1,3-DIMETHYLIMIDAZOLIN-2-YLIDENE CARBENE DONOR LIGATION IN LANTHANIDESILYLAMIDE COMPLEXES

The synthesis and X-ray crystal structures of Y[N(SiHMe(2))(2)](3)(car bene), (carbene = 1,3-dimethylimidazolin-2-ylidene, x = 1, 2) are desc ribed. The donor capability of the strongly nucleophilic carbene ligan d is expressed in both the displacement of two THF ligands by one carb ene ligand in precursor compound Y[N(SiHMe(2))(2)](3)(THF)(2) and by t he addition of a second carbene ligand to yield the preferred (3 + 2) trigonal bipyramidal coordination geometry. In particular, the structu ral 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 Pea rson's terminology such carbene ligands have to be classified as hard donor ligands.