Regioselective Bis-Selenation of Allenes Catalyzed by Palladium Complexes: A Theoretical Study

The reaction mechanism of Pd(O)-catalyzed allene bis-selenation reactions is investigated by using density functional methods. The overall reaction mechanism has been examined. It is found that with the bulkier PMe3 ligand, the rate-determining step is the reductive elimination process, while allene insertion and reductive elimination processes are competitive for the rate-determining step with the PH3 ligand, indicating the importance of the ligand effect. For both cis and trans palladium complexes, allene insertion into the Pd-Se bond of the trans palladium complex using the internal carbon atom attached to the selenyl group is prefer-red among the four pathways of allene insertion processes. The formation of sigma-allyl and pi-allyl palladium complexes is favored over that of the sigma-vinyl palladium species. By using methylallene, the regioselectivity of monosubstituted allene insertion into the Pd-Se bond is analyzed.

Synthesis, crystal structures and spectroscopic properties of copper(I) complexes containing beta-dialdiminato supporting ligands

Two mononuclear neutral copper(I) complexes, Cu(L-1)PPh3 (1), Cu(L-2)(PPh3)(2) (2) ([L-1](-) = [{N((C6H3Pr2)-Pr-i-2,6)C(H)}(2)CPh](-); [L-2](-) = [{N(C6H5)C(H)}(2)CPh](-)) have been synthesized and structurally characterized by X-ray crystallography. In complex 1, the copper(I) atom is in a distorted three-coordinate trigonal planar environment, whereas in complex 2 with the less sterically hindered beta-dialdiminato ligand, the copper(I) atom is the centre of a four-coordinate distorted tetrahedron. At room temperature complexes 1 and 2 in a film of PMMA exhibit green emission at 543 and 549 nm with lifetimes of 5.28 and 5.32 ns, respectively.

Oligoaniline-Functionalized terpyridine ligands and their ruthenium(II) complexes: synthesis, spectroscopic property and redox behaviors

A series of oligoaniline-functionalized mono- and bis-topic terpyridine ligands, i.e. C6H5[N(R)C6H4](n)TPY (R = H, butyl, tert-butyloxycarbonyl; n = 1-4; TPY = 2,2':6',2"-terpyridyl) and TPYC6H4[N(R)C6H4](m)TPY (R = H, tert-butyloxycarbonyl; m = 2, 4), and the corresponding monoand bis-nuclear ruthenium(II) complexes have been synthesized and verified. The spectroscopic results indicate that two kinds of pi-pi* transitions from TPY and oligoaniline fragments of ligands strongly shift to lower energy, and the metal-to-ligand charge-transfer transition ((MLCT)-M-1) bands of all obtained complexes are considerably red-shifted (Delta lambda(max) = 22-64 nm) and their intensities become much more intense (approximately 4-6 times), compared with those of the reported complex [Ru(TPY)(2)](2+). Moreover, the spectroscopic properties of the ligands and complexes with longer oligoaniline units (n = 3, 4) are markedly influenced by the external stimulus, such as the oxidation and proton acid doping.

Synthesis, characterization and electrophosphorescent properties of mononuclear platinum(II) complexes based on 2-phenylbenzoimidazole derivatives

The rational design, synthesis and characterization of five phosphorescent platinum complexes [(C boolean AND N) Pt(acac)] [Hacac = acetylacetone, HC boolean AND N = 1-methyl-2-(4-fluorophenyl)benzoimidazole (H-FMBI), 1-methyl-2-phenylbenzoimidazole (H-MBI), 1,2-diphenyl-benzoimidazole (H-PBI), 1-(4-(3,6-di-t-butylcarbazol-9-yl)) phenyl-2-phenylbenzoimidazole (t-BuCz-H-PBI), and 1-(4-(3,6-di-(3,6-di-t-butyl-carbazol-9-yl))carbazol-9-yl) phenyl-2-phenylbenzoimidazole (t-BuCzCz-H-PBI)] have been discussed. The crystal structure of (MBI) Pt(acac) shows a nearly ideal square planar geometry around Pt atom and the weak intermolecular interactions with pi-pi spacing of 3.55 angstrom. All of the complexes emit green phosphorescence from the metal-to-ligand charge-transfer (MLCT) excited state with high quantum efficiency (0.08-0.17) at room temperature.

Synthesis, photophysical and electrophosphorescent properties of mononuclear Pt(II) complexes with arylamine functionalized cyclometalating ligands

Four cyclometalated Pt(II) complexes, i.e., [(L-2)PtCl] (1b), [(L-3)PtCl] (1c), [(L-2)PtC CC6H5] (2b) and [(L-3)PtC CC6H5] (2c) (HL2 = 4-[p-(N-butyl-N-phenyl)anilino]-6-phenyl-2,2'-bipyridine and HL3 = 4-[p(-N,N'-dibutyl-N'-phenyl)phenylene-diamino]-phenyl-6-phenyl-2,2'-bipyridine), have been synthesized and verified by H-1 NMR, C-13 NMR and X-ray crystallography. Unlike previously reported complexes [(L-1)PtCl] (1a) and [(L-1)PtC CC6H5] (2a) (HL1 = 4,6-diphenyl-2,2'-bipyridine), intense and continuous absorption bands in the region of 300-500 nm with strong metal-to-ligand charge transfer ((MLCT)-M-1) (d pi(Pt) -> pi*(L)) transitions (epsilon similar to 2 x 10(4) dm(3) mol (1) cm (1)) at 449-467 nm were observed in the UV-Vis absorption spectra of complexes 1b, 1c, 2b and 2c.

