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A theoretical study of [M(PH3)(4)] (M = Ru or Fe), models for the highly reactive d(8) intermediates [M(dmpe)(2)] (dmpe = Me2PCH2-CH2PMe2). Zero activation energies for addition of CO and oxidative addition of H-2

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JournalJOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
DatePublished - 21 Jan 1998
Issue number2
Number of pages10
Pages (from-to)291-300
Original languageEnglish

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)(2)H-2] (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 D-2d geometries with trans P-M-P angles of 159 (M = Ru) and 172 degrees (M = Rh+). Singlet [Fe(PH3)(4)] was computed to have a C-2v structure with trans P-M-P angles of 137 and 160 degrees at Fe. The tripler configurations of [Fe(PH3)(4)] and [Ru(PH3)(4)] were predicted to adopt C-2v geometries with angles of ca. 155 and 95 degrees 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 H-2 to [M(PH3)(4)] (M = Ru or Fe) were calculated to be highly exothermic. In contrast, the reaction between [Rh(PH3)(4)](+) and H-2 is less thermodynamically favoured, consistent with the lower reactivity of experimental Rh+ analogues, Both the oxidative addition of H-2 and addition of CO were calculated to proceed without activation energy for [Ru(PH3)(4)](+) but only once the 'end-on' approach of H-2 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 H-2 required a very small activation energy (approximate to 1 kcal mol(-1)) at long Fe-H-2 distances. The reaction of [Rh(PH3)(4)](+) with H-2 has a somewhat larger activation barrier (approximate to 3 kcal mol(-1)) and is predicted to pass through a product-like C-2v transition state.

    Research areas

  • TRANSITION-METAL COMPLEXES, DENSITY-FUNCTIONAL THEORY, ORGANOMETALLIC REACTION-MECHANISMS, COORDINATIVELY UNSATURATED RHCL(PH3)2, BOND-DISSOCIATION ENERGIES, H-H ACTIVATION, MOLECULAR-STRUCTURES, NEUTRON-DIFFRACTION, METHANE ACTIVATION, X-RAY

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