NHC-derived bis(amidiniophosphine) ligands of Rh(I) complexes: versatile cis-trans chelation driven by an interplay of electrostatic and orbital effects.
The synthesis, structure, and electronic properties of a dicationic bis(amidiniophosphine) based on an o-phenylene bridge is described. In spite of the presence of two facing P-conjugated positive charges, this electron-poor diphosphine is shown to act as a versatile chelating ligand in a series of stable rhodium(I) complexes. IR analysis of a carbonyl complex showed that the sigma-donating versus pi-accepting character of the cationic ligand is comparable to that of a neutral trialkylphosphite. While the ligand is trans-chelating at a neutral Rh(I) center, it switches to cis-chelating at a cationic Rh(+) center. This and other unusual geometrical features revealed by X-ray diffraction analyses are interpreted by a subtle interplay between antisymbiotic trans preference, electrostatic repulsion, and relative Lewis acidity of the transition metal centers.
CNRS, Laboratoire de Chimie de Coordination, 205, route de Narbonne, F-31077 Toulouse, France. yves.canac@lcc-toulouse.fr
Yves
Y
Canac
Nathalie
N
Debono
Laure
L
Vendier
Remi
R
Chauvin