A new sterically loaded pentadentate N3S2 ligand and its zinc complexes

In quest of complexes having [MN₃S₂] cores in the monomeric form and trans-thiolate donor atoms, the new pentadentate thiolate amine py^tBuN₂H₂S₂-H₂ [] has been synthesized.The template condensation reaction of bis(2-mercapto-3,5-di-tert-butylaniline)zinc (II)[Zn(^tBu₂ma)₂] and pyridine-2,6-dicarbaldehyde in methanol at 40 °C leads to the formation of imine zinc complex [Zn(py^tBuN₂S₂)] (7), which is very unstable and decomposes to give thiazole 5. However, if the template condensation is followed by in situ reduction with an excess of NaBH₄, the stable saturated amine complex [Zn(py^tBuN₂H₂S₂)] (8) is formed. Demetallation of zinc complex 8 under acidic conditions leads to the formation of the desired dithiolate py^tBuN₂H₂S₂-H₂ ligand (9).     

DNA binding and cleavage activity of [Ru(NH3)4(diimine)]Cl2 complexes

The interaction of a series of mixed ligand complexes of the type [Ru(NH₃)₄(diimine)]Cl₂, where diimine=2,2^′-bipyridine (bipy), 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), 4,7-dimethyl-1,10-phenanthroline (4,7-dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp), 3,4,7,8-tetra-methyl-1,10-phenanthroline (Me₄phen), with calf thymus DNA has been studied using absorption, emission and circular dichroic spectral measurements and viscometry and electrochemical techniques. On interaction with DNA the complexes show hypochromism and red-shift in their MLCT band suggesting that the complexes bind to DNA. The magnitude of the binding constant (K_b) obtained from absorption spectral titration varies depending upon the nature of the diimine ligand: Me₄phen > 5,6-dmp > 4,7-dmp > phen suggesting the use of diimine ‘face’ of the octahedral complexes in binding to DNA. The interaction of phen complex possibly involves phen ring partially inserted into the DNA base pairs. In contrast, the methyl-substituted phen complexes would involve hydrophobic interaction of the phen ring in the grooves of DNA, which is supported by hydrogen bonding interactions of the ammonia ligands with the intrastrand nucleobases. Also the shape and size of the phen ligand as modified by the methyl substituents determine the DNA binding site sizes (0.12-0.45 base pairs). The relative emission intensities (I/I₀) of the DNA-bound complexes parallel the variation in K_b values. Almost all the metal complexes exhibit induced CD bands on binding to B DNA, with the 4,7-dmp and Me₄phen complexes inducing certain structural modifications on the biopolymer. DNA melting curves obtained in the presence of metal complexes reveal a monophasic melting of the DNA strands, the Me₄phen complex exhibiting a slightly enhanced tendency to stabilize the double-stranded DNA. There were slight to appreciable changes in the relative viscosities of DNA, which are consistent with enhanced hydrophobic interaction of the methyl-substituted phen rings. Upon interaction with CT DNA, the Me₄phen, 4,7-dmp and 5,6-dmp complexes, in contrast to bipy, phen and 2,9-dmp complexes, show a decrease in anodic peak current in their cyclic voltammograms suggesting that they exhibit enhanced DNA binding. DNA cleavage experiments show that all the complexes induce cleavage of pBR322 plasmid DNA, the Me₄phen and 5,6-dmp complexes being remarkably more efficient than other complexes.     

Host-guest properties of the trinuclear arene-ruthenium cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]

