Mixed-ligand platinum(II) complexes containing 2-(2′-pyridyl)phenyl and 8-quinolylphosphines: Synthesis and molecular structures in the crystals and in solution

(P^N^C) Ligands to Stabilize Gold(III): A Straightforward Access to Hydroxo, Formate, and Hydride Complexes

A novel class of (P^N^C) pincer ligands capable of stabilizing elusive gold(III) species is reported here. Straightforward access to (P^N^C)gold(III) hydroxo, formate, and hydride complexes has been streamlined by first incorporating a cycloauration step devoid of toxic metals or harsh conditions. The resulting gold complexes exhibit remarkable stability in solution as well as in the solid state under ambient conditions, which enabled their characterization by X-ray diffraction analyses. Interestingly, the influence of the ligand allowed the preparation of gold(III)-hydrides using mild hydride donors such as H-Bpin, which contrasts with sensitive super hydrides or strong acids and cryogenic conditions employed in previous protocols. A detailed bonding characterization of these species is complemented by reactivity studies.

Preparation, cytotoxic activity and DNA interaction studies of new platinum(II) complexes with 1,10-phenanthroline and 5-alkyl-1,3,4-oxadiazol-2(3H)-thione derivatives

This work describes the synthesis, characterization and in vitro anticancer activity of two platinum(II) complexes of the type [Pt(L1)₂(1,10-phen)] 1 and [Pt(L2)₂(1,10-phen)] 2, where L1 = 5-heptyl-1,3,4-oxadiazole-2-(3H)-thione, L2 = 5-nonyl-1,3,4-oxadiazole-2-(3H)-thione and 1,10-phen = 1,10-phenanthroline. As to the structure of these complexes, the X-ray structural analysis of 1 indicates that the geometry around the platinum(II) ion is distorted square-planar, where two 5-alkyl-1,3,4-oxadiazol-2-thione derivatives coordinate a platinum(II) ion through the sulfur atom. A chelating bidentate phenanthroline molecule completes the coordination sphere. We tested these complexes in two breast cancer cell lines, namely, MCF-7 (a hormone responsive cancer cell) and MDA-MB-231 (triple negative breast cancer cell). In both cells, the most lipophilic platinum compound, complex 2, was more active than cisplatin, one of the most widely used anticancer drugs nowadays. DNA binding studies indicated that such complexes are able to bind to ct-DNA with K_b values of 10⁴ M^-1. According to data from dichroism circular and fluorescence spectroscopy, these complexes appear to bind to the DNA in a non-intercalative, probably via minor groove. Molecular docking followed by semiempirical simulations indicated that these complexes showed favorable interactions with the minor groove of the double helix of ct-DNA in an A-T rich region. Thereafter, flow cytometry analysis showed that complex 2 induced apoptosis and necrosis in MCF-7 cells.

Crystal and mol-ecular structures of di-chlorido-palladium(II) containing 2-methyl- or 2-phenyl-8-(diphenyphosphan-yl)quinoline

The crystal structures of di-chlorido-palladium(II) complexes bearing 2-methyl- and 2-phenyl-8-(di-phenyl-phosphan-yl)quinoline, namely, di-chlorido-[8-(di-phenyl-phosphan-yl)-2-methyl-quinoline-κ2 N,P]palladium(II), [PdCl2(C22H18NP)] (1) and di-chlorido-[8-(di-phenyl-phosphan-yl)-2-phenyl-quinoline-κ2 N,P]palladium(II), [PdCl2(C27H20NP)] (2), were analyzed and compared to that of the 8-(di-phenyl-phosphan-yl)quinoline (PQH) analogue (3). In all three complexes, the phosphanyl-quinoline moiety acts as a bidentate P,N-donating chelate ligand. In the PQH complex (3), the PdII center has a typical planar coordination environment; however, both the methyl- and phenyl-substituted phosphanyl-quinoline (PQMe and PQPh, respectively) complexes (1) and (2) exhibit a considerable tetra-hedral distortion around the PdII center, as parameterized by the τ4 values of 0.1555 (4) and 0.1438 (4) for (1) and (2), respectively. The steric inter-action from the substituted group introduced at the 2-position of the quinoline ring enforces the cis-positioned Cl ligand to be displaced from the ideal coordination plane. Also, the ideally planar phosphanyl-quinoline five-membered chelate ring shows a large bending deformation by the displacement of the PdII center from the quinoline plane. In addition, in the phenyl-substituted complex (3), the coordinating quinolyl and the substituted phenyl rings are not co-planar to each other, having a dihedral angle of 33.08 (7)°. This twist conformation prohibits any inter-molecular π-π stacking inter-action between the quinoline planes, which is observed in the crystals of complexes (1) and (2).

Sterically Demanding 8-(Diphenylphosphino)quinoline Complexes of Group 10 Metal(II): Synthesis, Crystal Structures, and Properties in Solution

Several series of platinum(II), palladium(II), and nickel(II) complexes bearing 8-(diphenylphosphino)quinoline (PQ^H) or its 2-methyl or 2-phenyl derivatives (PQ^Me or PQ^Ph) were synthesized, and their crystal structures and behaviors in solution were investigated. Most of the complexes [M(PQ^R)₂]X₂ (M^II = Pt^II, Pd^II, or Ni^II; R = H, Me or Ph; X = monoanionic ions) characterized in this study have an approximately square-planar coordination geometry with two bidentate P,N-chelating or monodentate P-donating quinolylphosphine ligands in the cis(P,P) configuration. A large steric requirement from the Me or Ph substituent introduced at the 2-position of the quinoline ring gives the resulting complexes severe distortion. The Pt^II and Pd^II complex cations maintained the square-planar coordination geometry, but the M^II center was displaced from the chelating ligand plane. This bending of the chelate coordination makes the M-N(quinoline) bond weaker, as demonstrated by the longer M-N bonds. In accord with the bond weakening, the partial dissociation of the PQ^H or PQ^Me chelates by substitution with halide anions were observed using UV-vis spectroscopy and X-ray crystallography. In contrast, the PQ^Ph complexes were stable in solution toward the addition of halide anions; the intramolecular π-π stacking interaction between the coordinating quinolyl and the 2-substituted phenyl rings protects the M^II center from nucleophilic attack. In the corresponding Ni^II complexes, the steric congestion arising from the mutually cis-positioned PQ^R ligands resulted in a large tetrahedral distortion around the Ni^II center. However, the intramolecular π-π stacking interaction was still effective in the PQ^Ph complex, and this interaction can explain some unusual robustness and electrochemical properties of the Ni^II-PQ^Ph complex.