Synthesis and spectral studies on platinum complexes with mono- and bidentate N-donor organic ligands

Platinum(II) complexes of types PtLX₂, PtL₂X₂, PtLX″ and the Pt(IV) complexes PtLXY (where L = mono- or bidentate organic ligand containing nitrogen donor atoms; X = Cl or Br; X′ = oxalate or malonate and Y = Br) have been synthesized and characterized from their elemental analysis, IR and X-ray photoelectron spectral data. The Pt 4f_7/2 binding energies indicate that 1,8-naphthalene-diamine ligand is a better donor of electron density to the metal than other ligands studied here. The Cl 2p_3/2 binding energies in the square planar Pt(II) complexes are observed in the range 198.8 ± 0.8 eV. The ν (PtCl) vibrations (ca 335 and 320 cm^?1) corresponding to two cis-Cl ligands were observed in the IR spectra.The extent of the interaction between cis-dichloro-bis-(theophylline)platinum(II) with calf thymus DNA has beenstudied. The UV difference spectra resulting from aquated Pt^II(theoph)₂-DNA interaction exhibit bands at 282 and 292 nm attributable to the change in the electron distribution of the base moieties induced by binding with platinum and due to the loss of base stacking. Melting profiles for the DNA samples treated with Pt-complex showed decrease in the melting temperature. Binding of the guanine residues of the DNA, involving probably (N7)-0(6) positions to the metal is implied.     

Synthesis,DFT calculations and characterisation of new mixed Pt(II) complexes with 3-thiolanespiro-5<Emphasis Type="Italic">′</Emphasis>-hydantoin and 4-thio-1<Emphasis Type="Italic">H</Emphasis>-tetrahydropyranspiro-5<Emphasis Type="Italic">′</Emphasis>-hydantoin

Cisplatin is an anticancer drug widely used in the treatment of a wide range of solid tumours (head and neck, lung, bladder etc.), testicular and ovarian cancers. Because of its severe toxicity profile and spontaneous development of drug resistance in tumours, a number of Pt(II) complexes have been synthesised and tested for anti-tumour activity. Some of the investigations have focused on using ligands bearing donor atoms other than N (e.g., S, P, O). Two new mixed Pt(II) complexes of the general formula cis-[Pt(NH₃)LCl₂] where L is 3-thiolanespiro-5′-hydantoin and 4-thio-1H-tetrahydropyranspiro-5′-hydantom were synthesised. The complexes were studied by elemental analysis, melting points, IR and ¹H NMR spectra. The hybrid DFT calculations were used for optimisation of the structure geometries of the ligands III, IV and their Pt(II) complexes V and VI. The structural parameters so calculated, such as bond lengths and angles, are in good agreement with the experimental data for similar hydantoins and their platinum complexes. The results showed that the geometries of complexes V and VI are plane square and the bounding of ligands III and IV with platinum ions is effected by the sulphur atom from the cyclic ring. The complexes thus obtained were chemically examined in comparison with previously synthesised and published complexes of the general formula cis-[PtL₂Cl₂] (VII and VIII) with the same ligands. The new compounds V and VI, as well as the previously investigated complexes (VII and VIII), were analysed for cytotoxicity in vitro on SKW-3 and HL-60 human tumour cell lines. The results showed that all the complexes exerted concentration-dependent anti-proliferative activity.     

Stereoisomeric Pt(IV) complexes with threonine

Stereoisomeric Pt(IV) complexes with threonine (ThrH = HOCH(CH₃)CH(NH₂)COOH, ??-amino-??-hydroxybutyric acid) were obtained. In the complexes trans-[Pt(S-ThrH)₂Cl₄] and trans-[Pt(R-ThrH)(S-ThrH)Cl₄], the ThrH molecules act as monodentate ligands coordinated through the NH₂ group. In the complexes cis- and trans-[Pt(S-Thr)₂Cl₂] and trans-[Pt(R-Thr)(S-Thr)Cl₂], the deprotonated ligands are coordinated in a bidentate fashion through the NH₂ and COO^?-groups (R,S is the absolute configuration of the asymmetric carbon atom). All the complexes were identified using elemental analysis, IR spectroscopy, and ¹⁹⁵Pt, ¹³C, and ¹H NMR spectroscopy. The complexes trans-[Pt(S-ThrH)₂Cl₄] · 3H₂O and cis-[Pt(S-Thr)₂Cl₂] · 2H₂O were additionally characterized by X-ray diffraction.     

