Manganese complexes as models for manganese-containing pseudocatalase enzymes: Synthesis,structural and catalytic activity studies

Manganese complexes of the type [TpMn(X)] and [TpMn(μ-N₃)(μ-X)MnTp] (X = acetylacetonate, acac; picolinate, pic and Tp = Tp^Ph,Me for acac, Tp = Tp^ipr2 for pic complexes) having Tp^Ph,Me (hydrotris(3-phenyl,5-methyl-pyrazol-1-yl)borate)/Tp^ipr2 (hydrotris(3,5-diisopropyl-pyrazol-1-yl)borate) as a supporting ligand have been synthesized and structurally characterized. IR and X-ray structures suggest that complexes 7 and 9 are binuclear with azido and bidentate ligands (acac/pic) bridging, whereas complexes 6 and 8 are mononuclear with a 5-coordinated metal center. In complex 9 the picolinate is coordinated as tridentate in a η₃-fashion, but in complex 7 acac behaves as bidentate, whereas azide is coordinated in a bridging bidentate μ-1,3-manner in both 7 and 9. Since the coordination geometry of the manganese ions in complex 9 is very similar to the active site structure of manganese-containing pseudocatalase, we have tested the catalytic activity of the same towards the disproportionation of hydrogen peroxide. The catalytic results indicated that complex 9 has reasonably good catalase activity and may be suitable, structurally as well as functionally, as a model for the pseudocatalase enzyme.     

Titanium and zirconium complexes containing sterically hindered hydrotris(pyrazolyl)borate ligands: synthesis, structural characterization, and ethylene polymerization studies

The synthesis, characterization and ethylene polymerization behavior of a set of Tp^′MCl₃ complexes (4, M=Ti, Tp^′=HB(3-neopentyl-pyrazolyl)₃⁻(Tp^Np); 5, M=Ti, Tp^′=HB(3-tert-butyl-pyrazolyl)₃⁻(Tp^tBu); 6, M = Ti, Tp^′=HB(3-phenyl-pyrazolyl)₃⁻(Tp^Ph); 7, M=Zr, Tp^′=HB(3-phenyl-pyrazolyl)₃⁻(Tp^Ph); 8, M=Zr, Tp^′ = HB(3-tert-butyl-pyrazolyl)₃⁻(Tp^tBu)) is described. Treatment of these tris(pyrazolyl)borate Group IV compounds with methylalumoxane (MAO) generates active catalysts for ethylene polymerization. For the polymerization reactions performed in toluene at 60 °C and 3 atm of ethylene pressure, the activities varied between 1.3 and 5.1 × 10³ g of PE/mol[M] · h. The highest activity is reached using more sterically open catalyst precursor 4. The viscosity-average molecular weights () of the PE’s produced with these catalyst precursors varying from 3.57 to 20.23 × 10⁵ g mol⁻¹ with melting temperatures in the range of 127-134 °C. Further polymerization studies employing 7 varying Al/Zr molar ratio and temperature of polymerization showed that the activity as well as the polymer properties are dependent on these parameters. In that case, higher activity was attained at 60 °C. The viscosity-average molecular weights of the polyethylene’s decreases with increasing Al/Zr molar ratio.     

Syntheses, structures, and properties of metal complexes involving π-conjugated tetrathiafulvalene-pyridine ligand

Four metal complexes based on the phenyl-bridged pyridine ligand with tetrathiafulvalene unit (TTF-Ph-Py, L), Ni^II(acac)₂(L)₂ (1, acac = acetylacetonate), M(hfac)₂(L)₂ (M = Ni^II, 2; M = Cu^II, 3; hfac = hexafluoroacetylacetonato) and [Co^II(Tp^Ph2)(OAc)(L)]·H₂O (4, Tp^Ph2 = hydridotri(3,5-diphenylpyrazol-1-yl) borate), have been synthesized and structurally characterized. The absorption spectra and redox behaviors of these new compounds have been studied. Optimized conformation and molecular orbital diagram of L has been calculated with density functional theory (DFT).     

