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

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+ (12+-72+). The latter were isolated in good yields (65-91%) as the bis-chloride salts 1·Cl2-6·Cl2 and the mixed salt 7·(Cl)(pMeOC6H4CH2CO2). 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)(pMeOC6H4CH2CO2)], 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.