Electronic and geometrical manipulation of the excited state of bis-terdentate homo- and heteroleptic ruthenium complexes

International audienceThis work describes the synthesis and characterization of two new bis-terdentate Ru(II) complexes. Compound 1 is a homoleptic complex containing two CNC N-heterocyclic carbene (NHC) based ligands, whereas compound 2 bears one CNC ligand and an ancillary terpyridine ligand. The redox and photophysical properties of both compounds have been investigated and their X-ray crystal structures determined. Complex 1 displays a close-to-perfect octahedral coordination geometry and is not luminescent at room temperature while complex 2 features room temperature and 77 K luminescence despite its partially distorted geometry. The presence of the NHC moieties brings a significant amount of electronic density to the metal centre therefore lowering its oxidation potential with respect to that of analogous polypyridyl complexes

Bipyridyl/carbazolate silver(I) and gold(I) N-heterocyclic carbene complexes: A systematic study of geometric constraints and electronic properties

A series of silver(I) and gold(I) carbene complexes of the type [M(L)(2,2 '-bipyridine)][PF6] (L = 1-benzyl-3-(2-pyridylmethyl)benzimidazolylidene; M = Ag (1); M = Au (3)) and [M(L)(carbazole)] (M = Ag (2); M = Au (4)) were synthesized and analyzed using a range of spectroscopic and crystallographic techniques. Inspection of the solid-state structures of 1, 2 and 4 revealed a number of intermolecular noncovalent interactions. In the solid-state structure adopted by 1, pi-pi and Ag-Ag interactions directed the complexes to orient in a head-to-tail fashion. The photophysical properties were found to be influenced by the ancillary ligands in solution as well as in the solid-state. Calculations were performed to support the aforementioned structural and optoelectronic assignments

Au(I)- and Pt(II)-N-heterocyclic carbene complexes with picoline functionalized benzimidazolin-2-ylidene ligands; synthesis, structures,electrochemistry and cytotoxicity studies

Novel Au(I)-N-heterocyclic carbene complexes, 1-methyl-3-(2-pyridylmethyl)- benzimidazolylidenegold(I)-chloride, 1; 1-benzyl-3-(2-pyridylmethyl)- benzimidazolylidenegold(I)chloride, 2; and Pt(II)-N-heterocyclic carbene complexes 1-methyl-3-(2- pyridylmethyl) benzimidazolylidene platinum(II)chloride, 3; and 1-benzyl-3-(2-pyridylmethyl) benzimidazolylidene platinum-(II)chloride, 4, have been synthesized, based on CN-donor proligands 1-alkyl-3-(2-pyridylmeth-yl)-benzimidazoliumchloride L1 and L2 [alkyl, R = –CH3 = L1; R = –CH2Ph = L2]. All the compounds have been synthesized and characterized by different spectroscopic methods. The Au(I) complexes 1 and 2 have been synthesized by a silver carbene transfer method. The solid-state structures of 1 and 3 have been determined by single crystal X-ray diffraction studies. The square planar Pt(II) complexes 3 and 4 show a reversible Pt(II)/Pt(IV) couple at 0.69 eV and 0.67 eV respectively. Among the complexes 1–4, complexes 1 and 3 have been used for cytotoxicity studies on the cell lines B16F10 (mouse melanoma), HepG2 (human hepatocarcinoma) and HeLa (human cervical carcinoma). IC50 values are compared with cisplatin, among 1 and 3, the Au(I) complex 1 is more effective than Pt(II) complex 3

Osmium-carbonyl complexes of naphthylazoimidazoles. Single crystal X-ray structure of [Os(H)(CO)(PPh3)(2)(alpha-NaiEt)](PF6) {alpha-NaiEt=1-ethyl-2-(naphthyl-alpha-azo)imidazole}

