Platinum Chelates Research Articles

A versatile method to deliver platinum (II) drugs via thiol-ene/yne click reaction of polypeptide

Platinum (II) demonstrates potent anticancer activity, but it is hampered by drawbacks such as poor solubility, facile decomposition, bone marrow suppression, and nephrotoxicity, which severely restrict its clinical use. To overcome these limitations, polymer prodrugs were developed by conjugation of platinum drugs onto polymers. The protective shield provided by polymers enables drugs to evade enzymatic degradation and immune system attacks in the physiological environment, achieving sustained release and long-term efficacy. In this study, we synthesized novel vinyl- or alkynyl-substituted cysteine N-carboxyanhydride (NCA) monomers, followed by the preparation of amphiphilic poly(ethylene glycol)-poly(amino-acid) copolymers through the copolymerization of PEG with the NCAs. Next, 1,2-didentate dicarboxylic groups were introduced into the side chains of the block copolymer by employing the “Thiol-ene” or “Thiol-yne” reactions. These carboxylic acid groups were then chelated with (1R,2R)-1,2-diaminocyclohexane platinum (II)(DACH-Pt) and simultaneously assembled into nanoparticles. The morphology and particle size were characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS). Remarkably, the chelation of platinum (II) led to a decrease in micellar size. In vitro drug release experiments demonstrated a significantly faster release rate in the intracellular environment (pH 5.0) compared to physiological conditions (pH 7.4). MTT assays confirmed the excellent biocompatibility of the polymer. Moreover, concentration-dependent inhibition of cancer cell growth was observed with poly(amino acid)-platinum (II) chelate micelles. Overall, these findings suggest that self-assembled nanoparticles of poly(amino acid)-platinum (II) chelates hold immense potential for drug delivery applications.

A review on the chemistry of novel platinum chelates based on azo-azomethine ligands

Abstract Numerous platinum group metals (PGMs) complexes contain azo-azomethine-based ligands. Azo-azomethine ligands are N-donor ligands that have extended conjugated π-bonded systems and both azo (–N=N–) and aldimine (–C=N–) functions in their structure. Plenty of platinum (Pt) complexes with azo-imine ligands have been prepared and characterized. Various multidentate azo-imine ligands coordinated with different platinum metal substrates afforded structurally diverse platinum chelates. Nonetheless, many azo-imine-based platinum complexes demonstrated a wide range of biological activities, photo-switchable properties, and redox activities. The review encompasses a general overview of platinum complexes with versatile azo-azomethine ligands, their synthetic protocol, spectroscopic and structural features, chemical reactivity, and multipurpose applications in different areas.

Chelated metal ions modulate the strength and geometry of stacking interactions: energies and potential energy surfaces for chelate-chelate stacking.

Quantum chemical calculations were performed on model systems of stacking interactions between the acac type chelate rings of nickel, palladium, and platinum. CCSD(T)/CBS calculations showed that chelate-chelate stacking interactions are significantly stronger than chelate-aryl and aryl-aryl stacking interactions. Interaction energy surfaces were calculated at the LC-ωPBE-D3BJ/aug-cc-pVDZ level, which gives energies in good agreement with CCSD(T)/CBS. The stacking of chelates in an antiparallel orientation is stronger than the stacking in a parallel orientation, which is in agreement with the larger number of antiparallel stacked chelates in crystal structures from the Cambridge Structural Database. The strongest antiparallel chelate-chelate stacking interaction is formed between two platinum chelates, with a CCSD(T)/CBS interaction energy of -9.70 kcal mol-1, while the strongest stacking between two palladium chelates and two nickel chelates has CCSD(T)/CBS energies of -9.21 kcal mol-1 and -9.50 kcal mol-1, respectively. The strongest parallel chelate-chelate stacking was found for palladium chelates, with a LC-ωPBE-D3BJ/aug-cc-pVDZ energy of -6.51 kcal mol-1. The geometries of the potential surface minima are not the same for the three metals. The geometries of the minima are governed by electrostatic interactions, which are the ones determining the positions of the energy minima. Electrostatic interactions are governed by different electrostatic potentials above the metals, which are very positive for nickel, slightly positive for palladium, and slightly negative for platinum.

