Silver(I) Nitrate Adducts with Bidentate 2-, 3- and 4-pyridyl Phosphines. Solution 31P and [31P-109Ag] NMR Studies of 1:2 complexes and crystal structure of dimeric [{Ag(d2pype)(u-d2pype)}2]-[NO3]2.2CH2Cl2 [d2pype = 1,2-bis(di-2-pyridylphosphino)ethane]

Abstract

The 12 complexes of silver(I) nitrate with 1,2-bis(di-n-pyridylphosphino)ethane (dnpype) for n = 2, 3 and 4 have been synthesized and solution properties characterized by NMR spectroscopy, including variable-temperature one-dimensional 31P-{1H}, two-dimensional [31P–31P] COSY and [31P–109Ag] HMQC NMR experiments. The 3-pyridyl (d3pype) and 4-pyridyl (d4pype) complexes exist as bis-chelated monomeric [Ag(d3pype)2]+ and [Ag(d4pype)2]+ while the 2-pyridyl (d2pype) complex forms an equilibrium mixture of monomeric [Ag(d2pype)2]+, dimeric [{Ag(d2pype)2}2]2+ and trimeric [{Ag(d2pype)2}3]3+ species in which the d2pype ligands co-ordinate in both bridging and chelated modes via the phosphorus atoms. The relative percentages of the species present are dependent on both temperature and solvent. Crystals of the 2-pyridyl complex obtained from CH2Cl2–Et2O solution have been shown by crystal structure determination to be the dimer [{Ag(d2pype)(µ-d2pype)}2][NO3]2·2CH2Cl2. Each silver ion is co-ordinated by one chelated and two bridging d2pype ligands forming a ten-membered ring in a double boat conformation. The pyridyl nitrogen atoms do not co-ordinate to the silver. The differences in solution behaviour of the three systems and the potential significance of these complexes to the antitumour properties of chelated 12 silver(I) diphosphine complexes are discussed.