Cerium-carbon dative interactions supported by carbodiphosphorane.

A set of complexes containing dative interactions between a rare-earth metal and carbon are reported. Complex 2, Br3Ce(CDP)(THF), with a Ce←C bond was synthesized by the reaction of CeBr3 with a carbon(0) ligand, carbodiphosphorane (CDP). More significantly, a trivalent cerium complex 3, [BrCe(CDP)2](BPh4)2, with two σ dative interactions C→Ce←C was also isolated, which represents an unusual example of two dative interactions formed with the same atom in a molecule. Furthermore, π donation by the second lone-pair electrons of the CDP ligand is rather weak. Single-crystal X-ray diffraction shows that the Ce-C bond lengths in these complexes are comparable with those in cerium(iii)-carbene species. Density functional theory calculations support the dative interaction formation in these complexes and the strength of σ-donation in 3 is stronger than that in 2.