Theoretical investigation of the role of chelating biphosphine ligands in oxidative addition reactions of platinum complexes

DFT investigation of MeI oxidative addition reaction of the phosphine chelating platinum(II) complexes, [PtMe2(Me2P(CH2)nPMe2)] (n = 1–4) to afford the organoplatinum(IV) complexes, [PtMe3I(Me2P(CH2)nPMe2)], is reported. The first step of the oxidative addition reaction that proceeds via the usual SN2 mechanism is the nucleophilic attack of Pt center of platinum(II) complex to carbon atom of MeI. The reaction proceeds by formation of a transition state, which includes the Pt…C…I fragment, followed by formation of the intermediate [PtMe3(Me2P(CH2)nPMe2)]+I− with the incoming Me group in the apical position of five-coordinate intermediate and with the iodide ion out of coordination sphere of Pt(IV) intermediate. The effect of the P–Pt–P bite angle of phosphine chelate on the energy barrier of the reaction has been investigated in terms of the length of the diphosphine ligand backbone. The DFT studies are in agreement with the experimental findings.

Theoretical Insight Into the Role of Triarylboron Substituents in Tetradentate Dianionic Bis(N‐heterocyclic carbene) Platinum(II) Chelates – Improving the Performance of Blue Light Emission

AbstractThe electronic structures and photophysical properties of eleven PtII complexes divided into three series by their degree of π conjugation were studied through density functional theory (DFT) and time‐dependent density functional theory (TDDFT) calculations. To investigate the effect of triarylboron substituents and the changes caused by the extension of the π conjugation, the nonradiative and radiative decay efficiencies, the geometric relaxations, d orbital splitting, and spin–orbit couplings at the optimized S0 and T1 geometries were computed. The results show that complexes with triarylboron substituents may have higher phosphorescence efficiencies than those with cyano groups. Furthermore, complexes with larger π conjugation (anthracene groups) may weaken the effects caused by the introduction of triarylboron substituents and are less likely to possess enhanced phosphorescence efficiency. Predictions of the absorption spectra and emission colors indicated that complexes with triarylboron substituents would emit blue colors, whereas the emission colors of the complexes with larger π conjugation would be located in the near‐infrared region. This work highlights that the introduction of the triarylboron substituents and appropriate π conjugation (naphthalene groups) can result in highly efficient phosphorescence in complexes containing donor N‐heterocyclic carbene (NHC) ligands.

Mono‐ and Trinuclear Tripodal Platinum(II) Chelated Complexes Containing a Pyridine/Sulfoxide Based Anchoring Framework

AbstractNew tripodal ligands 2,4,6‐triethyl‐1,3,5‐tris{[1‐(2‐pyridinyl)ethenyl]sulfinylmethyl}benzenes 6, characterized by three pendant chains each containing both sulfoxide and pyridine moieties, were synthesized from the corresponding sulfenic acid and 2‐ethynylpyridine. Two diastereomeric mixtures were obtained and separated, one racemic mixture 6a, having a C3 symmetry axis and the other 6b with no symmetry. With the aim of studying the coordination ability of these chelating‐κN,κS type ligands, monobranched racemic [1‐(2‐pyridinyl)ethenyl]sulfinylbenzene 9 was also synthesized. Upon addition of an equivalent amount of the monochelating ligand 9 or the tripodal species 6a to a CD3CN solution of a platinum(II) complex of the type cis‐[PtMe2(Me2SO)2] (Pt1) or trans‐[PtMeCl(Me2SO)2] (Pt2), platinum(II) coordination and chelation occurred, as definitively indicated by a sharp change in the 1H NMR spectrum towards the final corresponding chelated platinum(II) species and free dimethyl sulfoxide. The prepared platinum(II) species contain one or three fragments of the type {PtMe2}(10 or 12) and {PtMeCl}(11 or 13) bound to the pyridinyl/sulfinyl skeleton in the coordinating ligands 9 and 6a. All the prepared species were fully characterized by NMR spectroscopy from the connectivities in 2D‐COSY, 1H‐13C HSQC and phase‐sensitive 2D‐NOESY spectra which confirm the molecular mechanics calculation predictions.

