Presence Of Cocatalyst Research Articles

Dynamic structural twist in metal-organic frameworks enhances solar overall water splitting.

Photocatalytic overall water splitting holds great promise for solar-to-hydrogen conversion. Maintaining charge separation is a major challenge but is key to unlocking this potential. Here we discovered a metal-organic framework (MOF) that shows suppressed charge recombination. This MOF features electronically insulated Zn2+ nodes and two chemically equivalent, yet crystallographically independent, linkers. These linkers behave as an electron donor-acceptor pair with non-overlapping band edges. Upon photoexcitation, the MOF undergoes a dynamic excited-state structural twist, inducing orbital rearrangements that forbid radiative relaxation and thereby promote a long-lived charge-separated state. As a result, the MOF achieves visible-light photocatalytic overall water splitting, in the presence of co-catalysts, with an apparent quantum efficiency of 3.09 ± 0.32% at 365 nm and shows little activity loss in 100 h of consecutive runs. Furthermore, the dynamic excited-state structural twist is also successfully extended to other photocatalysts. This strategy for suppressing charge recombination will be applicable to diverse photochemical processes beyond overall water splitting.

CO2 Fixation and PCHC Depolymerization by a Dinuclear β-Diketiminato Zinc Complex.

The production of cyclic carbonates and (or) polycarbonates from the coupling of carbon dioxide (CO2 ) with epoxides is a practical strategy for CO2 fixation. Chemically recycling of the polycarbonates is also urgently needed for sustainable development of plastics. Here a dinuclear β-diketiminato (BDI) methyl zinc complex((BDI-ZnMe)2 , 1) is reported to achieve not only selective cyclic carbonates from cycloaddition of CO2 to meso-CHO in the presence of cocatalyst, but also effective depolymerization of PCHC into trans-CHC. The trans-CHC can be further transformed into cis-CHC, thus demonstrating great application potentials of this strategy in CO2 fixation and chemical recycling of plastics.

Cu‐Catalyzed Atom Transfer Radical Polymerization: The Effect of Cocatalysts

AbstractAtom transfer radical polymerization (ATRP) is one of the most powerful methods to prepare well‐defined (co)polymers. Cu‐catalyzed ATRP methods are most commonly used because of the excellent control and tunable catalytic activities via ligand functionalization. This minireview summarizes the development of Cu‐catalyzed ATRP in the presence of cocatalysts, which are used to regenerate CuI complex activators during polymerizations. Fundamentals of Cu‐based ATRP catalysts are first introduced, followed by the discussion of different types of cocatalysts in different Cu‐catalyzed ATRP methods. Recent developments of photochemical cocatalysts for oxygen‐tolerant ATRP and ATRP using long‐wavelength irradiation are highlighted, which significantly expand the applications of Cu‐catalyzed ATRP. Methods to study the properties of cocatalysts and their roles in Cu‐catalyzed ATRP are discussed, with an outlook for the future development of cocatalysts.

A critical view of the contributions of photoelectrochemical technology to pharmaceutical degradation

The deterioration of water quality and its reuse has generated the necessity to develop water treatment processes with different qualities for industry, agriculture, and human consumption. The types of water contaminants have grown and diversified with different types of processes and activities such as urbanization, industrialization, agriculture, and livestock. In this sense, recalcitrant contaminants stand out, which are not easily removed by conventional water treatment methods. These recalcitrant compounds include pharmaceuticals, whose use has increased significantly, causing long-term danger to humans, animals, and the environment through cumulative exposure. Considering this aspect, it is not surprising that photoelectrochemical processes have become more popular in recent years due to the capacity to generate alternatively oxidizing species which lead to mineralization of organic compounds, improving the quality of water for reusing, even if such species are present in minimal concentrations. In this review, we highlight the main semiconductor materials used in photoelectrocatalysis for the degradation of pharmaceutical compounds, as well as their efficiency in degrading some drugs including antibiotics, analgesics, anti-inflammatories, antivirals, and antidepressants. The main semiconductors used are TiO2, WO3, ZnO, CuO, Cu2O, and BiVO4 photoelectrocatalysts pure or doped and in the presence of cocatalysts or heterostructures. Photocatalytic fuel cells (PFCs) were also investigated in relation to degradation and electricity generation. The system provides a double benefit to the environment: waste materials can be consumed, and solar radiation can be converted into useful energy sources, such as electricity, hydrogen, or fuel. Therefore, photoelectrochemical approaches are currently being considered as a viable method of degrading drugs in water.

