Competing C–H and C–F bond activation reactions of a fluorinated olefin at Rh: a fluorido vinylidene complex as an intermediate in an unprecedented dehydrofluorination step

The hydrofluoroolefin Z-1,3,3,3-tetrafluoropropene has been activated via an initial C–F bond activation and subsequent C–H bond activation using [Rh(H)(PEt(3))(3)] (1) or via C–H bond activation at [Rh(CH(3))(PEt(3))(3)] (8). In both cases the formation of [Rh{(E)-CF[double bond, length as m-dash]CHCF(3)}(PEt(3))(3)] (3) was observed. Importantly, the C–F activation product [Rh{(E)-CH[double bond, length as m-dash]CHCF(3)}(PEt(3))(3)] (2) reacts in the presence of Z-1,3,3,3-tetrafluoropropene into 3. The latter converted into [Rh(C[triple bond, length as m-dash]CCF(3))(PEt(3))(3)] (6) by an unprecedented dehydrofluorination reaction, presumably via a vinylidene complex as intermediate. When the carbonyl complex [Rh(C[triple bond, length as m-dash]CCF(3))(CO)(PEt(3))(3)] (12) was treated with an excess of NEt(3)·3HF or HBF(4) at low temperature, the formation of the phosphonioalkenyl compounds [Rh{(Z)-C(PEt(3))[double bond, length as m-dash]CHCF(3)}(CO)(PEt(3))(2)]X (X = F(HF)(x), BF(4)) (13) was observed. The formation of 13 can be explained by an attack of PEt(3) at the electrophilic α-carbon atom of an intermediate vinylidene complex. The employment of P(i)Pr(3) derivatives as model compounds allowed for the isolation of the unique fluorido vinylidene complex trans-[Rh(F)([double bond, length as m-dash]C[double bond, length as m-dash]CHCF(3))(P(i)Pr(3))(2)] (16), which in the presence of PEt(3) transforms into [Rh(C[triple bond, length as m-dash]CCF(3))(PEt(3))(3)] (6).