Synthesis and structure of penta-platinum σ-bonded derivatives of corannulene

The synthesis of a new class of Pt(II) complexes with corannulene by way of either oxidative addition or reductive coupling is reported and their crystal structures are investigated. The crystal structure for {trans-Pt(PEt₃)₂Cl}₄{cis-Pt(PEt₃)₂Cl}C₂₀H₅ (1) consists of two enantiomers in a unit cell and shows cis- and trans-configuration around Pt(II) due to bulky PEt₃ ligands. The pentanuclear Pt(II) complex, 1, readily reacts with 1-ethynyl-4-nitrobenzene to afford the penta-alkynyl substituted Pt(II) complex (2). Although there are still bulky PEt₃ ligands around the Pt atoms in 2, all five Pt(II) have trans-configurations. The bowl of corannulene in 2 is shallower than that of 1. Therefore, the bowl depth of corannulene plays a key role in the determination of molecular geometry of σ-bonded pentanuclear complexes bearing corannulene.     

Ligand effects on the Pt(II) → Pt(0) reduction of dichlorobis(tertiary phosphine)platinum(II) complexes: Correlations between electrochemical data,spectroscopic data,and electronic ligand parameters

Cyclic voltammetry has been employed to study the diffusive, irreversible platinum(II) → platinum(0) reduction of three sets of structurally related complexes: cis-[PtCl₂P{p-C₆H₄X}₃)₂] (X = H, CH₃, Cl, F, OCH₃, N(CH₃)₂); cis-[PtCl₂(PPh₂R)₂] (R = CH₃, n-C₃H₇, n-C₅H₁₁, n-C₆H₁₃, n-C₁₂H₂₅) and cis-[PtCl₂(PR₃)₂] (R = CH₃, C₂H₅, CH₂ch₂CN). Relationships between the peak potentials for the Pt(II) → Pt(0) reduction and thermodynamic parameters which measure the electronic properties of the ligands are shown to exist for complexes of P{p-C₆H₄X}₃ ligands, implying a thermodynamic origin for the sensitivity of the peak potentials to structural change. Complexes of both P{p-C₆H₄X}₃ and PPh₂R ligands show correlations between peak potentials for reduction and the ³¹P{¹H} NMR spectroscopic parameter, ¹J(¹⁹⁵Pt, ³¹P). Correlations with values of δ(³¹P) exist in both cases, but a correlation with the coordination chemical shift, Δδ(³¹P), exists for complexes of PPh₂R, and not for complexes of P{C₆H₄X}₃. Complexes of PR₃ ligands show no correlation between the peak potentials measured for the Pt(II) → Pt(0) reduction and electronic or spectroscopic parameters, except possibly ¹J(¹⁹⁵Pt, ³¹P).     

Synthesis and characterization of multimeric salicylaldimine thiosemicarbazones and their Pd(II) and Pt(II) complexes

A series of di- and trithiosemicarbazone ligands as well as their Pd(II) and Pt(II) 1,3,5-triaza-7-phosphaadamantane (PTA) complexes have been synthesised using templated reactions between various substituted salicylaldimine thiosemicarbazone ligands and metal precursors of the general formula cis-[M(PTA)₂Cl₂], where M = Pd or Pt. Characterization of these complexes was achieved using various analytical and spectroscopic techniques: elemental analysis, ESI-MS, FT-IR, and NMR (¹H, ¹³C{¹H} and ³¹P{¹H}) spectroscopy. The data revealed tridentate (O-N-S) coordination of the thiosemicarbazone moieties via the imine nitrogen, thiolato sulfur and phenolic oxygen to each metal center. In vitro biological evaluation of selected compounds was conducted against WHCO1 oesophageal cancer cells. Some of the multimeric compounds display some promising biological activity.     

