NMR and structural studies of gold(I) chloride adducts with bidentate 2-, 3- and 4-pyridyl phosphines

The 1 :2 adducts of gold(I) chloride with the diphosphine ligands, 1,2-bis( di-n-pyridylphosphino)ethane (dnpype) for n = 2, 3 and 4 have been synthesi zed and solution properties characterized by NMR spectroscopy, including va riable temperature one dimensional P-31{H} and 2D [P-31, P-31] COSY experim ents. The results show the 3-pyridyl (d3pype) and 4-pyridyl (d4pype) adduct s to exist as bis-chelated monomeric [Au(d3pype)(2)](+) and [Au(d4pype)(2)] (+) while the 2-pyridyl (d2pype) adduct forms an equilibrium mixture of mon omeric [Au(d2pype)(2)](+), dimeric [{Au(d2pype)(2)}(2)](2+) and possibly te trameric [{Au(d2pype)(2)}(4)](4+) species in which the d2pype ligands coord inate in both bridging and chelated modes ria the phosphorus atoms. The rel ative percentages of the species present are dependent on both temperature and solvent. A single crystal X-ray structure determination of the it-pyrid yl adduct obtained from ethanol/hexane shows the complex to crystallize as [Au(d4pype)(2)H]Cl-2. 6H(2)O with monomeric cations and one of the 4-pyridy l rings likely to be protonated. Crystals of the 2-pyridyl complex obtained from methanol solution have been shown by crystal structure determination to be the dimer [(d2pype)Au(mu-d2pype)](2)Cl-2. 14H(2)O, in which each gold atom is coordinated by one chelated and two bridging d2pype ligands. The s olubility properties and solution behaviour of these three systems are comp ared to the analogous 1,2-bis(diphenylphosphino)ethane (dppe) system and th e potential significance of these results to the antitumour properties of c helated 1 :2 Au(I) diphosphine complexes are discussed.