Recognition of a Novel Type X═N–Hal···Hal (X = C, S, P; Hal = F, Cl, Br, I) Halogen Bonding

The chlorination of the eight-membered platinum(II) chelates [PtCl2{NH═C(NR2)N(Ph)C(═NH)N(Ph)C(NR2)═NH}] (R = Me (1); R2 = (CH2)5 (2)) with uncomplexed imino group with Cl2 gives complexes bearing the ═N-Cl moiety [PtCl4{NH═C(NR2)N(Ph)C(═NCl)N(Ph)C(NR2)═NH}] (R = Me (3); R2 = (CH2)5 (4)). X-ray study for 3 revealed a novel type intermolecular halogen bonding ═N-Cl···Cl(-), formed between the Cl atom of the chlorinated imine and the chloride bound to the platinum(IV) center. The processing relevant structural data retrieved from the Cambridge Structural Database (CSDB) shows that this type of halogen bonding is realized in 18 more molecular species having X═N-Hal moieties (X = C, P, S, V, W; Hal = Cl, Br, I), but this weak ═N-Hal···Hal(-) bonding was totally neglected in the previous works. The presence of the halogen bonding in 3 was confirmed by theoretical calculations at the density functional theory (DFT, M06-2X) level, and its nature was analyzed.

Flat vs. Folded Chelate Rings in cis‐PtIIa2 (a = NH3, a2 = en, a2 = 2, 2′‐bpy) Complexes of Twofold Substituted Diazine Ligands

AbstractAcid‐base and ligating properties of three bis(substituted)pyrazine (pz) and pyrimidine (pym) ligands (pyrazine‐2, 5‐dicarboxylic acid, 2, 5‐pzdcH2, 2, 3‐bis(pyridine‐2‐yl)pyrazine, 2, 3‐bppz, pyrimidine‐4, 6‐dicarboxylic acid, 4, 6‐pmdcH2) toward cis‐PtIIa2 (a = NH3, a2 = en, a2 = 2, 2′‐bpy) have been studied. Combinations of pz‐N/pym‐N with donor atoms of the substituents lead to 5‐membered platinum chelates, but exclusive N, N‐coordination through the pyridyl substituents of 2, 3‐bppz can lead to a 7‐membered platinum chelate with a characteristic L‐shape of the resulting cation. It is observed for PtII(2, 2′‐bpy), yet not for PtII(en), and is a consequence of differences in sterical interactions between the 2, 3‐bppz ligand and the coligands of PtII.

Organoplatinum(II) Complexes with 2-Acetylthiophene Thiosemicarbazone: Synthesis, Characterization, Crystal Structures, and in Vitro Antitumor Activity

Novel organoplatinum(II) complexes with 2-acetylthiophene thiosemicarbazone (ATTSC) were synthesized. The reaction of K2PtCl4 with ATTSC in 1:1 and 1:2 metal to ligand ratios yielded 1 [Pt4(ATTSC-2H)4·4DMF] and 2 [Pt(ATTSC-H)(ATTSC)Cl·3CH3OH)]. The crystal structures of these platinum chelates have been solved by single-crystal X-ray diffraction structure determinations and revealed metalation of the thiophene ring at C2 through platinum atoms. Further characterization of 1 and 2 was performed using electronic, IR, UV/vis, and NMR spectroscopies and elemental analysis. The in vitro antitumor activity of the ligand as well as 1 and 2 was determined against two different human tumor cell lines (HT-29 and HuTu-80). These tests revealed that the platinum(II) complexes are more cytotoxic than their ligand. The tetranuclear complex 1 shows higher antiproliferative activity (IC50 = 1.2 and 1.5 μM) when compared to 2 (IC50 = 3 and 5.9 μM), while the ligand has IC50 values of 8.6 and >10 μM. Compounds 1 and 2 can ...