Electron delocalization refining via single atom substitution in conjugated organic polymers for enhanced photocatalytic CO2 conversion: Get the big picture from small details

The atom refining strategy is used for the design of COP-X (X = S, N, O) as the efficient photocatalysts for CO2 conversion. Both photoelectrochemical experiments and computational explorations demonstrate that the electron delocalization and reaction barrier can be well regulated by single atom substitution of S, N and O in the 1,3,5-triethynylbenzene linked COPs. Based on the prominent electron donating capacity of S, the fast electron transfer and prolonged lifetime of photoinduced charge carriers endow COP-S with superior photocatalytic CO2 conversion efficiency and selectivity. The CO production rate reaches 196.4 μmol g-1h−1 without the presence of cocatalysts and sacrificial agents, which is 2.1-folds and 2.5-folds of COP-N and COP-O. In particular, the oxidization of H2O to O2 is also realized on bulk COP-S. Our explorations expand the COPs skeleton engineering toolbox and provide new guidance for the design of efficient catalysts for solar energy utilizations.

Immobilized covalent triazine frameworks films as effective photocatalysts for hydrogen evolution reaction

Covalent triazine frameworks have recently been demonstrated as promising materials for photocatalytic water splitting and are usually used in the form of suspended powder. From a practical point of view, immobilized CTFs materials are more suitable for large-scale water splitting, owing to their convenient separation and recycling potential. However, existing synthetic approaches mainly result in insoluble and unprocessable powders, which make their future device application a formidable challenge. Herein, we report an aliphatic amine-assisted interfacial polymerization method to obtain free-standing, semicrystalline CTFs film with excellent photoelectric performance. The lateral size of the film was up to 250 cm2, and average thickness can be tuned from 30 to 500 nm. The semicrystalline structure was confirmed by high-resolution transmission electron microscope, powder X-ray diffraction, grazing-incidence wide-angle X-ray scattering, and small-angle X-ray scattering analysis. Intrigued by the good light absorption, crystalline structure, and large lateral size of the film, the film immobilized on a glass support exhibited good photocatalytic hydrogen evolution performance (5.4 mmol h−1 m−2) with the presence of co-catalysts i.e., Pt nanoparticles and was easy to recycle.

Syntheses and structures of bimetallic rare-earth complexes supported by pyrrolyl ligands and their high performance in isoprene polymerization

• A series of the pyrrolyl-ligated bimetallic rare earth metal amido complexes were synthesized and characterized. • Complexes used as catalyst for the polymerization of isoprene. • They were to be highly cis-1,4 selective for isoprene polymerization. The reactions of pyrrole with rare-earth metal amides [(Me 3 Si) 2 N] 3 RE( μ -Cl)Li(THF) 3 produced the bimetallic rare earth metal amido complexes (RE = Y( 1 ), Nd( 2 ), Yb( 3 )) in high yields. X-ray diffraction analysis revealed that the pyrrole was deprotonated with the pyrrolyl ring coordinated to one rare-earth metal in an η 5 mode and the nitrogen atom coordinated to another rare-earth metal in an η 1 modes forming the centrosymmetric structures. Complexes 1 – 3 as precatalysts for isoprene polymerization were investigated. Results showed that except for ytterbium system, all other complexes could initiate effectively the polymerization of isoprene to afford polyisoprene with high conversion, high regio- and stereo-selectivity (1,4- cis selectivity up to 95.2%) in the presence of cocatalysts. A types of pyrrolyl-ligated bimetallic rare earth metal amido complexes were constructed, and their coordinated modes and catalytic activity were studied.

