Water-Soluble Organometallic Compounds. 7.1 Further Studies of 1,3,5-Triaza-7-Phosphaadamantane Derivatives of Group 10 Metals, Including Metal Carbonyls and Hydrides

Beyond transition block metals: exploring the reactivity of phosphine PTA and its oxide [PTA(O)] towards gallium(iii)

The water-soluble cage-like phosphine PTA (1,3,5-triaza-7-phosphaadamantane) and its phosphine oxide derivative [PTA(O)] (1,3,5-triaza-7-phosphaadamantane-7-oxide) were used to explore their reactivity towards two gallium(iii)-halide precursors, namely GaCl3 and GaI3, for the first time. By using various reaction conditions, a series of N-mono-protonated phosphine salts with [GaCl4]- or [I]- as counterions were obtained in all cases, while the formation of coordinated Ga-PTA and Ga-[PTA(O)] complexes was not observed. All compounds were characterized in solution using multinuclear NMR spectroscopy (1H, 13C{1H}, 31P{1H} and 71Ga) and in the solid state using FT-IR spectroscopy and X-ray crystal diffraction. The new Ga-phosphine salts resulted stable and highly soluble in aqueous solution at room temperature. Density functional theory (DFT) calculations were also performed to further rationalize the coordination features of PTA with Ga3+ metal ion, highlighting that the phosphorus-gallium bond is about twice weaker than the phosphorus-metal bond commonly established by PTA with transition metals such as gold. Furthermore, the mono-protonation of PTA (or [PTA(O)]) makes the formation of ionic gallium-PTA coordination complexes thermodynamically unstable, as confirmed experimentally by the formation of Ga-phosphine salts reported herein.

Antibacterial properties of phosphine gold(I) complexes with 5-fluorouracil

New gold(I) complexes with coordination to 5-fluorouracil (5-FU), an anticancer drug with antibacterial properties, have been synthesised and characterised, and are the first reported examples of 5-FU-Au compounds. These new complexes show high solution stability, even in the presence of a cysteine derivative, and so were evaluated as antibacterial compounds against model Gram-positive and Gram-negative bacteria. All the complexes show excellent antibacterial activity against Gram-positive B. subtilis, most of them improving the activity of 5-FU alone. Furthermore, these new complexes are also active against Gram-negative E. coli, where [Au(5-FU)(PTA)], the complex with the smallest phosphane, is the most bactericidal, 32 times more active than 5-FU on its own.

Actual Symmetry of Symmetric Molecular Adducts in the Gas Phase, Solution and in the Solid State

This review discusses molecular adducts, whose composition allows a symmetric structure. Such adducts are popular model systems, as they are useful for analyzing the effect of structure on the property selected for study since they allow one to reduce the number of parameters. The main objectives of this discussion are to evaluate the influence of the surroundings on the symmetry of these adducts, steric hindrances within the adducts, competition between different noncovalent interactions responsible for stabilizing the adducts, and experimental methods that can be used to study the symmetry at different time scales. This review considers the following central binding units: hydrogen (proton), halogen (anion), metal (cation), water (hydrogen peroxide).

A five-coordinate cobalt bis-(di-thiol-ene)-phosphine complex [Co(pdt)2(PTA)] (pdt = phenyl-dithiol-ene; PTA = 1,3,5-tri-aza-7-phosphaadamantane)

The synthesis and crystal structure are reported for a five-coordinate cobalt di­thiol­ene-phosphine complex [Co(pdt)₂(PTA)] (pdt = phenyl­dithiol­ene; S₂C₂Ph₂), produced by PTA ligand-induced cleavage of the cobalt bis­(di­thiol­ene) dimer [Co₂(pdt)₄].

The title compound, bis­(1,2-diphenyl-2-sulfanyl­idene­ethane­thiol­ato-κ²S,S′)(1,3,5-tri­aza-7-phosphaadamantane-κP)cobalt(II) dichloromethane hemisolvate, [Co(pdt)₂(PTA)]·0.5C₂H₄Cl₂ or [Co(C₁₄H₁₀S₂)₂(C₆H₁₂N₃P)]·0.5C₂H₄Cl₂, contains two phenyl­dithiol­ene (pdt) ligands and a 1,3,5-tri­aza-7-phosphaadamantane (PTA) ligand bound to cobalt with the solvent 1,2-di­chloro­ethane mol­ecule located on an inversion center. The cobalt core exhibits an approximately square-pyramidal geometry with partially reduced thienyl radical monoanionic ligands. The supra­molecular network is consolidated by hydrogen-bonding inter­actions primarily with nitro­gen, sulfur and chlorine atoms, as well as parallel displaced π-stacking of the aryl rings. The UV–vis, IR, and CV data are also consistent with monoanionic di­thiol­ene ligands and an overall Co^II oxidation state.