Heteroleptic platinum(II) and palladium(II) complexes with thiacrown and diimine ligands

We wish to report the synthesis, crystal structures, spectroscopic and electrochemical properties of several new Pt(II) heteroleptic complexes containing the thiacrown, 9S3 (1,4,7-trithiacyclononane) with a series of substituted phenanthroline ligands and related diimine systems. These five ligands are 5,6-dimethyl-1,10-phenanthroline(5,6-Me₂-phen), 4,7-dimethyl-1,10-phenanthroline(4,7-Me₂-phen), 4,7-diphenyl-1,10-phenanthroline(4,7-Ph₂-phen), 2,2′-bipyrimidine(bpm), and pyrazino[2,3-f]quinoxaline or 1,4,5,8-tetraazaphenanthrene(tap). All complexes have the general formula [Pt(9S3)(N₂)](PF₆)₂ (N₂ = diimine ligand) and form similar structures in which the Pt(II) center is surrounded by a cis arrangement of the two N donors from the diimine chelate and two sulfur atoms from the 9S3 ligand. The third 9S3 sulfur in each structure forms a longer interaction with the platinum resulting in an elongated square pyramidal structure, and this distance is sensitive to the identity of the diimine ligand. In addition, we report the synthesis, structural, electrochemical, and spectroscopic properties of related Pd(II) 9S3 complex with tap. The ¹⁹⁵Pt NMR chemical shifts for the six Pt(II) complexes show a value near −3290 ppm, consistent with a cis-PtS₂N₂ coordination sphere although more electron-withdrawing ligands such as tap show resonances shifted by almost 100 ppm downfield. The physicochemical properties of the complexes generally follow the electron-donating or withdrawing properties of the phenanthroline substituents.     

Identification of Pt(II) and Pd(II) stereoisomeric complexes with aminobutyric acid by NMR and IR spectroscopy

Complexes of Pd(II) with aminobutyric acid AmH = NH₂CH(CH₂CH₃)COOH, namely, trans-[Pd(AmH)₂Cl₂] with monodentate (via the NH₂ group) AmH ligands and cis-, trans-Pd(Am)₂ with bidentate (via NH₂ and COO groups) ligands have been synthesized for the first time. Elemental analysis and IR and NMR spectroscopy were used to identify the synthesized compounds. The NMR spectra of the Pd(II) complexes were interpreted by comparing them with the NMR spectra of the analogous complexes of Pt(II). For Pt(II) and Pd(II) complexes with aminobutyric acid used as examples, an approach to identification of diastereomer bis-aminoacid complexes in specimens with racemic aminoacids by NMR spectroscopy is demonstrated.     

Synthesis and structure of highly substituted pyrazole ligands and their complexes with platinum(II) and palladium(II) metal ions

Reaction of 3-methoxycarbonyl-2-methyl- or 3-dimethoxyphosphoryl-2-methyl-substituted 4-oxo-4H-chromones 1 with N-methylhydrazine resulted in the formation of isomeric, highly substituted pyrazoles 4 (major products) and 5 (minor products). Intramolecular transesterification of 4 and 5 under basic conditions led, respectively, to tricyclic derivatives 7 and 8. The structures of pyrazoles 4a (dimethyl 2-methyl-4-oxo-4H-chromen-3-yl-phosphonate) and 4b (methyl 4-oxo-2-methyl-4H-chromene-3-carboxylate) were confirmed by X-ray crystallography. Pyrazoles 4a and 4b were used as ligands (L) in the formation of ML₂Cl₂ complexes with platinum(II) or palladium(II) metal ions (M). Potassium tetrachloroplatinate(II), used as the metal ion reagent, gave both trans-[Pt(4a)₂Cl₂] and cis-[Pt(4a)₂Cl₂], complexes with ligand 4a, and only cis-[Pt(4b)₂Cl₂] isomer with ligand 4b. Palladium complexes were obtained by the reaction of bis(benzonitrile)dichloropalladium(II) with the test ligands. trans-[Pd(4a)₂Cl₂] and trans-[Pd(4b)₂Cl₂] were the exclusive products of these reactions. The structures of all the complexes were confirmed by IR, ¹H NMR and FAB MS spectral analysis, elemental analysis and Kurnakov tests.     

