Synthesis, structure and unique reactivity of the ethylzinc derivative of a bicyclic guanidine

Abstract

An equimolar reaction between ZnEt₂ and 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) results in the formation of EtZn(hpp) (1) which crystallizes as a trinuclear agglomerate with the guanidinate ligands spanning 4-coordinate Zn centers. Exposure of a pre-formed THF solution of 1 to undried air leads to a ZnO-incorporating derivative 1₄·ZnO, while an analogous experiment with CH₂Cl₂ as solvent leads to a novel tetranuclear mixed aggregate formulated as [EtOZn(hpp)]₂[ClZn(hpp)]₂ (2). The composition of 2 indicates that its formation proceeds via a complex multi-step reaction route that involves not only the oxygenation of ZnEt moieties, but also the activation of CH₂Cl₂, causing the transfer of a chloride anion to the Zn center. Compounds were characterized by ¹H NMR spectroscopy and single-crystal X-ray diffraction analysis.