1-Alkyl-2-(naphthyl-alpha/beta-azo)imidazole (alpha-NaiR 1; beta-NaiR, 2) react with [Os(H)(Cl)(CO)(PPh3)(3)] in THF and synthesise [Os(H)-(CO)(PPh3)(2)(alpha/beta-NaiR)](PF6) (3, 4). The X-ray structure of [Os(H)(CO)(PPh3)(2)(alpha-NaiEt)](PF6) (3c) shows a distorted octahedral geometry. Other spectroscopic studies (IR, UV-Vis, NMR) support the stereochemistry of the complexes. Addition of Cl, in MeCN to 3 or 4 gives [Os(Cl)(CO)(alpha/beta-NaiR)(PPh3)(2)](PF6) (5, 6), which were characterized by spectroscopic studies. The redox properties of the complexes show Os(III)/Os(II), Os(IV)/Os(III) and azo reductions. (c) 2006 Elsevier Ltd. All rights reserved.</p

Cytotoxicity of silver(I), gold(I) and gold(III) complexes of a pyridine wingtip substituted annelated N-heterocyclic carbene

Starting from the proligand 1-methyl-2-pyridin-2-yl-2H-imidazo[1,5-a]pyridin-4-ylium chloride (1 HCl), three novel complexes [Ag(1)Cl] (2), [Au(1)Cl] (3) and [Au(1)Cl3] (4) were synthesized and characterized using various spectroscopic techniques. In addition, the structure of 2 was elucidated using single crystal X-ray diffraction analysis, which revealed that the carbene nucleus and the chloride ion bound to the silver(I) were nearly linear (165.37(9)??). The gold(I)-NHC complex 3 was synthesized via transmetallation from the aforementioned silver complex 2. Similarly, treatment of 3 with Au(SMe2)Cl afforded 4, ostensibly via a disproportionation process. The cytotoxicities of complexes 2, 3, and 4 were examined against HepG2 (human hepatocellular carcinoma), HCT 116 (human colorectal carcinoma), A549 (human lung adenocarcinoma), and MCF-7 (human breast adenocarcinoma) cells. Au(I)-NHC complex 3 exhibited a cytotoxicity that was similar to that of cisplatin towards all the four cancer cell lines tested; by comparison, Ag(I) NHC complex 2 and Au(III) NHC complex 4 appeared relatively less potent. Complex 3 was found to induce apoptosis in HepG2 cells.close0

Gold (I) N-heterocyclic carbene complex inhibits mouse melanoma growth by p53 upregulation

Cancer treatment using gold (I) complexes is becoming popular. In this study, a gold (I) N-heterocyclic complex designated as complex 3 was synthesized, its cytotoxicity was examined, and its anti-melanoma activity wasevaluated in vitro and in vivo. Viability of cancer cells was determined by MTT assay upon treatment with various concentrations of a gold (I) N-heterocyclic carbene complex (complex 3) in a dose and time dependent manner. Mouse melanoma cells B16F10 were selected for further apoptotic studies, including flowcytometric analysis of annexin binding, cell cycle arrest, intracellular ROS generation and loss in the mitochondrial membrane potential. ELISA based assays were done for caspase activities and western blots for determining the expression of various survival and apoptotic proteins. Immunocytology was performed to visualize the translocation of p53 to the nucleus. B16F10 cells were inoculated into mice and post tumor formation, complex 3 was administered. Immunohistology was performed to determine the expressions of p53, p21, NF-κB (p65 and p50), MMP-9 and VEGF. Student’s t test was used for determining statistical significance. The survival rate data were analyzed by Kaplan-Meier plots.Complex 3 markedly inhibited the growth of HCT 116, HepG2, and A549, and induced apoptosis in B16F10 cells with nuclear condensation, DNA fragmentation, externalization of phosphatidylserine, activation of caspase 3 and caspase 9, PARP cleavage, downregulation of Bcl-2, upregulation of Bax, cytosolic cytochrome c elevation, ROS generation, and mitochondrial membrane potential loss indicating the involvement of an intrinsic mitochondrial death pathway. Further, upregulation of p53, p-p53 (ser 15) and p21 indicated the role of p53 in complex 3 mediated apoptosis. The complex reduced tumor size, and caused upregulation of p53 and p21 along with downregulation of NF-κB (p65 and p50), VEGF and MMP-9. These results suggest that it induced anti-melanoma effect in vitro and in vivo by modulating p53 and other apoptotic factors. The gold (I) N-heterocyclic carbene complex (C22H26N6AuO2PF6) designated as complex 3 induced ROS and p53 dependent apoptosis in B16F10 cells involving the mitochondrial death pathway along with suppression of melanoma tumor growth by regulating the levels of pro and anti apoptotic factors (p53, p21, NF-κB, VEGF and MMP-9)

