A new mechanism of nucleophilic vinylic substitution and unexpected products in the reaction of chlorotrifluoroethylene with [Re(CO)5]Na and [CpFe(CO)2]K

The mechanism of chloride substitution in CF2CFCl with [Re(CO)5]− and [CpFe(CO)2]− anions is investigated experimentally and theoretically. The substitution reaction begins with the nucleophile addition to CF2CFCl producing the carbenoid anion [MCF2CFCl]− (A) (M = Re(CO)5, CpFe(CO)2). This is shown by trapping the intermediate A with electrophiles – proton donor (t-BuOH) to give MCF2CFClH or with CF2CFRe(CO)5 to give acylmetallate III, and by the formation of the substitution products CF2CFM from the anion A, generated by the deprotonation of MCF2CFClH with t-BuOK. 1,2-Shift of metal carbonyl group concerted with the α-elimination of chloride anion is proposed as the transformation pathway of carbenoid A into CF2CFM. A competing process of carbene insertion into Fe–CO bond is proposed to explain the formation of (XI). The feasibility of these two pathways is confirmed by DFT (B3LYP/SDD and 6-31G∗) calculations of the carbenes [MCF2CF:] and carbenoid anions [MCF2CFCl]−. Transition states (TS) for 1,2-shift (+3.2 kcal/mol) and for nucleophilic addition at CO ligand (+5.4 kcal/mol) are located for [(CO)5ReCF2CFCl]−, but only one TS corresponding to carbene insertion into Fe–CO bond (+2.1 kcal/mol) is located for [(CO)2CpFeCF2CFCl]−. The formation of other newly observed products, F(CO)CHFRe(CO)5 (V) and Cp(CO)2FeCCFeCp(CO)2 (VIII) is also discussed.

Graphical abstractReaction of chlorotrifluoroethylene with [Re(CO)5]Na and [CpFe(CO)2]K is shown to proceed via the carbenoid transformation of the intermediate carbanion [L(CO)nMCF2CFCl]−. 1,2-Shift of (CO)5Re group gives the nucleophilic substitution product, while the carbene insertion into Fe–CO bond leads to the five-membered metallocycle .Figure optionsDownload full-size imageDownload as PowerPoint slideFigure optionsDownload full-size imageDownload as PowerPoint slide