Issue 16, 2004

Theoretical studies of the oxidative addition of azolium salts to a model Wilkinson's catalyst

Abstract

The oxidative addition of 1,3-dimethylimidazolium to a model Wilkinson's catalyst (RhCl(PH3)3) has been studied with density functional calculations (B3LYP). According to our free energy calculations, the octahedral rhodium carbene hydride product forms from initial predissociation of a phosphine molecule to subsequently form a 5 ligand intermediate; however, results indicate that a six ligand, associative route with a concerted three-centred transition structure may also be competitive. Exchange of the phosphine molecule on the metal centre with trimethylphosphine had a significant effect in lowering the barrier to oxidative addition and decreasing the endothermicity of the reaction. Solvation was found to have a moderate effect on the overall reaction. Bulk solvent calculations reflected a relative stabilisation of reactants for both pathways, resulting in an endothermic overall reaction. A study of alternative azolium salts revealed the saturated 1,3-dimethyl-4,5-dihydroimidazolium resulted in little change to the reaction geometries or energies, while the use of 3-methylthiazolium salt significantly reduced the barrier to addition and increased the exothermicity of the reaction considerably.

Graphical abstract: Theoretical studies of the oxidative addition of azolium salts to a model Wilkinson's catalyst

Article information

Article type
Paper
Submitted
11 May 2004
Accepted
25 Jun 2004
First published
22 Jul 2004

Dalton Trans., 2004, 2505-2513

Theoretical studies of the oxidative addition of azolium salts to a model Wilkinson's catalyst

K. J. Hawkes, D. S. McGuinness, K. J. Cavell and B. F. Yates, Dalton Trans., 2004, 2505 DOI: 10.1039/B407088G

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