Photoluminescence of tetrameric platinum(II) acetate in solution

Tetrameric Pt(II) acetate shows a photoluminescence in solution at λ_max=510 nm and 630 nm which is assigned to a metal-centered fluorescence (τ<5 ns) and phosphorescence (τ=1.8 μs), respectively. It is suggested that in the emissive excited state the metal–metal bonds are weakened.     

Reduction of nitroaromatics with poly(vinylpyridine) complexes of palladium(II) and platinum(II)

Palladium(II) and platinum(II) anchored to 2- and 4-vinylpyridine polymers of different molecular weights were used for the dihydrogen reduction of various nitroaromatics and benzaldehyde in ethanol at 50°C. Palladium(II) complexes were far more effective than their platinum(II) analogues and the activity decreased with increasing molecular weights of the polymers. The nitroaromatics were selectively and almost completely reduced to the corresponding anilines. During reduction, the orange palladium(II) complexes changed to voluminous green precipitates, which could be used repeatedly and preserved for a long time without any loss of activity. A rate equation of the type: rate = K[Cat] [H₂] has been derived and a reduction mechanism has been proposed on the basis of experimental results and kinetic data.     

The structures and decomposition products of palladium(II) and platinum(II) terpyridine phenoxide complexes

A series of complexes of formula [Pd(OR)(terpy)]BF₄ and [Pt(OR)(terpy)]BF₄ (ROH=a substituted phenol; terpy=2,2^′:6^′,2^″-terpyridine) have been prepared by reaction of [M(OH)(terpy)]BF₄ (M=Pd, Pt) with ROH. One Pd(II) and one Pt(II) complex in this series have been structurally characterised. These compounds are very acid sensitive; decomposition products resulting from recrystallisation of two of these compounds from MeNO₂ or MeCN have been crystallographically characterised.     

Efficient metallation in diphenylether – A convenient route to luminescent platinum(II) complexes

The synthesis of luminescent platinum(II) complexes is described. The rapid platination of porphyrins and cyclometallating coumarins was performed in diphenylether using platinum(II) bis(benzonitrile)dichloride and platinum(II) bis(dimethyl sulfoxide)dichloride. Compared to conventional methods, the reaction times are lowered dramatically and yields are significantly improved. For the first time, a NIR-emitting platinum(II) complex with tetraphenyltetrabenzoporphyrin was obtained using a direct route starting from phthalimide and phenylacetic acid.     

Copper(I) and copper(II) complexes in solution and the crystalline state

Model studies on the copper-protein interaction that may catalyze lipid oxidation have been made by studying the copper complexes of glycyl-L-histidyl-glycine and ε-aminocaproic acid. The compositions of the complexes in solution were measured by emf methods. The structures of solid complexes were determined by x-ray diffraction techniques. The results indicate that all the solid complexes have their counterparts by species formed in solution. One of 28 papers presented at the Symposium, “Metal-Catalyzed Lipid Oxidation,” ISF-AOCS World Congress, Chicago, September 1970.     

Dinuclear alkylamine platinum(II) complexes of [1,2-bis(4-fluorophenyl)ethylenediamine]platinum(II): influence of endocytosis and copper and organic cation transport systems on cellular uptake

Various possible pathways for the uptake of cationic alkylamine platinum(II) complexes into the MCF-7 breast cancer cells were studied with di[meso-1,2-bis(4-fluorophenyl)ethylenediamine]di[sulfinylbis(methane)-S][mu-1,6-diaminohexaneN:N']diplatinum(II) disulfate (m-4F-PtDMSO-DAH) as an example. It was demonstrated that m-4F-PtDMSO-DAH competed neither for the copper transporter nor the organic cation transporters (OCT and OATP). Instead, adsorptive endocytosis by macropinocytosis played an essential role. Inhibitors of this processes such as amiloride, N-ethyl-N-isopropylamiloride (EIPA), wortmannin, and cytochalasin D decreased the intracellular uptake of m-4F-PtDMSO-DAH dramatically. These results support the understanding of the pharmacological behavior of this promising drug family, which showed no cross resistance with cisplatin.     

Palladium (II) and platinum (II) complexes containing organometallic thiosemicarbazone ligands: Synthesis,characterization, X-ray structures and antitubercular evaluation

A new series of palladium (II) and platinum (II) complexes containing ferrocenyl and cyrhetrenyl thiosemicarbazone ligands were synthesized and characterized. The two-step reaction of the organometallic thiosemicarbazones with i) K₂MCl₄ and ii) PPh₃ and their subsequent recrystallization from CH₂Cl₂/hexane yielded the binuclear complexes [Mˋ{ML_n(η⁵-C₅H₄)C(H)NNC(S)NHR}–(Cl)(PPh₃)] (M′Pd, Pt; ML_nRe(CO)₃, FeCp; RH, CH₃). The structures of the products were inferred from elemental analyses and IR, ¹H and ³¹P NMR spectroscopies. The molecular structures of 2b and 3d were confirmed by single crystal X-ray analysis. All complexes were screened in vitro against Mycobacterium tuberculosis and exhibited only moderate activity in the low micromolar range.     

