Selective Aromatic C−F and C−H Bond Activation with Silylenes of Different Coordinate Silicon

摘要

Herein we report on the reaction of stable two-coordinate silylene, L1Si [L1 = CH{(C═CH₂)(CMe)(2,6-iPr₂C₆H₃N)₂}] (1) and three-coordinate silylene (Lewis base stabilized silylene), L2SiCl [L2 = PhC(NtBu)₂] (2) with aromatic compounds containing C−F and C−H bonds. The reaction of 1 and 2 with hexafluorobenzene (C₆F₆) affords the silicon(IV) fluorides, L1SiF(C₆F₅) (3) and L2SiFCl(C₆F₅) (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 (C₆F₅CF₃), pentafluoropyridine (C₅F₅N) regioselective C−F bond activation occurs leading to the formation of L1SiF(4-C₆F₄CF₃) (5), L1SiF(4-C₅F₄N) (6), L2SiFCl(4-C₆F₄CF₃) (7), and L2SiFCl(4-C₅F₄N) (8), respectively. More interestingly, compounds 1 and 2 react with pentafluorobenzene (C₆F₅H) under formation of silicon(IV) hydride L1SiH(C₆F₅) (9) by chemoselective C−H bond activation, in the latter case producing silicon(IV) fluoride L2SiFCl(4-C₆F₄H) (10) by chemo- as well as regioselective C−F bond activation. Furthermore, the reaction of 1 with 1,3,5-trifluorobenzene (1,3,5-C₆F₃H₃) leads to the chemoselective formation of silicon(IV) hydride L1SiH(1,3,5-C₆F₃H₂) (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.