PdCl2 Research Articles

Fluorescence Amplification of Unsaturated Oxazolones Using Palladium: Photophysical and Computational Studies.

Weakly fluorescent (Z)-4-arylidene-5-(4H)-oxazolones (1), ΦPL < 0.1%, containing a variety of conjugated aromatic fragments and/or charged arylidene moieties, have been orthopalladated by reaction with Pd(OAc)2. The resulting dinuclear complexes (2) have the oxazolone ligands bonded as a C^N-chelate, restricting intramolecular motions involving the oxazolone. From 2, a variety of mononuclear derivatives, such as [Pd(C^N-oxazolone)(O2CCF3)(py)] (3), [Pd(C^N-oxazolone)(py)2](ClO4) (4), [Pd(C^N-oxazolone)(Cl)(py)] (5), and [Pd(C^N-oxazolone)(X)(NHC)] (6, 7), have been prepared and fully characterized. Most of complexes 3-6 are strongly fluorescent in solution in the range of wavelengths from green to yellow, with values of ΦPL up to 28% (4h), which are among the highest values of quantum yield ever reported for organometallic Pd complexes with bidentate ligands. This means that the introduction of the Pd in the oxazolone scaffold produces in some cases an amplification of the fluorescence of several orders of magnitude from the free ligand 1 to complexes 3-6. Systematic variations of the substituents of the oxazolones and the ancillary ligands show that the wavelength of emission is tuned by the nature of the oxazolone, while the quantum yield is deeply influenced by the change of ligands. TD-DFT studies of complexes 3-6 show a direct correlation between the participation of the Pd orbitals in the HOMO and the loss of emission through non-radiative pathways. This model allows the understanding of the amplification of the fluorescence and the future rational design of new organopalladium systems with improved properties.

Pd-Coordinated Salinidol-Modified Mixed MOF: An Excellent Active Center for Efficient Nitroarenes Reduction and Selective Oxidation of Alcohols.

Selective oxidation of active and inactive alcohol substrates and reduction of nitroarenes is a highly versatile conversion that remains a challenge in controlling functionality and adjustments in metal-organic frameworks (MOFs). On the other hand, it offers an attractive opportunity to expand their applications in designing the next generation of catalysts with improved performance. Herein, a novel mixed MOF consisting of supported 2-hydroxybenzamide (mixed MOF-salinidol) has been fabricated by post-synthetic modifications of mixed MOF. Subsequently, the prepared nanocomposites were modified to impart catalytic sites using palladium chloride ions mixed with MOF-salinidol/Pd (II). After successfully designing and structurally characterizing nanocomposites, we evaluated their activity in oxidizing primary and secondary alcohols using aerobic conditions with molecular oxygen and an air atmosphere. In addition, the stability of (mixed MOF-salinidol/Pd (II)) catalysts under catalytic conditions was also demonstrated by comparing the Fourier-transform infrared spectrum, scanning electron microscopy image, and ICP-OES method before and after catalysis. Based on the results, the active surface area of the synthesized nanocatalyst is large, which highlights its unique synergistic effect between post-synthetic modified MOF and Pd, and furthermore, the availability of catalytic sites from Pd, as demonstrated by outstanding catalytic activity.

Analysis of the binding mechanism for a water-soluble Pd(II) complex containing β-amino alcohols with HSA applying experimental and computational methods

