title: Synthesis and characterization of gold(III) complexes possessing 2,9-dialkylphenanthroline ligands: to bind or not to bind?
abstract: In an effort to discover potential alternatives to the anti-cancer drug cisplatin, the synthesis of gold(III) polypyridyl coordination complexes was pursued. Specifically, this report describes the synthesis and characterization of a series of 2,9-dialkyl-1,10-phenanthroline (Rphen) gold(III) coordination complexes (R = n-butyl, sec-butyl, and tert-butyl). Due to the steric hindrance imparted by the alkyl substituents, these ligands do not react with HAuCl4 to form square-planar gold(III) dichloride complex ions, as is the case with 1,10-phenanthroline, but instead form salts comprised of [AuCl(4)](-) anions and protonated 2,9-dialkylphenanthroline cations (compounds 1 and 2). In an effort to facilitate direct binding between the substituted phenanthroline and the gold(iii) metal center, reactions were carried out between the ligand and NaAuCl4 in the presence of a Ag(I) salt. The precipitation of one equivalent of AgCl afforded the formation of neutral, distorted square-pyramidal gold(iii) trichloride complexes (compounds 3 and 4). Primary or secondary substitutions at the alpha carbon of the alkyl substituent allow direct metal-ligand coordination, whereas a tertiary substituent inhibits chelation and results only in the formation of a salt comprised of a protonated phenanthroline cation and a [AuCl2]- anion (compound 5). Compounds 1-4 have been characterized by 1H NMR, UV/vis, IR spectroscopy, and X-ray crystallography.
authors.affiliation: Department of Chemistry, Division of Natural Science and Mathematics, Oxford College of Emory University, 100 Hamill Street, Oxford, GA 30054, USA.
authors.forename: Zachary D
authors.initials: ZD
authors.lastname: Hudson
authors.forename: Chinar D
authors.initials: CD
authors.lastname: Sanghvi
authors.forename: Melody A
authors.initials: MA
authors.lastname: Rhine
authors.forename: Julia J
authors.initials: JJ
authors.lastname: Ng
authors.forename: Scott D
authors.initials: SD
authors.lastname: Bunge
authors.forename: Kenneth I
authors.initials: KI
authors.lastname: Hardcastle
authors.forename: Mohammad R
authors.initials: MR
authors.lastname: Saadein
authors.forename: Cora E
authors.initials: CE
authors.lastname: MacBeth
authors.forename: Jack F
authors.initials: JF
authors.lastname: Eichler
mesh_terms: D002945:Cisplatin / Q000737:chemistry; D018360:Crystallography, X-Ray; D006046:Gold / Q000737:chemistry*; D008024:Ligands; D008968:Molecular Conformation; D010618:Phenanthrolines / Q000737:chemistry*
chemical_list: D008024:Ligands; D010618:Phenanthrolines; D006046:Gold; D002945:Cisplatin; C025205:1,10-phenanthroline