Selective activation of C–F and C–H bonds with iron complexes, the relevant mechanism study by DFT calculations and study on the chemical properties of hydrido iron complex

Abstract

The reactions of (2,6-difluorophenyl)phenylmethanone (2,6-F₂C₆H₃–C(O)–C₆H₅) (1) and (2,6-difluorophenyl)phenylmethanimine (2,6-F₂C₆H₃–C(NH)–C₆H₅) (3) with Fe(PMe₃)₄ afforded different selective C–F/C–H bond activation products. The reaction of 1 with Fe(PMe₃)₄ gave rise to bis-chelate iron(II) complex [C₆H₅–C(O)–3-FC₆H₃)Fe(PMe₃)]₂ (2) via C–F bond activation. The reaction of 3 with Fe(PMe₃)₄ delivered chelate hydrido iron(II) complex 2,6-F₂C₆H₃–C(NH)–C₆H₄)Fe(H)(PMe₃)₃ (4) through C–H bond activation. The DFT calculations show the detailed elementary steps of the mechanism of formation of hydrido complex 4 and indicate 4 is the kinetically preferred product. Complex 4 reacted with HCl, CH₃Br and CH₃I delivered the chelate iron halides (2,6-F₂C₆H₃–C(NH)–C₆H₄)Fe(PMe₃)₃X (X = Cl (5); Br (6); I (7)). A ligand (PMe₃) replacement by CO of 4 was observed giving (2,6-F₂C₆H₃–C(NH)–C₆H₄)Fe(H)(CO)(PMe₃)₂ (8). The chelate ligand exchange occurred through the reaction of 4 with salicylaldehydes. The reaction of 4 with Me₃SiCCH afforded (2,6-F₂C₆H₃–C(N)–C₆H₅)Fe(CC–SiMe₃)(PMe₃)₃ (11). A reaction mechanism from 4 to 11 was discussed with the support of IR monitoring. The molecular structures of complexes 2, 4, 6, 7, 10 and 11 were determined by X-ray diffraction.