In the study ahead, the binding interactions of the [Pd (HEAC) Cl2] complex with human serum albumin (HSA) protein have been assayed in vitro (pH= 7.40) utilizing computational and experimental procedures. The mentioned complex was synthesized as a water-soluble complex from {2-((2-((2-hydroxyethyl)amino)ethyl)amino) cyclohexanol} ligand = HEAC. The results of electronic absorption and circular dichroism investigations illustrated that the hydrophobicity of the Tryptophan microenvironment in HSA undergoes the changes by binding to the Pd(II) complex without substantial perturbations on the protein secondary structure. The fluorescence emission spectroscopy analysis revealed that with rising temperature, the quenching constant (K sv) in the Stern–Volmer’s relation decreases; so, it can be said that the interaction process is along with a static quenching mechanism. The values of 2.88 × 105 M−1, and 1.26 represent the binding constant (K b) and the number of the binding sites (n), respectively. The Job graph showed the maximum point at χ = 0.5, which means organizing a new set with 1:1 stoichiometry. Thermodynamic profile (ΔH < 0, ΔS < 0, and ΔG < 0) has affirmed that van der Waals forces and hydrogen bonds have a basic function in the Pd(II) complex-albumin bindings. The ligand-competitive displacement studies utilizing warfarin and ibuprofen have represented that Pd(II) complex interacts with albumin by site II (subdomain IIIA). The computational molecular docking theory approved the results of the site-competitive tests; also, it indicated the existence of hydrogen bonds and van der Waals forces in Pd(II) complex-albumin interactions. Communicated by Ramaswamy H. Sarma

Electronic and ring size effects of N-heterocyclic carbenes on the kinetics of ligand substitution reactions and DNA/protein interactions of their palladium(II) complexes

The synthesis, substitution kinetics and DNA/BSA interactions of four cationic Pd(II) complexes [Pd(1)Cl]BF4 (Pd1), [Pd(2)Cl]BF4 (Pd2), [Pd(3)Cl]BF4 (Pd3) and [Pd(4)Cl]BF4 (Pd4), derived from the reaction of [PdCl2(NCCH3)2] with ligands 2,6-bis(3-methylimidazolium-1-yl)pyridine dibromide (1), 2,6-bis(3-ethylimidazolium-1-yl)pyridine dibromide (2), 2,6-bis(1-methylimidazole-2-thione)pyridine (3), and 2,6-bis(1-ethylimidazole-2-thione)pyridine (4), respectively are reported. The complexes were characterised by various spectroscopic techniques and single crystal X-ray diffraction for compound Pd2. Kinetic reactivity of the complexes with the biologically relevant nucleophiles thiourea (Tu), L-methionine (L-Met) and guanosine 5′-monophosphate sodium salt (5’-GMP) was in the order: Pd1 > Pd2 > Pd3 > Pd4, which was largely dependent on the electronic and ring size of the chelate ligands, consistent with Density functional theory (DFT) simulations. The interactions of the complexes with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) binding titrations showed strong binding. Both the experimental and in silico data reveal CT-DNA intercalative binding mode.Graphical abstract

Palladium(II) Complexes of 1‐Phosphaisoprene Molecules and Polymers: Reversible Cross‐Linking of a Phosphorus‐Containing Polymer

AbstractThe anionic polymerization of 1‐phosphaisoprene [Mes*P=C(Me)−CH=CH2 (E‐1)] affords poly(1‐phosphaisoprene) 2 in high yield (75 %). Concentrated solutions of polymer 2 (Mn=21,800 g mol−1; Đ=1.02) a P‐analogue of natural rubber, undergo gelation upon treatment with [Pd(cod)Cl2] (0.15 P equiv). Evidence for P‐coordination of 2 to PdII was obtained by 31P and 1H NMR spectroscopy. The gelation is reversed by the addition of PMe3 and the reformation of recoverable 2 along with [PdII−PMe3] complexes were confirmed by 31P NMR spectroscopy. The use of labile metal‐ligand bonds to reversibly form gels is unprecedented and has relevance to self‐healing materials. In contrast, coordination of 2 to [Pd(η3‐C3H5)(μ‐Cl)]2 affords the well‐defined complex 2 ⋅ [Pd(η3‐C3H5)Cl] which was characterized by 31P, 1H, 13C{1H} NMR spectroscopy and GPC. This polymer chemistry was complemented by detailed molecular model studies of the coordination chemistry of monomer 1‐phosphaisoprene E‐1 with [Pd(cod)Cl2] and [Pd(η3‐C3H5)(μ‐Cl)]2].

Second-Generation Atroposelective Synthesis of KRAS G12C Covalent Inhibitor GDC-6036.

