The reactivity of ferrocenylalkyl azoles under the conditions of electrospray ionization

Under the conditions of electrospray ionization of ferrocenylalkyl azoles FcCH(R)X (Fc–η5-C5H5Fe-η5-C5H4, R – H, Me, XH – 2-methyl imidazole, pirazole) the processes of oxidation, protonation, fragmentation and ferrocenylalkylation to form, molecular ions [М]+, protonated molecules [М+Н]+, ferrocenylalkyl cations [FсCHR]+ and bisferrocenylalkyl azole cations [(FcCHR)2X]+, respectively, take place. Using special experimental techniques (deuterated solvents, saturation of ionic source of an ESI mass-spectrometer by the vapors of solvents, the experiments under the “inverse” ESI conditions when the solvent is subjected to electrospray in the presence of ferrocenylalkyl derivative vapours) and quantum-chemical calculations at the level of the B3LYP/LanL2DZ theory the scheme of the formation of these ions in a gas phase according to the mechanism of “activating protonation” was suggested. it was found that all these ions are formed through the protonation stage, which is taking place mainly in a gas phase. The key stage is the exothermic process of the protonation of the initial compounds by hydroxonium ions giving rise to protonated [M+H]+ molecules which further oxidize and alkylate ferrocenylalkylazoles to form molecular radical cations and bisferrocenylalkyl azole ions [FcCH(Me)-X-CH(Me)Fc]+. The decomposition of protonated ions with the elimination of the azole molecule gives rise to ferrocenylalkyl cations [FсCHR]+ capable in turn of oxidizing and alkylating the initial compounds.