A bulky platinum triamine complex that reacts faster with guanosine 5′-monophosphate than with N-acetylmethionine

A bulky platinum triamine complex, [Pt(Me₅dien)(NO₃)]NO₃ (Me₅dien = N,N,N′,N′,N′′-pentamethyldiethylenetriamine) has been prepared and reacted in D₂O with N-acetylmethionine (N-AcMet) and guanosine 5′-monophosphate (5′-GMP); the reactions have been studied using ¹H NMR spectroscopy. Reaction with 5′-GMP leads to two rotamers of [Pt(Me₅dien)(5′-GMP-N7)]⁺. Reaction with N-AcMet leads to formation of [Pt(Me₅dien)(N-AcMet-S)]⁺. When a sample with equimolar mixtures of [Pt(Me₅dien)(D₂O)]²⁺, 5′-GMP, and N-AcMet was prepared, [Pt(Me₅dien)(5′-GMP-N7)]⁺ was the dominant product observed throughout the reaction. This selectivity is the opposite of that observed for a similar reaction of [Pt(dien)(D₂O)]²⁺ with 5′-GMP and N-AcMet. To our knowledge, this is the first report of a platinum(II) triamine complex that reacts substantially faster with 5′-GMP than with N-AcMet; the effect is most likely due to steric clashes between the methyl groups of the Me₅dien ligand and the N-AcMet.     

Platinum(II) triammine antitumour complexes: structure-activity relationship with guanosine 5′-monophosphate (5′-GMP)

The multinuclear (¹H, ¹⁵N, ³¹P and ¹⁹⁵Pt) NMR spectroscopies, ES-MS and HPLC have been employed to investigate the structure-activity relationship for the reactions between guanosine 5′-monophosphate (5′-GMP) and the platinum(II)-triamine complexes of the general formulation cis-[Pt(NH₃)₂(Am)Cl]NO₃ (where Am represents a substituted pyridine). The order of reaction rate of the reactions was found to be: 3-phpy > 4-phpy > py > 4-mepy > 3-mepy > 2-mepy. The two basic factors, steric and electronic, were attributed to the order of the binding rate constants. A possible mechanism of the reaction of cis-[Pt(NH₃)₂(Am)Cl]⁺ with 5′-GMP suggested that the reactions proceed via direct nucleophilic attack and no loss of ammonia. cis-[Pt(NH₃)₂(Am)Cl]⁺ binds to the N7 nitrogen of the guanine residue of 5′-GMP to form a coordinate bond with the Pt metal centre. This mechanism is apparently different from that of cisplatin. The pK_a value of cis-[Pt(NH₃)₂(4-mepy)(H₂O)](NO₃)₂ (5.63) has been determined at 298 K by the use of distortionless enhancement by polarization transfer (DEPT) ¹⁵N NMR spectroscopy and compared to the pK_a value of cis-[PtCl(H₂O)(NH₃)₂]⁺.     

Novel palladium(II) and platinum(II) complexes of biocidal benzisothiazolinone (Bit); X-ray crystal structures of co-crystallised Bit/BitO and cis-Pd(en)(Bit−1H)2·H2O

Reaction of benzisothiazolinone (Bit), a well-known biocide, with the Pd(II) and Pt(II) am(m)ine precursors cis-[Pd(en)(H₂O)₂](NO₃)₂ and cis-[Pt(NH₃)₂(H₂O)₂](NO₃)₂ yielded cis-Pd(en)(Bit_−1H)₂ and cis-Pt(NH₃)₂(Bit_−1H)₂, respectively. Bit is bound to the metal centres in both cases through the deprotonated isothiazolinone N. The crystal structures of a Bit/BitO co-crystal and cis-Pd(en)(Bit_−1H)₂·H₂O are also described.     

