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.     

New mono and dinuclear arene ruthenium chloro complexes containing ester substituents

The dinuclear arene ruthenium complexes [RuCl₂{C₆H₅(CH₂)₃OCO-p-C₆H₄-OC₈H₁₇}]₂ (1) and [RuCl₂{p-C₆H₄(CH₂COOCH₂CH₃)₂}]₂ (2) have been obtained by dehydrogenation of the corresponding cyclohexadiene derivative with ruthenium chloride hydrate. The single-crystal X-ray structure analysis of 2 shows the arene ligands to be involved in slipped-parallel π-π stacking interactions with neighbouring molecules, thus forming infinite chains along the b-axis. The dinuclear complexes 1 and 2 react with two equivalents of triphenylphosphine (PPh₃) to give in excellent yield the corresponding mononuclear phosphine complexes [RuCl₂{C₆H₅(CH₂)₃OCO-p-C₆H₄-OC₈H₁₇}(PPh₃)] (3) and [RuCl₂{p-C₆H₄(CH₂COOCH₂CH₃)₂}(PPh₃)] (4), respectively. The single-crystal X-ray structure analysis of 4 reveals the formation of a dimer through two C-H?Cl interactions in the solid state.     

Synthesis and isomerisation of two metallated N,O-complexes of ruthenium: Models for the Murai reaction

Two isomers of the N,O-coordinated acetylpyrrolyl complex [Ru(PPh₃)₂(CO)(NC₄H₃C(O)CH₃)H] {cis-N,H (1) and trans-N,H (2)} have been prepared as models for catalytic intermediates in the Murai reaction. Complex 2 isomerises to 1 upon heating via a dissociative pathway (ΔH^‡ = 195 ± 41 kJ mol⁻¹; ΔS^‡ = 232 ± 62 J mol⁻¹ K⁻¹); the mechanism of this process has been modeled using density functional calculations. Complex 2 displays moderate catalytic activity for the Murai coupling of 2′-methylacetophenone with trimethylvinylsilane, but 1 proved to be catalytically inactive under the same conditions.     

Influence of ancillary ligand L in the nitric oxide photorelease by the [Ru(L)(tpy)NO] complex and its vasodilator activity based on visible light irradiation

The photochemical and pharmacological studies of the novel [Ru(L)(tpy)NO]³⁺ L = bpy (2,2′-bipyridine), NH · NHq (quinonediimine) and NH₂.NH₂cat (o-phenylenediamine) were investigated in aqueous medium. The synthesized nitrosyl ruthenium complexes showed nitric oxide (NO) release under light irradiation at 355 nm for [Ru(L)(tpy)NO]³⁺ complex with quantum yield of 0.14 ± 0.02, 0.47 ± 0.03 and 0.46 ± 0.02 mol Einstein⁻¹ for L = bpy, NH · NHq and NH₂ · NH₂cat, respectively, and 0.0065 ± 0.001 mol Einstein⁻¹ for light irradiation at 532 nm for [Ru(NH · NHq)(tpy)NO]³⁺ complex. The photochemical pathway at 355 nm light irradiation was described as a multi-step mechanism, although at 532 nm it was better attributed to a photo-induced electron transfer. The vasorelaxation induced by NO release produced by light irradiation in visible region from physiological solution of [Ru(NH · NHq)(tpy)NO]³⁺ complex was evaluated and compared with sodium nitroprusside (SNP). The results showed very similar vasodilator power between both species.     

Ruthenium(II) complex of the novel azoimine ligand, α-acetyl-α-phenylazo-4-chlorophenylazomethine

The novel azoimine ligand α-acetyl-α-phenylazo-4-chlorophenylazomethine (L) was prepared and characterized. Its coordination chemistry to Ru(II) was investigated by the preparation and characterization of the complex trans-[Ru(bpy)LCl₂] where bpy is 2,2′-bipyridine. A crystal structure of this complex showed that L is a bidentate ligand and coordinates to Ru(II) by azo-and imine-nitrogen donor atoms. Cyclic voltammetry and spectroelectrochemistry were performed on this complex and the visible region absorption bands assigned. L is shown to be a strong π-acid ligand.     

Syntheses, characterization, and DFT investigation of new mononuclear acetonitrile- and chloro-ruthenium(II) terpyridine complexes

A series of mononuclear acetonitrile complexes of the type [Ru(CH₃CN)(L)(terpy)]²⁺ {L = phen (1), dpbpy (3), and bpm (5)}, and their reference complexes [RuCl(L)(terpy)]⁺ {L = phen (2), dpbpy (4), and dpphen (6)} were prepared and characterized by electrospray ionization mass spectrometry, UV-vis spectroscopy, and cyclic voltammograms (CV). Abbreviations of the ligands (Ls) are phen = 1,10-phenanthroline, dpbpy = 4,4′-diphenyl-2,2′-bipyridine, bpm = 2,2′-bipyrimidine, dpphen = 4,7-diphenyl-1,10-phenanthroline, bpy = 2,2′-bipyridine, and terpy = 2,2′:6′,2″-terpyridine. The X-ray structures of the two complexes 2 and 3 were newly obtained. The metal-to-ligand charge transfer (MLCT) bands in the visible region for 1, 3, and 5 in acetonitrile were blue shifted relative to those of the reference complexes [RuCl(L)(terpy)]⁺. CV for all the [Ru(CH₃CN)(L)(terpy)]²⁺ complexes showed the first oxidation wave at around 0.95 V, being more positive than those of [RuCl(L)(terpy)]⁺. The time-dependent-density-functional-theory approach (TDDFT) was used to interpret the absorption spectra of 1 and 2. Good agreement between computed and experimental absorption spectra was obtained. The DFT approach also revealed the orbital interactions between Ru(phen)(terpy) and CH₃CN or Cl⁻. It is demonstrated that the HOMO-LUMO energy gap of the acetonitrile ligand is larger than that of the Cl⁻ one.     

