Synthesis of diaminoacetylene from cyanido ligands of the octacyanidotungstate complex

Abstract

The article describes for the first time the synthesis of the diaminoacetylene ligand, which is a by-product of the synthesis of [W(CN)₆(bpy)]²⁻ involving the thermal decomposition of (bpyH)₃(H₃O)[W(CN)₈]·H₂O. The formation of the diaminoacetylene ligand, H₂NCCNH₂, occurs through protonation of cyanido ligands and the formation of a C–C bond between two neighbouring CN⁻ ligands through a reductive coupling mechanism. In this way, three salts of the anion [W(CN)₆(C₂N₂H₄)]²⁻ with cations: PPh₄⁺ (1), rubidium (2), and caesium (3) were isolated and then structurally and spectroscopically characterised. The formation of an additional by-product (PPh₄)₃[W(CN)₈]·4.25H₂O (4) was also discussed. IR measurements of the reaction mixture indicate that proton transfer from the Hbpy⁺ cation is accompanied by the formation of the acetylene ligand. NMR spectra indicate strong interactions between the cyanido ligands and the protons of the acetylene ligand.