N-heterocyclic carbene gold(I) and copper(I) complexes in C-H bond activation

Environmental concerns have and will continue to have a significant role in determining how chemistry is carried out. Chemists will be challenged to develop new, efficient synthetic processes that have the fewest possible steps leading to a target molecule, the goal being to decrease the amount of waste generated and reduce energy use. Along this path, chemists will need to develop highly selective reactions with atom-economical pathways producing nontoxic byproduct. In this context, C-H bond activation and functionalization is an extremely attractive method. Indeed, for most organic transformations, the presence of a reactive functionality is required. In Total Synthesis, the "protection and deprotection" approach with such reactive groups limits the overall yield of the synthesis, involves the generation of significant chemical waste, costs energy, and in the end is not as green as one would hope. In turn, if a C-H bond functionalization were possible, instead of the use of a prefunctionalized version of the said C-H bond, the number of steps in a synthesis would obviously be reduced. In this case, the C-H bond can be viewed as a dormant functional group that can be activated when necessary during the synthetic strategy. One issue increasing the challenge of such a desired reaction is selectivity. The cleavage of a C-H bond (bond dissociation requires between 85 and 105 kcal/mol) necessitates a high-energy species, which could quickly become a drawback for the control of chemo-, regio-, and stereoselectivity. Transition metal catalysts are useful reagents for surmounting this problem; they can decrease the kinetic barrier of the reaction yet retain control over selectivity. Transition metal complexes also offer important versatility in having distinct pathways that can lead to activation of the C-H bond. An oxidative addition of the metal in the C-H bond, and a base-assisted metal-carbon bond formation in which the base can be coordinated (or not) to the metal complexes are possible. These different C-H bond activation modes provide chemists with several synthetic options. In this Account, we discuss recent discoveries involving the versatile NHC-gold(I) and NHC-copper(I) hydroxide complexes (where NHC is N-heterocyclic carbene) showing interesting Br?nsted basic properties for C-H bond activation or C-H bond functionalization purposes. The simple and easy synthesis of these two complexes involves their halide-bearing relatives reacting with simple alkali metal hydroxides. These complexes can react cleanly with organic compounds bearing protons with compatible pK(a) values, producing only water as byproduct. It is a very simple protocol indeed and may be sold as a C-H bond activation, although the less flashy "metalation reaction" also accurately describes the process. The synthesis of these complexes has led us to develop new organometallic chemistry and catalysis involving C-H bond activation (metalation) and subsequent C-H bond functionalization. We further highlight applications with these reactions, in areas such as photoluminescence and biological activities of NHC-gold(I) and NHC-copper(I) complexes.     

Ring-opening metathesis polymerisable charged platinum(II) complexes: Towards enhanced phosphorescent quantum yields by aggregation in polymers

Phosphorescent copolymers bearing a covalently linked charged platinum(II) dye were prepared using ring-opening metathesis polymerisation (ROMP). Absorption, emission as well as dynamic light scattering measurements of these polyelectrolytes indicate the formation of red luminescent aggregates in solution with quantum yields up to 17% and luminescence decay times in the range of 250-300 ns. Neither the quantum yield nor lifetime of the luminescence is affected by the presence of oxygen. The resulting polymers are solution processible and exhibit good film-forming properties. In contrast, the mononuclear platinum species are poorly soluble and non-luminescent at room temperature in deaerated solution.     

Well-defined N-heterocyclic carbenes-palladium(II) precatalysts for cross-coupling reactions

