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.