Synthesis and characterization of Pd(II) and Pt(II) complexes with triazolopyrimidine derivatives: The crystal structure of [Pd2L2Cl4] where L = 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine

The Pd(II) and Pt(II) complexes with triazolopyrimidine C-nucleosides L¹ (5,7-dimethyl-3-(2′,3′,5′-tri-O-benzoyl-β-d-ribofuranosyl-s-triazolo)[4,3-a]pyrimidine), L² (5,7-dimethyl-3-β-d-ribofuranosyl-s-triazolo[4,3-a]pyrimidine) and L³ (5,7-dimethyl[1,5-a]-s-triazolopyrimidine), [Pd(en)(L¹)](NO₃)₂, [Pd(bpy)(L¹)](NO₃)₂, cis-Pd(L³)₂Cl₂, [Pd₂(L³)₂Cl₄] · H₂O, cis-Pd(L²)₂Cl₂ and [Pt₃(L¹)₂Cl₆] were synthesized and characterized by elemental analysis and NMR spectroscopy. The structure of the [Pd₂(L³)₂Cl₄] · H₂O complex was established by X-ray crystallography. The two L³ ligands are found in a head to tail orientation, with a Pd?Pd distance of 3.1254(17) Å. L¹ coordinates to Pd(II) through N8 and N1 forming polymeric structures. L² coordinates to Pd(II) through N8 in acidic solutions (0.1 M HCl) forming complexes of cis-geometry. The Pd(II) coordination to L² does not affect the sugar conformation probably due to the high stability of the C-C glycoside bond.     

A model study of alternative approach toward a class of palladium(II) based self-assembly

A different approach developed for the preparation of palladium(II) based complexes [(Pd(bpy))_x(L)_y](NO₃)_2x is modelled by using 4-phenylpyridine as ligand (L = 1). Various solvent systems are inspected to optimize the reaction condition for the preparation of the model complex [Pd(bpy)(4-phenylpyridine)₂](NO₃)₂. The model complex is obtained quantitatively as a single product from a 1:1:2 mixture of Pd(NO₃)₂, 2,2′-bipyridine and 4-phenylpyridine when stirred at room temperature in CH₃CN:H₂O (1:1). The same reaction is performed in CD₃CN:D₂O (1:1) to monitor the progress of the reaction by recording ¹H NMR. The kinetic products that formed initially got self-healed to give the desired product with in 6 h. However, in DMSO-d₆ spontaneous arrangement leading to the targeted complex was observed and no kinetic product could be detected. When a similar reaction is performed with ethylenediamine instead of 2,2′-bipyridine a mixture of compounds are observed. Theoretical calculation throws some light on the principle behind the success of this method for the bpy based systems. The assembly, [Pd(bpy)(4-phenylpyridine)₂](NO₃)₂ has been characterised by NMR, ESI-MS and single-crystal X-ray diffraction methods.     

Hydrolysis of the amide bond in histidine- and methionine-containing dipeptides promoted by pyrazine and pyridazine palladium(II)-aqua dimers: Comparative study with platinum(II) analogues

Two dinuclear palladium(II) complexes, [{Pd(en)Cl}₂(μ-pz)](NO₃)₂ and [{Pd(en)Cl}₂(μ-pydz)](NO₃)₂, have been synthesized and characterized by elemental microanalysis and spectroscopic (¹H and ¹³C NMR, IR and UV–vis) techniques (en is ethylenediamine; pz is pyrazine and pydz is pyridazine). The square planar geometry of palladium(II) metal centers in these complexes has been predicted by DFT calculations. The chlorido complexes were converted into the corresponding aqua complexes, [{Pd(en)(H₂O)}₂(μ-pz)]⁴⁺ and [{Pd(en)(H₂O)}₂(μ-pydz)]⁴⁺, and their reactions with N-acetylated l-histidylglycine (Ac–l–His–Gly) and l-methionylglycine (Ac–l–Met–Gly) were studied by ¹H NMR spectroscopy. The palladium(II)-aqua complexes and dipeptides were reacted in 1:1 M ratio, and all reactions performed in the pH range 2.0 < pH < 2.5 in D₂O solvent and at 37 °C. In the reactions of these complexes with Ac–l–His–Gly and Ac–l–Met–Gly dipeptides, the hydrolysis of the amide bonds involving the carboxylic group of both histidine and methionine amino acids occurs. The catalytic activities of the palladium(II)-aqua complexes were compared with those previously reported in the literature for the analogues platinum(II)-aqua complexes, [{Pt(en)(H₂O)}₂(μ-pz)]⁴⁺ and [{Pt(en)(H₂O)}₂(μ-pydz)]⁴⁺.     