Synthesis and Utilization of the Bis( > P(O)CH2)amine Derivatives Obtained by the Double Kabachnik–Fields Reaction with Cyclohexylamine; Quantum Chemical and X-Ray Study of the Related Bidentate Chelate Platinum Complexes

Synthesis and Utilization of the Bis( > P(O)CH2)amine Derivatives Obtained by the Double Kabachnik–Fields Reaction with Cyclohexylamine; Quantum Chemical and X-Ray Study of the Related Bidentate Chelate Platinum Complexes

Antitumor activities and interaction with DNA of oxaliplatin-type platinum complexes with linear or branched alkoxyacetates as leaving groups

Five oxaliplatin-typed platinum complexes containing trans-1R, 2R-diaminocyclohexane chelating platinum cores, characteristic of linear or branched alkoxycarboxylates as leaving groups, were biologically evaluated. These compounds showed higher antitumor activity, lower toxicity in vivo than cisplatin or oxaliplatin. And the results revealed that the antitumor activity and interaction with DNA of these compounds were highly related to the nature of leaving groups. Among these complexes, 5a, cis-( trans-1R, 2R-diaminocyclohexane) bis (2- tert-butoxyacetate) platinum(II), showed the highest antitumor activity and the lowest toxicity.

Organoplatinum(ii) complexes containing chelating or bridging bis(N-heterocyclic carbene) ligands: formation of a platinum(ii) carbonate complex by aerial CO2 fixation

The preparation of two new bis(N-heterocyclic carbene) platinum(II) complexes, in which NHC rings are joined by a CH(2) linker group, is described. While, the chelate complex [PtMe(2)(bis-NHC1)], 1, was formed with large tert-butyl wingtips, the iso-propyl N-substituent analogue favors formation of the cluster complex [Pt(2)Me(4)(μ-SMe(2))(μ-bis-NHC2)](2)(μ-Ag(2)Br(2)), 2, in which two binuclear platinum(II) complexes are linked together by an Ag(2)Br(2) unit. The chelating platinum complex 1 undergoes aerial CO(2) fixation and forms platinum(II) carbonate complex [Pt(CO(3))(bis-NHC1)], 3.

Nitrile−Amidine Coupling at Pt(IV) and Pt(II) Centers. An Easy Entry to Imidoylamidine Complexes

