IPr* an easily accessible highly hindered N-heterocyclic carbene

Herein, we wish to describe the efficient three-step synthesis of a novel highly hindered, but flexible, N-heterocyclic carbene and its coordination chemistry to Ag(i) and Rh(i).

DNA cleavage and antitumour activity of platinum(II) and copper(II) compounds derived from 4-methyl-2-N-(2-pyridylmethyl)aminophenol: spectroscopic, electrochemical and biological investigation

The reaction of the redox-active ligand, Hpyramol (4-methyl-2-N-(2-pyridylmethyl)aminophenol) with K(2)PtCl(4) yields monofunctional square-planar [Pt(pyrimol)Cl], PtL-Cl, which was structurally characterised by single-crystal X-ray diffraction and NMR spectroscopy. This compound unexpectedly cleaves supercoiled double-stranded DNA stoichiometrically and oxidatively, in a non-specific manner without any external reductant added, under physiological conditions. Spectro-electrochemical investigations of PtL-Cl were carried out in comparison with the analogue CuL-Cl as a reference compound. The results support a phenolate oxidation, generating a phenoxyl radical responsible for the ligand-based DNA cleavage property of the title compounds. Time-dependent in vitro cytotoxicity assays were performed with both PtL-Cl and CuL-Cl in various cancer cell lines. The compound CuL-Cl overcomes cisplatin-resistance in ovarian carcinoma and mouse leukaemia cell lines, with additional activity in some other cells. The platinum analogue, PtL-Cl also inhibits cell-proliferation selectively. Additionally, cellular-uptake studies performed for both compounds in ovarian carcinoma cell lines showed that significant amounts of Pt and Cu were accumulated in the A2780 and A2780R cancer cells. The conformational and structural changes induced by PtL-Cl and CuL-Cl on calf thymus DNA and phiX174 supercoiled phage DNA at ambient conditions were followed by electrophoretic mobility assay and circular dichroism spectroscopy. The compounds induce extensive DNA degradation and unwinding, along with formation of a monoadduct at the DNA minor groove. Thus, hybrid effects of metal-centre variation, multiple DNA-binding modes and ligand-based redox activity towards cancer cell-growth inhibition have been demonstrated. Finally, reactions of PtL-Cl with DNA model bases (9-Ethylguanine and 5'-GMP) followed by NMR and MS showed slow binding at Guanine-N7 and for the double stranded self complimentary oligonucleotide d(GTCGAC)(2) in the minor groove.

Mono- and dinuclear platinum(II) compounds with 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine. Structure, cytotoxic activity and reaction with 5'-GMP

Mono- and dinuclear platinum(II) coordination compounds of formula cis-[PtCl(2)(NH(3))(dmtp)], 1, cis-[PtCl(2)(dmtp)(2)], 2 and {H(+)[C(28)H(32)Cl(2)N(16)Pt(2)](2+)(NO(3))(3)(H(2)O)(6)}, 3, in which dmtp is 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine have been synthesized and characterized by infrared and by (1)H, (13)C, (195)Pt NMR spectroscopy. The coordination units of the cationic species of formula [Pt(2)(mu-dmtp)(2)Cl(2)(dmtp)(2)](2+) are built up by two platinum atoms in a square-planar environment. Two sites are occupied by two 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) bridging ligands which are linked to both metal atoms through their nitrogen atoms in positions 3 and 4. The other two positions are occupied by one monodentate 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) molecule and a coordinated chloride. This compound is the first in which the same triazolopyrimidine ligand (dmtp) coordinates to a metal ion in two different ways, i.e. bridging bidentate and non-bridging monodentate. In addition, the interaction of compounds 1 and 2 with 5'-GMP was investigated in solution by (1)H NMR spectroscopy. The cytotoxicity of all the new platinum(II) compounds were studied by using two different cell lines: T47D (breast cancer) and HCV29T (bladder cancer).

2,2,6,6-Tetra-kis(biphenyl-2-yl)-4,4,8,8-tetra-methyl-cyclo-tetra-siloxane

The title compound, [–Si(C₁₂H₉)₂OSi(CH₃)₂O–]₂, was obtained unintentionally as the product of an attempted crystallization of caesium bis­(biphenyl-2,2′-di­yl)fluoro­silicate from dimethyl­formamide. In the crystal, the mol­ecule is located on an inversion center and the siloxane ring adopts a twist-chair conformation with the two dimethyl-substituted Si atoms lying 0.7081 (5) Å out of the plane defined by the two bis­(biphenyl-2-yl)-substituted Si atoms and the four O atoms. In each Si(C₁₂H₉)₂ unit, the orientation of one terminal phenyl ring relative to the phenyl­ene ring of the other biphenyl moiety suggests a parallel displaced π–π stacking inter­action [centroid distance = 4.2377 (11) Å and dihedral angle = 15.40 (9)°].

A novel ruthenium(III) complex with a tridentate dianionic P,O,O-ligand showing high cytotoxic activity

Tris(o-anisyl)phosphane was reacted with ruthenium(III) chloride forming a novel Ru(III) complex of formula [Ru(PAn(3))(P(An)(phenolate)(2))Cl] containing a tridentate dianionic P,O,O-ligand and a bidentate neutral P,O ligand. The tridentate ligand was formed by elimination of two methyl groups from the starting ligand in the reaction with the ruthenium salt. The molecular structure was determined by single crystal X-ray diffraction analysis. The compound shows a high cytotoxic activity in ovarian cancer cell lines comparable with cisplatin and overcoming cisplatin-resistance.

N-heterocyclic carbene-functionalized ruthenium phosphinidenes: what a difference a twist makes

Catalyst tuning by changing ligands is a well-established protocol in transition-metal chemistry. N-Heterocyclic carbenes (NHCs) and tertiary phosphines (R(3)P) are the ubiquitous ligand actors. Here we demonstrate that the relative sigma-donor/pi-acceptor ability of the NHC ligand itself can be influenced by a simple substituent-controlled conformational change, thereby directly impacting the reactivity of the transition-metal complex.