Abstract
New group 11 metal complexes have been prepared using the previously described tripodal bis(imidazole) thioether ligand (N-methyl-4,5-diphenyl-2-imidazolyl)2C(OMe)C(CH3)2S(tert-Bu) ({BITOMe,StBu}, 2). The pincer ligand offers a N2S donor atom set that can be used to coordinate the group 11 metals in different oxidation states [AuI, AuIII, AgI, CuI and CuII]. Thus the new compounds [Au{BITOMe,StBu}Cl][AuCl4]2 (3), [Au{BITOMe,StBu}Cl] (4), [Ag{BITOMe,StBu}X] (X = OSO2CF3- 5, PF6- 6) and [Cu{BITOMe,StBu}Cl2] (7) have been synthesized from reaction of 2 with the appropriate metal precursors, and characterized in solution. While attempting characterization in the solid state of 3, single crystals of the neutral dinuclear mixed AuIII-AuI species [Au2{BITOMe,S}Cl3] (8) were obtained and its crystal structure was determined by X-ray diffraction studies. The structure shows a AuIII center coordinated to the pincer ligand through one N and the S atom. The soft AuI center coordinates to the ligand through the same S atom that has lost the tert-butyl group, thus becoming a thiolate ligand. The short distance between the AuI-AuIII atoms (3.383 Å) may indicate a weak metal-metal interaction. Complexes 2-7 and the previously described CuI compound [Cu{BITOMe,StBu}]PF6 (9) have been evaluated in the oxidation of biphenyl ethylene with tert-butyl hydrogen peroxide (TBHP) as the oxidant. Results have shown that the AuI and AgI complexes 4 and 6 (at 10 mol % loading) are the more active catalysts in this oxidative cleavage. The antimicrobial activity of compounds 2-5, 7 and 9 against Gram-positive and Gram-negative bacteria and yeast has also been evaluated. The new gold and silver compounds display moderate to high antibacterial activity, while the copper derivatives are mostly inactive. The gold and silver complexes were also potent against fungi. Their cytotoxic properties have been analyzed in vitro utilizing HeLa human cervical carcinoma cells. The compounds displayed a very low cytotoxicity on this cell line (5 to 10 times lower than cisplatin) and on normal primary cells derived from C57B6 mouse muscle explants, which may make them promising candidates as potential antimicrobial agents and safer catalysts due to low toxicity in human and other mammalian tissues.
Highlights
In the last few years the use of mixed-donor pincer ligands has increased due to the catalytic potential of their metal complexes in different organic transformations [1]
We report here on the preparation and characterization of group 11 metal complexes with previously described potentially pincer tripodal bis(imidazole) thioether ligand (N-methyl-4,5-diphenyl-2imidazolyl)2C(OMe)C(CH3)2S(tert-Bu)
BIT ligands with bulkier S-alkyl groups such as BITOMe,StBu (2) had been employed by Nicholas and co-workers in an attempt to inhibit dinuclear Cu complex formation to potentially kinetically stabilize mono-Cu-O2 species
Summary
In the last few years the use of mixed-donor pincer ligands has increased due to the catalytic potential of their metal complexes in different organic transformations [1] They are important in homogenous catalysis since they provide stabilization and temporary coordinative saturation to the metal center via chelation until an active site is required. In the search for copper complexes that accurately mimic the electronic and features of the CuM site of copper hydroxylase enzymes, compounds of CuI have been successfully synthesized with these tripodal BIT ligands (Scheme 1) [9,10,11] Their reactivity towards dioxygen was studied and new. AuI, AuIII and AgI derivatives displayed high to moderate antibacterial/antifungal activity, while all the compounds were less cytotoxic against the HeLa tumor cells than cisplatin and even less toxic to normal primary cells derived from C57B6 mouse muscle explants
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
