Isomeric dinuclear gold(i) complexes with highly functionalised ditertiary phosphines: Self-assembly of dimers, rings and 1-D polymeric chains

Abstract

An isomeric series of six linear, dinuclear, gold(I) complexes (AuCl)₂{P,P-C₆H₄N(CH₂PPh₂)₂(CO₂H)(OH)} 6a–6f have been synthesised in high yields (>90%) from AuCl(tht) (tht = tetrahydrothiophene) and the appropriate building blocks C₆H₄N(CH₂PPh₂)₂(CO₂H)(OH) 3a–3f in CH₂Cl₂. The diphosphine ligands C₆H₄N(CH₂PPh₂)₂1, 4-CO₂HC₆H₄N(CH₂PPh₂)₂2 and their corresponding digold(I) complexes 4 and 5 have also been prepared. Solution NMR (³¹P{¹H}, ¹H), FT-IR and microanalytical data are in full agreement with the proposed structures. Single crystal X-ray studies confirm that in each case, compounds 4, 5, 6a–6e are linear, with typical Au–P [2.227(4)–2.2349(17) Å]/Au–Cl [2.271(2)–2.325(4) Å] bond lengths and P–Au–Cl [169.37(1)–179.05(4)°] bond angles. Furthermore these studies demonstrate the relationship between regioselectivity, with respect to the –N(CH₂PPh₂)₂, –CO₂H and –OH functionalities around the benzene core, and solid state structures of the gold(I) complexes 6a–6e. In 6a, molecules are associated into pairs through classical intermolecular O–H⋯O hydrogen bonding, whilst in 6b and 6c, dimer pairs are formed using intermolecular O–H⋯Cl hydrogen bonds. 1-D chains of alternate 20-/22- or 8-/18-membered hydrogen bonded rings are propagated using O–H⋯Cl and/or O–H⋯O hydrogen bonds in compounds 6d and 6e. The Au⋯Au separation decreases from 6.179(3) Å (for 6a) to 3.0722(9) Å (for 6e) suggesting that aurophilicity increases within this series. The X-ray structure of a representative diphosphine 3a is also presented.