Highly Reactive Ni-II-Bound Nitrile-Oxime Coupling Intermediates

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: whereas nitriles RCN (R = Alk, Ar) react with Ni-II/ketoxime systems to afford (1,3,5-triazapentadiene)Ni-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)CH2C(Me-2)NH2}(2)]Cl-2 ([6]Cl-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 NMe2 moiety in the chelate ligands leads to an increase in electron-density delocalization and also stabilizes the systems in terms of electrostatic factors.

C1 [Andrusenko, Elena V.; Kabin, Evgeniy V.; Novikov, Alexander S.; Bokach, Nadezhda A.; Starova, Galina L.; Zolotarev, Andrey A.; Kukushkin, Vadim Yu.] St Petersburg State Univ, Inst Chem, St Petersburg 198504, Russia.