A new amido-phosphine of dichloroacetic acid as an active ligand for metals of pharmaceutical interest. Synthesis, characterization and tests of antiproliferative and pro-apoptotic activity

We herein describe the synthesis and characterization of the new amido-phosphinic ligand 3,7‑bis(dichloroacetyl)‑1,3,7‑triaza‑5‑phosphabicyclo[3.3.1]nonane (DCP), a derivative of dichloroacetic acid (DCA), whose ability to reverse the suppressed mitochondrial apoptosis in cancer cells is known. DCP was obtained by a double N-acylation of PTA (1,3,5‑triaza‑7‑phosphaadamantane) occurring with loss of CH₂, in appropriate conditions_. Due to the hindered rotation around the amidic CN bonds, three rotameric forms of DCP were observed, whose ratio in solution was dependent on the solvent, while the X-ray crystal structure of DCP showed an opposite orientation of the two amidic carbonyl groups (anti rotamer). The lipophilic, air and thermally stable DCP was found able to act regiospecifically as a P-donor ligand toward soft metal ions. By ligand substitution on appropriate precursors, we obtained the complexes 1-9, where proapoptotic DCA is associated with metal ions of known cytotoxic activity on cancer cells (Pt²⁺, Pd²⁺, Ru²⁺, Re⁺, Au⁺). The antiproliferative activity of DCP and its complexes was tested in vitro, in comparison with cisplatin, on three human tumor cell lines: A2780 (ovarian cisplatin-sensitive), A2780cis (ovarian cisplatin-resistant) and K562 (erythroleukemic). The results showed that the simultaneous presence of DCP (containing two residues of proapoptotic DCA) and Pt(II) produces the best performances with respect to non-platinum complexes. Experiments of pro-apoptotic activity indicated that the antiproliferative activity of the most active DCP-Pt(II) complexes is associated with induction of apoptosis.

Syntheses and structural aspects of six-membered palladacyclic complexes derived fromN,N′,N′′-triarylguanidines with N- or S-thiocyanate ligands

Linkage isomers8·2/3PhMe and9·MeOH were synthesized, isolated and structurally characterized by SCXRD and the role of solvent of crystallization in the formation of these linkage isomers identified.

Thermodynamic stability and structure in aqueous solution of the [Cu(PTA)4]+ complex (PTA = aminophosphine‑1,3,5‑triaza‑7‑phosphaadamantane)

The chemistry of copper(I) with water-soluble phosphines is an emergent area of study which has the objective of finding ligands that stabilize copper in its lower oxidation state. Cu(I) has been found relevant in the mechanism of copper transports into cells, and the accessibility of this oxidation state has implications in oxidative stress processes. For these reasons the possibility to deal with stable, water soluble copper(I) is an attractive approach for devising new biologically relevant metal-based drugs and chelating agents. Here we present the X-ray absorption spectroscopy (XAS) and UV-visible spectrophotometric study of the [Cu(PTA)₄]BF₄ complex (PTA = aminophosphine‑1,3,5‑triaza‑7‑phosphaadamantane). In particular, we have studied the stability of the [Cu(PTA)_n]⁺ species (n = 2-4) in aqueous medium, and their speciation as a function of the total [Cu(PTA)₄]BF₄ concentration by means of competitive UV-visible spectrophotometric titrations using metallochromic indicators. Also, the structure in solution of the Cu(I)/PTA species and the nature of the first coordination sphere of the metal were studied by transformed XAS. Both techniques allowed to study samples with total [Cu(PTA)₄]BF₄ concentration down to 68-74 μM, possibly relevant for biological applications. Overall, our data suggest that the [Cu(PTA)_n]⁺ species are stable in solution, among which [Cu(PTA)₂]⁺ has a remarkable thermodynamic stability. The tendency of this last complex to form adducts with N-donor ligands is demonstrated by the spectrophotometric data. The biological relevance of PTA towards Cu(I), especially in terms of chemotreatments and chelation therapy, is discussed on the basis of the speciation model the Cu(I)/PTA system.

