Facile Ni(II)/Ketoxime-Mediated Conversion of Organonitriles into Imidoylamidine Ligands. Synthesis of Imidoylamidines and Acetyl Amides

• Published in: Inorganic chemistry 2003-11, Vol.42 (22), p.7239-7248
• Main Authors: Kopylovich, Maximilian N, Pombeiro, Armando J. L, Fischer, Andreas, Kloo, Lars, Kukushkin, Vadim Yu
• Format: Article
• Language: English
• Subjects: acyclic imides; amidines; complexes; coordinated nitriles; crystal-structure; metal-mediated hydrolysis; nickel(ii) site; nitro-compounds; phospha-s-triazines; samarium(ii) iodide
• ISSN: 0020-1669; 1520-510X; 1520-510X
• DOI: 10.1021/ic0349813

Treatment of alkyl nitriles with NiX2·6H2O (X = Cl, NO3) and 2-propanone oxime, followed by (X = Cl) addition of [i-Pr4N](NO3) for precipitation of the product, resulted in the formation of amidinium nitrates [RC(NH2)NH2](NO3) (R = Me, Et, n-Pr). The reaction went to another direction with NiX2·2H2O, i.e., the reaction between neat RCN (R = Me, Et, n-Pr, i-Pr, n-Bu, CH2Cl, CH2C6H4OMe-p) and NiCl2·2H2O/2-propanone oxime (other ketoximes can also be used) gave the (imidoylamidine)Ni(II) complexes [Ni{N(H)C(R)NHC(R)NH}2]2+ (1 2+−7 2+). The latter were isolated in good yields (65−91%) as the bis-chloride salts 1·Cl2−6·Cl2 and the mixed salt 7·(Cl)(p-MeOC6H4CH2CO2). Remarkably, the latter transformation does not proceed at all if NiCl2·2H2O or the ketoxime are taken alone. Liberation of imidoylamidines was performed for one alkyl-containing complex [2·Cl2] and one benzyl-containing complex [7·(Cl)(p-MeOC6H4CH2CO2)], by (i) addition of HBF4·Et2O to the acetonitrile solution of the complexes to yield [N(H)C(R)NHC(R)NH]·2HBF4 (R = Et 8 and R = CH2C6H4OMe-p 9) or (ii) substitution for ethanediamine (en) with following precipitation of the complex [Ni(en)3]Cl2 with formation of free N(H)C(R)NHC(R)NH (R = Et 10 and R = CH2C6H4OMe-p 11). In contrast to the liberation in nonaqueous media, treatment of 2·Cl2 and 7·(Cl)(p-MeOC6H4CH2CO2) with Na2EDTA·2H2O in water−methanol solutions led to substitution and hydrolysis to furnish the acyl amides {EtC(O)}2NH (12) and {p-MeOC6H4CH2C(O)}2NH (13). Alternatively, 12 and 13 were obtained by hydrolysis of 10 and 11 in water at pH ca. 8.5. It was shown that the oxime complexes trans-[NiCl2(C4H8CNOH)4] (14) or cis-[Ni(O,O-NO3)2(C4H8CNOH)2] (15) can be intermediates in the formation of amidines and imidoylamidines. The sequence of the Ni(II)/oxime mediated formation of (imidoylamidine)Ni complexes and liberation (or hydrolytic liberation) of the ligands opens up a novel, facile and environmentally benign route to imidoylamidines and acyl amides.