Zinc complexes with tricarballylic acid and Lewis bases with zero- and two-dimensional structures

Three ternary zinc complexes of the open chain polycarboxylic acid, tricarballylic (1,2,3-propane-tricarboxylic) acid (PTCH₃) have been isolated and characterized with crystallographic and physicochemical techniques. [Zn(PTCH)(phen)(H₂O)]₂ · 4H₂O (1) (where phen = 1,10-phenanthroline) has a unique dinuclear structure, while [Zn(PTCH)(bpy)]_n · 3nH₂O (2) and [Zn(PTCH)(epy)]_n · 4nH₂O (3) (where bpy = 4,4′-bipyridine and epy = 1,2-bis(4-pyridine)ethane) have 2D polymeric structures. The bis-deprotonated ligand, in all three complexes, uses for coordination only two oxygen atoms, which belong to the same carboxylate in 1, and to two different carboxylates in 2 and 3.     

Bridged dinucleating N-heterocyclic carbene ligands and their double helical mercury(II) complexes

A series of six 3,6-bis(imidazolium-3-yl)pyridazine derivatives with different imidazole-N substituents have been synthesized and isolated as the salts [H₂L]Cl₂ (1a)-(6a) and [H₂L](PF₆)₂ (1b)-(6b). Solid state structures have been determined crystallographically for eleven out of the twelve compounds, revealing diverse hydrogen bonding patterns that involve the imidazolium-C²H units and the anions. N-heterocyclic carbene (NHC) mercury(II) complexes [Hg₂L₂](PF₆)₄ (7)-(9) are readily formed in good yields from ligand precursors [H₂L](PF₆)₂ and Hg(OAc)₂, as long as imidazole-N substituents are not too bulky. X-ray crystallography reveals double helical bimetallic arrangements for the stable [Hg₂L₂]⁴⁺ cations. Ligand scrambling in [Hg₂L₂]⁴⁺ occurs only in the presence of free carbene precursor, presumably via an associative mechanism.     

Syntheses and characterization of titanium malonato and amino acid complexes: [Ti(cp)2(OOCCH2NMe2)] - The first structurally characterized α-amino acid titanium(III) complex

The reaction of [Ti(cp^∗)₂(BTMSA)] (1) (cp^∗ = η⁵-C₅Me₅, BTMSA = bis(trimethylsilyl)acetylene) with malonic acids ((HOOC)₂CR₂, R = H, Me) and N,N-dimethylglycine resulted in the formation of titanium(IV) dicarboxylato complexes [Ti(cp^∗)₂{(OOC)₂CR₂}] (R = H, 2; R = Me, 3) and an α-amino acid titanium(III) complex [Ti(cp^∗)₂(OOCCH₂NMe₂)] (4). The identities of complexes 2-4 were confirmed by microanalysis, ¹H and ¹³C NMR spectroscopy (2, 3), ESI-MS and CID experiments (2, 3) as well as by ESR and magnetic measurements (μ_eff = 1.81, 298 K) for 4. Single X-ray diffraction analyses of 2 and 4 exhibited monomolecular complexes in which the titanium atom is distorted tetrahedrally coordinated by two η⁵-C₅Me₅ rings and by the chelating bound malonato-κ²O,O′ (2) and N,N-dimethylglycinato-κ²O,O′ ligand (4).     

Ligand substitution reactions of the [ReX6] (X = Cl, Br) anions. Synthesis and crystal structure of novel oxalato complexes of rhenium(IV)

The reaction of K₂[ReX₆] (X = Cl, Br) with oxalic acid and triethylamine in dimethylformamide solution yields the substituted complexes [ReX₄(ox)]²⁻ and cis-[ReX₂(ox)₂]²⁻, which can be obtained separately depending on the amount of added amine. The crystal structures of (PPh₄)₂[ReBr₄(ox)], cis-(PPh₄)₂[ReBr₂(ox)₂] and cis-(AsPh₄)₂[ReCl₂(ox)₂] have been determined by single-crystal X-ray diffraction. The anionic complexes are octahedral with only slight distortions. The direct isolation of the pure complexes as well as the formation of only the cis isomers - without the presence of trans isomers and/or [Re(ox)₃]²⁻ - is probably due to the kinetic inertness of Re(IV)-X bonds, which increases with the number of oxalato ligands bound to the metal ion.