The dependence on temperature and concentration of ¹²⁹Xe NMR chemical shift values of organoxenon(II) salts [RXe][Y] and of the parent molecule XeF₂

Abstract

The dependence of the 129Xe NMR chemical shift value of XeF2 on temperature and concentration was determined in a variety of prototypic media: in acidic (anhydrous HF, aHF), nonprotic but polar (dichloromethane), and basic (CD3CN-EtCN, 1:3 v/v) solvents. The 129Xe NMR spectra of a representative series of organoxenon(II) salts [RXe][Y] (R = C6F5, heptafluoro-1,4-cyclohexadien-1-yl (cyclo-1,4-C6F7), pentafluoro-1,4-cyclohexadien-3-on-1-yl (cyclo-3-O-1,4-C6F5), CF2=C(CF3), (CF3)2CFC[triple bond]C, C4H9C[triple bond]C; Y = BF4, AsF6) in aHF showed, compared with XeF2-aHF, a quantitatively less distinct but qualitatively related dependence of delta(129Xe) vs temperature. The dependence of their delta(129Xe) values on concentration in aHF is negligible. An explanation for the different behavior of [RXe][Y] and XeF2 is offered.

Syntheses, Solution Multi-NMR Characterization, and Reactivities of [C6F5Xe]+ Salts of Weakly Coordinating Borate Anions, [BY4]- (Y = CF3, C6F5, CN, or OTeF5)

“…The 129 Xe NMR chemical shifts of [C 6 F 5 Xe][BY 4 ] and [C 6 F 5 Xe][BF 4 ] in CH 3 CN at 24 °C differ only slightly, ranging from −3792.6 ([B(CN) 4 ] - ) to −3802.8 ppm ([BF 4 ] - ), having spin−spin coupling constants of 3 J ( 19 F o − 129 Xe) = 66.6 ([BF 4 ] - ) to 67.6 Hz ([B(C 6 F 5 ) 4 ] - ), 4 J ( 19 F m − 129 Xe) = 8.6 ([BF 4 ] - ) to 9.1 Hz ([B(C 6 F 5 ) 4 ] - ), and 5 J ( 19 F p − 129 Xe) = 3.6 ([B(CF 3 ) 4 ] - ) to 4.2 Hz ([BF 4 ] - ) (Table ). The temperature dependencies of the 129 Xe NMR chemical shifts of [C 6 F 5 Xe] + salts are in good agreement with the previously published results for [C 6 F 5 Xe][AsF 6 ] in CD 3 CN/C 2 H 5 CN (1:3, v/v) of −0.35 ppm K -1 . The 129 Xe NMR chemical shifts of the [C 6 F 5 Xe][BY 4 ] salts in CH 3 CN at −40 °C (−3772.2 to −3783.0 ppm) are only slightly shifted to higher frequency when compared with that of C 6 F 5 XeF (−3793.4 ppm) in CH 2 Cl 2 at −40 °C.…”

“…F 5 Xe] + salts are in good agreement with the previously published results for[C 6 F 5 Xe][AsF 6 ] in CD 3 CN/ C 2 H 5 CN (1:3, v/v) of -0.35 ppm K -1 36. The129 Xe NMR chemical shifts of the[C 6 F 5 Xe][BY 4 ] salts in CH 3 CN at -40 °C (-3772.2 to -3783.0 ppm) are only slightly shifted to higher frequency when compared with that of C 6 F 5 XeF (-3793.4 ppm) in CH 2 Cl 2 at -40 °C.…”

Two New Types of Xenon–Carbon Species: The Zwitterion, 1-(Xe+)C6F4-4-(BF3–), and the Dication, [1,4-(Xe)2C6F4]2+

“…No significant temperature dependence of the δ- ( 19 F) and 3 J -values ( 129 Xe– 19 F) was found in aHF and CH 3 CN. The temperature dependence of the 129 Xe NMR shift of 1 and 3 in aHF is of comparable magnitude and is significantly lower than that of XeF 2 . The observed solvent dependence reflects the individual coordination property of the three solvents to the electrophilic xenon center as shown for F 2,6 (δ( 19 F) = −126.8 ppm (aHF, −10 °C), −129.3 ppm (27% aq HF, 24 °C), and −129.9 ppm (CH 3 CN, 24 °C) and Xe (δ( 129 Xe) = −3982 ppm, aHF, −10 °C, 3 J ( 129 Xe– 19 F) = 53 Hz) and (−3858 ppm, CH 3 CN, 0 °C, 3 J ( 129 Xe– 19 F) = 60 Hz).…”

“…The temperature dependence of the 129 Xe NMR shift of 1 and 3 in aHF is of comparable magnitude and is significantly lower than that of XeF 2 . 18 The observed solvent dependence reflects the individual coordination property of the three solvents to the electrophilic xenon center as shown for 2,6 ) and δ( 129 Xe) in 1 relative to 3 was observed in aHF and CH 3 CN solutions. Opposite to 1 the F 2,6 resonance of 3 appears deshielded from F 3,5 .…”

Organoxenonium Salts: Synthesis by "Xenodeborylation", Reactivities, and NMR Spectroscopic Properties

“…Later XeOF 4 was recommended by IUPAC as standard reference for l29 Xe NMR spectroscopy (52). Recently, the dependence of the 129 Xe NMR chemical shift of XeE 2 as well as of a representative series of organoxenonium(II) salts [RXe]Y on temperature and concentration was determined in a prototypic variety of media, in acidic anhydrous HF (aHF), weakly polar aprotic (dichloromethane), and basic (CD 3 CN -EtCN, 1 : 3 v/v) solvents (53)]. This allows the direct comparison of ,29 Xe NMR chemical shifts measured at various temperatures in these solvents, and for convenience, all 5( 129 Xe) values discussed below were extrapolated to -30 °C using these data (53).…”