Complexes 1b Research Articles

Multistimuli-Responsive Properties of Aggregated Isocyanide Cycloplatinated(II) Complexes

Here, we describe the neutral cyclometalated tert-butylisocyanide PtII complexes, [Pt(C∧N)Cl(CNBut)] 1, the double salts [Pt(C∧N)(CNBut)2][Pt(C∧N)Cl2] 2, and the cationic complexes [Pt(C∧N)(CNBut)2]ClO43 [C∧N = difluorophenylpyridine (dfppy, a), 4-(2-pyridyl)benzaldehyde (ppy-CHO, b)]. A comparative study of the pseudopolymorphs 1a, 1a·CHCl3, 1b, 1b·0.5Toluene, 1b·0.5PhF, and 3a·0.25CH2Cl2 reveals strong aggregation through Pt···Pt and/or π···π stacking interactions to give a variety of distinctive one-dimensional (1D) infinite chains, which modulate the photoluminescent properties. This intermolecular long-range aggregate formation is the main origin of the photoluminescent behavior of 1a and 1b complexes, which exhibit highly sensitive and reversible responses to multiple external stimuli including different volatile organic compounds (VOCs), solvents, temperatures, and pressures, with distinct color and phosphorescent color switching from green to red. Furthermore, complex 1b undergoes supramolecular self-assembly via Pt···Pt and/or π···π interactions into a polymer thin polystyrene (PS) film 10 wt % in response to toluene vapors, and 3a exhibits vapochromic and vapoluminescent behavior. Theoretical simulations on the dimer, trimer, and tetramer models of 1a and 1b have been carried out to get insight into the photophysical properties in the aggregated solid state.

Mononuclear Tricoordinate Copper(I) and Silver(I) Halide Complexes of a Sterically Bulky Thiourea Ligand and a Computational Insight of Their Interaction with Human Insulin.

Reaction of two equivalents of the bulky 1,3-bis(2,6-diethylphenyl)thiourea ligand (L) with MX (being M = Cu+, Ag+; and X = Cl−, Br−, I−) in acetonitrile afforded neutral complexes of the type [MXL2] [CuClL2].2CH3CN (1a); [CuBrL2].2CH3CN (1b); [CuIL2] (1c): [AgClL2] (2a); [AgBrL2] (2b) and [AgIL2] (2c). The two aromatic groups in free ligand were found to be trans with respect to the thiourea unit, which was a reason to link the ligand molecules via intermolecular hydrogen bonding. Intramolecular hydrogen bonding was observed in all metal complexes. The copper complexes 1a and 1b are acetonitrile solvated and show not only intra- but also intermolecular hydrogen bonding between the coordinated thiourea and the solvated acetonitrile molecules. Silver complexes reported here are the first examples of structurally characterized tricoordinated thiourea-stabilized monomeric silver(I) halides. Molecular docking studies were carried out to analyze the binding modes of the metal complexes inside the active site of the human insulin (HI) protein. Analysis of the docked conformations revealed that the electrostatic and aromatic interactions of the protein N-terminal residues (i.e., Phe and His) may assist in anchoring and stabilizing the metal complexes inside the active site. According to the results of docking studies, the silver complexes exhibited the strongest inhibitory capability against the HI protein, which possesses a deactivating group, directly bonded to silver. All compounds were fully characterized by elemental analysis, NMR spectroscopy, and molecular structures of the ligand, and five out of six metal complexes were also confirmed by single-crystal X-ray diffraction.

Enhancing quantum efficiency in Pt-based emitters using a pendant closo-monocarborane cluster to enforce charge neutrality

