Diphosphine bifunctional chelators for low-valent metal ions. Crystal structures of the copper(I) complexes [CuClL¹₂] and [CuL¹₂][PF₆] [L¹ = 2,3-bis(diphenylphosphino)maleic anhydride]

Abstract

The chelating diphosphine 2,3-bis(diphenylphosphino)maleic anhydride (L¹) reacted with CuCl to give [CuClL¹₂] 1a in which the copper is bound to three phosphorus atoms and one chlorine in a pseudo-tetrahedral structure, as demonstrated by X-ray crystallography. Compound L¹ reacted with [Cu(MeCN)₄][PF₆] to give the red salt [CuL¹₂][PF₆] 1b in which the copper is bound by four phosphorus atoms of two chelating bidentate ligands, as demonstrated by X-ray crystallography. Addition of chloride ions to 1b quantitatively affords 1a. Complex 1a can be converted quantitatively into [CuL¹₂][NO₃] 1c by treatment with AgNO₃. These complexes reacted quantitatively with water, benzylamine and methanol to give the corresponding [CuL²₂]⁺2, [CuL³₂]⁺3 and [CuL⁴₂]⁺4 where L² = 2,3-bis(diphenylphosphino)maleic acid and L³ and L⁴ are the monobenzylamide and monomethyl ester derivatives, respectively, of L². Uncomplexed L¹ can also be hydrolysed to L² or derivatised with benzylamine or methanol to give L³ and L⁴ respectively. Compounds L², L³ and L⁴ reacted with copper-(I) or -(II) salts to yield salts of 2, 3 and 4. This chemistry provides versatile routes to the synthesis of stable bioconjugates containing copper or radiocopper and of derivatised solids containing pendant diphosphine ligands.

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