Highly Reactive Ni super(II)-Bound Nitrile-Oxime Coupling Intermediates Stabilized by Substituting Conventional Nitriles with a Dialkylcyanamide

• Published in: European journal of inorganic chemistry Vol. 2015; no. 29; pp. 4894 - 4904
• Main Authors: Andrusenko, Elena V, Kabin, Evgeniy V, Novikov, Alexander S, Bokach, Nadezhda A, Starova, Galina L, Zolotarev, Andrey A, Kukushkin, Vadim Yu
• Format: Journal Article
• Language: English
• Published: 01-10-2015
• Subjects: Chelates; Cyanamides; Joining; Ligands; Mathematical analysis; Nitriles; Stability
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201500693

Nickel(II)-mediated coupling between the cyanamide Me sub(2)NCN and the ketoximes Me(R)C=NOH (R = Me, Ph) gives chelates of the general formula [NiCl sub(x)(H sub(2)O) sub(y){HN =C(NMe sub(2))(ON=C(R)Me)} sub(2)] super(n+) ([1] super(+): R = Me; x = 1, y = 0; salts with both Cl super(-) and [NiCl sub(4)] super(2-) were isolated; [2] super(2+): R = Me; x = 0, y = 2; salt with Cl super(-) was isolated; [3] super(+): R = Ph; x = 1, y = 1; salt with Cl super(-) was isolated) and the iminium salts [H sub(2)N=C(NMe sub(2))ON=C(R)Me ] super(+) ([4] super(+): R = Me; salt with [NiCl sub(4)] super(2-) was isolated; [5] super(+): R = Ph; salt with Cl super(-) was isolated). This reaction demonstrates the difference in the reactivity between conventional nitriles and dialkylcyanamides: whereas nitriles RCN (R = Alk, Ar) react with Ni super(II)/ketoxime systems to afford (1,3,5-triazapentadiene)Ni super(II) species, formed by postulated nitrile-oxime coupling intermediates, cyanamides under the same conditions give either stable cyanamide-oxime coupling products or the Busch-type complex [Ni{HN=C(Me)CH sub(2)C(Me sub(2)) NH sub(2)} sub(2)]Cl sub(2) ([6]Cl sub(2)). The reason for the different stability of the coupling products was interpreted theoretically on the basis of quantum chemical calculations (M06-L/6-31G* level of theory). The NMe sub(2) moiety in the chelate ligands leads to an increase in electron-density delocalization and also stabilizes the systems in terms of electrostatic factors. Conventional nitriles and dialkylcyanamides display different reactivity in Ni super(II)/oxime-mediated reactions. Whereas nitriles RCN react with Ni super(II)/ketoxime systems to afford (1,3,5-triazapentadiene)Ni super(II) species, formed by postulated nitrile-oxime coupling intermediates, cyanamides under the same conditions give either stable cyanamide-oxime coupling products or a Busch-type complex.