Synthesis and electrochemical properties of new cobalt and manganese phthalocyanine complexes tetra-substituted with 3,4-(methylendioxy)-phenoxy

The synthesis and electrochemical properties of new cobalt and manganese phthalocyanine complexes, tetra-substituted with 3,4-(methylendioxy)-phenoxy at the peripheral (complexes 3 and 5) and non-peripheral (complexes 4 and 6) positions, are reported. Complexes 3 and 4 showed Q-band absorption, in DMF, at 668 and 686 nm, respectively while Q-band due to complexes 5 and 6 appeared at 732 and 760 nm, respectively in CHCl₃. All the complexes showed well resolved redox processes attributed to both metal and ring based processes. Complexes 3 and 4 showed four redox processes, labeled I, II, III and IV. For complex 3, process I (Co^IPc⁻²/Co^IPc⁻³) was observed at −1.45 V, II (Co^IIPc⁻²/Co^IPc⁻²) at −0.38 V, III (Co^IIIPc⁻²/Co^IIPc⁻²) at +0.49 V and IV (Co^IIIPc⁻¹/Co^IIIPc⁻²) at +0.97 V versus Ag|AgCl. Similar processes were observed for complex 4 at −1.36 V, −0.27 V, +0.56 V, +1.03 V versus Ag|AgCl, respectively. Complexes 5 and 6 showed two redox processes (I and II). For complex 5, these processes appeared at −0.79 V (Mn^IIPc⁻²/Mn^IIPc⁻³, I) and −0.07 V versus Ag|AgCl (Mn^IIIPc⁻²/Mn^IIPc⁻², II), while for complex 6, they were observed at −0.86 V and −0.04 V versus Ag|AgCl. Spectroelectrochemistry was used to probe and confirm the origin of these processes.     

Reactions of trimethylsiloxychlorosilanes with lithium metal - On the mechanism of the formation of trimethylsiloxysilyllithium compounds LiSiRR’(OSiMe3)

The reaction pathway for the formation of the trimethylsiloxysilyllithium compounds (Me₃SiO)RR′SiLi (2a: R = Et, 2b: R = ⁱPr, 2c: R = 2,4,6-Me₃C₆H₂ (Mes); 2a-c: R′ = Ph; 2d: R = R′ = Mes) starting from the conversion of the corresponding trimethylsiloxychlorosilanes (Me₃SiO)RR′SiCl (1a-d) in the presence of excess lithium in a mixture of THF/diethyl ether/n-pentane at −110 °C was investigated.The trimethylsiloxychlorosilanes (Me₃SiO)RPhSiCl (1a: R = Et, 1b: R = ⁱPr, 1c: R = Mes) react with lithium to give initially the trimethylsiloxysilyllithium compounds (Me₃SiO)RPhSiLi (2a-c). These siloxysilyllithiums 2 couple partially with more trimethylsiloxychlorosilanes 1 to produce the siloxydisilanes (Me₃SiO)RPhSi-SiPhR(OSiMe₃) (Ia-c), and they undergo bimolecular self-condensation affording the trimethylsiloxydisilanyllithium compounds (Me₃SiO)RPhSi-RPhSiLi (3a-c). The siloxydisilanes I are cleaved by excess of lithium to give the trimethylsiloxysilyllithiums (Me₃SiO)RPhSiLi (2). In the case of the two trimethylsiloxydisilanyllithiums (Me₃SiO)RPhSi-RPhSiLi (3a: R = Et, 3b: R = ⁱPr) a reaction with more trimethylsiloxychlorosilanes (Me₃SiO)RPhSiCl (1a, 1b) takes place under formation of siloxytrisilanes (Me₃SiO)RPhSi-RPhSi-SiPhR(OSiMe₃) (IIa: R = Et, IIb: R = ⁱPr) which are cleaved by lithium to yield the trimethylsiloxysilyllithiums (Me₃SiO)RPhSiLi (2a, 2b) and the trimethylsiloxydisilanyllithiums (Me₃SiO)RPhSi-RPhSiLi (3a, 3b). The dimesityl-trimethylsiloxy-silyllithium (Me₃SiO)Mes₂SiLi (2d) was obtained directly by reaction of the trimethylsiloxychlorosilane (Me₃SiO)Mes₂SiCl (1d) and lithium without formation of the siloxydisilane intermediate. Both silyllithium compounds 2 and 3 were trapped with HMe₂SiCl giving the products (Me₃SiO)RR′Si-SiMe₂H and (Me₃SiO)RPhSi-RPhSi-SiMe₂H.     

