Aromatic C–F Bond Activation by Rare-Earth-Metal Complexes

Abstract

C-F bond activation is a challenging reaction with increasing importance in synthesis. The strength of the C-F bond and the shielding effect of the fluorine atom render its activation difficult. Rare-earth metals offer an exceptional opportunity for this process because the high dissociation energy of the M-F bond offsets the strength of the C-F bond. Herein we report a unique reaction for the C-F activation of aromatic bonds by rare-earth metal complexes. The strong C-F bond of perfluorobenzene is cleaved under reducing conditions in the presence of a rare-earth metal iodide to form initially an equimolar mixture of a metal fluoride and a metal perfluorophenyl complex; the latter eventually undergoes β-F elimination to a metal fluoride. A similar reactivity is observed when reacting inverse sandwich rare-earth metal arene complexes with perfluorobenzene. All compounds were characterized by X-ray crystallography, multi-nuclear NMR spectroscopy, and elemental analysis.

Reduction of Diphenylacetylene Mediated by Rare-Earth Ferrocene Diamide Complexes

“…The Y–C1 and Y–C4 distances were 2.504(4) and 2.489(5) Å, respectively. The Fe–Y distance of 3.406(1) Å is outside the range of the sum of the covalent radii, 3.22 Å, indicating the absence of an iron–yttrium interaction in this compound. ,− ,− Interestingly, the C1–C2 and C3–C4 distances were 1.357(7) and 1.340(1) Å, respectively, indicating the presence of double bonds. The C2–C3 distance of 1.512(6) Å is representative of a single bond.…”

Modern applications of low-valent early transition metals in synthesis and catalysis

“…Although C-F bond activation has been observed across the transition metal series 221–229 , early transition metals are exceptionally fluorophilic, making them excellent candidates for hydrodefluorination reactions. There are numerous examples in which low-valent early transition metals can mediate C-F bond activation to generate M-F species, including examples with Ti (REFS 230–233 ), Zr (REFS 233–239 ), Hf (REF 240 ), Nb (REFS 241–243 ) and Sc (REF 244 ). The challenge in these systems is rendering them catalytic, as the resultant M-F species is often a considerable thermodynamic sink 245 .…”

β‐Diketiminato Rare‐Earth Metal Complexes: The Influence of Monoatomic Substituents in the N‐aryl Moieties on Structures and Properties

“…Given that C–F bond activation is more difficult due to higher bond dissociation energy than that of C–H bond, ortho ‐fluorinated‐β‐diketiminate ligand HL F [(2,6‐F 2 C 6 H 3 )N = C(Me)CH=C(Me)NH(2,6‐F 2 C 6 H 3 )] was employed to react with rare‐earth metal trialkyl complexes, but the attempt to synthesize dialkyl rare‐earth complexes failed. Reaction of Y(CH 2 SiMe 3 ) 3 (THF) 2 with one equiv.…”