| Autor: |
Baber, R. Angharad, Collard, Simon, Hooper, Mark, Orpen, A. Guy, Pringle, Paul G., Wilkinson, Matthew J., Wingad, Richard L. |
| Zdroj: |
Dalton Transactions; 2005, Vol. 2005 Issue: 8 p1491-1498, 8p |
| Abstrakt: |
The four arsines, AsC6H3o-CH3p-Z3Z H 2a or OMe 2b and AsC6H3o-CHMe2p-Z3Z H 2c or OMe 2d react with PdCl2NCPh2 or PtCl2NCBut2 to give trans-MCl2L2 or trans-M2Cl2µ-Cl2L2. The crystal structures of trans-PdCl22a2 and PtCl22d2 have been determined, the latter as its dichloromethane solvate. The structures show that in these complexes, the ligands adopt ggatype conformations as do all analogous tri-o-tolyl- and tri-o-isopropylphenylphosphines in square-planar and octahedral complexes. The variable-temperature NMR behaviour of the complexes shows that they are fluxional due to restricted As–C bond rotation. The rate of the fluxionality is more rapid than in the analogous phosphine complexes and this is associated with longer As–C and As–M bonds allowing more free movement. The catalytic activity of the palladium complexes of the arsines and their phosphine analogues for the reaction of 4-bromoacetophenone and n-butyl acrylate has been screened. The results show that the arsines are generally superior to the phosphines as ligands for this catalysis. Trio-isopropylphenylphosphine and trio-isopropylphenylarsine are superior to tri-o-tolylphosphine as ligands for this Heck reaction and a p-methoxy substituent improves the arsine catalyst but not the phosphine catalyst. The phosphine catalysts are superior to the arsine catalysts for the reaction of 4-chloroacetophenone and n-butyl acrylate. These observations are discussed in the context of ligand stereoelectronic effects, as measured by the Tolman electronic parameter, νCOof the NiLCO3 L AsAr3or PAr3. |
| Databáze: |
Supplemental Index |
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