Substituted lithiumtrimethylsiloxysilanides LiSiRR′(OSiMe3) - Investigations of their synthesis, stability and reactivity

The reactions of the trimethylsiloxychlorosilanes (Me₃SiO)RR′SiCl (1a-h: R′ = Ph, 1a: R = H, 1b: R = Me, 1c: R = Et, 1d: R = ⁱPr, 1e: R = ^tBu, 1f: R = Ph, 1g: R = 2,4,6-Me₃C₆H₂ (Mes), 1h: R = 2,4,6-(Me₂CH)₃C₆H₂ (Tip); 1i: R = R′ = Mes) with lithium metal in tetrahydrofuran (THF) at −78 °C and in a mixture of THF/diethyl ether/n-pentane in a volume ratio 4:1:1 at −110 °C lead to mixtures of numerous compounds. Dependent on the substituents silyllithium derivatives (Me₃SiO)RR′SiLi (2b-i), Me₃SiO(RR′Si)₂Li (3a-g), Me₃SiRR′SiLi (4a-h), (LiO)RR′SiLi (12e, 12g-i), trisiloxanes (Me₃SiO)₂SiRR′ (5a-i) and trimethylsiloxydisilanes (6f^∗, 6h^∗, 6i^∗) are formed. All silyllithium compounds were trapped with Me₃SiCl or HMe₂SiCl resulting in the following products: (Me₃SiO)RR′SiSiMe₂R″ (6b-i: R″ = Me, 7c-i: R″ = H), Me₃SiO(RR′Si)₂SiMe₂R″ (8a-g: R″ = Me, 9a-g: R″ = H), Me₃SiRR′SiSiMe₂R″ (10a-h: R″ = Me, 11a-h: R″ = H) and (HMe₂SiO)RR′SiSiMe₂H (13e, 13g-i). The stability of trimethylsiloxysilyllithiums 2 depends on the substituents and on the temperature. (Me₃SiO)Mes₂SiLi (2i) is the most stable compound due to the high steric shielding of the silicon centre. The trimethylsiloxysilyllithiums 2a-g undergo partially self-condensation to afford the corresponding trimethylsiloxydisilanyllithiums Me₃SiO(RR′Si)₂Li (3a-g). (Me₃)Si-O bond cleavage was observed for 2e and 2g-i. The relatively stable trimethylsiloxysilyllithiums 2f, 2g and 2i react with n-butyllithium under nucleophilic butylation to give the n-butyl-substituted silyllithiums ⁿBuRR′SiLi (15g, 15f, 15i), which were trapped with Me₃SiCl. By reaction of 2g and 2i with 2,3-dimethylbuta-1,3-diene the corresponding 1,1-diarylsilacyclopentenes 17g and 17i are obtained.X-ray studies of 17g revealed a folded silacyclopentene ring with the silicon atom located 0.5 Å above the mean plane formed by the four carbon ring atoms.     

Syntheses and characterization of [(η-C6Me6)Ru(μ-N3)(X)]2 (X = N3 and Cl) complexes and their reactions towards mono- and bidentate ligands

The reaction of the complex [{(η⁶-C₆Me₆)Ru(μ-Cl)Cl}₂] 1 with sodium azide ligand gave two new dimers of the composition [{(η⁶-C₆Me₆)Ru(μ-N₃)(N₃)}₂] 2 and [{(η⁶-C₆Me₆)Ru(μ-N₃)Cl}₂] 3, depending upon the reaction conditions. Complex 3 with excess of sodium azide in ethanol yielded complex 2. These complexes undergo substitution reactions with monodentate ligands to yield monomeric complexes of the type [(η⁶-C₆Me₆)Ru(X)(N₃)(L)] {X = N₃, Cl, L = PPh₃ (4a, 9a); PMe₂Ph (4b, 9b); AsPh₃ (4c, 9c); X = N₃, L = pyrazole (Hpz) (5a); 3-methylpyrazole (3-Hmpz) (5b) and 3,5-dimethyl-pyrazole (3,5-Hdmpz) (5c)}. Complexes 2 and 3 also react with bidentate ligands to give bridging complexes of the type [{(η⁶-C₆Me₆)Ru(N₃)(X)]₂(μ-L)} {X = N₃, Cl, L = 1,2-bis(diphenylphosphino)methane (dppm) (6, 10); 1,2-bis(diphenylphosphino)ethane (dppe) (7, 11); 1,2-bis(diphenylphosphino)propane (dppp) (8, 12); X = Cl, L = 4,4-bipyridine (4,4′-bipy) (13)}. These complexes were characterized by FT-IR and FT-NMR spectroscopy as well as by analytical data.The molecular structures of the representative complexes [{(η⁶-C₆Me₆)Ru(μ-N₃)(N₃)}₂] 2, [{(η⁶-C₆Me₆)Ru(μ-N₃)Cl}₂] 3,[(η⁶-C₆Me₆)Ru(N₃)₂(PPh₃)] 4a and [{(η⁶-C₆Me₆)Ru(N₃)₂}₂ (μ-dppm)] 6 were established by single crystal X-ray diffraction studies.     