Synthesis of mononuclear and dinuclear palladium (II) complexes containing oxadithioether ligands and their catalytic activities in norbornene polymerization

AbstractThe Pd (II) complexes trans‐[PdCl2(μ‐L)]2 and [Pd(acac)(L)][BF4] (L = RS(CH2)2O(CH2)2SR, R = Me, Et, nPr, iPr, nBu, iBu, n‐hexyl, benzyl) were obtained through the reaction of Pd(cod)Cl2 or [Pd(acac)(MeCN)2][BF4] with one equivalent of oxadithioether (L). The structural features of these complexes were analyzed by nuclear magnetic resonance (NMR) and Fourier‐transform infrared spectroscopy (FTIR), as well as electrospray ionisation mass spectrometry and density functional theory calculations. The complexes di‐μ‐(2,10‐dimethyl‐6‐oxa‐3,9‐dithiaundecane‐κ2S,S′)‐bis[trans‐dichloropalladium (II)] and (acetylacetonate‐κ2O,O′)(2,10‐dimethyl‐6‐oxa‐3,9‐dithiaundecane‐κ2S,S′)palladium (II) tetrafluoroborate were characterized by X‐ray diffractometry. The X‐ray structures of each complex indicate an axial M–O interaction formed by the endodentate conformation of the oxadithioether ligand. Palladium (II) dichloride complexes with oxadithioethers were demonstrated to have a 16‐membered dinuclear structure with a trans‐configured S2PdCl2 fragment. In the case of cationic palladium acetylacetonate complexes, only mononuclear complexes with a cis configuration of the oxadithioether fragment were observed. Variable temperature 1H and 13C NMR studies of the complexes demonstrate dynamic bonding of the oxadithioether ligands consistent with the presence of diastereoisomers that differ in the orientation of the S‐R groups along with both endodentate and exodentate bonding modes in solution. FTIR studies of the complexes indicate the presence of isomers in the solid state. The palladium catalyst precursors trans‐[PdCl2(μ‐L)]2 and [Pd (acac)(L)][BF4] were found to be active in the addition polymerization of norbornene. In the presence of cocatalysts, such as diisobutylaluminum chloride and boron trifluoride etherate, Pd (II) complexes exhibited activities in the range of 105 to 107 g of polymer (mol of Pd)−1 h−1. The catalyst systems showed good thermostability with a high activity of 1.43 × 107 g of polymer (mol of Pd)−1 h−1 at 75°C. These complexes are examples of Pd (II) complexes bearing thioether ligands, which are rarely observed in the field of olefin polymerization.

An Artificial Hemoprotein with Inducible Peroxidase- and Monooxygenase-Like Activities.

A novel inducible artificial metalloenzyme obtained by covalent attachment of a manganese(III)-tetraphenylporphyrin (MnTPP) to the artificial bidomain repeat protein, (A3A3')Y26C, is reported. The protein is part of the αRep family. The biohybrid was fully characterized by MALDI-ToF mass spectrometry, circular dichroism and UV/Vis spectroscopies. The peroxidase and monooxygenase activities were evaluated on the original and modified scaffolds including those that have a) an additional imidazole, b) a specific αRep bA3-2 that is known to induce the opening of the (A3A3') interdomain region and c) a derivative of the αRep bA3-2 inducer extended with a His6 -Tag (His6 -bA3-2). Catalytic profiles are highly dependent on the presence of co-catalysts with the best activity obtained with His6 -bA3-2. The entire mechanism was rationalized by an integrative molecular modeling study that includes protein-ligand docking and large-scale molecular dynamics. This constitutes the first example of an entirely artificial metalloenzyme with inducible peroxidase and monooxygenase activities, reminiscent of allosteric regulation of natural enzymatic pathways.

Rare‐Earth Metal Alkyl Complexes with 3‐Arylamido‐Functionalized Indolyl Ligands: Synthesis, Characterization and Reactivity†