Synthesis and structural characterization of five-, six-, and seven-coordinate mononuclear manganese(II) complexes with N-tridentate ligands

A series of four mononuclear manganese (II) complexes with the N-tridentate neutral ligands 2,2^′:6,2^′′-terpyridine (terpy) and N,N-bis(2-pyridylmethyl)ethylamine (bpea) have been synthesized and crystallographically characterized. The complexes have five- to seven-coordinate manganese(II) ions depending on the additional ligands used. The [Mn(bpea)(Br)₂] complex (1) has a five-coordinated manganese atom with a bipyramidal trigonal geometry, while [Mn(terpy)₂](I)₂ (2) is hexa-coordinated with a distorted octahedral geometry. Otherwise, the reactions of Mn(NO₃)₂ · 4H₂O with terpy or bpea afforded novel seven-coordinate complexes [Mn(terpy)(NO₃)₂(H₂O)] (3) and [Mn(bpea)(NO₃)₂] (4), respectively. 3 has a coordination polyhedron best described as a distorted pentagonal bipyramid geometry with one nitrate acting as a bidentate chelating ligand and the other nitrate as a monodentate one. 4 possesses a highly distorted polyhedron geometry with two bidentate chelating nitrate ligands. These complexes represent unusual examples of structurally characterized complexes with a coordination number seven for the Mn(II) ion and join a small family of nitrate complexes.     

Reaction behavior of molybdocene dichloride towards ribonucleosides and ribonucleoside monophosphates: Rare example of sugar coordination

The coordination behavior of Cp₂Mo²⁺ towards the ribonucleosides and ribonucleoside monophosphates uridine, adenosine, cytidine, guanosine, 5′-UMP, 5′-AMP, 5′-CMP and 5′-GMP has been studied in solution in the range 4 ? pD ? 9 using NMR spectroscopy. The ribonucleosides were found to bind Cp₂Mo²⁺ exclusively through the ribose moiety giving rise to the chelate complexes [Cp₂Mo(urd-O2′,O3′)], [Cp₂Mo(ade-O2′,O3′)], [Cp₂Mo(cyd-O2′,O3′)], and [Cp₂Mo(gua-O2′,O3′)]. The ribonucleotides form three types of complex with Cp₂Mo²⁺ in neutral solution, namely N,PO-macrochelates, PO,O3′-coordinated species as well as O2′,O3′-chelates, while at pD 9 only sugar coordination is observed.     

Synthesis and characterization of new lanthanide complexes with hexadentate hydrazonic ligands

In this paper, we report the synthesis and the characterization of a novel series of lanthanide (III) complexes with two potentially hexadentate ligands.The ligands contain a rigid phenanthroline moiety and two flexible hydrazonic arms with different donor atom sets (NNN′N′OO and NNN′N′N″N″, respectively for H₂L¹ (2,9-diformylphenanthroline)bis(benzoyl)hydrazone and H₂L² (2,9-diformylphenanthroline)bis(2-pyridyl)hydrazone).Both nitrate and acetate complexes of H₂L¹ with La, Eu, Gd, and Tb were prepared and fully characterized, and the X-ray crystal structure of the complex [Eu(HL¹)(CH₃ COO)₂] · 5H₂O is presented.The stability constants of the equilibria Ln³⁺ + H₂L¹ = [Ln(H₂L¹)]³⁺ and Ln³⁺ + (L¹)²⁻ = [Ln(L₁)]⁺ (Ln = La(III), Eu(III), Gd(III), and Tb(III)) are determined by UV spectrophotometric titrations in DMSO at t = 25 °C. The nitrate complexes of H₂L² with La, Eu, Gd and Tb were also synthesized, and the X-ray crystal structures of [La(H₂L²)(NO₃)₂(H₂O)](NO₃), [Eu(H₂L²)(NO₃)₂](NO₃) and [Tb(H₂ L²)(NO₃)₂](NO₃) are discussed.     