A chromatography-free asymmetric synthesis of GDC-6036 (1) was achieved via a highly atroposelective Negishi coupling of aminopyridine 5 and quinazoline 6b catalyzed by 0.5 mol % [Pd(cin)Cl]2 and 1 mol % (R,R)-Chiraphite to afford the key intermediate (Ra)-3. An alkoxylation of (Ra)-3 with (S)-N-methylprolinol (4) and a global deprotection generates the penultimate heterobiaryl intermediate 2. A controlled acrylamide installation by stepwise acylation/sulfone elimination and final adipate salt formation and crystallization delivered high-purity GDC-6036 (1).

Facile Synthesis of Triptycene‐Azolium Salts and NHC‐Metal Complexes

AbstractThe cycloaddition reactions of eleven substituted anthracenes with nosylated quinone imines provides a convenient route to the respective triptycenes. Following re‐aromatization, selective O‐butylation and cleavage of the nosyl‐group the respective triptycene anilines are obtained, which are converted into the respective imidazolium salts according to established procedures. Deprotonation of the imidazolium salts provide new triptycene‐NHC‐metal complexes (M=AuCl, RhCl(cod), IrCl(cod), RhCl(CO)2, IrCl(CO)2, PdI2(py), PtCl2(py), Pd(allyl)Cl) with unusual ligand sterics.

Stereoselectivity of Acetylene Hydrochlorination over Supported PdCl&lt;sub&gt;2&lt;/sub&gt;/С Catalysts

The products of catalytic hydrochlorination of acetylene-D2 over palladium chloride complexes supported on activated carbon are a mixture of vinyl chloride stereoisomers resulting from syn- and anti-addition of the hydrogen chloride molecule to the triple bond. The reaction is accompanied by isomerization of primary trans-vinyl chloride into its cis-stereoisomer, but the characteristic isomerization times exceed significantly the duration of acetylene hydrochlorination. This fact allowed us to estimate the portion of products formed exclusively during the catalytic reaction, the difference in the effective activation energies of the syn- and anti-addition routes (~21 kJ/mol), and to demonstrate a monotonic increase in the part of the syn-addition product with increasing mass loading ω of the active metal, reaching saturation at ω 2 wt %.

One-Pot Construction of β-Selective Quinolines with γ-Quaternary Carbon from Vinylquinolines with Active Ylides via Pd/Sc/Brønsted Acid Co-Catalysis

Vinyl-substituted N-heterocycles, as more challenging inert olefins with more stable reactivity, have brought about widespread attention in the reaction of aza-Michael addition or reduction coupling reaction. Here, we report a [Pd(η3-C3H5)Cl]2/Sc(OTf)3-catalyzed catalytic process accelerated by Brønsted acids with a β-selective aza-Michael addition to yield a γ-quaternary carbon from vinyl-substituted quinolines, diazos, and anilines/alcohols in one pot. The generation of anhydride analogues from Brønsted acid and the counter anion (OTf–) of Lewis acid promotes the activation of the corresponding Lewis acid and the nearly quantitative transformation. Both π-cation and coordination interactions play pivotal roles in the activation of the vinyl-quinoline substrates by the activated Lewis acid Sc(OTf)3. The control mechanistic evidence and DFT calculations presented a Pd/Sc/Brønsted acid co-catalyzed addition mechanism. The triple co-catalytic system provides a strategy for the activation of vinyl-quinolines with a linear selectivity containing γ-quaternary carbon, and the developed method shows a broad substrate scope varying from alkyl/aryl alcohols and amines which provides a general and rapid strategy for the quinoline-based diverse library construction.

