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 (L ¹ ) reacted with CuCl to give [CuClL ¹ ₂ ] 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 L ¹ reacted with [Cu(MeCN) ₄ ][PF ₆ ] to give the red salt [CuL ¹ ₂ ][PF ₆ ] 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 [CuL ¹ ₂ ][NO ₃ ] 1c by treatment with AgNO ₃ . These complexes reacted quantitatively with water, benzylamine and methanol to give the corresponding [CuL ² ₂ ] ⁺ 2, [CuL ³ ₂ ] ⁺ 3 and [CuL ⁴ ₂ ] ⁺ 4 where L ² = 2,3-bis(diphenylphosphino)maleic acid and L ³ and L ⁴ are the monobenzylamide and monomethyl ester derivatives, respectively, of L ² . Uncomplexed L ¹ can also be hydrolysed to L ² or derivatised with benzylamine or methanol to give L ³ and L ⁴ respectively. Compounds L ² , L ³ and L ⁴ 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.