Platinum-Catalyzed Hydrofluorination of Alkynes: Hydrogen Bonding to Indolylphosphine Ligands to Provide Fluoride Reactivity

The reaction of the Pt complexes cis-[Pt(CH3)(2){R2P(Ind)}(2)] (Ind=2-(3-methyl)indolyl, R=Ph (1 a), 4-FC6H4 (1 b), 4-CF3C6H4 (1 c)) with HF afforded the fluorido complexes trans-[Pt(F(HF)(2))(CH3){R2P(Ind)}(2)] 2 a-c, which can be converted into trans-[Pt(F)(CH3){R2P(Ind)}(2)] (3 a-c) by treatment with CsF. Addition of 3-hexyne to 2 a-c gave alkyne complexes trans-[Pt(C,C-eta(2)-C2H5C equivalent to CC2H5)(CH3){R2P(Ind)}(2){F(HF)(2)}] (4 a-c) at which a fluoride is stabilised as polyfluoride in the coordination sphere by hydrogen bonding to the indolyl-substituted phosphine ligands. Subsequent heating of a solution of 4 a in the presence of PVPHF led to fluoroalkene formation. Selective catalytic hydrofluorination of alkynes to yield (Z)-fluoroalkenes were developed. The ability of hydrogen bonding to polyfluoride favours the fluorination step as demonstrated by studies with complexes bearing no indolyl groups at the phosphine ligands.