Water-soluble organometallic compounds. 3. Kinetic investigations of dissociative phosphine substitution processes involving water-soluble Group 6 metal derivatives in miscible aqueous/organic media
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Mechanistic aspects of ligand substitution reactions of group 6 metal carbonyl derivatives containing the trisulfonated phosphine P(m-C6H4SO3Na)3 (hereafter referred to as TPPTS) in pure water and water/THF media have been investigated by examination of the reactions of these derivatives with carbon monoxide as an incoming ligand. The reactions, which were carried out under 500 psi of CO in the temperature range 110–160 °C, were monitored in situ by infrared spectroscopy employing a cylindrical internal reflectance reactor. Kinetic measurements show the reactions are first-order in metal complex concentration and independent of CO pressure at high CO pressures, and the rates are retarded by added TPPTS. The activation parameters for TPPTS dissociation from M(CO)5TPPTS derivatives (M = Mo, W), e.g., in 1:1 THF/H2O, ΔH* = 28.8 ± 1.4 kcal/mol and ΔS* = −4.2 ± 3.5 eu and ΔH* = 31.8 ± 1.5 kcal/mol and ΔS* = −0.73 ± 3.6 eu, respectively were shown to be quite similar to those determined for the analogous processes involving the nonsulfonated PPh3 ligand in the same solvent systems. In addition only small solvent effects were noted in going from aqueous to organic solvents for these dissociative processes. For the cis-Mo(CO)4[TPPTS]2 derivative, in which the sodium ions are encapsulated by a cryptand, kryptofix-221, a steric acceleration of TPPTS dissociation is noted relative to its PPh3 analog. The steric requirements of the TPPTS ligand were defined by X-ray structural data obtained on [Na-kryptofix-221]3[W(CO)5P(C6H4SO3)3] and Fe(CO)4-TPPTS. By way of contrast for the cis-Mo(CO)4[TPPTS]2 derivative in which the Na+ ions are free to interact with the sulfonate groups, a stabilizing effect is noted which is attributed to intramolecular interligand interactions via the Na+ cations. In the case of cis-W(CO)4[TPPTS]2 and cis-W(CO)4[PPh3]2 an intramolecular rearrangement to the corresponding trans product was observed. © 1993, American Chemical Society. All rights reserved.
author list (cited authors)
Darensbourg, D. J., & Bischoff, C. J.