Katalytische C-F-Aktivierung und Hydrodefluorierung von Fluoralkylgruppen

Selective aromatic C-F and C-H bond activation with silylenes of different coordinate silicon

Herein we report on the reaction of stable two-coordinate silylene, L(1)Si [L(1) = CH{(C=CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}] (1) and three-coordinate silylene (Lewis base stabilized silylene), L(2)SiCl [L(2) = PhC(NtBu)(2)] (2) with aromatic compounds containing C-F and C-H bonds. The reaction of 1 and 2 with hexafluorobenzene (C(6)F(6)) affords the silicon(IV) fluorides, L(1)SiF(C(6)F(5)) (3) and L(2)SiFCl(C(6)F(5)) (4), respectively. The reaction proceeds through the unprecedented oxidative addition of one of the C-F bonds to the silicon(II) center without any additional catalyst. When 1 and 2 are treated with octafluorotoluene (C(6)F(5)CF(3)), pentafluoropyridine (C(5)F(5)N) regioselective C-F bond activation occurs leading to the formation of L(1)SiF(4-C(6)F(4)CF(3)) (5), L(1)SiF(4-C(5)F(4)N) (6), L(2)SiFCl(4-C(6)F(4)CF(3)) (7), and L(2)SiFCl(4-C(5)F(4)N) (8), respectively. More interestingly, compounds 1 and 2 react with pentafluorobenzene (C(6)F(5)H) under formation of silicon(IV) hydride L(1)SiH(C(6)F(5)) (9) by chemoselective C-H bond activation, in the latter case producing silicon(IV) fluoride L(2)SiFCl(4-C(6)F(4)H) (10) by chemo- as well as regioselective C-F bond activation. Furthermore, the reaction of 1 with 1,3,5-trifluorobenzene (1,3,5-C(6)F(3)H(3)) leads to the chemoselective formation of silicon(IV) hydride L(1)SiH(1,3,5-C(6)F(3)H(2)) (11). The formation of compounds 9 and 11 occurs via oxidative addition of the aromatic C-H bond to the silicon(II) center instead of C-F bond activation. All reported reactions proceed without any additional catalyst. Compounds 3, 4, 5, 6, 7, 8, 9, 10, and 11 were investigated by microanalysis and multinuclear NMR spectroscopy and compounds 3, 7, 8, and 9 additionally by single crystal X-ray structural analyses.