Addition of benzenethiol to terminal alkynes catalyzed by hydrotris(3,5-dimethylpyrazolyl)borate-Rh(III) bis(thiolate) complex: Mechanistic studies with characterization of the key intermediate

The Rh(III)-thiolate complex [Tp^∗Rh(SPh)₂(MeCN)] (2; Tp^∗ = hydrotris(3,5-dimethylpyrazolyl)borate) readily undergoes substitution of MeCN by XyNC (Xy = 2,6-dimethylphenyl) to give the isocyanide complex [Tp^∗Rh(SPh)₂(XyNC)] (3), whereas reaction of 2 with terminal alkynes results in the formation of the rhodathiacyclobutene complex [Tp^∗Rh(SPh){η²-CHCR(SPh)}] (4; R = aryl, alkyl). Molecular structures of 3 and 4 (R = CH₂Ph) have been determined by single crystal X-ray diffraction. Complex 2 as well as [Tp^∗Rh(cyclooctene)(MeCN)] have been found to catalyze regioselective addition of benzenethiol to terminal alkynes RCCH at 50 °C to give R(PhS)CCH₂ in moderate to high yields. The above products are selectively formed when R = CH₂Ph and n-C₆H₁₃, while cis-RCHCHSPh and RC(SPh)₂CH₃ are also obtained as by-products when R = p-MeOC₆H₄. Catalytic cycle involving 2 and 4 is proposed based on the mechanistic studies using NMR measurement.     

Synthesis, characterization and molecular structure of the [(η-C6Me6)Ru(μ-N3)(N3)]2 complex and its reactions with some monodentate ligands

The reaction of complex [(η⁶-C₆Me₆)Ru(μ-Cl)Cl]₂ (1) with sodium azide yielded complexes of the composition [(η⁶-C₆Me₆)Ru(μ-N₃)(N₃)]₂ (2) and [(η⁶-C₆Me₆)Ru(μ-N₃)(Cl)]₂ (3), depending upon the reaction conditions. Complex 3 with excess of sodium azide in ethanol yielded complex 2. Complexes 2 and 3 undergo substitution reactions with monodentate ligands such as PPh₃, PMe₂Ph and AsPh₃ to yield monomeric complexes. The structure of complex 2 was determined by X-ray crystallography. All these complexes were characterized by micro analytical data and by FT-IR and FT-NMR spectroscopy. Complex 2 crystallizes in the monoclinic space group P2₁/n with a = 8.5370(11) Å, b = 16.192(2) Å, c = 10.4535(13) Å and β = 110.877(2)°.     

Synthesis and reactivity of asymmetrically substituted ansa-bridged zirconocene complexes: X-ray crystal structures of [Zr{R(H)C(η-C5Me4)(η-C5H4)}Cl2] (R = Bu, Bu) and [Zr{Bu(H)C(η-C5Me4)(η-C5H4)}(CH2Ph)2]

The dialkyl complexes, (R = Prⁱ, R′ = Me (2a), CH₂Ph (3a); R = Buⁿ, R′ = Me (2b), CH₂Ph (3b); R = Bu^t, R′ = Me (2c), CH₂Ph (3c); R = Ph, R′ = Me (2d), CH₂Ph (3d)), have been synthesized by the reaction of the ansa-metallocene dichloride complex, [Zr{R(H)C(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] (R = Prⁱ (1a), Buⁿ (1b), Bu^t (1c), Ph (1d)), and two molar equivalents of the alkyl Gringard reagent. The insertion reaction of the isocyanide reagent, CNC₆H₃Me₂-2,6, into the zirconium-carbon σ-bond of 2 gave the corresponding η²-iminoacyl derivatives, [Zr{R(H)C(η⁵-C₅Me₄)(η⁵-C₅H₄)}{η²-MeCNC₆H₃Me₂-2,6}Me] (R = Prⁱ (4a), Buⁿ (4b), Bu^t (4c), Ph (4d)). The molecular structures of 1b, 1c and 3b have been determined by single-crystal X-ray diffraction studies.     

