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

The reaction of the Pt complexes cis-[Pt(CH 3 ) 2 {R 2 P(Ind)} 2 ] (Ind=2-(3-methyl)indolyl, R=Ph (1 a), 4-FC 6 H 4 (1 b), 4-CF 3 C 6 H 4 (1 c)) with HF afforded the fluorido complexes trans-[Pt(F(HF) 2 )(CH 3 ){R 2 P(Ind)} 2 ] 2 a-c, which can be converted into trans-[Pt(F)(CH 3 ){R 2 P(Ind)} 2 ] (3 a-c) by treatment with CsF. Addition of 3-hexyne to 2 a-c gave alkyne complexes trans-[Pt(C,C-η 2 -C 2 H 5 C≡CC 2 H 5 )(CH 3 ){R 2 P(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.