Ethylene Bridge Research Articles

Enhanced optoelectronic properties with aromatic bridges: A computational study on N‐methyl pyridinium and phenolate types of push‐pull zwitterions

AbstractA series of zwitterions with varying bridges, connecting N‐methyl pyridinium acceptor, with phenolate donor, are investigated using various methodologies like, HF, B3LYP, CAM‐B3LYP and ωB97xD. In this systematic study effects of various mono aromatic rings as bridges, on the response properties like, the dipole moments (μ), polarizabilities (α), hyperpolarizabilities (β) and adiabatic absorptions were analyzed using CPHF and TDDFT (or TDHF) theories. Compared to many traditional bridges, as well as without a bridge, enhanced nonlinear optical (2ND order NLO) responses were observed for these aromatically bridged zwitterions (with benzene ring as bridge ~5.3 times and ~7.9 times enhanced hyperpolarizabilities were observed compared to either the ethylene bridge or without any bridge cases, respectively). Also, many significant differences and large enhancements in response properties were observed compared to our earlier works on non‐zwitterionic system (~4.3 times enhanced hyperpolarizability—benzene as bridge case). For some bridge cases, 10‐ to 15‐fold enhanced hyperpolarizabilities were observed compared to without any bridge case. This work reports a class of non‐TICT chromophores, promoting bridge aromaticity control on structure–property correlation, as a suitable and efficient chromophore design strategy to create a wide range of function molecular chromophores. Also, unidirectional natures of response properties and large dipole moments can make these zwitterions suitable 1D‐molecular materials for various contemporary technological applications, as poled polymer‐based materials.

Probing the Electronic Structure of Dinuclear Carbon-Rich Complexes Containing an Octa-3,5-diene-1,7-diyndiyl Bridging Ligand

One electron oxidation of the monometallic alkenylacetylide complexes [Ru{C≡CC(R)=CH2}(dppe)Cp*] (1) and [Ru{C≡CC(R)=CH2}Cl(dppe)2] (2) (R = Ph (a); R = 4-MeS-C6H4 (b)) generates in each case a dinuclear bis(allenylidene) complex [{Ru}2{μ-C=C=C(R)–CH2–H2C–(R)C=C=C}][PF6]2 ({Ru} = Ru(dppe)Cp* ([3a,b][PF6]2); {Ru} = RuCl(dppe)2 ([4a,b][PF6]2), containing an unsaturated ethane bridge between both allenylidene moieties. Deprotonation of this ethane bridge results in the formation of the previously reported octa-3,5-diene-1,7-diyndiyl-bridged bimetallic species [{Ru}2{μ-C≡CC(R)=CH–HC=(R)CC≡C}] ({Ru} = Ru(dppe)Cp* (5a,b); {Ru} = RuCl(dppe)2 (6a,b). The isolation of these complexes illustrates a general synthetic route to these conjugated bimetallic species from monomeric alkenylacetylide precursors. Electrochemical and spectroelectrochemical investigations evince the ready formation of the representative redox series [5a]n+, and TD-DFT calculations performed on optimised structures featuring the simplified {Ru(dmpe)Cp} coordination sphere [{Ru(dmpe)Cp}2{μ-C≡CC(Ph)=HC–CH(Ph)CC≡C}]n+ ([5a†]n+) (n = 0, 1, 2) reveal significant delocalisation of the unpaired charge in the formally mixed-valent species (n = 1), consistent with Class III assignment within the Robin–Day classification scheme.

Structure of Tris[2-(4-pyridyl)ethyl]phosphine, Tris[2-(2-pyridyl)ethyl]phosphine, and Their Chalcogenides in Solution: Dipole Moments, IR Spectroscopy, and DFT Study.

Tris(hetaryl)substituted phosphines and their chalcogenides are promising polydentate ligands for the design of metal complexes. An experimental and theoretical conformational analysis of tris[2-(4-pyridyl)ethyl]phosphine, tris[2-(2-pyridyl)ethyl]phosphine, and their chalcogenides was carried out by the methods of dipole moments, IR spectroscopy and DFT B3PW91/6-311++G(df,p) calculations. In solution, these compounds exist as an equilibrium of mainly non-eclipsed (synclinal or antiperiplanar) forms with a predominance of a symmetrical conformer having a gauche-orientation of the Csp3-Csp3 bonds of pyridylethyl substituents relative to the P=X bond (X = lone pair, O, S, Se) and a gauche-orientation of the pyridyl rings relative to the zigzag ethylene bridges. Regardless of the presence and nature of the chalcogen atom (oxygen, sulfur, or selenium) in the studied molecules with many axes of internal rotation, steric factors-the different position of the nitrogen atoms in the pyridyl rings and the configuration of ethylene bridges-determine the realization and spatial structure of preferred conformers.