Summary of main observation and conclusionA series of dinuclear rare‐earth metal alkyl complexes {[μ‐η2:η1:η1‐3‐(LNCH)(CH2SiMe3)Ind]RE(CH2SiMe3)(THF)}2 (L1 = 2‐tBuC6H4, RE = Y, Gd, Dy, Er, Yb; L2 = 2,4,6‐Me3C6H2, RE = Dy, Er; Ind = indolyl) and {[μ‐η2:η1:η1‐3‐(LNCH2)Ind]RE(CH2SiMe3)(THF)}2 (L1, RE = Y, Dy, Er, Yb; L2, RE = Er, Yb) bearing 3‐arylamido functionalized indolyl ligands having diverse bonding modes with metal ions were synthesized either by the insertion reaction of the imino group to the RE—C bond or by the alkane elimination reaction. In the preparation of above complexes, rare‐earth metal alkyl complexes [μ‐η5:η1:η1‐3‐(L2NCH)(CH2SiMe3)Ind]Gd(CH2SiMe3)(THF)}2 with a μ‐η5:η1:η1 coordination mode to the gadolinium ion and {[μ‐η3:η1:η1‐3‐(L2NCH2)Ind]Dy(CH2SiMe3)(THF)}2 with a μ‐η3:η1:η1 coordination mode to the dysprosium ion were unexpectedly isolated. The reactions of 3‐(L2N=CH)Ind with Er(CH2SiMe3)3(THF)2 at room temperature, generated a tetranuclear imino‐indolyl erbium intermediate {[μ‐η1:η1‐3‐(L2N=CH)Ind]Er(CH2SiMe3)2(THF)}4, which can transform into the amido functionalized indolyl erbium complex in hot toluene. Moreover, the reactivities of the newly synthesized ytterbium complex with N‐heterocyclic compounds were investigated, affording the corresponding products of the mixed pyridyl‐indolyl, imidazolyl‐indolyl, and ortho‐metalated complexes. The yttrium complexes showed a high regioselectivity and steroselectivity for the isoprene polymerization with 1,4‐trans selectivity up to 91.7% and 1,4‐cis selectivity up to 96.1% in the presence of cocatalysts, respectively.

Mechanistic study on the effects of co-catalyst on ethylene polymerization over supported vanadocene catalyst

In this work, fundamental insight into the multifaceted role of co-catalyst in activation, propagation, and chain exchange of vanadocene in the immobilized single-site olefin polymerization catalyst has been obtained. The kinetics were followed for various Al/V ratios, at the same polymerization temperature with aluminium diethyl monochloride (DEAC) or triisobutylaluminium (TIBA) as co-catalyst. The results put forward a plausible deactivation reaction path of the catalyst for aluminium diethyl monochloride (DEAC) with irregular morphology of polyethylene particle due to the interaction between halogen atom and vanadium atom. This experimental set of data is supported by a computational investigation at the DFT level that rationalizes specific effects in the presence of co-catalyst at the molecular scale. This joint investigation offers a basic understanding for further catalyst developments in the field of supported metallocene catalyst for olefin polymerization.

Synergistic cobalt–nickel co-catalyst for enhanced visible light-induced photocatalytic water oxidation

The loading of co-catalyst is an efficient way to increase the activity of synthesized carbon-based photocatalysts in the energy and environmental applications. Herein, Co and Ni decorated on g-C3N4 was synthesized as a visible light active photocatalyst and characterized with XRD, FT-IR, BET, DRS, TGA, FE-SEM, EDX, and EIS techniques. From the characterization results, it was demonstrated that cobalt and nickel which were present in the structure of the nanocatalyst, were in the metallic form. The decoration of Ni and Co reduced bandgap energy of g-C3N4 and made the synthesized nanocomposite active under visible light. The operating condition of O2 photocatalytic generation was optimized (193.75 μmol L−1 O2 productions using 0.2 g Co2Ni1/g-C3N4/rGO at 7 h without sacrificial reagents). The effect of sacrificial reagents (Fe(NO3)3, AgNO3, and methanol) was investigated and Fe(NO3)3 showed the best results during water oxidation. The kinetics study indicates that the presence of cocatalysts could be helpful in reducing the apparent activation energy about 3.5 times. The photocatalyst represented acceptable stability (2% Ni and 3% Co leaching) and reusability up to six cycles. According to the obtained results, we can introduce Co2Ni1/g-C3N4/rGO as a potential powerful photocatalyst for water oxidation reaction under visible light. Co and Ni are decorated on g-C3N4/rGO to synthesize a novel photocatalyst with a synergistic effect for photocatalytic water oxidation under visible light. The photocatalyst shows high stability and reusability after six cycles.

