Copper(II) Complexes of Vitamin B₁ Analogues and Those of Structurally Related Ligands

Abstract

Copper (II) complexes of vitamin B₁. analogues (L¹), CuL¹X_n (X = Cl, Br, I, SCN; n = 2 or 3) and CuL¹(CH₃C00)C10₄, and those of structurally related ligands, L² - L⁷ (Fig.2) were isolated and their properties investigated. Reactions of Cu₂(CH₃C00).-2H₂0 with vitamin B₁ and the bromo, iodo and thiocyanato analogues in aqueous medium resulted in copper(I) complexes, CuThX₂ (X = Cl, Br, I, SCN). Parallel reactions carried out in methanol using thiamin and its analogues afforded both copper(I) and copper(II) complexes, depending on the duration of reaction. CuL¹ Cl₃ converted to the copper(I) complex on prolonged ( 3 months) storage. In contrast all the structurally related ligands (L² - L⁷) yielded stable copper(II) complexes. Thus, it appears that for the copper(II) complexes to undergo reduction both the pyrimidine and the thiazolium portions of the thiamin molecule must remain intact. The reduction process is faster in water but slow enough in methanol to afford the isolation of the copper(II) complexes.