Abstract
Combined use of 1H, 13C, and 51V NMR spectroscopy shows that the interaction of VOCl3 with 2 equiv of a ketone in solution at low temperatures produces complex mixtures of neutral and ionic adducts. In contrast, vanadium dichloride isopropoxide (4) forms neutral 1:2 adducts under similar conditions. These adducts are presumably octahedral, with ketones trans to the oxo and alkoxy oxygens. Bound and free ketones exchange by dissociation with free energies of activation near 7 kcal/mol. Analysis of the temperature dependence of the 51V chemical shift of mixtures of compound 4 and excess pinacolone gives ΔH = -10.9 kcal/mol and ΔS = -51 eu for the formation of the 1:2 adduct. At low temperatures, solutions of compound 4 containing 1 equiv of a ketone consist primarily of a 1:1 mixture of free compound 4 and the neutral 1:2 adduct. Vanadyl dichloride alkoxide 6, a bidentate Lewis acid, behaves similarly, and solutions containing 1 equiv of a ketone consist largely of free compound 6 and its unsymmetric 1:2 adduct 8. Significant amounts of symmetric 1:1 adduct 9 with a cooperatively bound carbonyl ligand are not formed, and no other unusual chemical effects can be attributed to the special juxtaposition of electrophilic sites in bidentate Lewis acid 6.
Original language | English |
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Pages (from-to) | 3026-3032 |
Number of pages | 7 |
Journal | Inorganic Chemistry |
Volume | 30 |
Issue number | 15 |
DOIs | |
State | Published - Jul 1 1991 |