The use of organometallic triplet emitters in OLED applications may be complicated when the luminescent complex bears a formal charge. By designing ligands containing pendant closo-monocarborane clusters [CB11H11]−, it is possible to neutralize the otherwise cationic cores of cyclometalated Pt(II) complexes bearing bis-carbenes, resulting in significantly enhanced photophysical properties. Herein, we report four Pt(II) complexes decorated with a monoanionic closo-monocarborane by coupling the cluster to the classic cyclometallating moiety, phenylpyridine (ppy). All four complexes were fully characterized by NMR, HR-MS, UV–Vis, and cyclic voltammetry. Complexes 1b, 1c and 2a were characterized by single-crystal X-ray diffraction. Moreover, all four complexes show interesting photophysical behaviors, with complex 1a exhibiting a photoluminescent quantum yield of 97% in a 2 wt% PMMA film. This high efficiency prompted the incorporation of 1a and 1c into an OLED device using solution processing, resulting in green emission with CIE coordinates of (0.28, 0.55) for 1a and yellow emission with CIE coordinates of (0.44, 0.50) for 1c. The measured maximum external quantum efficiency (EQEmax) was 18.51% for 1a, an EQEmax that is among the highest for solution-processed OLED devices containing Pt(II) complexes with simple cyclometalated ppy ligands.

Acridine Based N-Acylhydrazone Derivatives as Potential Anticancer Agents: Synthesis, Characterization and ctDNA/HSA Spectroscopic Binding Properties.

A series of novel acridine N-acylhydrazone derivatives have been synthesized as potential topoisomerase I/II inhibitors, and their binding (calf thymus DNA—ctDNA and human serum albumin—HSA) and biological activities as potential anticancer agents on proliferation of A549 and CCD-18Co have been evaluated. The acridine-DNA complex 3b (-F) displayed the highest Kb value (Kb = 3.18 × 103 M−1). The HSA-derivatives interactions were studied by fluorescence quenching spectra. This method was used for the calculation of characteristic binding parameters. In the presence of warfarin, the binding constant values were found to decrease (KSV = 2.26 M−1, Kb = 2.54 M−1), suggesting that derivative 3a could bind to HSA at Sudlow site I. The effect of tested derivatives on metabolic activity of A549 cells evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide or MTT assay decreased as follows 3b(-F) > 3a(-H) > 3c(-Cl) > 3d(-Br). The derivatives 3c and 3d in vitro act as potential dual inhibitors of hTopo I and II with a partial effect on the metabolic activity of cancer cells A594. The acridine-benzohydrazides 3a and 3c reduced the clonogenic ability of A549 cells by 72% or 74%, respectively. The general results of the study suggest that the novel compounds show potential for future development as anticancer agents.

Pd(II)-Schiff base complexes: Synthesis, characterization, Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions, enzyme inhibition and antioxidant activities

In this study, new coordination complexes (1a-1e) of Pd(II) with Schiff base ligands were synthesized and characterized by elemental analysis, magnetic susceptibility, molar conductivity, FT-IR, 1H–13C NMR spectroscopy, UV–vis spectroscopy, and mass spectrometry techniques. The ligands formed only 1:2 complexes with the Pd(II) except for the complex 1e. The thermal analysis of the complexes was performed by the TGA technique. The antioxidant potential, enzyme inhibition activity, and catalytic properties of the complexes were investigated as well. The Pd(II) complexes 1b and 1c indicated the best catalytic activity with 62.63% and 61.05% selectivity in the conversions of 82.61% and 87.84%. The in vitro antioxidant activity showed that the Pd(II) complexes, particularly 1a and 1e have effective antioxidant activities. According to the enzyme activity analyses, complex 1b (IC50 value 69.3 ± 5.2 μM) showed the most effective pancreatic lipase inhibition, whereas complex 1e (IC50 value 25.7 ± 3.2 μM) had the most effective tyrosinase inhibition among the synthesized compounds. Overall, the present paper discusses the synthesis, characterization and catalytic activities of various novel Pd(II)-Schiff base complexes with their antioxidant potentials, pancreatic lipase and tyrosinase inhibitory activities.

P-Ru-Complexes with a Chelate-Bridge-Switch: A Comparison of 2-Picolyl and 2-Pyridyloxy Moieties as Bridging Ligands.

