Alkali metal-mediated decarboxylation and C F activation reactions for the decomposition of perfluoropropionate into perfluoroethene.

Multistage mass spectrometry (MSn) experiments using a linear ion trap mass spectrometer in conjunction with density functional theory (DFT) calculations have been employed to determine the fragmentation pathways for the thermal decomposition of alkali metal perfluoropropionate complexes. Electrospray ionisation (ESI) in the negative ion mode was used to generate the precursor complexes, [CF 3 CF 2 CO 2 MO 2 CCF 2 CF 3 ] − (M = Li, Na and K) in the gas phase. Upon collision-induced dissociation (CID) a minor amount of CF 3 CF 2 CO 2 − formation was observed, consistent with DFT calculations which predict strong binding energies of the carboxylate to the metal centres (ΔH° calculated to be 50.8, 47.9 and 44.3 kcal/mol for M = Li, Na and K, respectively). The major fragmentation pathway involved formation of the fluoride complexes [CF 3 CF 2 CO 2 MF] − via the loss of “C 2 F 4 CO 2 ”. The organometallic complex [CF 3 CF 2 CO 2 MCF 2 CF 3 ] − formed via decarboxylation, although a minor pathway in all cases, was formed in sufficient yield to allow it to be mass selected to study its further fragmentation pathways. The dominant pathway for the fragmentation of the organometallic complexes [CF 3 CF 2 CO 2 MCF 2 CF 3 ] − involves formation of the fluoride complexes [CF 3 CF 2 CO 2 MF] − in all cases, and DFT calculations reveal a facile β‑fluorine elimination pathway process with low barriers (21.9, 22.1 and 21.8 kcal/mol for M = Li, Na and K, respectively). The fluoride complexes [CF 3 CF 2 CO 2 MF] − fragment via decarboxylation to give [CF 3 CF 2 MF] − in competition with CF 3 CF 2 CO 2 − formation. DFT calculations were carried out to explore potentially competing mechanisms for loss of “C 2 F 4 CO 2 ” including: concerted or stepwise loss of CO 2 and CF 2 CF 2 and a CF 2 CF 2 CO 2 lactone pathway. The loss of lactone is the most likely pathway due to its lower energy barriers. In addition, the possibility of forming [CF 3 CF 2 MCF 2 CF 3 ] − and [CF 3 CF 2 MF]−, via decarboxylation is discussed. Finally, the fluoride complexes [FMF]− M = Na and K were experimentally observed. • The decompsition of alkali metal perfluoropropionate complexes are examined. • Systems studied include [CF 3 CF 2 CO 2 MX] − (M = Li, Na and K, X = CF 3 CF 2 CO 2 ; CF 3 CF 2 ; F). • Both decarboxylation and C F bond activation reactions are observed. • When X = CF 3 CF 2 , β-fluoride elimination dominates as the barrier is lowest.