Coinage-Metal Mediated Ring Opening of <i>cis</i>-1,2-Dimethoxy­cyclo­propane: Trends from the Gold, Copper, and Silver Fischer Carbene Bond Strength

Abstract

N-heterocyclic carbene (NHC) supported coinage metal cations proved to react in the gas phase with the electron-rich <i>cis</i>-1,2-dimethoxy­cyclo­propane. Upon Collision Induced Dissociation (CID), several spectrometric fragment-ion signals were observed, one corresponding to the recovery of the bare cation IMes-M⁺ (IMes = 1,3-bis­(2,4,6-trimethyl­phenyl)­imidazol-2-ylidene) and the second to the methoxy­methylidene metal complex IMes–M–[HCOCH₃]⁺. The gold and copper complexes appear to stabilize the carbene sufficiently enough to promote the latter channel. On the contrary, the silver complex binds weakly to the methoxy­methylidene moiety as observed by the predominance of the bare cation IMes–M⁺ channel. Density Functional Theory (DFT) investigations of the Potential Energy Surface and Bond Energy Decomposition Analyses provided results that correlate well with the experimental data. In the case of the bare cation channel, two distinct reaction pathways were found: a straightforward decoordination of the cyclopropane and a cationic rearrangement of the three-membered ring into a dimethoxy­propylene isomer before dissociation. However, for the abstraction of the methoxy­methylidene moiety by the metal cation, only one pathway was found. In analogy to earlier studies by other groups, we found the trend Au > Cu > Ag for the metal–carbene bond strength