Starting from [Ru(pyO)2(nbd)] 1 and a N,P,N-tridentate ligand (2a: PhP(pic)2, 2b: PhP(pyO)2) (nbd = 2,5-norbornadiene, pic = 2-picolyl = 2-pyridylmethyl, pyO = 2-pyridyloxy = pyridine-2-olate), the compounds [PhP(μ-pic)2(μ-pyO)Ru(κ2-pyO)] (3a) and [PhP(μ-pyO)3Ru(κ2-pyO)] (3b), respectively, were prepared. Reaction of compounds 3 with CO and CNtBu afforded the opening of the Ru(κ2-pyO) chelate motif with the formation of compounds [PhP(μ-pic)2(μ-pyO)Ru(κ-O-pyO)(CO)] (4a), [PhP(μ-pic)2(μ-pyO)2Ru(CNtBu)] (5a), [PhP(μ-pyO)4Ru(CO)] (4b) and [PhP(μ-pyO)4Ru(CNtBu)] (5b). In dichloromethane solution, 4a underwent a reaction with the solvent, i.e., substitution of the dangling pyO ligand by chloride with the formation of [PhP(μ-pic)2(μ-pyO)Ru(Cl)(CO)] (6a). The new complexes 3a, 4a, 5a, 5b and 6a were characterized by single-crystal X-ray diffraction analyses and multi-nuclear (1H, 13C, 31P) NMR spectroscopy. The different coordination behaviors of related pairs of molecules (i.e., pairs of 3, 4 and 5), which depend on the nature of the P–Ru-bridging ligand moieties (μ-pic vs. μ-pyO), were also studied via computational analyses using QTAIM (quantum theory of atoms in molecules) and NBO (natural bond orbital) approaches, as well as the NCI (non-covalent interactions descriptor) for weak intramolecular interactions.

Theoretical Approach for the Luminescent Properties of Ir(III) Complexes to Produce Red-Green-Blue LEC Devices.

With an appropriate mixture of cyclometalating and ancillary ligands, based on simple structures (commercial or easily synthesized), it has been possible to design a family of eight new Ir(III) complexes (1A, 1B, 2B, 2C, 3B, 3C, 3D and 3E) useful as luminescent materials in LEC devices. These complexes involved the use of phenylpyridines or fluorophenylpyridines as cyclometalating ligands and bipyridine or phenanthroline-type structures as ancillary ligands. The emitting properties have been evaluated from a theoretical approach through Density Functional Theory and Time-Dependent Density Functional Theory calculations, determining geometric parameters, frontier orbital energies, absorption and emission energies, injection and transport parameters of holes and electrons, and parameters associated with the radiative and non-radiative decays. With these complexes it was possible to obtain a wide range of emission colours, from deep red to blue (701–440 nm). Considering all the calculated parameters between all the complexes, it was identified that 1B was the best red, 2B was the best green, and 3D was the best blue emitter. Thus, with the mixture of these complexes, a dual host–guest system with 3D-1B and an RGB (red–green–blue) system with 3D-2B-1B are proposed, to produce white LECs.

Synthesis and characterization of chiral bidentate bis(N-heterocyclic carbene)-carboxylate palladium and nickel complexes

Complexes [Pd{(S)-NHCMes,R}2] (R = Me, 2a; iPr, 2b; iBu, 2c) and [Pd{(R)-NHCMes,Me}2] (2a’) were prepared by reaction of the corresponding imidazolium precursor [ImMes,R] (namely (S)–2-alkyl(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1a-c, and (R)-2-methyl(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1a’), with Ag2O and subsequent interaction with Pd(OAc)2, under appropriate conditions. Alternatively, complexes 2 were also obtained by treating compounds [ImMes,R], 1, with an in-situ prepared lithium diisopropylamide solution and then reaction with [Pd(OAc)2]. On the other hand, the nickel complex [Ni{(S)-NHCMes,iPr}2], 3b, was synthesized by the interaction of the complex [NiCp2] (Cp = η5-C5H5) with [ImMes,iPr], 1b, in THF. If this reaction was carried out in acetonitrile, a mixture of complex 3b and the cyclopentadienyl monocarbene complex [NiCp{(S)-NHCMes,iPr}], 4b, was obtained. Similarly to 2b, compound 3b was also prepared by the in-situ formation of the carbene [(S)–NHCMes,iPr]- and then reaction with [NiBr2(dme)] (dme = 1,2-dimethoxyethane). Complexes 2, 3 and 4 were obtained with good yields and fully characterized by analytical (HR-ESI and microanalysis), spectroscopic (IR, 1H and 13C NMR and polarimetry) and X-ray methods (2c). In the solid state, 2c is a square planar complex containing two [(S)-NHCMes,iBu]- ligands coordinated in a κ2-C,O fashion, where the carbene and carboxylate donors have the expected trans configuration. The existence of two possible conformers of complexes 2 and 3 was analyzed using DFT methods.