Synthesis, characterization and cytotoxicity studies of palladium(II)-proflavine complexes

An investigation of the reaction of Pd(II) complexes with proflavine (3,6-diaminoacridine) resulted in the isolation of the compounds [Pd(terpy)(proflavine)](NO₃)(HSO₄)3H₂O, 1, (terpy = 2,2′:6′,2″-terpyridine), [Pd(en)(proflavineH))](NO₃)(SO₄), 2, (en = ethylenediamine), and [Pd(proflavineH)Cl₂](SO₄)_0.5H₂O, 3. They have been isolated and characterized by NMR, IR, and electro-spray ionization mass spectrometry techniques and by elemental analyses. The proflavine was bonded to the Pd(II) through the endocyclic nitrogen in 1, but through the proflavine NH₂ in 2. Compound 3 appeared to be polymeric in the solid state with a 1:1 mole ratio of Pd(II):proflavine. Upon solution of 3 in DMSO, two unique species were formed. In one species the Pd(II) was bonded to two proflavines through the endocyclic nitrogen (1:2 mole ratio) and in the other species, a Pd(II) was bonded to each NH₂ group of a single proflavine (2:1 mole ratio). Molecular modeling of the equilibrium geometry by Spartan 8 produced structures which were consistent with the experimental data on the solutions of the three compounds. In vitro cytotoxicity testing against two breast cancer cell lines and one ovarian cancer cell line showed that compounds 1 and 3 had significant activity.     

In situ 5-sulfosalicylate decarboxylation or dimethylformamide hydrolysis generating supramolecular assembly architectures

Six transition-metal complexes, {[Co(4,4′-bipy)(H₂O)₄](Hbs)₂ · 3H₂O}_n (1), [Mn(4,4′-bipy)₂(H₂O)₄](Hbs)₂ · 2H₂O (2), {[Mn(HCOO)(H₂O)₂(4,4′-bipy)]₂[Mn(4,4′-bipy)(Hssal)₂(H₂O)₂]}_n (3), [Cd(4,4′-bipy)₂(H₂O)₄](Hbs)₂ · 2H₂O (4), {[Cd₃(CH₃COO)₄(4,4′-bipy)₄](Hbs)₂ · 10H₂O}_n (5), and {[Cd(HCOO)(H₂O)₂(4,4′-bipy)]₂[Cd(4,4′-bipy)(Hssal)₂(H₂O)₂]}_n (6), have been synthesized by hydrothermal or reflux synthetic method and characterized by single-crystal X-ray diffraction, IR, elemental analysis, thermogravimetric analysis and fluorescence analysis, where Hssal²⁻ is doubly deprotonated 5-sulfosalicylate, Hbs⁻ is 4-hydroxybenzenesulfonate and 4,4′-bipy is 4,4′-bipyridine. The structural analyses showed that all of the six complexes are cation-anion species containing in situ synthesized ligands, Hbs⁻ or HCOO⁻, and the former arises from the decarboxylation of 5-sulfosalicylic acid under the hydrothermal conditions. The formate anions derived from the hydrolysis of DMF. A series of supramolecular compounds show that the structural diversity is strongly associated with their properties.     

Synthetic, structural and spectroscopic studies of complexes derived from the copper(II) perchlorate/succinamic acid/N,N′-donor tertiary reaction systems