Oligodentate Aminotriazole Ligands for CuAAC and Copper‐Mediated Monooxygenation of Phenols: Influence of Denticity, Chain Length and N‐Alkylation on Catalytic Activity

AbstractCopper complexes supported by a series of ligands containing different N‐donor groups were prepared, and the influence of the ligand design on the catalytic activity towards (i) the conversion of monophenols to o‐quinones and (ii) the CuAAC reaction was investigated. Increasing the number of methyltriazole moieties attached to an amine from one (TTA) over two (BTTA) to three (TTTA) decreases the catalytic mono‐phenolase activity of derived Cu complexes. By contrast, replacing the methylene group between the apical and the outer N‐donors of TTA with an ethylene bridge in TTEA increases the activity whereas alkylation of the amino group (dmTTEA, prlTTEA) has no positive effect on the catalytic activity. When employing the complexes in the CuAAC reaction, opposite trends in catalytic activity are observed. The results are interpreted in the context of the respective mechanistic pathways.

Structure‐Unit‐Based Total Synthesis of (−)‐Sinulochmodin C

AbstractHerein we report a structure‐unit‐based asymmetric total synthesis of sinulochmodin C, a norcembranoid diterpenoid bearing a transannular strained ether bridge β‐keto tetrahydrofuran moiety. Our synthetic route features an intramolecular double Michael addition to construct stereospecifically the [7,6,5,5] tetracyclic skeleton, a vinylogous hydroxylation/oxidation procedure or a stereospecific epoxide opening/oxidation sequence to establish the γ‐keto enone intermediate, a Lewis acid/Brønsted acid mediated transannular oxa‐Michael addition to fuse the β‐keto tetrahydrofuran moiety, a Mukaiyama hydration/Pd−C hydrogenation to reverse the C1‐configuration of the isopropenyl unit, and a bioinspired transformation of sinulochmodin C into scabrolide A.

Structure-Unit-Based Total Synthesis of (-)-Sinulochmodin C.

Herein we report a structure-unit-based asymmetric total synthesis of sinulochmodin C, a norcembranoid diterpenoid bearing a transannular strained ether bridge β-keto tetrahydrofuran moiety. Our synthetic route features an intramolecular double Michael addition to construct stereospecifically the [7,6,5,5] tetracyclic skeleton, a vinylogous hydroxylation/oxidation procedure or a stereospecific epoxide opening/oxidation sequence to establish the γ-keto enone intermediate, a Lewis acid/Brønsted acid mediated transannular oxa-Michael addition to fuse the β-keto tetrahydrofuran moiety, a Mukaiyama hydration/Pd-C hydrogenation to reverse the C1-configuration of the isopropenyl unit, and a bioinspired transformation of sinulochmodin C into scabrolide A.

Intramolecular Connections of Tetrazoles with N,N′-Alkylene and Ether Bridges: Toward Energetic Materials with High Nitrogen and Thermal Stability

Intramolecular Connections of Tetrazoles with <i>N</i>,<i>N</i>′-Alkylene and Ether Bridges: Toward Energetic Materials with High Nitrogen and Thermal Stability

Pretreatment of pine needles via torrefaction, oxidation and hydrothermal carbonization at 250 °C impacts subsequent pyrolysis and activation in distinct ways

Thermal pretreatment of biomass in varied medium (i.e. nitrogen, air or water) might further impact pyrolysis and activation in distinct ways. Herein, hydrothermal carbonization (HTC) or torrefaction of pine needles in nitrogen or air at 250 °C and further pyrolysis/activation of pretreated samples was conducted. The results indicated yield of solid followed the method of pretreatment: torrefaction > oxidation > HTC, due to significant oxidation of aliphatics in the pretreatment in air and structural reconstruction in HTC. Additionally, pretreatment in air remarkably increased overall production of biochar (35.1 %), owing to enhanced resistivity to cracking. HTC released nearly half of organics, leading to remarkably lower overall yields of biochar than that in blank experiment (24.7 % versus 30.6 %), but increased thermal stability of biochar through enhancing aromatic degree. Additionally, pretreatment in air removed some H species via oxidation but not nitrogen species while the HTC was the opposite while induced leaching of inorganics. In-situ IR characterization indicated conversion of aliphatic -OH to phenolic -OH in nitrogen-pretreatment, oxidation of ether bridging bond between benzene rings in air-pretreatment and formation of thermally carbonyls via HTC. During activation, all the pretreatments reduced specific surface area of activated carbon, following the order: blank (1351.1 m2 g−1) > torrefaction in N2 (1314.7 m2 g−1) > oxidation in air (1293.8 m2 g−1) > HTC (1218.2 m2 g−1). Oxidation or aromatization reactions in the pretreatment increased aromatic degree of the feedstock, making pore generation via cracking more difficult. Besides, pretreatments also changed morphologies of resulting biochar or activated carbon in distinct ways.