Cyclopentadienylaluminum donor-acceptor complexes - Molecular and supramolecular structure

Lewis acid-base complexes of cyclopentadienylaluminum derivatives Me_xCp_3−x Al (x = 0-2) and trimethylaluminum with selected aromatic amines (L): dmap = 4-dimethylaminopyridine, py-Me = 4-methylpyridyne, were synthesized and characterized by ¹H, ¹³C, ²⁷Al NMR: Cp₃Al · dmap (1), Cp₃Al · py-Me (2), MeCp₂Al · dmap (3), MeCp₂Al · py-Me (4), Me₂CpAl · dmap (5), Me₂CpAl · py-Me (6), Me₃Al · py-Me (7). ¹H NMR studies of 3-6 revealed small amounts of the ligand redistribution products. The crystal structures of 1, 2 and 3 were determined by single X-ray diffraction studies. The compounds 1, 2 and 3 are monomeric with Cp ligands bonded to the aluminum center in η¹(σ), η¹(π) manner. The change of Cp-Al bond character from η¹(π) to η¹(σ) was found to reasonable correlate with the aromaticity of Cp⁻ ligand described by HOMA index. Analysis of close intra- and intermolecular contacts showed presence of CH?π interactions leading to the formation of 2-D supramolecular networks. It was found that these interactions impact on the coordination sphere of aluminum and the conformation of Cp ring.     

Influence of sterically non-hindering methyl groups on adsorption properties of two classical zinc and copper MOF types

The metal-organic frameworks (three-dimensional porous coordination polymers) [Zn₄O(Me₄BPDC)₃] × 9 DMF, 2 · 9 DMF and [Cu₂(Me₄BPDC)₂] × 9 DMF, 3 · 9 DMF are representatives of the classical Zn-IRMOF series and Cu paddle-wheel complexes with H₂Me₄BPDC = 2,2′,6,6′-tetramethyl-4,4′-biphenyldicarboxylic acid, 1. The dicarboxylate linker of 1 is a representative of the non-planar biphenyl ligand family, known as an efficient scaffold for chiral molecules. There is a 90° twist angle between the phenyl rings in 1, dictated by the methyl groups, which leads to assembly of doubly interpenetrated pcu-a (in 2) and nbo-a (in 3) nets under low temperature solvothermal conditions in dimethylformamide (DMF). Activation by degassing (to yield 2), exchange with methanol or tetrahydrofuran and subsequent evacuation at elevated temperatures (to yield 3^I) gave materials with BET surface areas of 1735 m²/g (2) and 1041 m²/g (3^I). Adsorbed quantities of H₂ were 1.26 wt% (2) and 1.02 wt% (3^I) (77 K, 1 bar), CO₂ 30.8 cm³/g (2) and 50 cm³/g (3^I) (273 K, 1 bar) and CH₄ 12.9 cm³/g (2) and 11.4 cm³/g (3^I) (273 K, 1 bar). The H₂ and CO₂ sorption values for 2 are similar to those of MOF-5 (IRMOF-1) with its almost doubled BET surface area. An increase is found concerning the adsorbed amounts of N₂, H₂, and CO₂ for 3^I compared to related doubly interpenetrated nbo-a-type MOF-601, MOF-602, MOF-603 ([Cu₂L₂] with L = 2,2′-R₂-4,4′-biphenyldicarboxylate, R = CN, Me, I, respectively).     