Antimicrobial Properties of Amino-Acid-Derived N-Heterocyclic Carbene Silver Complexes.

Complexes {Ag[NHCMes,R]}n (R = H, 2a; Me, 2b and 2b’; iPr, 2c; iBu, 2d), were prepared by treatment of imidazolium precursor compounds [ImMes,R] (2-(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1a, (S)-2-alkyl(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1b–d, and (R)-2-methyl(3-mesityl-1H-imidazol-3-ium-1-yl)acetate, 1b’, with Ag2O under appropriate conditions. They were characterised by analytical, spectroscopic (IR, 1H, and 13C NMR and polarimetry), and X-ray methods (2a). In the solid state, 2a is a one-dimensional coordination polymer, in which the silver(I) cation is bonded to the carbene ligand and to the carboxylate group of a symmetry-related Ag[NHCMes,H] moiety. The coordination environment of the silver centre is well described by the DFT study of the dimeric model {Ag[NHCMes,H]}2. The antimicrobial properties of these complexes were evaluated versus Gram-negative bacteria E. coli and P. aeruginosa. From the observed MIC and MBC values (minimal inhibitory concentration and minimal bactericidal concentration, respectively), complex 2b’ showed the best antimicrobial properties (eutomer), which were significantly better than those of its enantiomeric derivative 2b (distomer). Additionally, analysis of MIC and MBC values of 2a–d reveal a clear structure–antimicrobial effect relationship. Antimicrobial activity decreases when the steric properties of the R alkyl group in {Ag[NHCMes,R]}n increase.

Self-assembly synthesis of diorganotin complexes based on arylformylhydrazone possessing ONO donor set: anticancer activity and mechanism.

Fourteen new organotin(IV) complexes were successfully synthesized and characterized by elemental analyses, Fourier transform infrared spectroscopy (FT-IR), multinuclear (1H, 13C, and 119Sn) NMR spectroscopy, high-resolution mass spectrometry (HRMS), and X-ray single-crystal techniques. Crystallographic data showed that the complexes 1b, 2b, 3b, and 5b were macrocyclic compounds, 4b exhibited a one-dimensional spiral chain structure with distorted trigonal bipyramidal geometry, other complexes were centrosymmetric dimers, and there was an Sn2O2 four-membered ring in the middle of the molecule. In-vitro anticancer activity against the three human tumor cell lines NCI-H460, MCF-7, and HepG2 was studied, and the dibutyltin complex 5a is a more potent antitumor agent than other complexes and cisplatin. Cell apoptosis study of 5a with the highest activity on HepG2 cancer cell lines was done by flow cytometry; it was shown that the antitumor activity of 5a was related to apoptosis, and it inhibited proliferation by blocking cells in the G2/M phase. The single-cell gel electrophoresis assay results show that 5a induces DNA damage. 5a interacts with ct-DNA by intercalating the mode of interaction. UV-visible absorption spectrometry, fluorescence competitive, viscosity measurements, and gel electrophoresis results also support the intercalative mode of interaction for 5a with DNA.

Silver(I) complexes with phenolic Schiff bases: Synthesis, antibacterial evaluation and interaction with biomolecules.

