Synthesis and Reactivity of the Fluoro Complex trans-[Pd(F)(4-C₅NF₄)(ⁱPr₂PCH₂CH₂OCH₃)₂]: C–F Bond Formation and Catalytic C–F Bond Activation Reactions

Abstract

The reaction of [Pd(Me) 2 (tmeda)] (tmeda = N,N,N′,N′-tetramethylethylendiamine) with the phosphine i Pr 2 PCH 2 CH 2 OCH 3 resulted in the formation of the palladium(0) complex [Pd( i Pr 2 PCH 2 CH 2 OCH 3 ) 2 ] (1). Treatment of 1 with pentafluoropyridine at room temperature yielded the C−F activation product trans-[Pd(F)(4-C 5 NF 4 )-( i Pr 2 PCH 2 CH 2 OCH 3 ) 2 ] (2). The triflato and bromo complexes trans-[Pd(OTf)(4-C 5 NF 4 )( i Pr 2 PCH 2 CH 2 OCH 3 ) 2 ] (4) and trans-[Pd(Br)(4-C 5 NF 4 )( i Pr 2 PCH 2 CH 2 OCH 3 ) 2 ] (5) could be prepared on reaction of complex 2 with EtOTf or 3-bromopropene, respectively. Treatment of 2 with Me 3 SiCl or HBpin (HBpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolane, pinacolborane) effects the formation of trans-[Pd(Cl)(4-C 5 NF 4 )( i Pr 2 PCH 2 CH 2 OCH 3 ) 2 ] (6) and trans-[Pd(H)(4-C 5 NF 4 )-( i Pr 2 PCH 2 CH 2 OCH 3 ) 2 ] (7). In catalytic experiments pentafluoropyridine could be converted into the 4-aryl-tetrafluoropyridines (8, aryl = Ph; 9, aryl = Tol) and into 2,3,5,6-tetrafluoropyridine in the presence of the boronic acids PhB(OH) 2 , TolB(OH) 2 , or HBpin when 5 mol % of 2 is employed as catalyst.

Activation and Formation of Aromatic C–F Bonds

“…The palladium complex (70) having extended alkyl chains on phosphorus ligands was found to activate pentafluoropyridine exclusively at the 4-position giving (71) (Scheme 24) [130]. The OMe group on the ligand is thought to accelerate the reaction in some way; however, the exact role is not currently understood.…”

Palladium-Mediated Organofluorine Chemistry

“…238 In contrast to the Suzuki and Stille processes described, electron withdrawing substitutents on the ring are not necessary for the coupling of fluoroaryls with Grignard reagents to occur, the so called Kumada-Corriu process. 239 Although nickel catalysis is more common in these processes, palladium catalyzed reactions have also been reported.…”

Palladium-Catalyzed Cross-Coupling Reactions of Perfluoro Organic Compounds

“…Most of the reported Suzuki-Miyaura type cross-coupling reactions via C-F bond cleavage, employing either highly electron-deficient organofluorine compounds or those bearing a directing group, have traditionally been conducted in the presence of a base [59,[75][76][77][78][79][80][81][82][83][84][85], whereas fluoride anion itself is regarded as a good activator for neutral organoboron reagents. The role of a base in a Suzuki-Miyaura coupling reaction is generally considered to follow one of two patterns; either converting a neutral organoboron compound into a nucleophilic boronate, or converting a palladium halide intermediate into an active palladium species via a ligand exchange reaction by the base [86,87].…”