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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

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posted on 27.02.2012, 00:00 by David Breyer, Thomas Braun, Paul Kläring
The reaction of [Pd­(Me)2(tmeda)] (tmeda = N,N,N′,N′-tetramethylethylendiamine) with the phosphine iPr2PCH2CH2OCH3 resulted in the formation of the palladium(0) complex [Pd­(iPr2PCH2CH2OCH3)2] (1). Treatment of 1 with pentafluoropyridine at room temperature yielded the C–F activation product trans-[Pd­(F)­(4-C5NF4)­(iPr2PCH2CH2OCH3)2] (2). The triflato and bromo complexes trans-[Pd­(OTf)­(4-C5NF4)­(iPr2PCH2CH2OCH3)2] (4) and trans-[Pd­(Br)­(4-C5NF4)­(iPr2PCH2CH2OCH3)2] (5) could be prepared on reaction of complex 2 with EtOTf or 3-bromopropene, respectively. Treatment of 2 with Me3SiCl or HBpin (HBpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolane, pinacolborane) effects the formation of trans-[Pd­(Cl)­(4-C5NF4)­(iPr2PCH2CH2OCH3)2] (6) and trans-[Pd­(H)­(4-C5NF4)­(iPr2PCH2CH2OCH3)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.