Novel Ag(I) complexes (2a–2c) with phenolic Schiff bases were synthesized using 4,6-di-tert-butyl-3-(((5-mercapto-1,3,4-thiadiazol-2-yl)imino)methyl)benzene-1,2-diol (1a), 4,6-di-tert-butyl-3-(((4-mercaptophenyl)imino)methyl)benzene-1,2-diol (1b), and 4,6-di-tert-butyl-3-(((3-mercaptophenyl)imino)methyl)benzene-1,2-diol (1c). They were examined by elemental analysis, FT-IR, UV-Vis, 1H-NMR spectroscopy, XRD, cyclic voltammetry, conductivity measurements, and biological methods. The complexes are characterized by distorted geometry of the coordination cores AgN2S2 (2c), AgNS (2b) and AgS2 (2a). These stable complexes were not typified by the intramolecular redox reaction in organic solvents resulting in the formation of silver nanoparticles (AgNPs). Antibacterial activity of 1a–1c and 2a–2c was evaluated in comparison with AgNPs and commonly used antibiotics. All the complexes were more active than the ligands against the bacteria tested (14), but they were less active than AgNPs and commonly used antibiotics. Both 1a–1c and their complexes 2a–2c exhibited the capability for the bovine heart Fe(III)-Cyt c reduction. The ligands 1b and 1c were characterized by the highest reduction rate among the compounds under study, and they showed a higher reducing ability (determined by cyclic voltammetry) as compared with that of their Ag(I) complexes 2b and 2c.

Cyclic Palladium Formamidinate: Synthesis, Structure, Reactivity, and Application to Suzuki-Miyaura Cross-Coupling.

The deprotonation of acyclic palladium amidine chloride (1) with potassium tert-butoxide in tetrahydrofuran results in palladium bis(formamidinate) (2). 2 undergoes a nucleophilic addition reaction with acetonitrile in the presence of PdCl2 or Pd(OAc)2 (OAc = acetate) to give dinuclear cyclic six-membered (triazapentadiene)palladium complexes (4a and 4b). These compounds are also prepared from cyclic six-membered (tap)PdCl2 (5; tap = triazapentadiene) or formamidinium salts (6a-6c) with Pd(OAc)2/NaOAc in acetonitrile, whereas the direct reaction of 2 with acetonitrile or acrylonitrile resulted in palladium black or an acyclic C-N-coupled product (3). A comparison of structure 4 from 2 suggests a possible intermediate dinuclear palladium complex whose structure was identified through theoretical calculations. Further, Suzuki-Miyaura cross-coupling reactions were carried out under different solvents notably in an ethanol/water medium at room temperature.

Iron-Catalyzed H/D Exchange of Primary Silanes, Secondary Silanes, and Tertiary Siloxanes.

A synthetic study into the catalytic hydrogen/deuterium (H/D) exchange of 1° silanes, 2° silanes, and 3° siloxanes is presented, facilitated by iron-β-diketiminato complexes (1a and 1b). Near-complete H/D exchange is observed for a variety of aryl- and alkyl-containing hydrosilanes and hydrosiloxanes. The reaction tolerates alternative hydride source pinacolborane (HBpin), with quantitative H/D exchange. A synthetic and density functional theory (DFT) investigation suggests that a monomeric iron-deuteride is responsible for the H/D exchange.

