Issue 6, 1979

A comparative dynamic nuclear magnetic resonance study of degenerate enantiomerization and dionate site exchange in octahedral diolatobis(pentane-2,4-dionato)titanium(IV) complexes

Abstract

Dynamic 1H n.m.r. spectroscopy is used to investigate the mechanism of metal-centred rearrangement in the title complexes containing 2,4-dimethylpentane-2,4-diolate, 2,3-dimethylbutane-2,3-diolate, and isopropoxide ligands. The rate of degenerate enantiomerization (k1), determined from the coalescing diolate gem-dimethyl signals, is compared with the rate (k2) of dionate methyl-site exchange. The value of k1/k2 is relatively insensitive to solvent but varies between 2.0 and 1.0 according to the nature of the diolate ligands. The free-energy barriers lie in the range 11.9–16.2 kcal mol–1. The balance of evidence favours a common non-rupture trigonal twisting mechanism for both processes. A higher-energy process (ΔG 25 kcal mol–1) bringing about coalescence of the pentanedionate and acetyl methyl signals in the spectrum of bis(3-acetylpentane-2,4-dionato)(2,4-dimethylpentane-2,4-diolato)-titanium(IV) at 196 °C involves rupture of a Ti–O bond.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1979, 1128-1134

A comparative dynamic nuclear magnetic resonance study of degenerate enantiomerization and dionate site exchange in octahedral diolatobis(pentane-2,4-dionato)titanium(IV) complexes

N. Baggett, D. S. P. Poolton and W. B. Jennings, J. Chem. Soc., Dalton Trans., 1979, 1128 DOI: 10.1039/DT9790001128

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