A novel Tp(Me2)-supported (Tp(Me2) = tri(3,5-dimethylpyrazolyl)borate) rare earth metal complex promoted Me-Si cleavage of the bis(trimethylsilyl) amide ligand ([(Me3Si)(2)N](-)) was observed. Reaction of Tp(Me2)LnCl(2) with 2 equiv of K[(RN)(2)CN(SiMe3)(2)] (KGua) gave the methylamidinate complexes Tp(Me2)Ln[(RN)(2)CMe][N(SiMe3)(2)] (R = isopropyl, Ln = Y (1(Y)), Er (1(Er)); R = cyclohexyl, Ln = Y (2(Y))) in moderate yields. In contrast, Tp(Me2)YCl(2)(THF) reacted with 1 equiv of KGua to afford a C-N cleavage product Tp(Me2)Y(Cl)N(SiMe3)(2)(THF) (4), indicating that this guanidinate ligand is not stable in the yttrium complex with the Tp(Me2) ligand, and a carbodiimide deinsertion takes place easily. The mechanism for the formation of complexes 1 and 2 was also studied by controlling the substrate stoichiometry and the reaction sequence and revealed that the bis(trimethylsilyl)amine anion N(SiMe3)(2)(-) can undergo two routes of gamma-methyl deprotonation and Si-Me cleavage for its functionalizations. All these new complexes were characterized by elemental analysis and spectroscopic methods, and their solid-state structures were also confirmed by single-crystal X-ray diffraction.