Platinum‐Catalyzed Hydrofluorination of Alkynes: Hydrogen Bonding to Indolylphosphine Ligands to Provide Fluoride Reactivity
Stefan Sander, Thomas Braun
Abstract
Abstract 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 ≡ C C 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.