Bis(NHC)-Pd(II) and Pd(0) complexes supported on magnetic SBA-15 for the selective aerobic oxidation of benzyl alcohols to benzaldehydes and reduction of nitroarenes

The present study describes the synthesis, characterization, and use of two new supported magnetic Pd-NHC catalysts based on Pd(II) and Pd(0). A composite of magnetite-silica core shells and SBA-15 was successively treated with (3-aminopropyl) triethoxysilane (APTES), cyanuric chloride (CC), imidazole, 2-bromopyridine, and trans-[Pd(Cl)2(SMe2)2] complex. The obtained supported bis(NHC)-Pd(II) complex, Fe3O4@SiO2@SBA-AP-CC-bis(NHC)-Pd(II), was characterized by Fourier transform infrared spectroscopy (FT-IR), X‐ray diffraction spectroscopy (XRD), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), energy‐dispersive X‐ray analysis (EDX), and Brunauer-Emmett-Teller surface area measurement (BET). The catalytic potential of the supported bis(NHC)-Pd(II) complex was explored for the selective preparation of benzaldehydes from the corresponding benzyl alcohols. The Pd(0) catalyst, Fe3O4@ SiO2@SBA-AP-CC-bis(NHC)-Pd(0), was obtained via reduction of the Pd(II)-catalyst with NaBH4. The obtained Pd(0)-catalyst efficiently reduced nitroarenes to anilines in the presence of hydrazine hydrate. The Pd contents of the Pd(II)-catalyst (2.83%wt.; 0.266 mmol/g) and Pd(0)-catalyst (2.26%wt., 0.212 mmol/g) were measured by atomic absorption spectroscopy. Both reactions are conducted under optimal reaction conditions of the solvent, the base, and the catalyst dosage. The catalysts enjoy easy magnetic separation, recyclability over eight runs without significant loss activity, and noticeable stability. They showed negligible palladium leaching (0.83% in the oxidation of benzyl alcohol and 0.1% in the reduction of nitroarenes).

Eco-friendly synthesis of graphene oxide–palladium nanohybrids

Nanostructured hybrids of graphene oxide and palladium were fabricated by means of one-step solvent-free gas phase treatment of graphene oxide with the aliphatic amines 1-octadecylamine and 1,8-diaminooctane, followed by in situ decoration with palladium in the liquid medium using palladium chloride as the precursor and citric acid as a mild and environmentally friendly stabilizing and reducing agent. The proposed synthesis method represents an eco-friendly alternative for obtaining nanohybrids of graphene oxide and palladium nanoparticles under mild conditions. Spectroscopic studies evidenced -COOH group derivatization of graphene due to the amidation reaction; transmission electron microscopy demonstrated the formation of nanometer-sized crystalline palladium particles and evidenced that the diamine-functionalization results in a larger particle sizes than observed for monoamine- or non-functionalized substrates. The hybrids obtained have a slightly lower thermal stability than pristine graphene oxide.

C–H Metalation of Terpyridine Stereoisomers with Ni(II), Pd(II), and Pt(II)

Ni(II), Pd(II), and Pt(II) complexes [M(Y-terpy)X] (X = Cl or Br) containing the tridentate N^C^N-cyclometalating 2,3′:5′,2″and 2,2′:4′,2″ stereoisomers of the well-known tridentate N^N^N ligand 2,2′:6′,2″-terpyridine (terpy) were synthesised in moderate to good yields through C–H activation. For the Pt complexes, the phenyl ethynide derivatives [Pt(Y-terpy)(C≡CPh)] were also obtained under Sonogashira conditions. In contrast to this, C^N^N cyclometalated complexes using the 2,2′:6′,3″- and 2,2′:6′4″-terpy isomers were not obtained. Comparison of the N^C^N complexes of the cyclometalated 2,3′:5′,2″- and 2,2′:4′,2″-terpy ligands with complexes [M(dpb)Cl] of the prototypical N^C^N cyclometalating ligand dpb− (Hdpb = 2,6-diphenyl-pyridine) showed higher potentials for the terpy complexes for the ligand-centred reductions in line with the superior π-accepting properties of the terpy ligands compared with dpb. Metal-centred oxidations were facilitated by the dpb ligand carrying a central σ-donating phenyl group instead of a metalated pyridine moiety. The same trends were found for the long-wavelength absorptions and the derived electrochemical and optical band gaps. The lower σ-donating capacities of the cyclometalated terpy derivatives is also confirmed by a reduced trans influence in the structure of [Ni(2,3′:5′,2″-terpy)Br0.14/OAc0.86]. Attempts to re-crystallise some poorly soluble Pd(II) and Pt(II) complexes of this series under solvothermal conditions (HOAc) gave two structures with N-protonated cyclometalated pyridine moieties, [Pt(2,3′:5′,2″-terpyH)Cl].Cl and [Pd(2,3′:5′,2″-terpyH)Cl2].