The trinuclear arene-ruthenium cluster cation [H₃Ru₃(C₆H₆)(C₆Me₆)₂(O)]⁺, containing a μ₃-oxo cap and three arene ligands that span a hydrophobic pocket above the metal skeleton, has been crystallised as tetrafluoroborate salt in the presence of various guest molecules. The host-guest complexes have been characterised by single-crystal X-ray structure analysis. With chloroform as the guest molecule, a CHCl₃ molecule sits perfectly in the hydrophobic pocket, the hydrogen atom being encapsulated inside the cavity. When dioxane is added during the crystallisation process, the cluster forms infinite chains which are connected by a complex network of hydrogen bonds involving the μ₃-oxo ligand, water and dioxane molecules. Interestingly, in the presence of phenol, a water molecule is hydrogen-bonded between the μ₃-oxo ligand and the phenol molecule, forming a one-dimensional μ₃-O ? H₂O ? HO hydrogen-bonded chain. Finally, with benzoic acid, a head-to-tail host-guest chain is obtained, the phenyl ring being incorporated in the hydrophobic pocket, while the acid group is hydrogen-bonded to the μ₃-oxo ligand.     

X-ray structure, redox and spectroscopic properties of ruthenium phosphine complexes [Ru(tpy)(bpy)(PPh3)] and [Ru(tpy)(bpy)(PCy3)]

The synthesis and crystal structures of two new phosphine ruthenium polypyridine complexes [Ru(tpy)(bpy)(PR₃)]²⁺ with R = Ph (1), Cy (2) are reported. Their geometrical parameters are intimately related to the electronic and steric properties of the phosphine ligand. Electrochemical and UV-Vis analyses showed the influence of the substituents of the coordinated phosphorus atom on the Ru^III/Ru^II potential and on the frontier orbitals energy gap. The results are discussed in terms of steric effects and net donor power of the phosphine ligands.     

Photochemical reactions of trans-[Ru(NH3)4L(NO)] complexes

The photochemical behavior of a series of trans-[Ru(NH₃)₄L(NO)]³⁺ complexes, where L=nitrogen bound imidazole, L-histidine, 4-picoline, pyridine, nicotinamide, pyrazine, 4-acetylpyridine, or triethylphosphite is reported. In addition to ligand localized absorption bands (<300 nm), the electronic spectra of these complexes are dominated by relatively low intensity bands assigned as ligand field (LF) and metal to ligand (d_π → NO) charge transfer (MLCT) transitions. Irradiation of aqueous solutions of these complexes with near-UV light (300-370 nm) labilizes NO, i.e.,

     

Electrochemical behaviour and reactivity of [Os(bpy)2(CO)(OTf)] in halogenated solvents

The dimethylaminopyridine (DMAP) promoted reaction between [Os(bpy)₂(CO)(OTf)]OTf (where ) and methylene chloride is reported. C-Cl bond breaking of a solvent molecule leads to the formation of the [Os(bpy)₂(CO)(Cl)]OTf complex. The reactivity and redox properties of [Os(bpy)₂(CO)(OTf)]OTf were investigated by means of room- and low-temperature electrochemical experiments. In CH₂Cl₂, at low temperature, the complex undergoes two 1e electrochemical and chemical reversible reductions (E_rE_r mechanism), but at room temperature a more complex electrochemical mechanism is observed, leading to the electro-synthesis of [Os(bpy)₂(CO)(Cl)]OTf via electrochemical reversible and chemical irreversible reduction processes (E_rC_i mechanism). The DMAP nucleophilicity was used to produce the new [Os(bpy)₂(CO)(Br)]OTf and [Os(bpy)₂(CO)(I)]OTf complexes which have been fully characterized.     

Convenient preparation of [CuX(PCy3)2](X = Br, I, SCN, N3) complexes. X-ray crystal structure of [Cu(N3)(PCy3)2] (Cy = cyclo-C6H11)

The labile cations [Cu(F-BF₃)(PCy₃)₂] and [Cu(OTf)(PCy₃)₂] are versatile precursors for the formation of [Cu(X)(PCy₃)₂] (X = Br, I, SCN, N₃) complexes by metathesis with NaX. The azide [Cu(N₃)(PCy₃)₂] is triclinic, space group , a = 9.755(4), B = 22.78(1), C = 9.284(6) Å, = 96.76(3), β = 115.36(3), γ = 94.20(5)°, Z = 2.     

