M. Naseem Akhtar

13C, 15N AND 31P NMR STUDY OF THE DISPROPORTIONATION OF CYANOGOLD(I) COMPLEXES : R3PAU13C15N

Abstract The disproportionation of cyanogold(I) complexes of general formula [R 3 PAu 13 C 15 N] forming [(R 3 P) 2 Au] + and [Au( 13 C 15 N) 2 ] − ions has been investigated using 13 C, 15 N and 31 P NMR spectroscopy for a series of phosphines with R=cyclohexyl, i -propyl, Et, Me, cyclohexyl/diphenyl, o -tolyl, p -tolyl, m -tolyl, p -tolyl/diphenyl, allyl/diphenyl, phenyl, tri(cyanoethyl) CEP, and 1-naphthyl. The 13 C NMR of the 13 C 15 N group in these complexes exhibited two distinct resonances, one due 13 C in the starting [R 3 PAu 13 C 15 N] complex and the second in the [Au( 13 C 15 N) 2 ] − anion. The 31 P NMR spectra revealed two 31 P resonances due to [R 3 PAu 13 C 15 N] complex, and the [(R 3 P) 2 Au] + cation. The 15 N NMR revealed only an averaged resonance due to [R 3 PAu 13 C 15 N] and [Au( 13 C 15 N) 2 ] − anion, except in the cases of [Me 3 PAu 13 C 15 N] and [Et 3 PAu 13 C 15 N] where two resonances were observed. The coupling constants, 1 J( 13 C– 15 N), 2 J( 31 P– 13 C) and 3 J( 31 P– 15 N) were obtained for all complexes and the free energies of activation for ligand disproportionation were determined using 31 P–{ 1 H} NMR band shape analysis.

Synthesis and spectroscopic characterization of (trialkll/triaryl)-phosphine gold(I) thiocyanate complexes

Abstract R 3 PAuS 13 C 15 N (where R 3 P = Me 3 P, Et 3 P, i -Pr 3 P, p -TolPh 2 P, Ph 3 P and cyanoethyl-phosphine CEP) complexes have been prepared. The AuNCS/AuSCN ratios for these complexes have been determined, using IR spectroscopy ( v CN integrated absorption intensity ratios). The observation that the AuNCS/AuSCN ratio increases as the trans influence of the phosphine ligand increases is completely in agreement with the trend predicted by the antisymbiotic trans influence theory. In the solid state only the S-bonded isomer of each complex is observed. The 13 C, 15 N and 31 P NMR chemical shifts of these complexes were also measured and are compared with R 3 PAu 13 C 15 N complexes. The results show that unlike R 3 PAu 13 C 15 N complexes, which undergo disproportion in solution, the R 3 PAuS 13 C 15 N complexes do not undergo disproportion.

Gold(I) Complexation with Trialkyl/Triaryl Phosphine Selenide Ligands

Abstract A number of phosphine selenide ligands and their gold(I) complexes of general formula R3P˭Se‒Au‒X (where X is Cl−, Br− and CN− and R = phenyl, cyclohexyl and tolyl) were prepared. The complexes were characterized by elemental analysis, IR and 31P NMR spectroscopic methods. In the IR spectra of all complexes a decrease in frequency of P˭Se bond upon coordination was observed, indicating a decrease in P˭Se bond order. 31P NMR showed that the electronegativity of the substituents is the most important factor determining the 31P NMR chemical shift. It was observed that phosphorus resonance is more downfield in alkyl substituted phosphine selenides, as compared to the aryl substituted ones. Ligand disproportionation in the complex Cy3P˭SeAuCN in solution to form [Au(CN)2]− and [(Cy3P˭Se)2Au]+ was investigated by 13C and 15N NMR spectroscopy.