Convenient One-Pot Synthesis of L2Pd(0) Complexes for Cross-Coupling Catalysis

A convenient one-pot synthesis of (tBu3P)2Pd(0) was successfully carried out by using various air-stable Pd(II) salts, such as Pd(cod)Cl2, Pd(nbd)Cl2, Pd(CH3CN)2Cl2, or Pd(PhCN)2Cl2, without the use of an external reducing agent. Using Pd(cod)Cl2 as the precursor, large-scale synthesis of (tBu3P)2Pd(0) was accomplished in excellent yield and purity. Another protocol was also developed for L2Pd(0) complexes via an atom economical one-pot method by reacting in situ generated LPd(R-allyl)Cl complexes (L = tBu3P, Cy3P, (o-Tol)3P, CataXCium A, AmPhos, QPhos: R = H, Me, Ph) with 1 equivalent of L in the presence of a base with yields ranging from 74% to 92%, although the process can be further optimized. These methods are superior to those reported in the literature.

Noble-Metal Nanoparticle-Embedded Silicon Nanogratings via Single-Step Laser-Induced Periodic Surface Structuring.

Here, we show that direct femtosecond laser nanostructuring of monocrystalline Si wafers in aqueous solutions containing noble-metal precursors (such as palladium dichloride, potassium hexachloroplatinate, and silver nitrate) allows for the creation of nanogratings decorated with mono- (Pd, Pt, and Ag) and bimetallic (Pd-Pt) nanoparticles (NPs). Multi-pulse femtosecond-laser exposure was found to drive periodically modulated ablation of the Si surface, while simultaneous thermal-induced reduction of the metal-containing acids and salts causes local surface morphology decoration with functional noble metal NPs. The orientation of the formed Si nanogratings with their nano-trenches decorated with noble-metal NPs can be controlled by the polarization direction of the incident laser beam, which was justified, for both linearly polarized Gaussian and radially (azimuthally) polarized vector beams. The produced hybrid NP-decorated Si nanogratings with a radially varying nano-trench orientation demonstrated anisotropic antireflection performance, as well as photocatalytic activity, probed by SERS tracing of the paraaminothiophenol-to-dimercaptoazobenzene transformation. The developed single-step maskless procedure of liquid-phase Si surface nanostructuring that proceeds simultaneously with the localized reduction of noble-metal precursors allows for the formation of hybrid Si nanogratings with controllable amounts of mono- and bimetallic NPs, paving the way toward applications in heterogeneous catalysis, optical detection, light harvesting, and sensing.

Synthesis, characterization and anticancer properties: A series of highly selective palladium(II) substituted-terpyridine complexes

Ten new palladium(II) complexes [PdCl(L1−10)]Cl have been synthesized by the reaction of palladium(II) chloride and ten 4′-(substituted-phenyl)-2,2′:6′,2′′-terpyridine ligands bearing hydrogen(L1), p-hydroxyl(L2), m-hydroxyl (L3), o-hydroxyl (L4), methyl (L5), phenyl (L6), fluoro (L7), chloro (L8), bromo (L9), or iodo (L10). Their structures were confirmed by FT-IR, 1H NMR, elemental analysis and/or single crystal X-ray diffraction analysis. Their in vitro anticancer activities were investigated based on five cell lines, including four cancer cell lines (A549, Eca-109, Bel-7402, MCF-7) and one normal cell line (HL-7702). The results show that these complexes possess a strong killing effect on the cancer cells but a weak proliferative inhibition on the normal cells, implying their high inhibitory selectivity for the proliferation of the cancer cell lines. Flow cytometry characterization reveals that these complexes affect cell proliferation mainly in the G0/G1 phase and induce the late apoptotic of the cells. The quantity of palladium(II) ion in extracted DNA was determined by ICP-MS, which proved that these complexes target genomic DNA. And the strong affinity of the complexes with CT-DNA were confirmed by UV–Vis spectrum and circular dichroism (CD). The possible binding modes of the complexes with DNA were further explored by molecular docking. As the concentration of complexes 1–10 gradually increases, the fluorescence intensity of bovine serum albumin (BSA) decreases by a static quenching mechanism.

