Diphosphine bifunctional chelators for low-valent metal ions. Crystal structures of the copper(I) complexes [CuClL(2)(1)] and [CuL(2)(1)][PF6] [L(1) equals 2,3-bis(diphenylphosphino)maleic anhydride]

The chelating diphosphine 2,3-bis(diphenylphosphino)maleic anhydride (L(1)) reacted with CuCl to give [CuClL(2)(1)] 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)][PF6] to give the red salt [CuL(2)(1)][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 [CuL(2)(1)][NO3] 1c by treatment with AgNO3. These complexes reacted quantitatively with water, benzylamine and methanol to give the corresponding [CuL(2)(2)](+) 2, [CuL(2)(3)](+) 3 and [CuL(2)(4)](+) 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.