Mechanism of attack by trialkylphosphines on dicarbonyl(dienyl)iodo-iron complexes
- 1 January 1979
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 12,p. 2003-2010
- https://doi.org/10.1039/dt9790002003
Abstract
The reactions of [Fe(1–5-η-C6H7)(CO)2I] and [Fe(1–5-η-C7H9)(CO)2I] with PBun 3and PPri 3 have been shown to proceed via the stepwise process: [Fe(dienyl)(CO)2I]+ PR3 [graphic omitted] [Fe(R3P.diene)(CO)2I] [graphic omitted] [Fe(R3P.diene)(CO)2(PR3)]I Kinetic studies of the rapid first step with PBun 3 in acetone gave the rate law, Rate =k1[complex][PBun 3] for both complexes. The activation parameters {ΔH1 ‡= 32.2 ± 1.3 kJ mol–1, ΔS1 ‡=–130 ± 3 J K–1 mol–1} and the much faster (ca. 80 times) rate for the C6H7, complex support a mechanism involving direct addition to the dienyl ligands. The complex rate law, Rate =k2K3[complex][PBun 3]///k–2[I–]+k3[PBun 3] , observed in both cases for the much slower second step, indicates a dissociative mechanism for the iodide replacement. ΔH2 ‡= 91.1 ± 4.1 kJ mol–1 and ΔS2 ‡=–32 ± 8 J K–1mol–1 for the iodide dissociation of the C6H7 complex. In contrast to an earlier study, [Fe(1–3-η-C3H5)(CO)3I] has been shown to react with PPh3 and PPri 3 at room temperature to give phosphonium salts [PR3(C3H5)]I. Comparison with other related reactions suggests that in general addition to the π-hydrocarbon ligands by trialkylphosphines is kinetically favoured over attack at the metal.Keywords
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