Evidence for C−F Bond Formation through Formal Reductive Elimination from Tellurium(VI)

Abstract

The fundamental challenge of C−F bond formation by reductive elimination has been met by compounds of select transition metals and fewer main group elements. The work detailed herein expands the list of main group elements known to be capable of reductively eliminating a C−F bond to include tellurium. Surprising and novel modes of both sp2 and sp3 C−F bond formation were observed alongside formation of TeIV cations during two separate attempts to synthesize/characterize fluorinated organotellurium(VI) cations in superacidic media (SbF5/SO2ClF). Following detailed low‐temperature NMR experiments, the mechanisms of the two unique reductive elimination reactions were probed and investigated using density functional theory (DFT) calculations. Ultimately, we found that an “indirect” reductive elimination pathway is likely operative whereby Sb plays a key role in fluoride abstraction and C−F bond formation, as opposed to unimolecular reductive elimination from a discrete TeVI cation.

Air-stable aryl derivatives of pentafluoroorthotellurate

“…The easy access to these compounds has therefore allowed the study of the properties and reactivity of the TeF 5 moiety. 11,18,19 Compound PhTeF 5 was found to be an air-stable molecule, in contrast to previous descriptions, yet could be hydrolysed quantitatively to cis -PhTeF 4 OH in a mixture of acetonitrile and water. 18…”

“…The easy access to these compounds has therefore allowed the study of the properties and reactivity of the TeF 5 moiety. 11,18,19 Compound PhTeF 5 was found to be an air-stable molecule, in contrast to previous descriptions, yet could be hydrolysed quantitatively to cis-PhTeF 4 OH in a mixture of acetonitrile and water. 18 Herein we report on the synthesis and characterization of two different aryl-substituted derivatives of the pentafluoroorthotellurate, namely [cis-PhTeF 4 O] À and [trans-(C 6 F 5 ) 2 TeF 3 O] À , 20 and their corresponding Brønsted acids.…”

“…The OÁ Á ÁO distance is 270.7 pm, therefore being in the expected range for such noncovalent interaction. 21 The 19 F NMR spectrum of 1 shows the characteristic ABC 2 X spin system with signals at À25.8, À47.0, and À50.5 ppm and corresponding 2 J( 19 F, 19 F) coupling constants of 148, 134, and 109 Hz. The NMR spectroscopic data are in agreement with those previously reported by Togni et al, 18 and are also comparable with the signals reported for cis-PhTeF 4 Cl.…”

“…18,26 More interestingly, it shows the tolerance of the system to compounds with ortho-substituted aromatics, in contrast to previous assumptions. 18 The trans arrangement of the two C 6 F 5 rings at the Te centre is easily assigned from the 19 F NMR spectrum, as only one resonance for the equatorial fluorine atoms is observed. It appears as a quintet at a chemical shift of À21.4 ppm, with coupling constants of 4 J( 19 F, 19 F o ) = 19 Hz and 1 J( 19 F, 125 Te) = 3104 Hz.…”

“…18 The trans arrangement of the two C 6 F 5 rings at the Te centre is easily assigned from the 19 F NMR spectrum, as only one resonance for the equatorial fluorine atoms is observed. It appears as a quintet at a chemical shift of À21.4 ppm, with coupling constants of 4 J( 19 F, 19 F o ) = 19 Hz and 1 J( 19 F, 125 Te) = 3104 Hz. The 125 Te NMR spectrum shows a quintet of multiplets at 770 ppm due to coupling of the tellurium to the four directly bound equatorial F, as well as to the fluorine atoms of the aromatic rings.…”