Binuclear complexes of Pt(II) with platinated 2-phenylbenzothiazole and bridged derivatives of pyridin- and benzothiazol-2-thiols

Binuclear complexes of Pt(II) cycloplatinated with 2-phenylbenzothiazole and bridging ligands have been shown to contain the Pt-Pt bond. The complexes have been studied by X-ray diffraction, ¹H NMR and electronic absorption spectroscopy, and electrochemical methods. The complexes cis-N_(bt),S-isomers with antisymmetric positions of the cyclometalated and the bridging ligands have been detected in the crystals as well as in the solutions. The low-wavelength absorption and luminescence of the complexes have been assigned to the metal-metal-ligand charge transfer. The two-electron oxidation and reduction waves in the voltamperograms are associated with the metal- and the ligand-centered processes, respectively.     

Pt(ii)-coordinated tricomponent self-assemblies of tetrapyridyl porphyrin and dicarboxylate ligands: are they 3D prisms or 2D bow-ties?

Thermodynamically favored simultaneous coordination of Pt(ii) corners with aza- and carboxylate ligands yields tricomponent coordination complexes with sophisticated structures and functions, which require careful structural characterization to paint accurate depiction of their structure–function relationships. Previous reports claimed that heteroleptic coordination of cis-(Et₃P)₂Pt^II with tetrapyridyl porphyrins (M′TPP, M′ = Zn or H₂) and dicarboxylate ligands (XDC) yielded 3D tetragonal prisms containing two horizontal M′TPP faces and four vertical XDC pillars connected by eight Pt(ii) corners, even though such structures were not supported by their ¹H NMR data. Through extensive X-ray crystallographic and NMR studies, herein, we demonstrate that self-assembly of cis-(Et₃P)₂Pt^II, M′TPP, and four different XDC linkers having varied lengths and rigidities actually yields bow-tie (⋈)-shaped 2D [{cis-(Et₃P)₂Pt}₄(M′TPP) (XDC)₂]⁴⁺ complexes featuring a M′TPP core and two parallel XDC linkers connected by four heteroleptic Pt^II corners instead of 3D prisms. This happened because (i) irrespective of their length (∼7–11 Å) and rigidity, the XDC linkers intramolecularly bridged two adjacent pyridyl-N atoms of a M′TPP core via Pt^II corners instead of connecting two cofacial M′TPP ligands and (ii) bow-tie complexes are entropically favored over prisms. The electron-rich ZnTPP core of a representative bow-tie complex selectively formed a charge-transfer complex with highly π-acidic 1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-heaxacarbonitrile but not with a π-donor such as pyrene. Thus, this work not only produced novel M′TPP-based bow-tie complexes and demonstrated their selective π-acid recognition capability, but also underscored the importance of proper structural characterization of supramolecular assemblies to ensure accurate depiction of their structure–property relationships.

Thermodynamically favored heteroleptic coordination of Pt(ii) corners with tetrapyridyl porphyrins and dicarboxylate ligands produces 2D bow-tie shaped complexes instead of previously mischaracterized 3D tetragonal prisms.     

Bis(saccharinato)palladium(II) and platinum(II) complexes with 2,2′-bipyridine: Syntheses,structures, spectroscopic,fluorescent and thermal properties

New palladium(II) and platinum(II) complexes, cis-[Pd(bpy)(sac)₂] (1) and cis-[Pt(bpy)(sac)₂] (2), where sac = saccharinate, bpy = 2,2′-bipyridine, have been synthesized and characterized by elemental analysis, UV–Vis, IR, ¹H NMR and ¹³C NMR. The structures of the DMSO solvated complexes are determined by X-ray diffraction. Both complexes are isomorphous and the metal ions are coordinated by two N-bonded sac ligands, and two nitrogen atoms of pyridyl groups of bpy in a cis fashion. The mononuclear species interact each other through weak intermolecular C–H?O hydrogen bonds, C–H?π and π?π interactions leading to three-dimensional supramolecular networks. All complexes exhibit a high thermal stability in the solid state, and are fluorescent in the solution.     

