Amidine compounds as products of a piperidine reaction with acetonitrile in the presence of zinc(II) precursors

Abstract

The influence of the zinc(II) starting material in the nucleophilic addition of piperidine (abbreviated as pipe) to acetonitrile to form amidine, piperidinoacetamidine (pipeam), was assessed. Thus, zinc(II) oxide, zinc(II) chloride or zinc(II) acetate were reacted with picolinic acid or pyrazinoic acid, piperidine and acetonitrile. The acid was used as a source of an N,O-donor ligand. The reactions with picolinic acid (picH) gave pipeamH[Zn(pic)3]·0.5H2O (1), an amidinium salt of a homoleptic complex [Zn(pic)3]–. The same product was obtained when [Zn(pic)(picH)Cl], an already known picolinate complex, was reacted under similar conditions. The chloride-containing mixtures produced another amidine compound, (pipeamH)Cl. The reactions with pyrazinoic acid (pyrazH) gave pipeamH[Zn(pyraz)3] (3), the amidinium salt of a homoleptic complex [Zn(pyraz)3]–. The acetate-containing mixture yielded acetamidinium acetate. The latter product indicates the presence of ammonia in the reaction. Notably, no amidine species was isolated when the coordinatively saturated pyrazinoate complex, [Zn(pyraz)2]n (2), was reacted with piperidine and acetonitrile. A detailed structural characterization of the new compounds and a discussion of their formation are presented.