Metal-catalyzed cross-coupling reactions, notably those permitting C-C bond formation, have witnessed a meteoritic development and are now routinely employed as a powerful synthetic tool both in academia and in industry. In this context, palladium is arguably the most studied transition metal, and tertiary phosphines occupy a preponderant place as ancillary ligands. Seriously challenging this situation, the use of N-heterocyclic carbenes (NHCs) as alternative ligands in palladium-catalyzed cross-coupling reactions is rapidly gaining in popularity. These two-electron donor ligands combine strong sigma-donating properties with a shielding steric pattern that allows for both stabilization of the metal center and enhancement of its catalytic activity. As a result, the number of well-defined NHC-containing palladium(II) complexes is growing, and their use in coupling reactions is witnessing increasing interest. In this Account, we highlight the advantages of this family of palladium complexes and review their synthesis and applications in cross-coupling chemistry. They generally exhibit high stability, allowing for indefinite storage and easy handling. The use of well-defined complexes permits a strict control of the Pd/ligand ratio (optimally 1/1), avoiding the use of excess costly ligand that usually requires end-game removal. Furthermore, it partly removes the "black box" character often associated with cross-coupling chemistry and catalyst formation. In the present Account, four main classes of NHC-containing palladium(II) complexes will be presented: palladium dimers with bridging halogens, palladacycles, palladium acetates and acetylacetonates, and finally pi-allyl complexes. These additional ligands are best described as a protecting shell that will be discarded going from the palladium(II) precatalyst to the palladium(0) true catalyst. The synthesis of all these precatalysts generally requires simple and short synthetic procedures. Their catalytic activity in different cross-coupling reactions is discussed and put into context. Remarkably, some NHC-containing catalytic systems can achieve extremely challenging coupling reactions such as the formation of tetra-ortho-biphenyl compounds and perform reactions at very low loadings of palladium (ppm levels). The chemistry described here, combining fundamental organometallic, catalysis, and pure organic methodology, remains rich in opportunities considering that only a handful of palladium(II) architectures have been studied. Hence, en route to an "ideal catalyst", [(NHC)Pd(II)] compounds exhibit remarkable stability and allow for fine-tuning of the NHC and of surrounding ligands in order to control the activation and the catalytic activity. Finally, unlike [Pd(PPh(3))(4)], [(NHC)Pd(II)] compounds have so far been examined only in palladium-mediated reactions (most often cross-coupling such as the Suzuki-Miyaura and Heck reactions), leaving a treasure trove of exciting discoveries to come.     

Luminescent palladium(0) complexes bearing N-heterocyclic carbene and phosphine ligands

Palladium(0) complexes bearing a monodentate phosphine ligand and an N-heterocyclic carbene ligand have been prepared. In these complexes, photophysical properties of the complexes, [Pd(IPr)(PPh₃)] and [Pd(IPr)(P(o-tol)₃)] have been studied (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene). The emissive excited states have been tentatively assigned to ³MLCT. In addition to the results of the luminescent complexes, the synthesis of the related complexes, [Pd(O₂)(IPr)(P(m-tol)₃)] and [PdCl(CH₂Cl)(IPr)(P(MeOPh)₃)] (P(MeOPh)_3 = tris(pmethoxyphenyl)phosphine) have been studied and the structures were characterized by X-ray.     

The extraction of platinum from Pt(II) chloride solution by a quaternary ammonium compound

The fundamental aspects of the extraction and stripping of platinum (II) from its chloride solution by Aliquat 336 diluted with toluene have been studied. The extraction and stripping was at 99.5 and 97.6% equilibrium within 30 s and 20 min respectively. The percentage extraction increased slightly with decreasing hydrochloric acid concentration. In 0.1 mol dm^?3 hydrochloric acid, 1.0 volume percent Aliquat 336 in toluene could load 9.8 mmol dm^?3 of platinum (II). The percentage stripping of platinum (II) from Pt(II)-load organic solvent increased with increasing sodium bisulphite concentration. The enthalpy changes of extraction and of stripping were 12.8 and 114.9 kJ mol^?1 respectively. Both of the reactions were endothermic.     

Synthesis, structural characterization, and pro-apoptotic activity of 1-indanone thiosemicarbazone platinum(II) and palladium(II) complexes: potential as antileukemic agents

In the search for alternative chemotherapeutic strategies against leukemia, various 1‐indanone thiosemicarbazones, as well as eight novel platinum(II) and palladium(II) complexes, with the formula [MCl₂(HL)] and [M(HL)(L)]Cl, derived from two 1‐indanone thiosemicarbazones were synthesized and tested for antiproliferative activity against the human leukemia U937 cell line. The crystal structure of [Pt(HL1)(L1)]Cl^.2M eOH, where L1=1‐indanone thiosemicarbazone, was solved by X‐ray diffraction. Free thiosemicarbazone ligands showed no antiproliferative effect, but the corresponding platinum(II) and palladium(II) complexes inhibited cell proliferation and induced apoptosis. Platinum(II) complexes also displayed selective apoptotic activity in U937 cells but not in peripheral blood monocytes or the human hepatocellular carcinoma HepG2 cell line used to screen for potential hepatotoxicity. Present findings show that, in U937 cells, 1‐indanone thiosemicarbazones coordinated to palladium(II) were more cytotoxic than those complexed with platinum(II), although the latter were found to be more selective for leukemic cells suggesting that they are promising compounds with potential therapeutic application against hematological malignancies.     

Synthesis and characterization of poly(vinyl carbazole) complexes with copper(II) chloride in THF solution

Several polymer-metal complexes were prepared by reacting poly(vinyl carbazole) (PNVC) with copper(II) chloride, CuCl₂.2H₂O, in refluxing tetrahydrofurane (THF) for mole ratios of CuCl₂.2H₂O to monomeric unit (Cu:PNVC ratio) ranging between 0.086 and 4.98. Complexes were characterized by infrared (IR) and elemental analysis. Thermal behavior of complexes was studied by differential thermal analysis (DTA). It appears that THF behaves as a specific solvent for complexation of PNVC with copper(II) chloride.     