The use of succinamic acid (H₂sucm) in Cu(ClO₄)₂·6H₂O/N,N′-donor [2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4′-dimethyl-2,2′-bipyridine (dmbpy), 4,4′-bipyridine (4,4′-bpy)] reaction mixtures yielded compounds [Cu₂(Hsucm)₃(bpy)₂](ClO₄)·0.5MeOH (1·0.5MeOH), [Cu₂(Hsucm)(OH)(H₂O)(bpy)](ClO₄)₂ (2), [Cu₄(Hsucm)₅(dmbpy)₄]_n(ClO₄)_3n·nH₂O ·0.53nMeOH (3·nH₂O·0.53nMeOH), [Cu₂(Hsucm)₂(dmbpy)₂(H₂O)₂](ClO₄)₂·2H₂O (4·2H₂O), [Cu₂(Hsucm)₂(phen)₂(H₂O)₂](ClO₄)₂·1.8MeOH (5·1.8MeOH), [Cu₂(Hsucm)₂(phen)₂(MeOH)₂](ClO₄)₂·MeOH (6·MeOH) and [Cu(Hsucm)₂(H₂O)(4,4′-bpy)]_n (7). The succinamate(−1) ligand exists in five different coordination modes in the structures of 1-7, i.e. the common syn, syn μ₂-κO:κO′ in 1-6, the μ₂-κ²O in 1, the μ₂-κ²O:κO′ in 1, the μ₃-κ²O:κ²O′ in 3, and the monodentate κO in 7. The primary amide group of Hsucm⁻ remains uncoordinated and participates in intra- and intermolecular hydrogen bonding interactions leading to interesting crystal structures. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm⁻ ligands. The thermal decomposition of representative complexes was monitored by TG/DTG and DTA measurements.     

Synthesis,structures and characterization of the dinuclear nickel(II) complexes containing N,N,N′,N′-tetrakis[(1-ethyl-2-benzimidazolyl)methyl]-2-hydroxy-1,3-diaminopropane and an azide ion

Two dinuclear nickel(II) complexes, [Ni₂(L-Et)(N₃)(H₂O)₃](NO₃)₂ · 2H₂O (1) and [Ni₂(L-Et)(μ-1,3-N₃)(H₂O)₂](NO₃)₂ · 4H₂O (2) containing (HL-Et = N,N,N′,N′-tetrakis[(1-ethyl-2-benzimidazolyl)methyl]-2-hydroxy-1,3-diaminopropane), have been synthesized and characterized by their IR and UV–Vis spectra and magnetic susceptibilities. The crystal structures of [Ni₂(L-Et)(N₃)(H₂O)₃](NO₃)₂ · CH₃OH (1′) and [Ni₂(L-Et)(μ-1,3-N₃)(H₂O)₂](NO₃)₂ · 2C₂H₅OH (2′) similar to 1 and 2 were determined by X-ray crystallography. In 1′, the two nickel(II) ions are bridged by only an alkoxo group of L-Et⁻, while an azido and an alkoxo connect two nickel(II) ions in 2′. Magnetic susceptibility measurements (2–300 K) showed a weak ferromagnetic exchange coupling between the two nickel(II) ions (2J = 10.1 cm⁻¹) for 1. On the other hand, antiferromagnetic interactions were observed for 2 (2J = −15.8 cm⁻¹).     

A structural study of late transition metal diethylenetriamine complexes

The synthesis and X-ray crystal structures of u-fac-[Ni(dien)₂](NO₃)₂, s-fac-[Ni(dien)₂](tos)₂, fac-fac-[(H₂O)(dien)Ni(μ-Cl)₂(dien)(H₂O)]Cl₂, s-fac-[Ni(dien)₂][ZnCl₄], mer-[Ni(dien)₂][CdCl₄] · H₂O, fac-[Ni(dien)(H₂O)₃](tos)₂ · (H₂O), mer-[Cu(dien)(H₂O)](tos)₂, fac-[Zn(dien)(H₂O)₂](tos)₂ (dien = bis(2-aminoethyl)amine = diethylenetriamine; tos = p-toluenesulfonate) are described. The mode of binding of the tridentate amine is examined in detail.     

Exploring water-soluble Pt(II) complexes of diethylenetriamine derivatives functionalized at the central nitrogen. Synthesis, characterization, and reaction with 5′-GMP