Chiral Salan Aluminium Ethyl Complexes and Their Application in Lactide Polymerization

Synthetic routes to aluminium ethyl complexes supported by chiral tetradentate phenoxyamine (salan-type) ligands [Al(OC6H2(R-6-R-4)CH2)(2){CH3N(C6H10)NCH3}-C2H5] 7: R = H ; 5, 8: R = Cl; 6, 9: R = CH3) are reported. Enantiornerically pure salan ligands 1-3 with (R,R) configurations at their cyclohexane rings afforded the complexes 4, 5, and 6 as mixtures of two diastereoisomers (a and b). Each diastereoisomer a was, as determined by X-ray analysis, monomeric with a five-coordinated aluminium central core in the solid state, adopting a cis-(O,O) and cis-(Me,Me) ligand geometry. From the results of variable-temperature (VT) H-1 NMR in the temperature range of 220-335 K, H-1-H-1 NOESY at 220 K, and diffusion-ordered spectroscopy (DOSY), it is concluded that each diastereoisomer b is also monomeric with a five-coordinated aluminium central core.

Polymerization of Lactide Using Achiral Bis(pyrrolidene) Schiff Base Aluminum Complexes

A series of aluminum ethyls and isopropoxides based on a bis(pyrrolidene) Schiff base ligand framework has been prepared and characterized. NMR studies of the dissolved complexes indicate that they adopt a symmetric structure with a monomeric, five-coordinated aluminum center core. The aluminum ethyls used as catalysts in the presence of 2-propanol as initiator and the aluminum isopropoxides were applied for lactide polymerization in toluene to test their activities and stereoselectivities. All polymerizations are living, as evidenced by the narrow polydispersities and the good fit between calculated and found number-average molecular weights of the isolated polymers. All of these aluminum complexes polymerized (S,S)-lactide to highly isotactic PLA without epimerization of the monomer, furnished isotactic-biased polymer from rac-lactide, and gave atactic polymer from meso-lactide.

Carbon dioxide/propylene oxide coupling reaction catalyzed by chromium salen complexes

A series of chromium/Schiff base complexes N,N'-bis(salicylidene)-1,2-phenylenediamino chromium(III) X were prepared and employed for the alternating copolymerization of carbon dioxide with racemic propylene oxide in the presence of (4-dimethylamino)pyridine. The effect of the complex structure and reaction conditions on the catalytic activity, the poly(propylene carbonate)/cyclic carbonate (PPC/PC) selectivity, and the polymer head-to-tail linkages was examined. The experiments indicated that N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-phenylenediamino chromium(III) (NO3) exhibited the highest PPC/PC selectivity as well as polymer head-to-tail linkages and N,N'-bis(3,5-dichlorosalicylidene)-1,2-phenylenediimino chromiu(III) (NO3) possessed the highest catalytic activity among these chromium/Schiff base complexes. The structure of the produced copolymer was characterized by the IR, H-1 NMR, and C-13 NMR measurements.

The synthesis and properties of meso-tetra(4-alkylamidophenyl)porphyrin liquid crystals and their Zn complexes

A series of novel, long-chain-substituted, porphyrin derivatives, meso-tetra (4-alkylamidophenyl) porphyrin ligands and their Zn complexes (alkyl = 8,10,12,14,16,18) were prepared by acylation of the amino groups of 5,10,15,20-tetra(4-aminophenyl)porphyrin by alkyl chloride. Mesomorphism was investigated by DSC, polarized optical microscopy (POM) and X-ray diffraction (XRD). Only ligands containing chains > 12 carbon atoms displayed liquid crystalline behaviour, which exhibited a high phase transition temperature and a broad mesophase temperature span, Zn complexes showed no liquid crystalline behaviour. Cyclic voltammetry, luminescence spectra and surface photovoltage spectroscopy revealed that covalent linking of an alkylamido group to the tetraphenylporphyrin molecule influences, significantly, the properties of the porphyrin macrocycle.

Ordered magnetic core-manganese oxide shell nanostructures and their application in water treatment

In this paper, we have reported a facile method for the synthesis of ordered magnetic core-manganese oxide shell nanostructures. The process included two steps. First, manganese ferrite nanoparticles were obtained through a solvothermal method. Then, the manganese ferrite nanoparticles were mixed directly with KMnO4 solution without any additional modified procedures of the magnetic cores. It has been found that Mn element in the core can react with KMnO4 to form manganese oxide which acts as a seed for the in-situ growth of manganese oxide shells. This is significant for the controllable fabrication of symmetrical ordered manganese oxide shell structures. The shell thickness can be easily controlled through the reaction time. Transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction and energy-dispersive X-ray spectroscopy have been employed to characterize the products at different reaction time.

