Lanthanide iodides as promoters of acetonitrile amination. Molecular structure of MeC(NH)NHPri, MeC(NH)NHBut and {Dy[MeC(NH)NEt2]6}I3

Amination of acetonitrile by the amines MeNH2, PrnNH2, PriNH2, ButNH2, and Et2NH is efficiently promoted by the lanthanide iodides LnI2 (Ln = Nd, Dy, Tm), LnI3 (Ln = Pr, Nd, Dy) and LnI3(THF)3 (Ln = Pr, Nd, Dy). The formed mono- and N,N′-disubstituted amidines MeC(NH)NHR (R = Pri, But), MeC(NH)NEt2, MeC(NR)NHR (R = Me, Prn) were isolated mainly as the complexes with starting iodide of general composition LnI2(amidine)x (1) or LnI3(amidine)x (2) (x = 3–8). In the products 1, which evidently are the mixtures of LnI2+, LnI2+ and LnI3 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 LnI2(amidine)y (3) or LnI3(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. SmI2 and especially YbI2 revealed lower activity. The structure of isopropylacetamidine (5), tert-butylacetamidine (6) and {Dy[MeC(NH)NEt2]6}I3(MeCN) (7) were determined by X-ray diffraction analysis.

Graphical abstractLanthanide iodides LnI2 and LnI3 effectively catalyze amination of acetonitrile to give mono- and disubstituted amidines. Intermediate complex {Dy[MeC(NH)NEt2]6}I3 and the amidines MeC(NH)NHiPr and MeC(NH)NHt-Bu were characterized structurally.Figure optionsDownload full-size imageDownload as PowerPoint slide