A New Bis‐(NHC)‐P(II) Complex Supported on Magnetic Mesoporous Silica: An Efficient Pd(II) Catalyst for the Selective Buchwald‐Hartwig Monoarylation of Ammonia

AbstractWe report the synthesis and identification of a new bis(NHC)‐Pd(II) catalyst supported on magnetic SBA‐15 (Fe3O4@SBA‐15). The surface of magnetic SBA‐15 was subsequently treated with (3‐aminopropyl) triethoxysilane (APTES), cyanuric chloride (CC), imidazole, and 2‐bromopyridine. The modified magnetic mesoporous material was then further treated with separately prepared trans‐[Pd(Cl)2(SMe2)2] complex to give Fe3O4@SBA‐AP‐CC‐bis(NHC)‐Pd(II) as a supported bis(NHC)‐Pd(II) complex. The catalyst was fully characterized by common spectroscopic methods. X‐ray photoelectron spectroscopy (XPS) revealed that some imine nitrogens interact with palladium atoms. The supported Pd(II) complex catalyzed the direct monoarylation of ammonia with iodo‐, bromo‐, and chloroarenes, selectively. The effects of reaction components and parameters were investigated to establish the optimal reaction conditions. The catalyst was separated by a magnet, washed, and applied in the subsequent run. It exhibited noticeable stability and reused over seven catalytic cycles with negligible deactivation. A small Pd leaching (1.04 %) was observed in the first run.

Anti‐proliferative and Apoptotic Effects of Coordination Compounds of Zinc(II), Palladium(II), and Platinum(II) with Tridentate 4‐(6‐hydroxyphenyl)‐2,6‐di(thiazol‐2‐yl)pyridine

AbstractThe mononuclear coordination compounds, [Zn(L)Cl2] (1), [Pd(L)Cl]Cl (2), and [Pt(L)Cl]Cl (3) (L) is a tridentate‐coordinated of 4‐(6‐hydroxyphenyl)‐2,6‐di(thiazol‐2‐yl)pyridine) were synthesized and characterized by different spectroscopic methods (FTIR, MALDI‐TOF‐MS, 1H NMR, 13C NMR, and UV/Vis). By using density functional theory (DFT) and time‐dependent DFT (TD‐DFT) methods, the geometrical parameters, UV/Vis absorption spectra, and infrared vibrational frequencies for the investigated compounds were explored. Anticancer activities of these compounds were determined by SRB viability assay in human lung (A549 and H1299), prostate (LNCAP), colorectal (HT‐29), breast cancer (MDA‐MB‐231) and healthy bronchial (BEAS‐2B), breast (MCF‐10A), colon (CCD‐18Co), and prostate (WPMY‐1) epithelial cells. Caspase 3/7 activity, cleaved cytokeratin‐18, and PARP levels were measured to determine apoptosis in the metal compounds found to be effective. Among the compounds, 1 showed a selective inhibiting effect and induced apoptosis on the cancer cells, thus further analyses are needed to evaluate its antitumor/anticancer activity.

A method for the infectivity discrimination of enveloped DNA viruses using palladium compounds pre-treatment followed by real-time PCR.