The aims of our program are to develop coordination complexes that can be used as selective probes, fluorescent agents and inorganic medicinal agents. In order to accomplish this, the design, synthesis, characterization and X-ray structure of new water-soluble monofunctional Pt(II) complexes with useful spectroscopic properties for assessing metal binding to biomolecules were investigated. Two diethylenetriamine (dien) derivatives, 2-(bis(2-aminoethyl)amino)acetic acid (acdien) and N′-[7-(acetamido)-4-(trifluoromethyl)coumarin]diethylenetriamine (atfcdien), were used. The latter was designed to allow the fluorophore group, 7-amino-4-(trifluoromethyl)coumarin (atfc), to be attached to metal centers through the dien moiety. ¹H NMR spectroscopy and X-ray crystallography were employed to characterize the [Pt(atfcdien)Br][Pt(Me₂SO)Br₃] (8a) and [Pt(acdien)Br]Br (9a) complexes. ¹H NMR and fluorescence spectroscopic methods were used to characterize the [Pt(atfcdien)Br]Br (8b) and [Pt(acdien)Br]Br (9a) complexes. ¹H NMR studies of the monofunctional [Pt(acdien)Br]Br (9a) complex conducted to examine its interaction with guanosine 5′-monophosphate (5′-GMP) in D₂O solutions revealed one downfield-shifted H8 and one downfield-shifted H1′ signal, consistent with 5′-GMP binding via N7 and fast rotation about the Pt-N7 bond.     

Monotheophylline and monotheophyllinato complexes of palladium(II) and their interactions with nucleosides

The interaction of potassium tetrachloropalladate(II) with theophylline in a 1:1 molar ratio resulted in the formation of the monotheophylline (K[Pd(ThH)Cl₃]) or monotheophyllinato ([Pd(Th)Cl]₂) complexes, depending on the solvent and the acidity conditions. In the first complex, theophylline coordinates to Pd(II) as a neutral molecule through its N9 atom, while in the second as a monoanion through both its N7 and O6 atoms. Both complexes react with nucleosides, giving the complexes [Pd(Nucl)(ThH)Cl₂] and [Pd(Nucl)(Th)Cl], respectively. Those complexes with one N(1)H ionizable imino-proton undergo deprotonation and two new series of mixed ligand complexes, [Pd(Nucl − H⁺)(ThH)Cl] and [Pd(Nucl − H⁺(Th)] are formed. In the mixed ligand complexes, theophylline maintains its coordination modes. The nucleosides, on the other hand, exhibit their usual coordination sites; i.e. in the nondeprotonated complexes they coordinate only through their N7 atoms, while in the deprotonated they act as bidentate through both their N7 and O6 atoms. All complexes were characterized with elemental analyses, conductivity measurements and various spectroscopic techniques.     

Structure and properties of cobalt ortho-phenylenediacetate coordination polymers with rigid dipyridyl ligands

Divalent cobalt coordination polymers containing both ortho-phenylenediacetate (ophda) and rigid dipyridyl ligands 4,4′-bipyridine (bpy) or 1,2-bis(4-pyridyl)ethylene (dpee) display different topologies depending on carboxylate binding mode, tether length, and inclusion of charged species. [Co(ophda)(H₂O)(dpee)]_n (1) displays a common (4,4) grid layer motif. Use of the shorter bpy tether afforded {[Co₂(ophda)₂(bpy)₃(H₂O)₂][Co(bpy)₂(H₂O)₄](NO₃)₂·2bpy·7H₂O}_n (2) or [Co(ophda)(bpy)]_n (3) depending on cobalt precursor. Compound 2 manifests 5-connected [Co₂(ophda)₂(bpy)₃(H₂O)₂]_n pillared bilayer slabs with rare 4⁸6² SnS topology and entrained [Co(bpy)₂(H₂O)₄]²⁺ complex cations. The 3-D coordination polymer 3 has an uncommon 4,6-connected binodal (4⁴6²)(4⁴6¹⁰8) fsc topology, and shows ferromagnetic coupling (J = +1.5(2) cm⁻¹) along 1-D spiro-fused [Co(OCO)₂]_n chain submotifs.     