Metallo-tetraazaporphyrin based anion sensors: regulation of sensor characteristics through central metal ion coordination

The iron(III) and cobalt(III) complexes of 2,3,7,8,12,13,17,18-octakis(benzylthio)-5,10,15,20-tetraazaporphyrin, (OBTAP) were synthesized and incorporated into PVC matrix as ionophores to fabricate anion selective membrane electrodes that exhibit selective potentiometric response to azide and nitrite ions, respectively. The membrane of [Fe(OBTAP)]⁺ (III) with a composition of 6:190:200 (III:DBP:PVC) (w/w), and of [Co(OBTAP)]⁺ (IV) with a composition of 10:148:200 (IV:DOP:PVC) (w/w), i.e. 1a and 2b, respectively (where DBP:dibutylphthalate and DOP=dioctylphthalate) gave the best performance. The membrane 1a showed a slope of 29.2±0.2 mV per decade of activity for N₃⁻ in the working concentration range of 8.9×10⁻⁶ to 1.0×10⁻¹ M. The membrane 2b showed a slope of 30.0±0.2 mV per decade of activity for NO₂⁻ in the working concentration range of 1.1×10⁻⁵ to 1.0×10⁻¹ M. The membranes worked satisfactorily in the pH range of 4.3-10.5 (1a) and 2.8-6.4 (2b) and had fast response time of 12±2 and 13±2 s, respectively. Electrodes exhibited a high degree of selectivity for N₃⁻ and NO₂⁻, respectively, over several other monovalent and bivalent anions. Only SCN⁻ and S²⁻ (at >1.0×10⁻⁴ M) cause moderate interference for electrode 1a and Cl⁻ and S²⁻ (at >1.0×10⁻⁵ M) for electrode 2b. They gave reproducible results with the relative standard deviation in the observed values of potentials (σ) of 1.96 and 1.80 mV for electrodes 1a and 2b, respectively, from the least-squares fit line. The 90% confidence limit lies within ±0.2 mV per decade of activity. Reproducible results were obtained over a period of 5 months. Their performance in non-aqueous solvent mixtures having up to 50% (v/v) methanol, ethanol and acetone were evaluated and were found satisfactory. The proposed sensors are superior in terms of detection limit and response time in comparison to the reported ones.     

Development of electrochemical sensors for nano scale Tb(III) ion determination based on pendant macrocyclic ligands

The two macrocyclic pendant ligands 3,4,5:12,13,14-dipyridine-2,6,11,15-tetramethyl-1,7,10,16-tetramethylacrylate-1,4,7,10,13,16-hexaazacyclooctadeca-3,13-di ene (L₁) and 3,4,5:12,13,14-dipyridine-2,6,11,15-tetramethyl-1,7,10,16-tetra(2-cyano ethane)-1,4,7,10,13,16-hexaazacyclooctadeca-3,13-diene (L₂) have been synthesized and explored as neutral ionophores for preparing poly(vinylchloride) (PVC) based membrane sensors selective to Tb(III) ions. Effects of various plasticizers and anion excluders were studied in detail and improved performance was observed. The best performance was obtained for the membrane sensor having a composition of L₁: PVC:1-CN:NaTPB in the ratio of 6: 32: 58: 4 (w/w; mg). The performance of the membrane based on L₁ was compared with polymeric membrane electrode (PME) as well as with coated graphite electrode (CGE). The electrodes exhibit Nernstian slope for Tb³⁺ ions with limits of detection of 3.4 × 10⁻⁸ mol L⁻¹ for PME and 5.7 × 10⁻⁹ mol L⁻¹ for CGE. The response time for PME and CGE was found to be 10 s and 8 s, respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 3.0-7.5 for PME and 2.0-8.5 for CGE. The CGE has found to work satisfactorily in partially non-aqueous media upto 30% (v/v) content of methanol, ethanol and 20% (v/v) content of acetonitrile and could be used for a period of 5 months. The CGE was used as indicator electrode in the potentiometric titration of Tb³⁺ ions with EDTA and in determination of fluoride ions in various samples. It can also be used in direct determination of Tb³⁺ ions in tap water and various binary mixtures with quantitative results.     

