Synthesis of a Water-Stable 2, 4-Bis(trifluoromethyl)phenyl-Substituted Phosphonous Acid Palladium Complex and its Catalytic Activity in Cross-Coupling Reactions

Coordination Properties of Perfluoroethyl- and Perfluorophenyl-Substituted Phosphonous acids, R(f)P(OH)2

Phosphinic acids, R(f)P(O)(OH)H (R(f)=CF3, C2F5, C6F5), turned out to be excellent preligands for the coordination of phosphonous acids, R(f)P(OH)2. Addition of C2F5P(O)(OH)H to solid PtCl2 under different reaction conditions allows the isolation and full characterization of the mononuclear complexes [ClPt{P(C2F5)(OH)O}{P(C2F5)(OH)2}2] and [Pt{P(C2F5)(OH)O}2{P(C2F5)(OH)2}] containing hydrogen-bridged [R(f)P(OH)O](-) and R(f)P(OH)2 units. Further deprotonation of [Pt{P(C2F5)(OH)O}2{P(C2F5)(OH)2}2] leads to the formation of the dianionic platinate, [Pt{P(C2F5)(OH)O}4](2-), revealing four intramolecular hydrogen bridges. With PdCl2 the dinuclear complex [Pd2(μ-Cl)2{[P(C2F5)(OH)O]2H}2] was isolated and characterized. The Cl(-) free complex [Pd{P(C2F5)(OH)O}2{P(C2F5)(OH)2}2] was also prepared and deprotonated to the dianionic palladate, [Pd{P(C2F5)(OH)O}4](2-). Both compounds were characterized by NMR spectroscopy, IR spectroscopy, and X-ray analyses. In addition, the C6F5 derivatives [ClPt{P(C6F5)(OH)O}{P(C6F5)(OH)2}2] and [Pd2(μ-Cl)2{[P(C6F5)(OH)O]2H}2] as well as the CF3 derivative [Pd2(μ-Cl)2 {[P(CF3)(OH)O]2H}2] were synthesized and fully characterized. Phosphonous acid complexes are inert towards air and moisture and can be stored for several months without decomposition. The catalytic activity of the palladium complexes in the Suzuki cross-coupling reaction between 1-bromo-3-fluorobenzene and phenyl boronic acid was demonstrated.