Pt(II) stereoisomeric complexes with serine

There have been synthesized Pt(II) stereoisomeric complexes with hydroxy-α-amino acid serine (SerH = NH₂CH(CH₂OH)COOH is α-amino-β-hydroxypropionic acid): trans-[Pt(S-SerH)₂Cl₂], trans-[Pt(R-SerH)(S-SerH)Cl₂] with monodentately (through NH₂ group ) bound SerH and cis-, trans-[Pt(R-Ser)(S-Ser)], trans-[Pt(S-Ser)₂] with bidentately bound (through groups NH₂ and COO) ligands (R, S is the absolute configuration of asymmetric carbon atom). The successive phases in the synthesis of Pt(II) stereoisomeric complexes with serine were studied by ¹⁹⁵Pt NMR spectroscopy. To identificate the compounds synthesized the method of elemental analysis, IR and NMR (¹⁹⁵Pt, ¹³C, ¹H) spectroscopy were used. For trans-[Pt(R-Ser)(S-Ser)] the X-ray diffraction data were obtained.     

On the Coordination Properties of New Bicyclophosphite-Carbohydrates

Summary. The coordination behavior of newly developed bicyclophosphite ligands toward Mo(0), Rh(I), and Pt(II) was studied.Reactions at different ratios of metal to ligand were done. It was found that the ligands act as monodentate ones and form with hexacarbonylmolybdenum(0) complexes with the general formula Mo(CO)₅L by replacing only one carbonyl ligand. Coordination experiments toward acetylacetonatodicarbonylrhodium(I) resulted in the formation of undefined compounds. Toward dichlorocyclooctadienylplatinum(II) the monomeric phosphorus ligands act as monodentate ligands forming complexes of the general structure cis-PtCl₂L₂. All the synthesized platinum-complexes possess cis-configuration (proven by ³¹P NMR). The corresponding coordination compounds were isolated and characterized by elemental analyses and ¹H, ¹³C, and ³¹P NMR.     

1,2- and 1,7-Dicarba-closo-dodecarborane(12)platinum(II) complexes formed through metal—carbon σ bonds: cis- and trans-monohydrido derivatives

New neutral platinum(II) monohydridocarborane complexes of general formula cis- and trans-L₂PtH(σ-carb), where L = (C₂H₅)₃P, (C₆H₅)₃P, (C₆H₅)₂(CH₃)P, (C₆H₅)(CH₃)₂P and carb = 2-R-1,2- or 7-R-1,7-B₁₀C₂H₁₀^? (R = H, CH₃, C₆H₅), have been prepared. The configurations of the complexes obtained have been assigned by ¹H NMR spectroscopy. The _cis-monohydridocarborane complexes here reported are the first examples of neutral _cis-monohydrido derivates of platinum(II) containing platinum—carbon σ bonds. ¹H NMR chemical shifts and coupling constants of the prepared complexes are also reported, and used in a tentative evaluation of the _trans-influence of the carbonage ligands.     

Mixed dimethyl sulfoxide-thiocarbamic ester complexes of platinum(II) halides

Summary The platinum(II) halidecis-[Pt(DMTC)(DMSO)X₂] andcis-[Pt(DETC)(DMSO)X₂](X=Cl or Br; DMSO=dimethyl sulfoxide; DMTC=EtOSCN-Me₂; DETC=EtOSCNEt₂) adducts and the platinum(II) and palladium(II) halide adducts,trans-[M(DETC)₂X₂] (M=Pt or Pd; X=Cl or Br), have been prepared. The complexes were characterized by i.r., and¹H and¹³Cn.m.r. spectroscopy. Both DMTC and DETC coordinate through the sulphur atoms. The 1:2 DETC complexes present the usualtrans configuration, whereas the presence of DMSO favourscis geometry in the mixed species.     