New nickel complexes with an S4 coordination sphere; synthesis, characterization and reactivity towards nickel and iron compounds

Three new nickel complexes have been synthesized with the ligands Hbss (4-mercapto-2-thia-1-butylbenzene) and Hbsms (2-(benzylsulfanyl)-2-methyl-1-propanethiol). [Ni(bss)₂] is a mononuclear complex with an S₄ coordination environment. [Ni₃(bss)₄](BF₄)₂ and [Ni₃(bsms)₄](BF₄)₂ are linear trinuclear complexes that can be synthesized either directly from the ligands Hbss and Hbsms in a reaction with Ni(BF₄)₂, or via the mononuclear complexes [Ni(bss)₂] and [Ni(bsms)₂] in a reaction with Ni(BF₄)₂. These reactions have been monitored with ligand field spectroscopy. Crystals suitable for X-ray diffraction were obtained for [Ni₃(bss)₄](BF₄)₂. The complex crystallizes in the space group P2₁/c. The nickel centers are in a square-planar environment; two peripheral nickel centers with an S₂S₂^′ (S=thiolato; S^′=thioether) coordination environment and the central nickel ion with an S₄ coordination environment.The mononuclear nickel complexes [Ni(bss)₂] and [Ni(bsms)₂] were reacted with FeCl₂, resulting in the hetero-tetranuclear nickel-iron complexes [Ni(bss)₂FeCl₂]₂ and [Ni(bsms)₂FeCl₂]₂. All complexes were characterized by analytical and spectroscopic methods.     

Synthesis, structure and reactivity of complexes containing [M(S2)2] fragments (M=Ru, Os; (S2)=1,2-benzenedithiolate (2−))

Subsequent addition of 1,2-benzenedithiol (S₂-H₂) and nBuLi to a solution of [Ru(NO)Cl₃ · xMeOH] in THF afforded exclusively the monomeric species NBu₄[Ru^II(NO)(S₂)₂] (1). Formation of dimeric (NBu₄)₂[Ru^II(NO)(S₂)₂]₂ (2) has been confirmed when the deprotonated ligand S₂-Li₂ was added to [Ru(NO)Cl₃ · xMeOH] and allowed to stir for 30 h. The monomer 1 undergoes aerial oxidation to give (NBu₄)₂[Ru^IV(S₂)₃] (3). The reaction between RuCl₃ · xH₂O and S₂-H₂ in the presence of NaOMe, afforded the dinulear Ru^III species (NMe₄)₂[Ru^III(S₂)₂]₂ (4). A modified method for the preparation of 1 is being employed to synthesize the osmium analogue NBu₄[Os(NO)(S₂)₂] (5) effectively. The solid state structures of 1, 2 and 3 were determined by X-ray crystal structure analysis. A comparison of relevant bond distance data suggests that 1,2-benzenedithiolate acts as an “innocent” ligand.     

New metal complexes of N2S2 tetradentate ligands: Synthesis and spectral studies

New tetradentate ligands 2-(2-mercaptoethylthio)-N-(pyridin-2-ylmethyl)acetamide H₂L¹ and 2-chloro-2-(2-mercaptoethylthio)-N-(pyridin-2-ylmethyl)acetamide H₂L² were synthesised from the reaction of 2-aminomethanepyridine with 1,4-dithian-2-one and 3-chloro-1,4-dithian-2-one, respectively. Monomeric complexes of these ligands, of general formulae K[Cr^III(Lⁿ)Cl₂], K₂[Mn^II(Lⁿ)Cl₂] and [M(Lⁿ)] (M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II); n = 1, 2) are reported. The mode of bonding and overall geometry of the complexes were determined through IR, UV-Vis, NMR and mass spectral studies, magnetic moment measurements, elemental analysis, metal content and conductance. These studies revealed octahedral geometries for the Cr(III), Mn(II) complexes, square planar for Ni(II) and Cu(II) complexes and tetrahedral for the Fe(II), Co(II), Zn(II), Cd(II) and Hg(II) complexes. The study of complex formation via molar ratio in DMF solution has been investigated and results were consistent to those found in the solid complexes with a ratio of (M:L) as (1:1).     