CATALYSIS OF HYDRODEHALOGENATION RE­ACTION OF HALOARENES BY CARBENE PEPPSI-PALLADIUM COMPLEXES

The synthesis of a number of carbene PEPPSI-complexes of palladium with various pyridine and carbene ligands was carried out by reactions of 1,3-bis-(2,6-dibenzhydryl-4-methyl­phenyl)imidazolium chloride IPr*.HCl [compounds 7a-c IPr*PdCl2L’, L’ = pyridine (а), 3-chloropyridine (b), 4-dimethylaminopyridine (с)], 1,3-bis-(2,6-diisopropylphenyl)­imida­zo­li­um perchlorate IPr.HClO4 [compounds 8a,b IPr.PdCl2L’, L’ = 3-chloropyridine (а), о-phenanthroline (b)], 1,3-diphenyl-4-(2,6-diisopropylphenyl)-1,2,4-triazolium perchlorate L.HClO4 (complex 9 LPdCl2L’, L’ = 3-chloropyridine) and 1,3-dicetyl­imidazolium bromide L.HBr (complex 11 LPdCl2L’, L’ = pyridine) with palladium chloride in pyridines (pyridine, 3-chloropyridine), or acetonitrile in the presence of potassium carbonate. Yields of compounds – from high (56–100%) to moderate (36 %). The structure of the compounds was confirmed by 1H and 13C NMR spectroscopy. Chemical shifts of carbene atoms in the 13C NMR spectra of complexes 7a-c. 8a, b 11 are in the region 151.0-156.2 ppm, for complex 9 - at  174.4 ppm A high catalytic effect of sterically shielded complexes 7a, b, 8a, b in the hydrodehalogenation reaction of p-dichlorobenzene and hexachlorobenzene under the action of potassium tert-butoxide in isopropanol was established. 1,3-Bis-(2,6-dibenzhydryl-4-methylphenyl)-imidazol-2-ylidene complexes 7a, b (quantitative conversions with p-dichlorobenzene are achieved with 0.013 mol% of catalyst) show the highest efficiency, but the compound with 4-dimethylaminopyridine ligand 7c has significantly lower efficiency (22% conversion under these conditions). Complexes with 1,3-bis-(2,6-diisopropylphenyl)-imidazol-2-ylidene ligand 8a, b are close in efficiency to compounds 7a, b (for 7a quantitative conversion is achieved with 0.026 mol% of catalyst). Phenanthroline-containing complex 8b is less effective than complex 8a (87% conversion with 0.052 mol% of catalyst). Complex 9 is much less effective (even with 0.13 mol% of catalyst 13% conversion is achieved). Compound 11 catalyzes the reaction well only when the amount of catalyst is up to 1.3 mol% (98% conversion). Thus, compounds 7a, b, 8a are the best PEPPSI-catalysts for hydrodehalogenation of haloarenes promising for industrial decontamination of persistent orga­nic pollutants (hexachlorobenzene, DDT, di­oxins and polychlorinated biphenyls, etc.).

P–Nitrobenzyl-substituted N–heterocyclic carbene in Silver(I) and Gold(I) complexes and their antibacterial activities

The synthesis of the silver(I) N–heterocyclic carbene [Ag(NBMIM)Cl]2 (2) from the reaction of imidazolium salt {NBMIM}Cl (1a) (NBMIM = 1–methyl–3–(4–nitrobenzyl)–1H–imidazol–3–ium) and silver(I) oxide was achieved. Compound {NBMIM}PF6 (1b) was also obtained by a counteranion exchange reaction. Compound 2 was used as a transmetalation agent to form Au(I) monocarbene complex (3a) and biscarbene complex (3b), by using [AuCl(SMe2)]. All compounds were characterized in solution by infrared spectroscopy and by 1H and 13C{1H} NMR. The molecular structures of compounds {NBMIM}PF6 (1b), [Ag(NBMIM)Cl]2 (2), and [Au(NBMIM)Cl] (3a) were also determined by single crystal X–ray diffraction studies. The molecular structure of silver complex 2 showed a 1D–staircase structure with Ag⋯Ag and Ag⋯Cl intermolecular interactions. Compounds 2 and 3a were also characterized by elemental analysis, powder X–ray diffraction (PXRD), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) measurement. In preliminary in vitro antibacterial assays, compounds 2 and 3a were tested against four bacterial strains: two Gram positive (S. aureus and B. subtilis) and two Gram negative species (P. aeruginosa and E. coli) by Kirby–Bauer’s disk diffusion method. Compound 2 exhibited moderate antibacterial activity against both types of bacteria. Both silver(I) and gold(I) N–heterocyclic carbenes showed from good to high antibacterial activity against S. aureus and P. aeruginosa and moderate activity against B. subtilis and E. coli strains.

Crystal structures of two dioxomolybdenum complexes stabilized by salan ligands featuring phenyl and cyclo-hexyl backbones.

