1,3-Dimethylimidazolin-2-ylidene Carbene Donor Ligation in Lanthanide Silylamide Complexes

The synthesis and X-ray crystal structures of Y[N(SiHMe2)2]3(carbene)x (carbene = 1,3-dimethylimidazolin-2-ylidene, x = 1, 2) are described. The donor capability of the strongly nucleophilic carbene ligand is expressed in both the displacement of two THF ligands by one carbene ligand in precursor compound Y[N(SiHMe2)2]3(THF)2 and by the addition of a second carbene ligand to yield the preferred (3 + 2) trigonal bipyramidal coordination geometry. In particular, the structural data reveal that the carbene ligands affect the coordination mode of the bis(dimethylsilyl)amide counterligands by forcing them to form close β-Si−H(silylamide)−yttrium agostic contacts. According to Pearson's terminology such carbene ligands have to be classified as hard donor ligands.