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Straightforward Synthesis of Donor‐Stabilised Phosphenium Adducts from Imidazolium‐2‐carboxylate and Their Electronic Properties
Author(s) -
Azouri Michèle,
Andrieu Jacques,
Picquet Michel,
Richard Philippe,
Hanquet Bernard,
Tkatchenko Igor
Publication year - 2007
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200700590
Subject(s) - chemistry , lone pair , cationic polymerization , steric effects , carboxylate , lewis acids and bases , coordination complex , catalysis , rhodium , adduct , acceptor , medicinal chemistry , inorganic chemistry , polymer chemistry , metal , organic chemistry , molecule , physics , condensed matter physics
Cationic imidazolium‐2‐phosphanes were obtained by the addition of a chlorophosphane (R 2 PCl, R = Ph, i Pr or Cy) to 1,3‐dimethylimidazolium‐2‐carboxylate without the need for a purification step. An additional anion exchange reaction with KPF 6 led to the corresponding halide‐free ligands in excellent yields. The molecular structure of one of them was examined both in the solid state and in solution. The lone pair of electrons on the phosphorus atom is not delocalised to the imidazolium fragment and thus remains available for further metal coordination. As such compounds can be described as phosphenium cations stabilised by a N‐heterocarbene donor base, the electronic properties of the Lewis acceptor phosphorus centre was evaluated upon nickel tricarbonyl coordination, and the properties are surprisingly similar to those found for phosphites. The stronger π‐acceptor character of these imidazolium‐2‐phosphanes relative to that of neutral tertiary phosphanes can thus explain the higher catalytic activities observed with the corresponding rhodium complexes in styrene hydroformylation reactions. Additionally, a preliminary study of platinum coordination chemistry indicated that the steric demand of 1,3‐dimethylimidazolium‐2‐phosphanes is comparable to mixed arylalkylphosphanes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)