Nickel fluoro complexes as intermediates in catalytic cross-coupling reactions

The C–F activation of pentafluoropyridine or 2,3,5,6-tetrafluoropyridine at [Ni(COD)2] (COD = 1,5-cyclooctadiene) in the presence of iPr2PCH2CH2OMe resulted in the formation of the nickel(II) fluoro bisphosphine complexes trans-[Ni(F)(2-C5NF4){κ1-(P)-(iPr2PCH2CH2OMe)2}] (1), trans-[Ni(F)(4-C5NF4){κ1-(P)-(iPr2PCH2CH2OMe)2}] (2) and trans-[Ni(F)(2-C5NHF3){κ1-(P)-(iPr2PCH2CH2OMe)2}] (3). The employment of iPr2PCH2CH2NMe2 gave the nickel(II) fluoro monophosphine complexes [Ni(F)(2-C5NF4){κ2-(P,N)-iPr2PCH2CH2NMe2}] (4), [Ni(F)(4-C5NF4){κ2-(P,N)-iPr2PCH2CH2NMe2}] (5) and [Ni(F)(2-C5NHF3){κ2-(P,N)-iPr2PCH2CH2NMe2}] (6) instead, in which the amino moiety coordinates at the metal center. In catalytic experiments pentafluoropyridine could be converted into 3,5,6-trifluorodiphenylpyridine (7) and 3,5-difluoro-2,4,6-triphenylpyridine (8) in the presence of PhB(OH)2 and 5 mol% of a mixture of 1 and 2 (ratio 8:1) or 5 and 4 (ratio 2:1) as catalysts. Additionally 2,3,5,6-tetrafluoropyridine could be converted catalytically into 3,5-difluoro-2,6-diarylpyridines (9: aryl = Ph; 10: aryl = Tol; 11: aryl = 4-(F3C)C6H5; 12: aryl = 4-MeOC6H5) in the presence of boronic acids when 5 mol% of 3 was employed as catalyst.