Two cis-dioxomolybdenum complexes based on salan ligands with different backbones are reported. The first complex, dioxido{2,2'-[l,2-phenyl-enebis(imino-methyl-ene)]bis-(phenolato)}molybdenum(VI) di-methyl-formamide disolvate, [Mo(C20H18N2O2)O2]·2C3H7NO (PhLMoO2, 1b), features a phenyl backbone, while the second complex, (6,6'-{[(cyclo-hexane-1,2-di-yl)bis(aza-nedi-yl)]bis-(methyl-ene)}bis-(2,4-di-tert-butyl-phenolato))dioxidomolybdenum(VI) methanol disolvate, [Mo(C36H56N2O2)O2]·2CH3OH (CyLMoO2, 2b), is based on a cyclo-hexyl backbone. These complexes crystallized as solvated species, 1b·2DMF and 2b·2MeOH. The salan ligands PhLH2 (1a) and CyLH2 (2a) coordinate to the molybdenum center in these complexes 1b and 2b in a κ2 N,κ2 O fashion, forming a distorted octa-hedral geometry. The Mo-N and Mo-O distances are 2.3475 (16) and 1.9567 (16) Å, respectively, in 1b while the corresponding measurements are Mo-N = 2.3412 (12) Å, and Mo-O = 1.9428 (10) Å for 2b. A key geometrical feature is that the N-Mo-N angle of 72.40 (4)° in CyLMoO2 is slightly less than that of the PhLMoO2 angle of 75.18 (6)°, which is attributed to the flexibility of the cyclo-hexane ring between the nitro-gen as compared to the rigid phenyl ring in the PhLMoO2.

Aluminium alkyl complexes supported by imino-phosphanamide ligand as precursors for catalytic guanylation reactions of carbodiimides.

Herein, we report the synthesis, characterisation, and application of three aluminium alkyl complexes, [κ2-{NHIRP(Ph)NDipp}AlMe2] (R = Dipp (2a), Mes (2b); tBu (2c), Dipp = 2,6-diisopropylphenyl, Mes = mesityl, and tBu = tert-butyl), supported by unsymmetrical imino-phosphanamide [NHIRP(Ph)NDipp]− [R = Dipp (1a), Mes (1b), tBu (1c)] ligands as molecular precursors for the catalytic synthesis of guanidines using carbodiimides and primary amines. All the imino-phosphanamide ligands 1a, 1b and 1c were prepared in good yield from the corresponding N-heterocyclic imine (NHI) with phenylchloro-2,6-diisopropylphenylphosphanamine, PhP(Cl)NHDipp. The aluminium alkyl complexes 2a, 2b and 2c were obtained in good yield upon completion of the reaction between trimethyl aluminium and the protic ligands 1a, 1b and 1c in a 1 : 1 molar ratio in toluene via the elimination of methane, respectively. The molecular structures of the protic ligands 1b and 1c and the aluminium complexes 2a, 2b and 2c were established via single-crystal X-ray diffraction analysis. Complexes 2a, 2b and 2c were tested as pre-catalysts for the hydroamination/guanylation reaction of carbodiimides with aryl amines to afford guanidines at ambient temperature. All the aluminium complexes exhibited a high conversion with 1.5 mol% catalyst loading and broad substrate scope with a wide functional group tolerance during the guanylation reaction. We also proposed the most plausible mechanism, involving the formation of catalytically active three-coordinate Al species as the active pre-catalyst.

Финальная стадия раннего верхнего палеолита Северной Монголии: каменная технология и региональные аналогии: Толбор-4, слои 4a и 4b

The article considers the lithic assemblage of archaeological horizon 4a of Tolbor 4 site in Northern Mongolia (excavation campaign of 2017) in the context of development of Early Upper Paleolithic lithic industries during MIS-3 stage. On the basis of radiocarbon dates, stratigraphic position and techno-typological features of lithic assemblage this complex along with the industry of archaeological horizon 4b of Tolbor 4 is classified as terminal Early Upper Paleolithic. Th is industry is characterized by predominantly flake-based orthogonal and small-blade unidirectional reduction techniques. Th e collection of complex 4a revealed a geometric microlith — trapeze, previously considered a characteristic feature of the late Upper Paleolithic of the region. It was determined that the Early Upper Paleolithic of Tolbor 4 archaeological complexes shows a smooth sequential evolution from the Initial Upper Paleolithic of Archaeological Horizon 5, through the terminal Early Upper Paleolithic of Horizon 4c/5 to the terminal Early Upper Paleolithic of Horizons 4b and 4a. The radiocarbon dates obtained allow the chronological framework of the Terminal Upper Paleolithic to be shifted closer to the lower boundary of the Last Glacial maximum. The Terminal Early Upper Paleolithic technocomplex defined on the basis of complexes 4a and 4b of Tolbor-4, as well as Archaeological Horizon 4 Kharganyn-gol-5 have undoubted cultural and/or stadial reminiscence with the lithic industries of the Kunaley culture of Russian Transbaikal.

