A series of four coordinate rare earth metal amides with general formula {(CH2SiMe2)[(2,6-'Pr2C6H3)N](2)}LnN-(SiMe3)(2)(THF) [(Ln = Yb(2), Y (3), Dy (4), Sm (5), Nd (6)] containing a diamido ligand (CH2SiMe2)[(2,6-(Pr2C6H3)-Pr-i)N](2)(2-) with a CH2SiMe2 link were synthesized in good yields via reaction of [(Me3Si)(2)N](3)Ln(III)(mu-Cl)Li(THF)(3) with the corresponding diamine (CH2SiMe2)[(2,6-(Pr2C6H3)-Pr-i)NH](2) (1). All compounds were fully characterized by spectroscopic methods and elemental analyses. The structures of complexes 2, 3, 4, 5, and 6 were determined by single-crystal X-ray analyses. Investigation of the catalytic properties of the complexes indicated that all complexes exhibited a high catalytic activity on the cyclotrimerization of aromatic isocyanates, which represents the first example of cyclopentadienyl-free rare earth metal complexes exhibiting a high catalytic activity and a high selectivity on cyclotrimerization of aromatic isocyanates. The temperatures, solvents, catalyst loading, and the rare earth metal effects on the catalytic activities of the complexes were examined.