Syntheses, structures and intermolecular interactions of tetraorganoammonium, -phosphonium and -stibonium dimethyl- and diphenyltetrahaloantimonates

The syntheses and spectroscopic (NMR, MS) investigations of the antimonates [Ph₄P]⁺[Me₂SbCl₄]⁻ (1), [Me₄Sb]⁺[Me₂SbCl₄]⁻ (2), [Et₄N]⁺[Ph₂SbCl₄]⁻ (3), [Bu₄N]⁺[Ph₂SbCl₄]⁻ (4), [Me₄Sb]⁺[Ph₂SbCl₄]⁻ (5), [Et₃MeSb]⁺[Ph₂SbCl₄]⁻ (6), [Et₄N]⁺[Ph₂SbF₄]⁻ (7) and [Et₄N]⁺[Ph₂SbBr₄]⁻ (8) are reported. Halogen scrambling reactions of Et₄NBr or Ph₄EBr (E = P, Sb) with R₂SbCl₃ (R = Me, Ph) produce mixtures of compounds from which crystals of [Et₄N]⁺[Ph₂SbBr_1.24Cl_2.76]⁻ (9), [Et₄N]⁺[Ph₂SbBr_2.92Cl_1.08]⁻ (10) or [Ph₄Sb]⁺[Me₂SbCl₄]⁻ (11) were isolated. The crystal and molecular structures of 1 and 3-11 are reported.     

Cytotoxic half-sandwich rhodium(III) complexes: Polypyridyl ligand influence on their DNA binding properties and cellular uptake

The DNA binding of polypyridyl (pp) (η⁵-C₅Me₅)Rh^III complexes of the types [(η⁵-C₅Me₅)RhCl(pp)](CF₃SO₃) (2-6) (pp = bpy, phen, dpq, dppz, dppn), [(η⁵-C₅Me₅)Rh{(Me₂N)₂CS}(pp)](CF₃SO₃)₂ (7-9) (pp = dpq, dppz, dppn) and [(η⁵-C₅Me₅)Rh(L)(pp)](CF₃SO₃) (10) (L = C₆H₅S⁻) and (11) (L = C₁₀H₇S⁻) has been studied by UV/Vis spectroscopy, circular dichroismus and viscosity measurements. Complexes 3-11 are cytotoxic towards the human MCF-7 breast and HT-29 colon cancer cell lines and exhibit IC₅₀ values in the range 0.56-10.7 μM. Stable intercalative binding into CT-DNA is indicated for the dpq and dppz complexes by large increases ΔT_m of 6-12 °C in the DNA thermal denaturation temperature for r = [complex]/[DNA] = 0.1 and by induced CD bands and large viscosity increases. In contrast, significant DNA lengthening is not observed after incubation of the biopolymer with the dppn complexes 2 and 9 at molar ratios of r < 0.08. Pronounced hypochromic shifts for the π-π^∗ transitions of the dppn ligands in the range 320-425 nm indicate the possible presence of surface stacking. The in vitro cytotoxicities of the chloro complexes 4-6 and the (Me₂N)₂CS complexes 7-9 are dependent on the size of the polypyridyl ligand with IC₅₀ values decreasing in the order dpq > dppz > dppn. For instance, IC₅₀ values of 5.3, 1.5 and 0.91 μM were determined for 7-9 against MCF-7 cells. Rapid Cl⁻/H₂O exchange leads the formation of aqua dications for 4-6, whose levels of cellular uptake and cytotoxicities are similar to those established for 7-9. Intramolecular interactions between the aromatic thiolate and dppz ligands of 10 and 11 prevent significant DNA intercalation. X-ray structural determinations have been performed for 2-7 and 11.     

Synthesis and structural characterisation of rhodium hydride complexes bearing N-heterocyclic carbene ligands

Addition of excesses of N-heterocyclic carbenes (NHCs) IEt₂Me₂, IⁱPr₂Me₂ or ICy (IEt₂Me₂ = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene; IⁱPr₂Me₂ = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; ICy = 1,3-dicyclohexylimidazol-2-ylidene) to [HRh(PPh₃)₄] (1) affords an isomeric mixture of [HRh(NHC)(PPh₃)₂] (NHC = IEt₂Me₂ (cis-/trans-2), IⁱPr₂Me₂ (cis-/trans-3), ICy (cis-/trans-4) and [HRh(NHC)₂(PPh₃)] (IEt₂Me₂(cis-/trans-5), IⁱPr₂Me₂ (cis-/trans-6), ICy (cis-/trans-7)). Thermolysis of 1 with the aryl substituted NHC, 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (IMesH₂), affords the bridging hydrido phosphido dimer, [{(PPh₃)₂Rh}₂(μ-H)(μ-PPh₂)] (8), which is also the reaction product formed in the absence of carbene. When the rhodium precursor was changed from 1 to [HRh(CO)(PPh₃)₃] (9) and treated with either IMes (=1,3-dimesitylimidazol-2-ylidene) or ICy, the bis-NHC complexes trans-[HRh(CO)(IMes)₂] (10) and trans-[HRh(CO)(ICy)₂] (11) were formed. In contrast, the reaction of 9 with IⁱPr₂Me₂ gave [HRh(CO)(IⁱPr₂Me₂)₂] (cis-/trans-12) and the unusual unsymmetrical dimer, [(PPh₃)₂Rh(μ-CO)₂Rh(IⁱPr₂Me₂)₂] (13). The complexes trans-3, 8, 10 and 13 have been structurally characterised.     

