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- Title
A Variable-Pressure 2D <sup>1</sup>H-NMR Study of the Mechanism of Trimethyl Phosphate Intermolecular Exchange and cis/ trains-Isomerisation of Tetrachlorobis(trimethyl phosphate)zirconium(IV).
- Authors
Frey, Urban; Helm, Lothar; Merbach, André E.
- Abstract
In chloroform, [ZrCl4·2(MeO)3PO] exists in both cis- and trans-isomeric forms. Three reactions can be envisaged in the presence of excess (MeO)3PO = L: ( 1) cis-[ZrCl4·2L] + *L⇆ cis-[ZrCl4·L*L]+ L; ( 2) trans-[ZrCl4·2L] + *L ⇆ trans-[ZrCl4·L*L] + L; ( 3) cis-[ZrCl4·2L]⇆ trans-[ZrCl4·2L]. To distinguish between these possible reaction pathways, we have used 2D 1H-NMR spectroscopy. For the first time, variable-pressure 2D exchange spectra were used for mechanistic assignments. cis/ trans-Isomerisation was found to be the fastest reaction (in CHCl3/CDCl3), with a small acceleration at higher pressure: it is concluded to be an intramolecular process with a slightly contracted six-coordinate transition state. The intermolecular (MeO)3PO exchange on the cis- and trans-isomer are second-order processes and are strongly accelerated by increased pressure: Ia mechanisms are suggested without ruling out limiting A mechanisms.
- Publication
Helvetica Chimica Acta, 1990, Vol 73, Issue 1, p199
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/hlca.19900730123