Treatment of trans-[PtCl4(RCN)2] (R = Me, Et, Ph, NEt2) with 2 equiv of the amidine PhC(=NH)NHPh in a suspension of MeCN (R = Me), CHCl3 (R = Et, Ph), or in CHCl3 solution (R = NEt2) results in the formation of the imidoylamidine complexes trans-[PtCl4{NH=C(R)N=C(Ph)NHPh}2] (1-4) isolated in good yields (66-84%). The reaction of soluble complexes 3 and 4 with 2 equiv of Ph3P=CHCO2Me in CH2Cl2 (40 degrees C, 5 h) leads to dehydrochlorination resulting in a chelate ring closure to furnish the platinum(IV) chelates [PtCl2{NH=C(R)NC(Ph)=NPh}2] (R = Ph, 5; R = NEt2, 6), accordingly, and the phosphonium salt [Ph3PCH2CO2Me]Cl. Treatment of 5 with 3 equiv of Ph3P=CHCO2Me at 50 degrees C for 5 d resulted in only a 30% conversion to the corresponding Pt(II) complex [Pt{NH=C(NEt2)NC(Ph)=NPh}2] (15). The reduction can be achieved within several minutes, when Ph2PCH2CH2PPh2 in CDCl3 is used. When the platinum(II) complex trans-[PtCl2(RCN)2] is reacted with 2 equiv of the amidine, the imidoylamidinato complexes [PtCl(RCN){NH=C(R)NC(Ph)=NHPh}] (8-11) and [PhC(=NH)NHPh] x HCl (7) are formed. The reaction of trans-[PtCl2(RCN)2] with 4 equiv of the amidine under a prolonged reaction time or treatment of [PtCl(RCN){NH=C(R)NC(Ph)=NHPh}] (8-11) with 2 more equiv of the amidine yields the complex bearing two chelate rings [Pt{NH=C(R)NC(Ph)=NHPh}2] (12-15). The treatment of cis-[PtCl2(RCN)2] (R = Me, Et) with the amidine gives ca. 50-60% yield of [PtCl2{NH=C(R)NHC(Ph)=NHPh}] (16 and 17). All of the platinum compounds were characterized by elemental analyses; FAB mass spectrometry; IR spectroscopy; 1H, 13C{1H}, and 195Pt NMR spectroscopies, and four of them (4, 6, 8, and 15) were also characterized by X-ray crystallography. The coupling of the Pt-bound nitriles and the amidine is metal-mediated insofar as RCN and PhC(=NH)NHPh do not react in the absence of the metal centers in conditions more drastic than those of the observed reactions. The nitrile-amidine coupling reported in this work constitutes a route to the synthesis of imidoylamidine complexes, some of them exhibiting luminescent properties.

Platinum cross-linking of adenines and guanines on the quadruplex structures of the AG3(T2AG3)3 and (T2AG3)4 human telomere sequences in Na+ and K+ solutions.

The quadruplex structures of the human telomere sequences AG3(T2AG3)3 I and (T2AG3)4 II were investigated in the presence of Na+ and K+ ions, through the cross-linking of adenines and guanines by the cis- and trans-[Pt(NH3)2(H2O)2](NO3)2 complexes 1 and 2. The bases involved in chelation of the cis- and trans-Pt(NH3)2 moieties were identified by chemical and 3'-exonuclease digestions of the products isolated after denaturing gel electrophoresis. These are the four adenines of each sequence and four out of the 12 guanines. Two largely different structures have been reported for I: A from NMR data in Na+ solution and B from X-ray data of a K+-containing crystal. Structure A alone agrees with our conclusions about the formation of the A1-G10, A13-G22, A1-A13 platinum chelates at the top of the quadruplex and A7-A19, G4-A19 and A7-G20 at the bottom, whether the Na+ or K+ ion is present. At variance with a recent proposal that structures A and B could be the major species in Na+ and K+ solutions, respectively, our results suggest that structure A exists predominantly in the presence of both ions. They also suggest that covalent platinum cross-linking of a human telomere sequence could be used to inhibit telomerase.

Synthesis, Stereochemistry and Ligating Properties of Tetraalkyl-Substituted Ethanedithioamides − Evidence for the Lowering of High-Energy Rotation Barriers under the trans Influence of Pt-σ-Bonded Aryl Groups