Unexpected formation of dihaloplatinum(II) and platinum(IV) complexes in the reaction of [PtMe2(bu2bpy)] with 1,2-dibromotetrachloroethane: Crystal structure of trans-[PtMe2BrCl(bu2bpy)]

The platinum(II) complex [PtMe₂(bu₂bpy)] (bu₂bpy = 4,4′-di-tert-butyl-2,2′-bipyridine) (1) reacted with 1,2-dibromotetrachloroethane in a 2:1 mole ratio of Pt(II): (CBrCl₂)₂ to afford trans-[PtMe₂BrCl(bu₂bpy)] (2) and [PtCl₂(bu₂bpy)] (3). The ¹H NMR spectroscopy shows that the Pt–Me bond cleavage is mainly involved after a fast oxidative addition reaction. Complex trans-[PtMe₂BrCl(bu₂bpy)] (2) has been characterized by X-ray diffraction which shows that platinum adopts an octahedral geometry.     

Poly(l-lactide) initiated by silver N-heterocyclic carbene complexes: synthesis, characterization and properties

Poly(l-lactide) (PLLA) was successfully synthesized by ring-opening polymerization (ROP) in bulk using silver N-heterocyclic carbene (Ag–NHC) complex. The effect of reaction time, temperature and monomer/initiator ratio on polymerization process were determined. The optimum conditions were found as 130 °C, 4 h and M/I molar ratio of about 100. The polymers were characterized by FTIR, ¹H-NMR, GPC and TG. High-molecular-weight PLLA (M _w = 3.78 × 10⁴, M _n = 1.91 × 10⁴, PDI = 1.97) was synthesized by the ROP of l-lactide (LLA) with bis-(N-methyl N′-dodecylimidazole) silver(I) di-bromo argentate (1a) in bulk. The effect of different N-substituted ligand groups on the polymerization was studied. The antimicrobial activity of the synthesized polymers were investigated by using minimum inhibitory concentration test against gram positive (Staphylococcus aureus) and gram negative (Escherichia coli and Pseudomonas aeruginosa). It was observed that the synthesized polymers displayed moderate antimicrobial activity.     

Investigations in platinum metal group electrochemistry: II The Pd(II)-Pd° reduction

The Norbide boron carbide electrode has been satisfactorily applied to polarographic studies of Pd(II)–Pd° and some other systems involving deposition of metal. By its means the following thermodynamic and kinetic data have been established: standard oxidation-reduction potentials, Pd²⁺–Pd°, 0.91 V; Ag⁺–Ag°, 0.805 V; stability constants, PdCl ₄ ^2– , log ₄, 9·38; logK ₄, 1·44; Pd(SO₄) ₂ ^2– , log ₂, 3·16; activation energies, Pd²⁺–Pd°:Q _D, 18·6; Q°, 188 kJ mole^–1. Analytical applications have been briefly examined.List of symbols A Area of the working electrode - (A°) Apparent frequency factor of the Arrhenius relationship - n Nominally the product of the transfer coefficient, , and the number of electrons,n, involved in an electrochemical process. In practice it is the value obtained from the slopeRT/anF of the lineE v. ln(i ₁–i)/i orv. ln(i ₁–i) - _j Product of dissociation constants of successive complexes:K ₁×K ₂×...×K _j - C ₀ Bulk concentration in the aqueous phase of species undergoing electrochemical reduction or oxidation - D ₀ Diffusivity of that species in the aqueous phase immediately adjacent to the electrode surface - Thickness of a diffusion layer - E _1/2 Half-wave potential, at whichi=i ₁/2 in a polarographic wave of the formE=E _1/2+RT/anF ln(i ₁–i)/i - E _mid Potential at whichi=i ₁/2 in a wave of the formE=E _mid+RT/anF ln(i ₁–i)/i - E _1/2 Displacement of half-wave potential caused by complexing of reducing species - _1/2 Overpotential at the half-wave potentialE _1/2 - _mid Overpotential atE _mid - f Activity coefficient, e.g.f _Pd ^2+(x=0) the activity coefficient of Pd²⁺ species in the aqueous phase at the electrode surface - i ₁ Limiting current - i Current at any stage of the electro-chemical processes governed byE v. ln(i ₁–i)/i relationships - j Number of complexing ligands associated with a cation—e.g. for PdCl ₃ ^– =3 - Q Arrhenius activation energy of the electrochemical process of a reduction at a working electrode [8] - Q _D Arrhenius activation energy of the diffusion stage of an electrochmical reduction [8]