The synthesis and structural characterization of the technetium nitrosyl complexes [TcCl(NO)(SC5H4N)(PPh3)2] and [Tc(NO)(SC5H4N)2(PPh3)]

The reaction of the Tc(I) complex [Tc(NO)Cl₂(HOMe)(PPh₃)₂] with stoichiometric amounts of 2-mercatopyridine and a proton scavenger yields [Tc(NO)Cl(Spy)(PPh₃)₂] or [Tc(NO)(Spy)₂(PPh₃)], depending upon quantities of ligands employed. These two complexes have been structurally characterized. The small bite angles of the bidentate mercaptopyridine ligands cause significant deviation from octahedral coordination geometry.     

Substituents effect on the electronic structure, spectra and photochemistry of [Ru(NH3)5(Py-X)] complexes

The diagrams of MLCT and d-d excited states of the complexes [Ru(NH₃)₅(py-X)]²⁺ are calculated using semiempirical CINDO/S method. Comparison of the relative energies of MLCT and d-d excited states leads to the understanding of the background of the rules, found earlier by Ford et al., that govern photochemical activity of the Ru(II) complexes under consideration.     

Synthesis and structures of the cuboidal iron-sulfur-nitrosyl-phosphine clusters [Fe4S3(NO)4(PR3)3] (R = Et, Pr, C6H11)

A series of cuboidal iron-sulfur clusters [Fe₄S₃(NO)₄(PR₃)₃]^0,1+ (R = Et, Prⁱ, Cy) were synthesized by two routes: reductive desulfurization of [Fe₄S₄(NO)₄] by tertiary phosphines, and substitution of triphenylphosphine in [Fe₄4S₃(NO)₄(PPh₃)₃] by a more basic phosphine. The structures of 3[Fe₄S₃(NO)₄(PEt₃)₃] · 0.5Et₂O, [Fe₄S₃(NO)₄(PEt₃)₃] [Fe₄S₃(NO)₇] and partially substituted [Fe₄S₃(NO)₄(PPh₃)_2⁻ (PPrⁱ₃)] have been determined by X-ray diffraction in order to define the cuboidal Fe₄S₃ core, previously known only in Roussin's black anion and its reduced form, [Fe₄S₃(NO)₇7]^1−,2−, and as a part of the iron-molybdenum cofactor of nitrogenase.     

Cyclopentadienyl ruthenium(II) dithiocarbamate complexes: Crystal structures of [CpRu(PPh3)(S2CNPr2)] and [CpRu(PPh3)(S2CNMeBu)]

Thermolysis of [CpRuCl(PPh₃)₂] and NaS₂CNPr₂ or NaS₂CNMeBu in methanol affords the ruthenium(II) dithiocarbamate complexes, [CpRu(PPh₃)(S₂CNPr₂)] and [CpRu(PPh₃)(S₂CNMeBu)], which have been crystallographically characterized. A similar treatment of two equivalents of [CpRuCl(PPh₃)₂] with the bis(dithiocarbamate) ligand derived from 1,3-homopiperazine affords [{CpRu(PPh₃)}₂(μ-S₂CNC₅H₁₀NCS₂)].     

Ruthenium(II) thiacrown complexes: Synthetic, spectroscopic, electrochemical, DFT, and single crystal X-ray structural studies of [Ru([15]aneS5)Cl](PF6)