The structural and coordinating properties of five tetrasubstituted tetraalkyldithioxamides (R4DTO) have been studied: tetraethyldithioxamide (Et4DTO, 1), tetrabenzyldithioxamide (Bz4DTO, 2), (E,E)-N,N′-dibenzyl-N,N′-diethyldithioxamide [(E,E)-Bz2Et2DTO, 3], (E,Z)-N,N′-dibenzyl-N,N′-diethyldithioxamide [(E,Z)-Bz2Et2DTO, 4], (Z,Z)-N,N′-dibenzyl-N,N′-diethyldithioxamide [(Z,Z)-Bz2Et2DTO, 5]. The solid structure of 4, determined by single-crystal X-ray diffraction, is characterised by two planar thioamide groups positioned almost orthogonally to each other, connected by a C−C single bond. Each of these dithioxamides showed high-energy barriers to rotation around both the C−N and the central C−C bond. This latter is a chiral torsion, so that R4DTO species exist as pairs of enantiomers. Compounds 3, 4 and 5 slowly isomerised in solution to give equimolar mixtures of the three isomers; the activation enthalpy of the process was 30.0 kcal mol−1. The ligands 1−5 reacted with [Pt(Me2SO)2X2] (X = Cl, Br, Me, Ph) to give chiral chelate complexes [(R4DTO-κ-S,S′)PtX2], but 3 (and also 4 and 5) provided a mixture of three isomeric platinum chelates in which the S,S′-coordinated ligands showed the (E,E), (E,Z) and (Z,Z) conformations. Furthermore, the presence of small amounts of the platinum complexes cis-[Pt(Me2SO)2Ph2] or [(Et4DTO-κ-S,S′)PtPh2] caused the fast isomerisation of large quantities of a given isomerically pure ligand. We have explained the collapse of the R4DTO rotational barriers by assuming that a release of electrons from the metal atom to incoming ligands in the transition state twists these into a partially reduced, dithiolenic form. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Spectrophotometric and potentiometric study on platinum(II) chelates of mercapto carboxylic acids

The coordination of Pt(II) with different mercapto and dimercapto compounds has been studied using both potentiometric titration at 25°C in KCl 0.1 M and UV–Vis spectroscopy. The slow complex formation kinetics has been followed spectrophotometrically for several days on samples with different ligand molar fractions ranging from 0.1 to 1, keeping the ligand and metal concentration below 8×10 −4 M. For the potentiometric titration, the ligand concentrations were kept constant at 10 −3 M, and the 0.25, 0.5, 0.75 and 1.00 metal/ligand ratios were titrated in the pH range 2.5–11 for each ligand. The solutions were kept in a thermostatted bath at 25°C for 2 days before titration. The stabilization of the absorbance values under these conditions after 2 days, and the back titration with hydrochloric acid 0.1 M, led us to conclude that the proper equilibrium complex formation is reached under these conditions. Using KCl 0.1 M as an ionic strength medium, the reported formation constants are referred to the complexation reaction starting from [PtCl 4] 2−. Some models are proposed on the basis of the estimated stoichiometries.

Room temperature phosphorescence characteristics of platinum(II) chelates with 8-quinolinol derivatives in aqueous micellar solutions

Phosphorescence from platinum(II) chelates of 8-quinolinol (8-Q), 5-sulfo-8-quinolinol (SQ), and 5-sulfo-7-iodo-8-quinolinol (SIQ) at ca. 630 nm is strongly enhanced in certain kinds of surfactant micellar solutions in the presence of sulfite ion as a chemical de-oxygenator. Among these ligand systems the [Pt(II)(SIQ) 2] 2− chelate is most highly phosphorescent with a quantum yield of 0.028 in n-dodecyl-β- d-maltoside (DOM) micelles at 298 K because of the heavy-atom effect of iodine. The emission due to the dianionic 1 : 2 chelates of SQ and SIQ are strongly facilitated either in cationic and non-ionic surfactant micelles such as hexadecyltrimethylammonium chloride (CTAC) or bromide (CTAB), Brij-35, Triton X-100, and DOM in sharp contrast to the slight sensitization by sodium dodecylsulfate (SDS) micelles of similar charge. Anionic SDS micelles do not work well even for the uncharged [Pt(II)(8-Q) 2] chelate. The emission decay lifetimes of the chelates in de-oxygenated micellar solutions are in a similar range of 28 μs with CTAB to 37 μs with DOM, at 298 K. In a pre-micellar region of CTAC, below the critical micelle concentration, the chelate is also luminescent as the ion-pair of (CTA) 2[Pt(II)(SIQ) 2]. The highly sensitive phosphorescence detection of Pt(II) ion is achievable using the SIQ–DOM–sulfite system, giving a 3 σ detection limit of 30 nM or 6 ng Pt ml −1