Synthesis and structure of a pyridine-stabilized silanone molybdenum complex and its reactions with PMe3 and acetone.

Silanones (OSiR2) are highly reactive species that readily convert to oligomeric siloxane (O-SiR2)n. The coordination of silanones to transition metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Herein, a pyridine-stabilized silanone molybdenum complex Cp*(OC)2Mo{OSiMes2(py)}(SiMe3) (2b, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2, and py: pyridine) was synthesized by reacting the silyl(silylene) complex Cp*(OC)2Mo(SiMes2)(SiMe3) (4b) with pyridine-N-oxide in pyridine. X-ray crystal structure analysis revealed that the geometry of complex 2b is similar to those of the previously synthesized DMAP-stabilized analogue Cp*(OC)2Mo{OSiMes2(DMAP)}(SiMe3) (2a, DMAP: 4-(dimethylamino)pyridine). The SiO and Mo-O bond distances in 2b are similar to those observed in 2a, but the N-Si coordination bond of 2b is slightly longer (approximately 0.05 Å) than that of 2a, indicating weaker pyridine coordination than that of DMAP. The reaction of 2a with excess PMe3 in C6D6 at room temperature for 28 h afforded Cp*(OC)2Mo(PMe3)(SiMe3) (5c) in a 43% NMR yield. In contrast, reacting 2b with excess PMe3 in C6D6 at room temperature for 9 h afforded 5c and the five-membered metallacyclic carbene complex Cp*(OC)Mo(C(SiMe3)OSiMes2O)(PMe3) (6) in 10% and 41% NMR yields, respectively. The reactions of pyridine-stabilized silanone complexes Cp*(OC)2M(OSiMes2(py))(SiMe3) (M = Mo (2b) and W (1b)) with acetone proceeded via pyridine elimination, coordination of acetone to the Si center in the silanone ligand, and elimination of HSiMe3 to give Cp*(OC)2M{OSiMes2OC(Me)CH2} (M = Mo (8) and W (9)) in high yields.

Ti and Zr amino-tris(phenolate) catalysts for the synthesis of cyclic carbonates from CO2 and epoxides

Herein, we report the application of four amino-tris(phenolate)-based metal complexes incorporating Ti(IV) or Zr(IV) centres (2a-3b) as homogeneous catalysts for the conversion of CO2 and epoxides into cyclic carbonates. The four complexes were synthesised, characterised and then evaluated in combination with tetrabutylammonium iodide, bromide or chloride as binary catalytic systems for the reaction of CO2 with 1,2-epoxyhexane as epoxide substrate at 12 bar CO2 pressure and 90 °C for 2 h. The catalytic systems comprising the two Ti(IV) complexes (2a and 2b) showed similar performance. One notable exception was the catalytic system consisting of titanium complex 2b, bearing an axial Cl-ligand, and tetrabutylammonium chloride, which displayed higher catalytic activity compared to other titanium-based systems. Even higher activity was achieved with Zr(IV) complex 3a, bearing an axial isopropoxide ligand, which reached turnover numbers (TONmetal) up to 1920 for the reaction of CO2 with 1,2-epoxyhexane at 12 bar CO2 pressure and 90 °C for 2 h. This performance is comparable with that of state-of-the-art catalysts for this reaction. The catalytic system consisting of complex 3a and tetrabutylammonium bromide was explored further by investigating its applicability with a broad substrate scope, achieving quantitative conversion of several epoxides with CO2 into cyclic carbonate products at 90 °C and 12 bar CO2 pressure for 18 h. The selectivity towards the cyclic carbonate products was ≥ 98% for all studied terminal epoxides and ≥ 80% for all examined cyclohexene-type epoxides.