SIMULTANEOUS REPLACEMENTS OF TRIETHYL PHOSPHINE AND TETRAACETYL THIOGLUCOSE LIGANDS FROM AURANOFIN (AN ANTIARTHRITIC DRUG) WITH SELENOCYANATE 13C AND 31P NMR STUDIES

Abstract The interaction of SeCN− with a new gold-based antiarthritic drug auranofin (Et3PAuSATg, where SATg− = 2, 3, 4, 6-tetra-O-acetyl-l-thio-β-D-glucopyranosato-S) in aqueous methanol has been studied by 13C and 31P NMR spectroscopy. It is observed that SeCN−releases bom ligands (i. e., SATg− and Et3P) to form [ATgS-Au-CN]− and [Et3P-Au-SeCN]. These newly generated species undergo further disproportionation and decomposition to generate species such as [(Et3P)2Au]+, [Au(CN)2]−, Et3PO and metallic selenium. The formation of [(Et3P)2Au]+ and [Au(CN)2]− is found to be much faster for Et3PAuNO3 than for Et3PAuSATg when reacted wim SeCN−. Exchange between unlabelled CN− of Au(CN)2 − and labelled Se13CN− was observed without selenium being precipitated from Se13CN−.

THE REDOX REACTION OF GOLD(I)-THIOMALATE IN THE PRESENCE OF SELENOUREA

Abstract The interaction of thiourea (TU) and selenourea (SeU) with aurothiomalate (Autm) has been studied by 13C NMR spectroscopy. At a 1:1 ratio of TU:Autm, TU binds to Autm forming a ternary TU-Au-tm complex. However, in the presence of SeU at various mol ratios, some of the thiomalate (Htm) was ejected from Autm as a free ligand, oxidized to tm2, and gold(I) was reduced to metallic gold. This redox reaction is observed only in the presence of SeU which may be acting as a catalyst.

Synthesis of thionato(trimethylphosphine)gold(I) complexes

SummaryNew compounds of formula [AuL(PMe3)]Cl [L = imidazolidine-2-thione (Imt), 1,3-diazinane-2-thione (Diaz), 1,3-diazepine-2-thione (Diap) and their derivatives] have been synthesized and characterized by elemental analysis, and i.r., 13C- and 31P-n.m.r. spectroscopies. The Diap ligand, which incorporates the thione in a seven-membered heterocyclic ring, binds more strongly to AuI compared to its Diaz (six-membered ring) and Imt (five-membered ring) analogues.

COMPARATIVE 13C NMR STUDIES OF COMPLEXATION OF IMIDAZOLIDINE-2-SELENONE AND ITS ANALOGOUS THIONE TO GOLD(I) THIOMALATE

Abstract The interaction of gold(I) thiomalate (AuStm)n (Myocrisin) with imidazolidine-2-selenone (SeImt) was studied in an aqueous solution at pH 7.40 using 13C NMR spectroscopy. It was found that SeImt binds more strongly to (AuStm)n than imidazolidine-2-thione and its derivatives as determined by 13C NMR spectroscopy. SeImt reacts differently with Au(Stm)2 −, as compared to (AuStm)n. With (AuStm)n, SeImt forms a ternary complex of ImtSe-Au-Stm, releasing free Stm− to solution. Redox reaction of gold(I) to metallic gold and free thiomalate (Stm−) to disulfide (Stm)2 occurs when Au(Stm)2 − reacts with SeImt.

Carbon-13 nuclear magnetic resonance studies of the redox reactions of aurothiomalates with selenocyanate in aqueous solution

The interactions of SCN– and SeCN– with aurothiomalate [Au(tm)]n in aqueous solution were studied by 13C NMR spectroscopy. The [Au(tm)]n is further polymerized in the presence of SCN–, however, SeCN– binds to [Au(tm)]n forming monomeric [Au(SeCN)(tm)]–. This complex initially disproportionates to give [Au(SeCN)2]– and [Au(tm)2]–. The [Au(SeCN)2]– eventually decomposed to give [Au(CN)2]– and metallic selenium. The free tm– released from [Au(tm)]n is oxidized to the thiomalic disulfide (tm)2. When the bis complex [Au(tm)2]– reacted with SeCN– it did not form [Au(SeCN)(tm)]–, but instead gave (tm)2, [Au(CN)2]– and Se22–.