Highly reactive NiII-bound nitrile–oxime coupling intermediate stabilized by substituting conventional nitriles with a dialkylcyanamide

Abstract

Nickel(II)-mediated coupling between the cyanamide Me2NCN and the ketoximes Me(R)C=NOH (R = Me, Ph) gives chelates of the general formula [NiClx(H2O)y{HN=C(NMe2)ON=C(R)Me)}2]n+ ([1]+: R = Me; x = 1; y = 0, salts with both Cl– and [NiCl4]2– were isolated; [2]2+: R = Me, x = 0; y = 2, salt with Cl– was isolated; [3]+: R = Ph, x = 1; y = 1, salt with Cl– was isolated) and the iminium salts [H2N=C(NMe2)ON=C(R)Me]+ ([4]+: R = Me, salt with [NiCl4]2– was isolated; [5]+: R = Ph, salt with Cl– was isolated). This reaction demonstrates the difference in the reactivity between conventional nitriles and dialkylcyanamides, viz. if RCN (R = Alk, Ar) react with NiII/ketoxime system achieving (1,3,5-triazapentadiene)NiII species, formed via postulated nitrile–oxime coupling intermediate, the cyanamide under the same conditions gives either stable cyanamide–oxime coupling products or the Busch’s type complex [Ni{HN=C(Me)CH2C(Me2)NH2}2]Cl2 ([6]Cl2). Complexes [1]Cl, [2]Cl2•H2O, [3]Cl, and [6]Cl2 were characterized by elemental analyses (C,H,N), high resolution ESI+-MS, IR, DTA/TG, and also by X-ray crystallography. Compounds [1]2[NiCl4], [4]2[NiCl4], and [5]Cl were identified by single-crystal X-ray diffraction. The reason of different stability of the coupling products was interpreted theoretically based on the quantum chemical calculations (M06-L/6-31G* level of theory). The NMe2 moiety in the chelate ligands leads to an increase in electron density delocalization and also stabilize the systems in terms of electrostatic causes.