Cultivation-based assays represent the gold standard for the assessment of virus infectivity; however, they are time-consuming and not suitable for every virus type. Pre-treatment with platinum (Pt) compounds followed by real-time PCR has been shown to discriminate between infectious and non-infectious RNA viruses. This study examined the effect of Pt and palladium (Pd) compounds on enveloped DNA viruses, paying attention to two significant pathogens of livestock - bovine herpesvirus-1 (BoHV-1) and African swine fever virus (ASFV). Native or heat-treated BoHV-1 suspension was incubated with the spectrum of Pt/Pd compounds. Bis(benzonitrile)palladium(II) dichloride (BB-PdCl 2) and dichloro(1,5-cyclooctadiene) palladium(II) (PdCl 2-COD) produced the highest differences found between native and heat- -treated viruses. Optimized pre-treatment conditions (1 mM of Pd compound, 15 min, 4°C) were applied on both virus genera and the heat inactivation profiles were assessed. A significant decrease in the detected quantity of BoHV-1 DNA and ASFV DNA after heat-treatment (60°C and 95°C) and consequent incubation with Pd compounds was observed. BB-PdCl 2 and PdCl 2-COD could help to distinguish between infectious and non-infectious enveloped DNA viruses such as BoHV-1 or ASFV.

Expanding the Role of Dimeric Species: On-Cycle Involvement, Improved Stability, and Control of Stereo-Specificity. A Case Study of Atom-Economic Catalytic Hydrothiolation

A common assumption that dimeric metal complexes in many catalytic systems represent a resting state and are not directly involved in catalytic processes was revised in a combined experimental and theoretical study. On-cycle participation of dimeric metal complexes, rather than typically assumed off-cycle involvement, was revealed, and advantageous performance in terms of improved selectivity was observed. The conceptual rationalization for the participation of dimeric species in the catalytic cycle was developed. The Pd-catalyzed hydrothiolation process (where strong Pd–S binding is well established and a persistent opinion for the inactive/poisoning role of dimeric species is presumed) was evaluated as a challenging system to test the concept. Activation of an (NHC)Pd(Cl)(acac) precatalyst (NHC─N-heterocyclic carbene and acac─acetylacetonate) under the reaction conditions produced monomeric (NHC)Pd(SPh)2 or dimeric (NHC)2Pd2(SPh)4 species depending on the steric bulkiness of the NHC ligand. Dimeric complexes possessed higher selectivity and tolerated disulfide impurities in contrast to monomeric complexes. Quantum chemical modeling suggested that dimeric catalysis proceeds through the opening of only one (μ-SPh)–Pd bridging bond with retention of the dimeric structure. The second bridging bond is maintained, which prevents the monomerization of the complex. Catalytically active species were detected in a hydrothiolation reaction by high-resolution mass spectrometry and NMR spectroscopy. Proving the opportunity for productive homogeneous catalysis via strongly coordinated dimeric metal species opens new opportunities for catalyst design in the increased nuclearity dimension.

Metallodrugs against Breast Cancer: Combining the Tamoxifen Vector with Platinum(II) and Palladium(II) Complexes.

The luminal A-subtype of breast cancer, where the oestrogen receptor α (ERα) is overexpressed, is the most frequent one. The prodrug tamoxifen (1) is the clinically used agent, inhibiting the ERα activity via the formation of several active metabolites, such as 4-hydroxytamoxifen (2) or 4,4'-dihydroxytamoxifen (3). In this study, we present the tamoxifen derivative 4-[1,1-bis(4-methoxyphenyl)but-1-en-2-yl]-2,2'-bipyridine (4), which was combined with platinum or palladium dichloride, the former a well-known scaffold in anticancer treatment, to give [PtCl2(4-κ2N,N')] (5) or [PdCl2(4-κ2N,N'] (6). To prevent fast exchange of weakly coordinating chlorido ligands in aqueous solution, a bulky, highly stable and hydrophobic nido-carborate(-2) ([C2B9H11]2-) was incorporated. The resulting complexes [3-(4-κ2N,N')-3,1,2-PtC2B9H11] (7) and [3-(4-κ2N,N')-3,1,2-PdC2B9H11] (8) exhibit a dramatic change in electronic and biological properties compared to 5 and 6. Thus, 8 is highly selective for triple-negative MDA-MB-231 cells (IC50 = 3.7 μM, MTT test), while 7 is completely inactive against this cell line. The observed cytotoxicity of compounds 4-6 and 8 against this triple-negative cell line suggests off-target mechanisms rather than only ERα inhibition, for which these compounds were originally designed. Spectroscopic properties and electronic structures of the metal complexes were investigated for possible explanations of the biological activities.