Catalytic Fluorination by Halide Exchange with 16-Electron Ruthenium(II) Complexes. X-ray Structure of [Tl(μ-F)2Ru(dppe)2]PF6

The 16-electron ruthenium(II) complexes [RuCl(dppe) 2 ]PF 6 ( 2; dppe = 1,2-bis(diphenylphosphino)ethane), [RuCl(chiraphos) 2 ]PF 6 ( 3; chiraphos = ( S,S )-3,4-bis(diphenylphosphino)butane), and [RuCl(PNNP)]PF 6 ( 4; PNNP = (1 S, 2 S )- N,N ‘ -bis[2-(diphenylphosphino)benzylidene]diaminocyclohexane) catalyze the nucleophilic fluorination of activated alkyl halides with a catalyst loading as low as 1 mol %. The alkyl halides (CH 3 ) 3 CX (X = Br, 5c; X = I, 5d ), Ph 2 CHBr ( 6c ), and PhCH(Me)Br ( 7c ) are converted to the fluoro analogues in the presence of TlF as the fluoride source. Yields are between 31 and 83%. The chiral complex 4 converts 7c to PhCH(Me)F ( 7a ) with 49% yield after 24 h. At 1% conversion, 7a is nonracemic (16% ee), which indicates that kinetic resolution occurs, albeit at a low level. The fluorination of 1,2-dibromo-1,2,3,4-tetrahydronaphthalene ( 8c ) is highly regioselective and gives 1-fluoro-2-bromo-1,2,3,4-tetrahydronaphthalene ( 8a ) in 68% yield. The difluoro-bridged thallium adduct [Tl(μ-F) 2 Ru(dppe) 2 ]PF 6 ( 9 ) was observed by 31 P NMR during catalysis with 2 and independently prepared by reaction of 2 with TlF (2 equiv). Complex 9 was characterized by 1 H, 31 P, 19 F, and 205 Tl NMR spectroscopy, as well as by X-ray diffraction.