4,5-Bis[(triorganotin)thiolato]-1,3-dithiole-2-thione, (R3Sn)2(dmit), 4,5-bis[(triorganotin)thiolato]-1,3-dithiole-2-one, (R3Sn)2(dmio), compounds: Crystal structures of (cyclohexyl3Sn)2(dmio), (Ph3Sn)2(dmit) and (Ph3Sn)2(dmio)

The synthesis and crystal structures of 4,5-bis[(triorganotin)thiolato]-1,3-dithiole-2-thione, (R₃Sn)₂(dmit), 1, and 4,5-bis[(triorganotin)thiolato]-1,3-dithiole-2-one, (R₃Sn)₂(dmio), 2, compounds are reported. Compounds, (1 or 2: R = Ph or cyclohexyl, Cy), have been obtained from reaction of R₃SnCl with Cs₂dmit or Na₂dmio. The presence of the two tin centres in (2: R = Ph) is shown in the ¹³C NMR spectrum by the couplings of both Sn atoms to the dmio olefinic carbons with J values of 29.4 and 24.7 Hz. The δ¹¹⁹ Sn values for (1: R = Ph) and (2: R = Ph) differ by about 30 ppm, values being −20.7 and −50.1 ppm, respectively, in CDCl₃ solution. X-ray structure determinations for (1: R = Ph) and (2: R = Ph or Cy) reveal the compounds to have 4-coordinate, distorted tetrahedral tin centres. The dithiolato ligands, dmit and dmio, act as bridging ligands, in contrast to their chelating roles in R₂Sn(dmit) and R₂Sn(dmio). A further difference between R₂Sn(dmit) and R₂Sn(dmio), on one hand, and 1 and 2 on the other, is that intermolecular Sn-S and Sn-O interactions are absent in 1 and 2. However, weak intermolecular hydrogen bonding interactions are found in (1: R = Ph) [C-H?π] and in (2: R = Ph) [C-H?π and C-H?O].     

Pd(II) polymeric compounds directed by intermolecular C–H⋯X–C interactions (X = F,Cl): Suzuki–Miyaura cross-coupling catalytic activity by a novel N4-type saturated Pd complex

New palladium polymeric compounds containing novel tetradentate halogen-substituted 6Me₂bpX²⁻ ligands (6Me₂bpX²⁻ = 1,2-bis(6-methylpyridine-2-carboxamide) halobenzene dianion, X = F for 4, Cl for 5) were constructed by non-classical C–H?X–C interactions, and the novel catalyst 5 was used to carry out Suzuki coupling reactions with aryl iodides and aryl boronic acids under mild conditions.     

(Cyclopentadienyl)chromiumtricarbonyl dimers as a source of metal-centered free-radicals to form stable η-bonded spin-adducts with fullerenes

Spin-adducts (I, IIb-c) of C₆₀ and C₇₀ with metal-centered free radicals CpCr(CO)₃ (I, IIa) have been generated in toluene via interaction between fullerenes and the weakly metal-metal bonded dimeric complexes [CpCr(CO)₃]₂ (Cp = η⁵-C₅H₅ (I); Cp = η⁵-C₅Me₅ (II)). Their structures have been investigated using ESR spectroscopy and DFT-PBE calculations and η²-bonding to the CC bond between two hexagons in C₆₀ has been established. Calculations have been extended to investigate the nature of the intermediate η²-coordinated toluene chromium complexes (I, IId).