Effect of aluminium triflate on Cd(II) recovery by peanut hull-g-methyl methacrylate: optimisation and modelling using a response surface methodology

ABSTRACT In the present study, a response surface methodology (RSM) was used to investigate the effects of independent variables, their simultaneous interactions and quadratic effects on Cd(II) adsorption onto peanut hull-methyl methacrylate (PH-g-MMA) biopolymer. The biopolymer was fabricated through radical polymerisation using benzoyl peroxide (BPO) initiator in the presence or absence of aluminium triflate (Al(OTf)3) as cocatalyst to evaluate the effect of the cocatalyst on adsorption capacity of the adsorbent. The optimum adsorption conditions were pH 6.5, contact time 63.75 min, dosage 0.2250 g, initial concentration 76.25 mg/L in the presence of a cocatalyst and pH 5.7, contact time 63.75 min, dosage 0.2250 g, initial concentration 76.25 mg/L in the absence of a cocatalyst. The model adequacy and validity were confirmed by performing additional experiments under the proposed optimum conditions. The Cd(II) adsorption process best fitted pseudo-second-order kinetic which suggested that the process was controlled by the chemisorption mechanism. The adsorption process was also in accordance with the Langmuir isotherm model with maximum adsorption capacities of 65.80 mg/g and 46.9 mg/g in the presence or absence of cocatalyst, respectively. Consequently, the study demonstrated the cocatalyst enhanced the adsorption properties of the adsorbent and that RSM is suitable for optimising experimental conditions for Cd(II) adsorption capacity.

A Rational Investigation of the Lewis Acid-Promoted Coupling of Carbon Dioxide with Cyclohexene Oxide: Towards CO2-Sourced Polycyclohexene Carbonate under Solvent- and Cocatalyst-Free Conditions

We report a rational investigation of the selective synthesis of poly(cyclohexene carbonate) from CO2 and cyclohexene oxide by using commercially available Lewis acids with nontoxic metal centers. After a preliminary screening, we focused on the use of zinc salts, and the effect of the pressure, the temperature, the catalyst loading, and the presence of cocatalyst or a solvent on the reaction yields, selectivity, and molar masses was evaluated for selected catalytic platforms. Thus, we found that ZnTosylate in catalytic amounts under solvent- and cocatalyst-free conditions enables the selective synthesis of poly(cyclohexene carbonate) with a molecular weight of about 62.1 kg/mol with about 70% yields at 343 K and 4 MPa. To the best of our knowledge, this is a rare example of high molar mass polycyclohexene carbonates that are moreover obtained under solvent- and cocatalyst-free conditions. The high selectivity of ZnTos towards the formation of poly(cyclohexene carbonate) was interpreted, thanks to in situ FTIR spectroscopy and DFT calculations, as resulting from its ability to coactivate CO2.

The investigation of novel D-π-A type dyes (MK-3 and MK-4) for visible light driven photochemical hydrogen evolution

Two novel donor-π-acceptor (D-π-A) semiconductor organic dyes have been synthesized for the photochemical hydrogen evolution reaction (HER) to sensitize TiO2 for the first time. The molecular structures of D-π-A semiconductor organic dyes, which are entitled as MK-3 and MK-4, have been characterized by NMR spectroscopy method; and also electrochemical and optical properties have been investigated by cyclic voltammetry and UV–Vis absorption techniques, respectively. Amount of dye loading on TiO2 surface has been investigated by EDX method. The HER activities have been explored in the presence of triethanolamine (TEOA) as a electron donor reagent under sunlight (solar simulator illumination limited by cut-off filter λ ≥ 420 nm) in the absence and presence of co-catalysts (Pt and Cu2WS4). Transient photocurrent densities of MK-3/TiO2 and MK-4/TiO2 electrodes have been reached to 110 μA cm−1 and 275 μA cm−1, respectively. The photocatalytic HER activities have been relatively enhanced in the presence of the Pt or Cu2WS4 co-catalysts (dye/TiO2/Cu2WS4 or dye/TiO2/Pt) when compared to only dye/TiO2. The HER rates have been found as 427, 1277, 675, 682, 1027 and 795 μmolg−1h−1 for the MK-3/TiO2, MK-3/TiO2/Pt, MK-3/TiO2/Cu2WS4, MK-4/TiO2, MK-4/TiO2/Pt and MK-4/TiO2/Cu2WS4, respectively. The differences of photochemical activities of MK-3/TiO2 and MK-4/TiO2 have been stated taking into account dye molecule structures. Moreover, the HER mechanism have been described by using electrochemical band energy levels of dyes, TiO2 and Cu2WS4 co-catalyst.