Hydrolysis of the amide bond in methionine-containing peptides catalyzed by various palladium(II) complexes: Dependence of the hydrolysis rate on the steric bulk of the catalyst

¹H NMR spectroscopy was applied to study the reactions of cis-[Pd(L)(H₂O)₂]²⁺ complexes (L is en, pic and dpa) with the N-acetylated tripeptides L-methionylglycylglycine, MeCOMet–Gly–Gly, and glycyl–L-methionyl–glycine, MeCOGly–Met–Gly. All reactions were performed in the pH range 2.0–2.5 with equimolar amounts of the cis-[Pd(L)(H₂O)₂]²⁺ complex and the tripeptide at 60 °C. The hydrolytic reactions of the cis-[Pd(en)(H₂O)₂]²⁺, cis-[Pd(pic)(H₂O)₂]²⁺ and cis-[Pd(dpa)(H₂O)₂]²⁺ complexes with MeCOMet–Gly–Gly were regioselective and only the amide bond involving the carboxylic group of methionine was cleaved. However, in the reactions of these three Pd(II) complexes with MeCOGly–Met–Gly, two amide bonds, Met–Gly and MeCO–Gly, were cleaved. From UV–Vis spectrophotometry studies, it was found that the rate-determining step of these hydrolytic reactions is the monodentate coordination of the corresponding Pd(II) complex to the sulfur atom of the methionine side chain. The rate of the cleavage of these amide bonds is dependent on the nature of the bidentate coordinated diamine ligand L (en > pic > dpa). The hydrolytic reaction of cis-[Pd(L)(H₂O)₂]²⁺-type complexes with MeCOMet–Gly–Gly, containing the methionine side chain in the terminal position of the peptide, is regioselective while in the reaction of these Pd(II) complexes with MeCOGly–Met–Gly, none selective cleavage of the peptide occurs. This study contributes to a better understanding of the selective cleavage of methionine-containing peptides employing palladium(II) complexes as catalysts.     

Influence of cis-protecting groups toward ligand exchange reactions in polynuclear Pd(II)-based coordination cages

Polynuclear self-assembly molecules of general formula [{Pd(en)}_x(ligand)_y](NO₃)_2x (A) undergo ligand exchange reaction when heated in DMSO. A mixture of [Pd_m(ligand)_n](NO₃)_2m (B) and [Pd(en)₂](NO₃)₂ (C) is generated in this process. The binuclear compound (A) containing a bidentate, non-chelating ligand 1,4-bis(4′-pyridylmethyl)-2,3,5,6-tetrafluorobenzene, is subjected to ligand exchange where upon the compound (A) remains in a dynamic equilibrium with the mixture of ensuing (B) and (C). Combination of separately prepared (B) and (C) also generates (A), thus equilibrium of (A) with (B) and (C) is again observed. We predict [{Pd(bpy)}_x(ligand)_y](NO₃)_2x (A′) where 2,2′-bipyridyl (bpy) is the cis-protecting group would not probably undergo ligand exchange. The idea was conceived from the fact that (bpy) is more rigid compared to (en) moreover one of the expected products in the event of ligand exchange [Pd(bpy)₂](NO₃)₂ (C′) is not really very stable unlike (C). In fact, when (A′) is heated in DMSO no ligand exchange is observed at all. More interestingly combination of (B) and (C′) generated (A′) smoothly. Mononuclear complexes obtained from the ligand 4-phenylpyridine are also used for similar study for comparison. It is suggested that (bpy) could serve as a better cis-protecting group for Pd(II)-based self-assembly coordination cage compounds particularly when dissolution of the assemblies in polar solvents and heating of the resultant solution is required.     

Ruthenium polypyridyl complexes containing the bischelating ligand 2,2′-azobispyridine. Synthesis, characterization and crystal structures

Three ruthenium polypyridyl compounds of structural formula [Ru(apy)(tpy)Lⁿ⁻](ClO₄)_(2−n) (apy = 2,2′-azobispyridine; tpy = 2,2′:6′,2″-terpyridine; L = Cl, H₂O, CH₃CN) (1a-c) were synthesized and crystallized. These complexes were fully characterized by means of 1D and 2D ¹H NMR spectroscopy, as well as mass spectrometry and elemental analysis. Although in theory two isomers are possible, i.e. the one in which the central N atom in tpy is trans to the azo N in apy and the one in which the former is trans to the pyridine N in apy, in all cases only the latter was observed. The molecular structures of the compounds were elucidated by single-crystal X-ray diffraction.