A series of lanthanide amide complexes supported by bridged bis(amidinate) ligand L, LLnNHAr1(DME) (L = [Me3SiNC(Ph)N(CH2)3NC(Ph)NSiMe3], Ar1 = 2,6-iPr2C6H3, DME = dimethoxyethane, Ln = Y (1), Pr (2), Nd (3), Gd (4), Yb (5)), [Yb(μ2-NHPh)]2(μ2-L)2 (6) and [LYb]2(μ2-NHAr2)2 (7) (Ar2 = (o-OMe)C6H4), were synthesized by reaction of LLnCl(THF)2 with the corresponding lithium amide in good yields and structurally characterized by X-ray crystal structure analyses. All complexes were found to be precatalysts for the catalytic addition of aromatic amines to aromatic nitriles to give monosubstituted N-arylamidines. The catalytic activity was influenced by lanthanide metals and the amido groups with the active sequence of Y (1) < Gd (4) < Nd (3) < Pr (2) ∼ Yb (5) for the lanthanide metals and –NHAr2 < –NHPh < –NHAr1 for the amido groups. The catalytic addition reaction with complex 5 showed a good scope of aromatic amines. Some key reaction intermediates were isolated and structurally characterized, including the amidinate complexes LLn[NPhCNAr1](PhCN) (Ln = Y (8), Ln = Yb (9)), LYb[NAr2CNAr1](Ar2CN) (10), and amide complex 5 prepared by protonation of 9 by Ar1NH2. Reactivity studies of these complexes suggest that the present catalytic formation of monosubstituted N-arylamidines proceeds through nucleophilic addition of an amido species to a nitrile, followed by amine protonolysis of the resultant amidinate species.