Hydrodefluorination – Do We Need a Metal Catalyst?

Bis(cyclopentadienyl)difluoridotitanium(IV) has been shown to be an effective precatalyst for the catalytic hydrodefluorination of fluoro aromatics and alkenes [1]. Its efficient use in organic synthesis could be demonstrated [2]. The mechanism of these reactions was studied experimentally and by computational chemistry revealing that the catalytically active species Cp2TiH is present only in very small concentrations [3]. Cp3Ln (Ln = Ce, Nd, Sm, Er, Yb) are applied as precatalysts in the presence of LiAlH4 for the C–F bond activation of hexafluoropropene, 1,1,3,3,3‐pentafluoropropene, trifluoropropene, chlorotrifluoroethene, and octafluorotoluene. 100 % conversion and TONs up to 155 could be observed for the hydrodefluorination reaction (HDF) [4]. In control experiments we have demonstrated that the hydrodefluorination reaction of fluoro aromatic compounds and alkenes in toluene can be even achieved by using Lewis basic organo catalysts [5]. No reaction occurs in toluene in the absence of Lewis bases or metal catalysts.