Conformational flexibility within the chelate rings of [Pt(en)(CBDCA-O,O′)], an analogue of the antitumour drug carboplatin: X-ray crystallographic and solid-state NMR studies

The X-ray crystal structure of [Pt(en)(CBDCA-O,O′)] 1, an analogue of the anticancer drug carboplatin, shows that platinum has an approximate square-planar coordination. The crystals are orthorhombic with space group Pnma. The Pt-CBDCA chelate ring adopts a flattened-boat conformation, similar to that found for carboplatin, and the Pt-ethylenediamine chelate ring exhibits both δ and λ conformations with equal populations. Ethylenediamine chelate ring inversion was observed by 13C CP/MAS NMR spectroscopy. The exchange rate and the activation free energy (ΔG‡) at 317 K were determined to be ca. 415 s-1 and 62 kJ mol-1, respectively. The CBDCA ligand appears to have a direct effect on the dynamics of the en ring. Conformational flexibility of the CBDCA ring is also discussed. Such dynamic processes within chelated platinum complexes could play a role in the biological recognition of anticancer complexes.

Reactivity of trans-[PtX(2)(ketoxime)(2)] Complexes toward m-Chloroperoxybenzoic Acid: An Efficient Route to Coordinated Nitrosoalkanes and Solvent Dependence of the Reaction.

The platinum(II) compounds trans-[PtX(2)(RR'C=NOH)(2)] [X = Cl, R = R' = Me, RR' = (CH(2))(4), (CH(2))(5); X = Br, R = R' = Me] react with m-chloroperoxybenzoic acid (MCPBA) in dimethylformamide to give the platinum(II) complexes [PtX(2){N(=O)CRR'ONCRR'}] containing coordinated nitrosoalkane ligands. The complexes [PtX(2){N(=O)CRR'ONCRR'}] were characterized by elemental analysis, EI-MS, IR, electronic absorption, and (1)H NMR spectroscopy; X-ray structure analysis was performed for [PtCl(2){N(=O)CC(5)H(10)ONCC(5)H(10)}]. The latter compound crystallizes in the triclinic P&onemacr; space group with a = 9.214(2) Å, b = 9.577(2) Å, c = 10.367(2) Å, alpha = 109.14(2) degrees, beta = 91.87(2) degrees, gamma = 115.62(2) degrees, V = 762.8(3) Å(3), Z = 2, and rho(calcd) = 2.135 g cm(-)(3). The reaction between trans-[PtX(2)(RR'C=NOH)(2)] and MCPBA displays a solvent dependence: interaction of these reagents in ketones, R(1)R(2)C=O, yields the platinum(IV) chelates [PtX(2)(OCR(1)R(2)ON=CRR')(2)], while the oxidation state of the oxime N atom remains unchanged. Heating [PtCl(2)(OCR(1)R(2)ON=CRR')(2)] in DMF or in DMF-d(7) at 100 degrees C leads to the extrusion of R(1)R(2)C=O and the formation of [PtCl(2){N(=O)CRR'ONCRR'}].

Vacuum Sublimation Behavior of Nickel(II), Palladium(II), and Platinum(II) Chelates with Dimethylglyoxime

Abstract A sublimation apparatus in perpendicular style with a continuous-temperature gradient (30–200 °C) along the glass tube (15–0 cm) at 10−2 Torr (1 Torr=133.322 Pa) was used. Dimethylglyoxime (DMG) and its chelates of nickel(II) and palladium(II) in milligram amounts were sublimed without any thermal decomposition, while platinum(II) chelate was accompanied by a remarkable thermal decomposition during the sublimation process. All metal chelates, Ni(DMG)2 (brick-red), Pd(DMG)2(yellow), and Pt(DMG)2 (grayish violet), form needle-like crystals after purification with a sublimator under low pressure.