3 years ago

Formation of Methane versus Benzene in the Reactions of (C5Me5)2Th(CH3)2 with [CH3PPh3]X (X=Cl, Br, I) Yielding Thorium-Carbene or Thorium-Ylide Complexes

Formation of Methane versus Benzene in the Reactions of (C5Me5)2Th(CH3)2 with [CH3PPh3]X (X=Cl, Br, I) Yielding Thorium-Carbene or Thorium-Ylide Complexes
Ludovic Castro, Justin R. Walensky, Pokpong Rungthanaphatsophon, Adrien Bathelier, Laurent Maron, Charles L. Barnes, Andrew C. Behrle
The reaction of (C5Me5)2Th(CH3)2 with the phosphonium salts [CH3PPh3]X (X=Cl, Br, I) was investigated. When X=Br and I, two equivalents of methane are liberated to afford (C5Me5)2Th[CHPPh3]X, rare terminal phosphorano-stabilized carbenes with thorium. These complexes feature the shortest thorium–carbon bonds (≈2.30 Å) reported to date, and electronic structure calculations show some degree of multiple bonding. However, when X=Cl, only one equivalent of methane is lost with concomitant formation of benzene from an unstable phosphorus(V) intermediate, yielding (C5Me5)2Th[κ2-(C,C′)-(CH2)(CH2)PPh2]Cl. Density functional theory (DFT) investigations of the reaction energy profiles for [CH3PPh3]X, X=Cl and I showed that in the case of iodide, thermodynamics prevents the production of benzene and favors formation of the carbene. Picky thorium: Reaction of (C5Me5)2Th(CH3)2 with the phosphonium salts [CH3PPh3]X affords terminal thorium-carbene complexes when X=Br and I, showing thorium–carbon multiple bonding. When X=Cl, a thorium-ylide complex is formed.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201706496

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