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Issue 2, 1998
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A theoretical study of [M(PH3)4] (M = Ru or Fe), models for the highly reactive d8 intermediates [M(dmpe)2] (dmpe = Me2PCH2CH2PMe2). Zero activation energies for addition of CO and oxidative addition of H2

Abstract

Density functional calculations have been carried out on [M(PH3)4] species as models for transient [M(dmpe)2] formed from the photolysis of [M(dmpe)2H2] (M = Ru or Fe, dmpe = Me2PCH2CH2PMe2). Calculations have also been performed on [Rh(PH3)4]+ as a model for the relatively inert [Rh(dmpe)2]+. The singlet electron configurations of [Ru(PH3)4] and [Rh(PH3)4]+ were found to have D2d geometries with trans P–M–P angles of 159 (M = Ru) and 172° (M = Rh+). Singlet [Fe(PH3)4] was computed to have a C2v structure with trans P–M–P angles of 137 and 160° at Fe. The triplet configurations of [Fe(PH3)4] and [Ru(PH3)4] were predicted to adopt C2v geometries with angles of ca. 155 and 95° for both species. Singlet [Ru(PH3)4] is calculated to be 11.7 kcal mol–1 more stable than the triplet, but the triplet form of [Fe(PH3)4] is the more stable by 8.0 kcal mol–1. The addition of CO and oxidative addition of H2 to [M(PH3)4] (M = Ru or Fe) were calculated to be highly exothermic. In contrast, the reaction between [Rh(PH3)4]+ and H2 is less thermodynamically favoured, consistent with the lower reactivity of experimental Rh+ analogues. Both the oxidative addition of H2 and addition of CO were calculated to proceed without activation energy for [Ru(PH3)4], but only once the ‘end-on’ approach of H2 and an angled approach of CO at long ruthenium–substrate separations are considered. The calculations on [Ru(PH3)4] also reproduced the UV/VIS spectrum and geometry of [Ru(dmpe)2] satisfactorily. The reaction of singlet [Fe(PH3)4] with CO was calculated to be barrierless, while the oxidative addition of H2 required a very small activation energy (≈1 kcal mol–1) at long Fe–H2 distances. The reaction of [Rh(PH3)4]+ with H2 has a somewhat larger activation barrier (≈3 kcal mol–1) and is predicted to pass through a product-like C2v transition state.

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Supplementary files


Article type: Paper
DOI: 10.1039/A706081E
Citation: J. Chem. Soc., Dalton Trans., 1998,0, 291-300
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    A theoretical study of [M(PH3)4] (M = Ru or Fe), models for the highly reactive d8 intermediates [M(dmpe)2] (dmpe = Me2PCH2CH2PMe2). Zero activation energies for addition of CO and oxidative addition of H2

    S. A. Macgregor, O. Eisenstein, M. K. Whittlesey and R. N. Perutz, J. Chem. Soc., Dalton Trans., 1998, 0, 291
    DOI: 10.1039/A706081E

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