1,3-dimethylimidazolin-2-ylidene carbene donor ligation in lanthanide silylamide complexes

The synthesis and X-ray crystal structures of Y[N(SiHMe(2))(2)](3)(carbene), (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(SiHMe(2))(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 beta-Si-H(silylamide)-yttrium agostic contacts. According to Pearson's terminology such carbene ligands have to be classified as hard donor ligands.