Nuclear magnetic resonance studies of alkali metal anions

Abstract

The NMR chemical shift and line width has been measured for 23Na~in tetrahydrofuran (THF), ethylamine (EA), and methylamine (MA), for 87Rb~in THF and EA, and for 133Cs~in THF. In all cases, the counterion was the 2,2,2 cryptate complex of the corresponding cation. The chemical shift of Na~i s, within experimental error, the same as that calculated for the gaseous anion (based upon the measured value for the gaseous atom) and is independent of solvent. Comparison with the solvent-dependent chemical shift of Na+ provides conclusive evidence that Na" is a "genuine" anion with two electrons in a 3s orbital which shield the 2p electrons from the influence of the solvent. The line width increases from THF to EA to MA, suggesting either an increasing exchange rate with the cryptated cation or, more probably, the influence of an increasing concentration of solvated electrons. In the case of sodium solutions in all solvents, both Na+C and Naare detected by their NMR peaks. However, probably because of extreme line broadening, Rb+C and Cs+C are not observed, but only the relatively narrow line of the corresponding anion. The chemical shifts (diamagnetic shift in ppm from the infinitely dilute aqueous ion) are 185 and 197 for Rb" in EA and THF, respectively, and 292 for Cs~in THF, compared with 212 and 344, respectively, for the gaseous Rb and Cs atoms. When 18-crown-6 is used instead of the 2,2,2 cryptand complex, it is still possible to obtain solutions which are about 0.4 M in total metal when methylamine is used as the solvent. However, in this case, both the Naand the Na+C NMR peaks are exchange broadened, even at -50°C, and coalesce as the temperature is raised to about -15 to 0°C, depending upon the concentrations. The variation of the rate of exchange of the sodium nucleus between Na+C and Nawith concentration should permit determination of the exchange mechanism. Possible exchange mechanisms and the information obtainable from them are discussed.

The Electronic Properties of Metal Solutions

“…spectra of Na-, Rb-and Cs-have now been reported. 61 The chemical shift of Na-, large and diamagnetic, is the same as that calculated for the gaseous anion and is essentially independent of solvent. The apparent absence of a large paramagnetic shift of Na-upon solvation and the independence of solvent, have been in support of a model in which solvent is excluded from the region occupied by the sodium 2p electrons.…”

Strategies for the preparation of compounds of alkali metal anions

“…Both of these predictions have been shown to be correct in this case. The solubility of sodium in MA in the presence of either complexing agent is a t least 0.1 M and the integrated intensities of the *3Na NMR absorptions of Na+C222 and Na-are equal within experimental error, 11,12 showing that the relative concentration of esolv-is low.…”

Electron-transfer reduction of selected alcohols with alkalide K−, K+(15-crown-5)2 via organometallic intermediates

“…Gaseous reaction products were searched for by GC with a 2.4-m stainless steel column packed with Al 2 O 3 , 0.02-0.03 mm, deactivated with 5% K 2 CO 3 in an INCO 505 gas chromatograph equipped with a flame ionization detector. 1 H and 13 C NMR spectra were recorded at 20°C on a Varian VXR-300 multinuclear spectrometer at the 1 H resonance frequency of 300 MHz, and at the 13 C resonance frequency of 75 MHz. Deuterated acetone was used as the solvent.…”

“…Mass spectrum (m=e): 134 [M þ , 4]; 116 (7); 105 (11); 91 (100); 77 (7); 65 (30); 51 (9); 39 (11). 1 H and 13 C NMR spectra (in CDCl 3 ) have been already presented in [39,40].…”

“…Alkalides, M À , M þ C, are salts containing alkali metal anions and cations complexed by a ligand, e.g., crown ether [1][2][3][4]. They are known as two-electron-transfer species [5], used in the reactions with alkenes [6][7][8][9], alkines [10], alkyl halides [11,12], silyl halides [13], ketones [14,15], esters [16][17][18][19][20], and ethers [12,[20][21][22][23][24][25][26][27][28].…”