A perspective on catalysis in solid acids

Solid Bronsted acids continue to be important for a large number of catalytic processes, and it is important to have reliable methods to characterize both the site concentrations and strengths. Solid Bronsted acids are very different from homogeneous acids and attempts to equate the two should be discouraged. Some of the most commonly used techniques for measuring site densities and strengths, such as NH3 TPD, are unreliable. Site densities can be determined from TPR measurements of alkylamines or IR measurements of adsorbed pyridine but determining site strengths remains a challenge. Reaction rates are the most reliable means for defining site strengths; however, the presence of co-catalysts (in the case of alkane activation), adsorption geometry, surface coverage, and diffusion can all influence rates and product selectivities, so that higher reaction rates do not always imply “stronger” sites.

Bulky guanidinate calcium and zinc complexes as catalysts for the intramolecular hydroamination

Mixed guanidinato-amido supported complexes of calcium, LCaN(SiMe3)2∙2THF (1) [L = {ArNC(NiPr2)NAr} (Ar = 2,6-Me2-C6H3)] and zinc, LZnN(SiMe3)2 (2) & L1ZnN(SiMe3)2 (3) [L1 = {Ar'NC(NiPr2)NAr'} (Ar' = 2,6- iPr2-C6H3)] have been synthesized by salt metathesis method. Reaction between LH or L1H and two equivalents of KN(SiMe3)2 in THF and the resultant reaction mixture upon treatment with CaI2 or ZnCl2 led to the formation of heteroleptic calcium or zinc complexes. All three compounds (1–3) were characterized by multinuclear (1H, 13C, 29Si) magnetic resonance spectroscopy, elemental analysis and single crystal X-ray diffraction methods. Solid state structures confirm that all are monomeric species. Furthermore, we have shown the catalytic application of these complexes for intramolecular hydroamination of amino alkenes. Interestingly, compound 1 exhibits as an excellent pre-catalyst for intramolecular hydroamination of various primary amino alkenes in the absence of any additional activator (co-catalyst). However, both compounds 1 and 2 show very good catalytic activity of hydroamination of various secondary amines in the presence of co-catalyst.

Air-stable di-nuclear yttrium complexes as versatile catalysts for lactide polymerization and copolymerization of epoxides with carbon dioxide or phthalic anhydride

Four novel di-nuclear yttrium catalysts coordinated by bis(benzotriazole iminophenolate) (BiIBTP) ligands have been synthesized and structurally characterized. The one-pot procedure of BiIBTP pro-ligand with [Y(NO3)3.6H2O] (1.0 equiv.) and 2-nitrophenol derivative (1.0 equiv.) in the presence of triethylamine (5.0 equiv.) under refluxing MeOH solution gave bimetallic yttrium nitrophenolate complexes 1–4, [(μ-BiIBTP)Y(L)]2 (BiIBTP = C13CBiIBTP or C83CBiIBTP; L = 2-nitrophenolate or 2,4-dinitrophenolate) with good to high yields. The solid-state structure of 1 and 3–4 exhibits a di-yttrium(III) di-nitrophenolate species with the pentadentate BiIBTP ligand chelating two metal atoms. Versatile catalysis towards ring-opening polymerization of cyclic ester and copolymerization of internal epoxides with carbon dioxide (CO2) or phthalic anhydride (PA) catalyzed by these di-yttrium nitrophenolate complexes was systematically studied. Experimental results revealed that air-stable complexes 3 and 4 were shown to effectively catalyze not only lactide polymerization but also copolymerization of cyclohexene oxide (CHO) with CO2 or PA. Among these compounds, di-Y complex 4 was the most active catalyst for the ring-opening polymerization of l-lactide in combination with 9-anthracenemethanol, providing poly(l-lactide)s having the expected molecular weight and narrow molecular weight distribution. Furthermore, catalyst 3 was capable of copolymerizing CO2 and CHO in the presence of co-catalysts under mild conditions, producing perfectly alternating poly(cyclohexene carbonate)s with the controllable character. In addition, the molecular weight controllable poly(PA-co-CHO)s with high ester linkage contents could be afforded on copolymerizing PA and CHO utilizing di-yttrium complex 3 as the catalyst. This work provides the facilely synthesized di-nuclear yttrium complexes as versatile catalysts for three different types of polymerization catalysis.