Synthesis and Study of Palladium(II) and Platinum(II) Complexes Supported by a Common &quot;Wingtip&quot; N-Heterocyclic Carbene

Two annulated imidazolium salts, 2-(phenyl)imidazo[1,5-a]pyridin-4-ylium hexafluorophosphate 1 center dot H(PF6) and 1-methyl-2-(phenyl)imidazo[1,5-a]pyridin-4-ylium hexafluorophosphate 2 center dot H(PF6), were synthesized via formylative cyclization of the corresponding Schiff bases followed by anion metathesis with KPF6. Independently treating 1 center dot H(PF6) or 2 center dot H(PF6) with silver oxide and then palladium chloride in acetonitrile led to the formation of the complexes [Pd(1)(2)Cl(CH3CN)]PF6 (1a) and [Pd(2)(2)Cl(CH3CN)]PF6 (2a), respectively. Likewise, [Pt(1)(2)Cl(CH3CN)]PF6 (1b) and [Pt(2)(2)Cl(CH3CN)]PF6 (2b) were synthesized using similar transmetallation chemistry. The complexes were characterized using various spectroscopic techniques and the solid state structures of 1-H(PF6) as well as 2a were elucidated using X-ray diffraction analyses. A series of DFT calculations were also performed to gain further insight into the respective structures of the complexes. Complexes 1a and 2a were found to facilitate Suzuki coupling reactions under relatively mild conditions

Pd(II)–N-heterocyclic carbene complexes of 2,6-bis{N-methyl-(imidazolium/benzimidazolium)}pyrazinechloride: Synthesis, structure, catalysis and theoretical studies

The multitopic pyrazine functionalized pro-ligand 2,6-bis(N-methylimidazolium)pyrazinedichloride, L-1; 2,6-bis(N-methylbenzimidazolium)pyrazinedichloride, L-2 and their respective Pd(II)–NHC complexes 1 and 2 have been synthesised and characterized by different spectroscopic methods and have been analyzed within a conceptual DFT framework. Single crystal X-ray structures of (L-1)PF6 and complex 1 have been determined. X-ray structure revels that 1 form a 12 member palladacycle. Both complex 1 and 2, catalyse the Suzuki coupling reaction very well and from experimental and theoretical findings it is concluded that complex 1 is slightly catalytically more active than 2

Electronic Tuning and Catalytic Activity of a Novel Pd(II) Complex Supported by a Tetracoordinate Ligand

The synthesis and study of a novel Pd(II) complex (2) supported by a new tetracoordinate ligand that is based on a bis(N-heterocyclic carbene) with two pendant pyrimidinyl donors is described. The complex was characterized using a series of spectroscopic, analytical, and computational techniques. A preliminary assessment showed that 2 displayed good performance in Suzuki-Miyaura coupling reactions between phenyl boronic acid and an assortment of substituted bromobenzenes. Finally, the intrinsic electronic characteristics of the complex were elucidated through DFT-based molecular orbital calculations which revealed that the coordinated metal center was relatively electron deficient and stabilized by a series of ligand dominated interactions