We wish to report the synthesis of the Ru(II) crown thioether complex, (1,4,7,10,13-pentathiacyclopentadecane)chlororuthenium(II) hexafluorophosphate, [Ru([15]aneS₅)Cl](PF₆), and a study of its properties utilizing single crystal X-ray diffraction, electronic spectroscopy, NMR spectroscopy, density functional theory calculations and cyclic voltammetry. The crystal structure shows a single [15]aneS₅ macrocycle and a chloro ligand coordinated in a distorted octahedral fashion around the ruthenium(II) center. A significant shortening (0.15 Å) of the trans Ru-S bond length occurs in this complex compared to the related PPh₃ complex (2.4458(10) to 2.283(1) Å) due to the differences in the trans influence of the two ligands. ¹³C NMR spectroscopy demonstrates that the structure of [Ru([15]aneS₅)Cl]⁺ is retained in solution. As expected for a Ru(II) complex, the electronic absorption spectrum shows two d-d transitions at 402 and 331 nm. These are red-shifted compared to hexakis(thioether)ruthenium(II) complexes and consistent with the weaker ligand field effect of the chloro ligand. The electrochemical behavior of the complex in acetonitrile shows a single one-electron reversible oxidation-reduction at +0.722 V versus Fc/Fc⁺ which is assigned as the Ru(II)/Ru(III) couple. DFT calculations for [Ru([15]aneS₅)Cl]⁺ show a HOMO with orbital contributions from a t_2g type orbital of the Ru ion, a π component from a p orbital of the axial S atom of [15]aneS₅, and a p orbital of the chloro ligand while the LUMO consists of orbital contributions of d_x²-y² orbital of the Ru center and p orbitals of the four equatorial S donors.     

[Ni(L)(MeCN)]complex cation as a template for the assembly of extended I3 · I5 and I5 · I7 polyiodide networks {L=2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane}. Synthesis and structures of [Ni(L)(MeCN)]I8 and [Ni(L)(MeCN)]I12

The compounds [Ni(L)(MeCN)]I₈ (1) and [Ni(L)(MeCN)]I₁₂ (2) have been obtained from the reactions of the complexes [Ni(L)(L^′)][BF₄]_(2 + n) {L=2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane; L^′=MeCN, Cl⁻, Br⁻, I⁻; n=charge of L^′} with an excess of I₂ (molar ratios of 6, 10 and 20 have been used), in the presence of the stoichiometric amount of I⁻ (as Bu₄ⁿNI) necessary to balance the charge of the complex cation [Ni(L)(L^′)]^(2 + n)+. An X-ray diffraction analysis shows that, independently of the nature of L^′, both 1 and 2 contain the complex cation [Ni(L)(MeCN)]²⁺, which is therefore capable of templating two different polyiodide networks based on interacting I₃⁻/I₅⁻ and I₅⁻/I₇ units, respectively. The solid state FT-Raman spectra of 1 and 2 are discussed based on their structural features.     

Oxidative addition of methyl iodide to [Rh(CH3COCHCOCH3)(CO)(P(OCH2)3CCH3)]

The reaction rate of the oxidative addition and the following CO insertion step of methyl iodide with [Rh(acac)(CO)(P(OCH₂)₃CCH₃)] is determined. The key finding is that while [Rh(acac)(CO)(P(OCH₂)₃CCH₃)] oxidatively adds methyl iodide ca 300 times faster than the Monsanto catalyst, the CO insertion step is much slower. However, the rate-determining step of the oxidative addition reaction of the phosphorus-containing acetylacetonato-rhodium(I) complex, the carbonyl insertion step, is still in the same order or faster than the rate-determining oxidative addition step of iodomethane to [Rh(CO)₂I₂]⁻.     

Carbonyl ligand substitution at rhodium in the heterometallic cluster [PPN]2[Re7C(CO)21Rh(CO)2]. A reactivity comparison with mononuclear (n-C5H5Rh(CO)2 and related compounds

The heteometallic cluster compound [PPN]₂[Re₇C(CO)₂₁Rh(CO)₂] reacts with tertiary phosphines and phosphites selectively at the rhodium center to form the mono-substituted products [PPN]₂[Re₇C(CO) (L)]. Isolated compounds have been characterized by standard analytical and spectroscopic methods. Kinetics studies have shown that the reaction proceeds by an overall second-order process, first order in complex and first order in nucleophile. The second-order rate constants have been analysed in terms of electronic and steric effects. The substitution rates at the rhodium center in the cluster are compared with those for the analogous mononuclear complexes (n⁵-C₅H₄X)Rh(CO)₂ previously studied by Basolo and co-workers.