Amination of acetonitrile by the amines MeNH 2, Pr n NH 2, Pr i NH 2, Bu t NH 2, and Et 2NH is efficiently promoted by the lanthanide iodides LnI 2 (Ln = Nd, Dy, Tm), LnI 3 (Ln = Pr, Nd, Dy) and LnI 3(THF) 3 (Ln = Pr, Nd, Dy). The formed mono- and N, N′-disubstituted amidines MeC( NH)NHR (R = Pr i , Bu t ), MeC( NH)NEt 2, MeC( NR)NHR (R = Me, Pr n ) were isolated mainly as the complexes with starting iodide of general composition LnI 2(amidine) x ( 1) or LnI 3(amidine) x ( 2) ( x = 3–8). In the products 1, which evidently are the mixtures of LnI 2+, LnI 2 + and LnI 3 derivatives, the metal exists in trivalent state but one of the ligands actually is amidinate anion. A part of the generated amidines remains in the reaction solutions in free form. Heating of the 1 and 2 in vacuum at 150–200 °C affords corresponding amidine and the complexes with reduced amount of the amidine ligands LnI 2(amidine) y ( 3) or LnI 3(amidine) y ( 4) ( y = 2–3). The products 3 and 4 displayed the same catalytic activity in the acetonitrile-amine cross-coupling as the initial iodides. SmI 2 and especially YbI 2 revealed lower activity. The structure of isopropylacetamidine ( 5), tert-butylacetamidine ( 6) and {Dy[MeC( NH)NEt 2] 6}I 3(MeCN) ( 7) were determined by X-ray diffraction analysis.