Photoactivated in Vitro Anticancer Activity of Rhenium(I) Tricarbonyl Complexes Bearing Water-Soluble Phosphines

Fifteen water-soluble rhenium compounds of the general formula [Re(CO)3(NN)(PR3)]+, where NN is a diimine ligand and PR3 is 1,3,5-triaza-7-phosphaadamantane (PTA), tris(hydroxymethyl)phosphine (THP), or 1,4-diacetyl-1,3,7-triaza-5-phosphabicylco[3.3.1]nonane (DAPTA), were synthesized and characterized by multinuclear NMR spectroscopy, IR spectroscopy, and X-ray crystallography. The complexes bearing the THP and DAPTA ligands exhibit triplet-based luminescence in air-equilibrated aqueous solutions with quantum yields ranging from 3.4 to 11.5%. Furthermore, the THP and DAPTA complexes undergo photosubstitution of a CO ligand upon irradiation with 365 nm light with quantum yields ranging from 1.1 to 5.5% and sensitize the formation of 1O2 with quantum yields as high as 70%. In contrast, all of the complexes bearing the PTA ligand are nonemissive and do not undergo photosubstitution upon irradiation with 365 nm light. These compounds were evaluated as photoactivated anticancer agents in human cervical (HeLa), ovarian (A2780), and cisplatin-resistant ovarian (A2780CP70) cancer cell lines. All of the complexes bearing THP and DAPTA exhibited a cytotoxic response upon irradiation with minimal toxicity in the absence of light. Notably, the complex with DAPTA and 1,10-phenanthroline gave rise to an IC50 value of 6 μM in HeLa cells upon irradiation, rendering it the most phototoxic compound in this library. The nature of the photoinduced cytotoxicity of this compound was explored in further detail. These data indicate that the phototoxic response may result from the release of both CO and the rhenium-containing photoproduct, as well as the production of 1O2.

New Class of Half-Sandwich Ruthenium(II) Arene Complexes Bearing the Water-Soluble CAP Ligand as an in Vitro Anticancer Agent

Ruthenium(II) arene complexes of 1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP) were obtained. Cytotoxicity studies against cancer cell lines reveal higher activity than the corresponding PTA analogues and, in comparison to the effects on noncancerous cells, the complexes are endowed with a reasonable degree of cancer cell selectivity.

Brønsted-Lowry Acid Strength of Metal Hydride and Dihydrogen Complexes

Transition metal hydride complexes are usually amphoteric, not only acting as hydride donors, but also as Brønsted-Lowry acids. A simple additive ligand acidity constant equation (LAC for short) allows the estimation of the acid dissociation constant Ka(LAC) of diamagnetic transition metal hydride and dihydrogen complexes. It is remarkably successful in systematizing diverse reports of over 450 reactions of acids with metal complexes and bases with metal hydrides and dihydrogen complexes, including catalytic cycles where these reactions are proposed or observed. There are links between pKa(LAC) and pKa(THF), pKa(DCM), pKa(MeCN) for neutral and cationic acids. For the groups from chromium to nickel, tables are provided that order the acidity of metal hydride and dihydrogen complexes from most acidic (pKa(LAC) -18) to least acidic (pKa(LAC) 50). Figures are constructed showing metal acids above the solvent pKa scales and organic acids below to summarize a large amount of information. Acid-base features are analyzed for catalysts from chromium to gold for ionic hydrogenations, bifunctional catalysts for hydrogen oxidation and evolution electrocatalysis, H/D exchange, olefin hydrogenation and isomerization, hydrogenation of ketones, aldehydes, imines, and carbon dioxide, hydrogenases and their model complexes, and palladium catalysts with hydride intermediates.

Electronic and steric Tolman parameters for proazaphosphatranes, the superbase core of the tri(pyridylmethyl)azaphosphatrane (TPAP) ligand

The Tolman electronic parameters (TEP) and cone angles were experimentally measured for a series of substituted proazaphosphatranes ligands by synthesizing their respective Ni(L^R)(CO)₃ complexes, where L = P(RNCH₂CH₂)₃N and R = Me, iPr, iBu and Bz.

Structural analysis of ruthenium–arene complexes using ion mobility mass spectrometry, collision-induced dissociation, and DFT

Electrospray ionization of [RuCl₂(p-cymeme)(PTA)] afforded a mixture of two molecular ions resulting from an in source oxidation of Ru^II into Ru^III or from protonation of the 1,3,5-triaza-7-phosphaadamantane (PTA) ligand.

Post-assembly guest oxidation in a metallo-supramolecular host and structural rearrangement to a coordination polymer

PTA hosted in a copper metallo-supramolecular triangle undergoes post-assembly oxidation to form PTAO in aerated solutions. The oxidation is triggered by selected co-solvents that also govern the formation of the final crystalline product leading to a discrete host-guest triangle {PTAO@[Cu(o-L)]3} or to a 1D coordination polymer {(PTAO)2@[Cu8][Cu2]}∞ containing a {Cu8} ring with a double hosting pocket.

Copper(I) targeting in the Alzheimer's disease context: a first example using the biocompatible PTA ligand

Copper(I) coordinating ligands in the Alzheimer's disease context have remained unexplored, despite the biological relevance of this redox state of the copper ion. Here, we show that the PTA ligand can remove copper from Aβ, prevent reactive oxygen species production and oligomer formation, two deleterious events in the disease's etiology.