Palladium(II) and platinum(II) saccharinate complexes containing pyridine and 3-acetylpyridine: Synthesis, crystal structures, fluorescence and thermal properties

New palladium(II) and platinum(II) complexes of saccharinate (sac), trans-[Pd(py)₂(sac)₂] (1), cis-[Pt(py)₂(sac)₂] (2), trans-[Pd(3-acpy)₂(sac)₂] (3) and cis-[Pt(3-acpy)₂(sac)₂] (4) (py = pyridine and 3-acpy = 3-acetylpyridine) have been synthesized. Elemental analysis, UV-Vis, IR, NMR and TG/DTA characterizations have been carried out. The structures of 1-4 were determined by X-ray diffraction. The palladium(II) and platinum(II) ions are coordinated by two N-bonded sac ligands, and two nitrogen atoms of py or 3-acpy, forming a distorted square-planar geometry. The palladium(II) complexes (1 and 3) are trans isomers, while the platinum(II) complexes (2 and 4) are cis isomers. The mononuclear species in the solid state are connected by weak intermolecular C-H?O hydrogen bonds, C-H?π and π?π stacking interactions. The platinum(II) complexes show significant fluorescence at the room temperature.     

NMR (195Pt and 13C) contribution to the study of some Pt(II), Pt(IV) and mixed-valence thioamido complexes

The ¹⁹⁵Pt and ¹³C chemical shifts (δ_Pt and δ_c) are reported for platinum(II), platinum(IV) and class II mixed-valence complexes, with general formula [PtL₄]X₂, cis- and trans-PtL₂X₂, PtL₂X₄ and Pt₂L₄X₆ (where L may be thiourea, 2-imidazolidine-thione, tetrahydro 2-pyrimidinethione, thiocaprolactam, pyridine-2-thione and tetramethylthiourea, and X may be Cl or Br). The ¹⁹⁵Pt chemical shifts can be understood in view of ¹³C data in terms of variations of electronegativities and σ-donor abilities of ligands attached to platinum.     

Four-coordinated palladium(II) and platinum(II) complexes containing the Lewis-acid {M(S2CNHR)(PR3′)} group combined with a variety of other ligands

A new series of four-coordinated Pd(II) and Pt(II) complexes in which the Lewis-acid (14-electron) {M(S₂CNHR)(PR₃′)} group is combined with a variety of other ligands (such as RHNCS₂^?, I^?, SCN^?, SnCl₂I^?) has been synthesised and studied. The structures of the new compounds are discussed in relation to their specroscopic, magnetic and thermal properties. In the case of [M(S₂CNHR)₂(PR₃′)] complexes both the spectroscopic data (IR, ¹H NMR, UV-Vis) and their thermal behaviour strongly suggest the coexistence of two kinds of gem-disulphide ligands, one acting as a bidentate ligand and the other one as a unidentate. Also it was confirmed that the chemical behaviour of the bis(N-alkyldithiocarbamato) complexes of Pd(II) and Pt(II) towards tertiary phosphines is similar to that of the isoelectronic xanthate complexes rathe than to the bis(N,N-dialkyldithiocarbamato) complexes.     

Synthesis,structure and spectroscopic properties of some thiosemicarbazone complexes of platinum

Reaction of salicyldehyde thosemicarbazone (H₂L¹), 2-hydroxyacetophenone thiosemicarbazone (H₂L²) and 2-hydroxynapthaldehyde thiosemicarbazone (H₂L³) (general abbreviation H₂L, where H₂ stands for the two dissociable protons, one phenolic proton and one hydrazinic proton) with K₂[PtCl₄] afforded a family of polymeric complexes of type [{Pt(L)}_n]. Reaction of the polymeric species with two monodentate ligands (D), viz. triphenylphosphine (PPh₃) and 4-picoline (pic), yielded complexes of the type [Pt(L)(D)]. These mixed-ligand complexes were also obtained from the reaction of the thiosemicarbazones with [Pt(PPh₃)₂Cl₂] and [Pt(pic)₂Cl₂]. The crystal structure of [Pt(PPh₃)(L²)] has been determined. The thiosemicarbazone ligands are coordinated, via dissociation of the two protons, as dianionic tridentate O,N,S-donors. The [Pt(L)(D)] complexes show characteristic ¹H NMR spectra and intense absorptions in the visible and ultraviolet region. They also fluoresce in the visible region at ambient temperature.