Multicolor Tuning of Manganese-Doped ZnS Colloidal Nanocrystals

In this paper, we report a facile route which is based Oil tuning doping concentration of Mn2+ ions in ZnS nanocrystals, to achieve deliberate color modulation from blue to orange-yellow under single-wavelength excitation. X-ray diffraction (XRD), transmission electron microscopy (TEM), as well as photoluminescence (PL) spectra were employed to characterize the obtained samples. In this process, the relative emission intensities of both ZnS host (blue) and Mn2+ dopant (orange-yellow) are sensitive to the Mn2+ doping concentration, due to the energy transfer from ZnS host to Mn2+ dopant. As a result of fine-tuning of these two emission components, white emission can be realized for Mn2+-doped ZnS nanocrystals. Furthermore.

Synthesis, characterization, photophysics and electrophosphorescent applications of phosphorescent platinum cyclometalated complexes with 9-arylcarbazole moieties

A series of cyclometalating platinum(II) complexes with substituted 9-arylcarbazolyl chromophores have been synthesized and characterized. These complexes are thermally stable and most of them have been characterized by X-ray crystallography. The phosphorescence emissions of the complexes are dominated by (MLCT)-M-3 excited states. The excited state properties of these complexes can be modulated by varying the electronic characteristics of the cyclometalating ligands via substituent effects, thus allowing the emission to be tuned from bright green to yellow, orange and red light. The correlation between the functional properties of these metallophosphors and the results of density functional theory calculations was made. Because of the propensity of the electron-rich carbazolyl group to facilitate hole injection/transport, the presence of such moiety can increase the highest occupied molecular orbital levels and improve the charge balance in the resulting complexes relative to the parent platinum(II) phosphor with 2-phenylpyridine ligand.

Electrically-controlled near-infrared chiroptical switching of enantiomeric dinuclear ruthenium complexes

Enantiomerically pure dinuclear ruthenium complexes with 1,2-dicarbonylhydrazide as a bridging ligand are optically active in the visible and near infrared spectral regions depending on the oxidation states of the metal centers and are useful as an electrochemically driven near infrared chiroptical switch.

Rare-earth metal complexes stabilized by amino-phosphine ligand. Reaction with mesityl azide and catalysis of the cycloaddition of organic azides and aromatic alkynes

Stoichiometric reactions between mesityl azide (MesN(3), Mes = 2,4,6-C6H2Me3) and amino-phosphine ligated rare-earth metal alkyl, LLn(CH2SiMe3) (2)(THF) (L = (2,6-C6H3Me2)NCH2C6H4P(C6H5)(2); Ln = Lu (1a), Sc (1b)), amide, LLu(NH(2,6-(C6H3Pr2)-Pr-i))(2)(THF) (2) and acetylide at room temperature gave the amino-phosphazide ligated rare-earth metal bis(triazenyl) complexes, [L(MesN(3))]Ln[(MesN(3))-(CH2SiMe3)](2) (Ln = Lu (3a); Sc (3b)), bis(amido) complex [L(MesN3)] Lu[NH(2,6-C6H3 Pr-i(2))](2) (4), and bis(alkynyl) complex (5) (L(MesN(3))Lu (C CPh)(2))(2), respectively. The triazenyl group in 3 coordinates to the metal ion in a rare eta(2)-mode via N-beta and N-gamma atoms, generating a triangular metallocycle. The amino-phosphazide ligand, L(MesN(3)), in 3, 4 and 5 chelates to the metal ion in a eta(3)-mode via N-alpha and N-gamma atoms. In the presence of excess phenylacetylene, complex 3a isomerized to 3', where the triazenyl group coordinates to the metal ion in a eta(3) mode via Na and Ng atoms.

Reactivity of Rare-Earth Metal Complexes Stabilized by an Anilido-Phosphinimine Ligand

Treatment of anilido-phosphinimine-ligated yttrium mono(alkyl) complex 1a, LY(CH2Si(CH3)(3))(THF) (L = o-(2,6-(C6H3Pr2)-Pr-i)NC6H4P(C6H4)(C6H5)N(2,4,6-C6H2Me3)), with 2 equiv of phenylsilane in DME afforded methoxy-bridged complex 2, [LY(mu-OCH3)](2), via the corresponding hydrido intermediate. When excess isoprene was added to the mixture of la and phenylsilane, a eta(3)-isopentene product, 3, LY(CH2C(CH3)=CHCH3)(THF), was isolated. A lutetium chloride, LLuCl(DME) (4), was generated through the reaction of lutetium mono(alkyl) complex 1b, LLu(CH2Si(CH3)(3))(THF), with [Ph3C]-[B(C6F5)(4)]center dot LiCl accompanied by the formation of [Li(DME)(3)](+)[B(C6F5)(4)](-). Metathesis reaction of 1b with excess AlMe3 at room temperature gave a methyl-terminated counterpart, 5, LLu(CH3)(THF)(2). In all these reactions, the Ln-C-phenyl bonds of complexes 1 remained untouched.