Living 3,4‐(Co)Polymerization of Isoprene/Myrcene and One‐Pot Synthesis of a Polyisoprene Blend Catalyzed by Binuclear Rare‐Earth Metal Amidinate Complexes

Mononuclear amidinate yttrium complex C4 H9 C(NR)2 Y(o-CH2 C6 H4 NMe2 )2 (R=2,6-iPr2 C6 H3 ) and a series of binuclear rare-earth metal complexes bearing a bridged amidinate ligand [(RN)2 C(CH2 )4 C(NR)2 ][RE{CH2 C6 H4 (o-NMe2 )}2 ]2 (R=2,6-iPr2 C6 H3 , RE=Y, Lu, Sc) were synthesized and fully characterized. The catalytic behavior of these complexes for (co)polymerization of conjugated dienes such as isoprene and myrcene in the presence of co-catalyst [Ph3 C][B(C6 F5 )4 ] was investigated. These catalytic systems show impressively high activity and 3,4-regioselectivity in living (co)polymerization. The binuclear bridged amidinate yttrium catalytic system not only exhibits the highest activity among the reported catalytic systems for 3,4-polymerization of isoprene but also allows the steady polymerization in a living manner from -20 to 80 °C. Compared with the dramatic drop of 3,4-selectivity for the mononuclear analogue, the binuclear catalytic system still shows moderate 3,4-selectivity at 80 °C. Moreover, a facile one-pot synthetic strategy for a polymer blend containing 3,4- and 1,4-polyisoprene (PIP) was established through the in situ modification of the active amidinate yttrium species by addition of an excess amount of AlMe3 .

Synthesis, characterization, and reactivity of dinuclear organo-rare-earth-metal alkyl complexes supported by 2-amidate-functionalized indolyl ligands: substituent effects on coordination and reactivity.

Two series of new dinuclear organo-rare-earth-metal alkyl complexes supported by 2-amidate-functionalized indolyl ligands with different haptic modes were synthesized and characterized. The treatment of [RE(CH2SiMe3)3(THF)2] with 1 equiv. of 2-(2,6-iPr2C6H3NHC[double bond, length as m-dash]O)C8H5NH (H2L1) and 2-(2-tBuC6H4NHC[double bond, length as m-dash]O)C8H5NH (H2L2) in toluene yielded the dinuclear organo-rare-earth-metal alkyl complexes {[η1:(μ2-η1:η1)-L1]RE(CH2SiMe3)(THF)2}2 [RE = Gd (1a), Dy (1b), Y (1c), Er (1d), and Yb (1e)] and {[η1:(μ2-η1:η1):η1-L2]RE(CH2SiMe3)(THF)2}2 [RE = Gd (2a), Dy (2b), Y (2c), Er (2d), and Yb (2e)] in good yields. When [RE(CH2SiMe3)3(THF)2] were treated with 2 equiv. of H2L1 or H2L2 in THF, the dinuclear organo-rare-earth-metal complexes {(η1:η1-HL)[η1:(μ2-η1:η1):η1-L]RE(THF)}2 (1ca: RE = Y, L = L1; 2ea: RE = Yb, L = L2) were obtained. The complexes could react with small organic molecules such as N,N'-diisopropylcarbodiimide (DIC), phenyl isocyanate, N-methylallylamine, phenylacetylene, pyridine, N-phenylimidazole, or 4-dimethylaminopyridine (DMAP) to yield a series of new complexes with different reactivity patterns along with the reported rare-earth-metal alkyl complexes. In the presence of cocatalysts, these dinuclear organo-rare-earth-metal alkyl complexes could initiate isoprene polymerization with high activity (100% conversion of 2000 equiv. of isoprene in 12 h), yielding polymers with high regioselectivity (1,4 polymers up to 96.1%).