Water-Soluble Phosphine Capable of Dissolving Elemental Gold: The Missing Link between 1,3,5-Triaza-7-phosphaadamantane (PTA) and Verkade's Ephemeral Ligand

We herein describe a tricyclic phosphine with previously unreported tris(homoadamantane) cage architecture. That water-soluble, air- and thermally stable ligand, 1,4,7-triaza-9-phosphatricyclo[5.3.2.1(4,9)]tridecane (hereinafter referred to as CAP) exhibits unusual chemical behavior toward gold and gold compounds: it readily reduces Au(III) to Au(0), promotes oxidative dissolution of nanocrystalline gold(0) with the formation of water-soluble trigonal CAP-Au(I) complexes, and displaces cyanide from [Au(CN)2](-) affording triangular [Au(CAP)3](+) cation. From the stereochemical point of view, CAP can be regarded as an intermediate between 1,3,5-triaza-7-phosphaadamantane (PTA) and very unstable aminophosphine synthesized by Verkade's group: hexahydro-2a,4a,6a-triaza-6b-phosphacyclopenta[cd]pentalene. The chemical properties of CAP are likely related to its anomalous stereoelectronic profile: combination of strong electron-donating power (Tolman's electronic parameter 2056.8 cm(-1)) with the low steric demand (cone angle of 109°). CAP can be considered as macrocyclic counterpart of PTA with the electron-donating power approaching that of strongest known phosphine electron donors such as P(t-Bu)3 and PCy3. Therefore, CAP as sterically undemanding and electron-rich ligand populates the empty field on the stereoelectronic map of phosphine ligands: the niche between the classic tertiary phosphines and the sterically undemanding aminophosphines.

Tuning heavy metal compounds for anti-tumor activity: is diversity the key to ruthenium’s success?

This review aims to bring the reader up to date with the more recent ruthenium compounds that have been synthesized and tested for their cytotoxicity. The chemistry of these transition metal complexes will be introduced and the basic principles that govern their common behavior outlined. The recent history of established compounds within this field will be presented alongside those that now represent the cutting-edge. The inherent variety within this class of compounds will lead the reader to appreciate their diversity and pose questions as to their similarities aside from the presence of a shared metal ion. This review aims to discuss and contextualize the state-of-the-art research within the context of the speculative advancement of this developing field. There is an evident need to specify the molecular and cellular targets of these drug molecules in order to ultimately elucidate their mode or modes of action. The evidence presented herein suggests that new avenues of research require novel analytical probes and methods for tracing the fate of ruthenium complexes in cells in order to understand their very promising cytotoxic activity.

Systematic reactions of [Pt(PF3)4]

Tetrahedral [Pt(PF(3))(4)] reacts with H(+) to form trigonal bipyramidal [Pt(PF(3))(4)H](+). This in turn looses PF(3) to form square-planar [Pt(PF(3))(3)H](+). The complex [Pt(PF(3))(4)] can be oxidized with AsF(5) to form the square-planar complex, [Pt(PF(3))(4)](2+), which can be more conveniently obtained from PtF(4) and PF(3) in HF/SbF(5) solution. [Pt(PF(3))(4)](2+) reacts with F(-) in HF under cluster formation to [Pt(4)(PF(3))(8)H](+).

Extending the coordination chemistry of 1,3,5-triaza-7-phosphaadamantane (PTA) to cobalt centers: first examples of co-PTA complexes and of a metal complex with the PTA oxide ligand

Water-soluble Co (III) and Co (II) complexes with P- or N-coordinated PTA or PTA oxide ligands, respectively, have been prepared and fully characterized, constituting the first examples of cobalt compounds bearing PTA or any ligand with a cage-like PTA core, the latter complex providing also the first PTA oxide coordination to a metal center.

Three-dimensional hydrogen-bonded supra-molecular assembly in tetrakis-(1,3,5-triaza-7-phosphaadamantane)copper(I) chloride hexa-hydrate

The structure of the title compound, [Cu(PTA)₄]Cl·6H₂O (PTA is 1,3,5-triaza-7-phosphaadamantane, C₆H₁₂N₃P), is composed of discrete monomeric [Cu(PTA)₄]⁺ cations, chloride anions and uncoordinated water mol­ecules. The Cu^I atom exhibits tetra­hedral coordination geometry, involving four symmetry-equivalent P–bound PTA ligands. The structure is extended to a regular three-dimensional supra­molecular framework via numerous equivalent O—H⋯N hydrogen bonds between all solvent water mol­ecules (six per cation) and all PTA N atoms, thus simultaneously bridging each [Cu(PTA)₄]⁺ cation with 12 neighbouring units in multiple directions. The study also shows that PTA can be a convenient ligand in crystal engineering for the construction of supra­molecular architectures.