaction barrier) for CH 2 + CH 3 on model surfaces as the metal is changed, moving from the left to the right side of the Periodic Table. No wonder copper and silver are the only two metals to date that have been reported to catalyze carbon chain propagation via methylene insertion. , On Cu(110), the thermal interaction of coadsorbed mixtures of methyl and methylene groups yields ethylene , which is produced by β -hydride elimination from the ethyl moieties resulting from CH 2 insertion into the Cu−CH 3 bond . However, this proof of insertion is somewhat implicit considering the self-coupling of methylene, which generates ethylene at similar temperatures as well.…”

“…Understanding the methylene insertion reaction should help in developing methods (better catalysts) for transforming coal to gasoline. In a previous communication, 7 we reported our discovery of CH 2 insertion into the Ag-CF 3 bond, utilizing methylene iodide (CH 2 I 2 ) and trifluoromethyl iodide (CF 3 I) as precursors for preparing coadsorbed methylene and perfluoromethyl fragments. As a consequence, we were able to demonstrate that the Ag(111) surface catalyzes the formation of a new C-C bond between these two C 1 moieties via the CH 2 insertion reaction.…”

DFT study of surface reactivity of CX3I (XH and F) with CH2I2 to form CH2CX2 on the Ag(111) surface

“…Therefore, it is of great interest to determine the chemical requirements for causing the demanded reactions and to understand their reaction mechanisms and corresponding reactivity. Recently, Wu and Chiang [8] and Wu and coworkers [9] reported the discovery of CH 2 insertion into AgOCF 3 bond, that is, Fisher-Tropsch process, followed by ␤-fluoride elimination to generate an isolated CH 2 ACF 2(g) when they utilized methylene iodide (CH 2 I 2(g) ) and trifluoromethyl iodide (CF 3 I (g) ) as precursors of coadsorbed methylene (CH 2(ads) ) and trifluoromethyl (CF 3(ads) ) fragments for bimolecular interaction on the Ag(111) surface. Consequently, the researchers were able to demonstrate that the Ag(111) surface catalyzes the formation of COC bond between these two C 1 moieties, that is, CH 2(ads) and CF 3(ads) , via the CH 2 insertion reaction.…”

The chemistry of C2 perfluoroalkyl iodide on the Cu(111) single crystal surface

“…In the past two decades the chemistry [1][2][3][4][5] and the reaction kinetics [6][7][8] of alkyl moieties below C 3 prepared by the dissociative adsorption of alkyl halides on transition-metal have been widely studied. These results show that the alkyl moieties of C 2 or C 3 decompose on transition-metal surface by b-hydrogen elimination to form olefins (ethylene or propylene) and no C-C coupling reactions have been observed [1][2][3][4][5][6][7][8]. Fluorine-substituted alkyl surface moieties have also drawn increasing attention because the replacement of hydrogen with fluorine can result in a marked change in the physical and chemical properties.…”