EqPhotochemistry of a water-soluble coumarin-based photoswitch

A novel water-soluble stilbene-type molecular photoswitch (CP) has been synthesized by attaching an N-methylpyridinium unit to 7-diethylamino-4-methylcoumarin (coumarin 1) via an ethylene bridge. The photoisomerization cycle of CP and the spectroscopic properties of the two isomers were studied in acetonitrile and in water. In both solvents, the illumination of trans-CP with green light leads to a photostationary state (PSS) with 90% cis isomer and irradiating then this PSS mixture with near UV light, the trans isomer is almost fully recovered. In water, the quantum yield for the trans-cis photoisomerization is 0.042, for the cis-trans photoisomerization it is 0.23. In acetonitrile, the photoisomerization quantum yields are even higher, the respective values are 0.12 and 0.56. The trans isomer of CP is fluorescent with red emission and it has a large Stokes shift, whereas the cis isomer is non-fluorescent. The two isomers are thermally stable at room temperature. The efficient photoisomerization of CP in both direction, the thermal stability of both isomeric forms and the distinct fluorescence of the trans isomer suggest that some water-soluble coumarin-based photoswitches may be promising candidates for applications in fluorescence imaging of biological samples.

Synthesis and Photochromic Properties of Diaryl [5]Helicene Derivatives.

Photoinduced tuning of aromaticity and correlative molecular properties has attracted enormous interest in recent years both for modulating photochromism properties and designing novel photochromic materials. Here, we report the synthesis and photochemical characterization of diaryl[5]helicene-based diarylethene molecular switches. 3,4-Bis(2,4-dimethyl-5-phenylthiophen-3-yl)dibenzo[c,g]phenanthrene derivative 1 a showed no photochromic reaction, whereas 3,4-bis(2-methyl-5-phenylthiophen-3-yl)dibenzo[c,g]phenanthrene derivative 2 a and 3,4-bis(5-methyl-2-phenylthiazol-4-yl)dibenzo[c,g]phenanthrene derivative 3 a exhibited reversible photochromism in different aprotic solvents with specific light irradiation. Meanwhile, the diarylethene compounds 2 a and 3 a underwent turn-off mode fluorescence photoswitching together with photoisomerization upon light irradiation. Remarkably, the photoinduced changes in the aromaticity of [5]helicene as a central ethene bridge along with the relative smaller activation energy and higher frequency factor facilitated the thermal bleaching rates of diarylethene switches 2 and 3 in solution. This research provides new insight for designing aromatic diarylethene photoswitches for reversible fluorescence switching, photoinduced changes in aromaticity and further fast thermal back reactions.

Biodegradable Packaging Based on Poly(vinyl Alcohol) and Carboxymethyl Cellulose Films Incorporated with Ascorbic Acid for Food Packaging Applications.

Petroleum-based plastics are used as packaging materials because of their low cost and high availability; however, continuous use of these nondegradable materials especially in the food industry has led to environmental pollution. The present study aimed to synthesize antibacterial and biodegradable films based on natural biopolymers carboxymethyl cellulose (CMC), poly(vinyl alcohol) (PVA), and ascorbic acid (AA) cross-linked in the presence of glutaraldehyde (GA). The films were synthesized in two different concentrations, 60PVA:40CMC:AA and 70PVA:30CMC:AA with a fixed amount of AA. Films with smooth texture and overall uniform thickness were obtained. Fourier transform infrared spectroscopy (FTIR) confirmed the cross-linking between the aldehyde group of GA and hydroxyl of PVA through detection of acetal and ether bridges. The synthesized films were thermally stable in the temperature range of 180-300 °C; however, 70PVA:30CMC:AA showed higher weight loss in this range as compared to the 60PVA:40CMC:AA film. Soil burial test demonstrated that the 60PVA:40CMC:AA film was more degradable (71% at day 15) as compared to the 70PVA:30CMC:AA film (65% at day 15). The films exhibited excellent antimicrobial activity against Gram-positive staphylococcus aureus(inhibition zone of 21 mm) and Gram-negative Escherichia coli (inhibition zone of 15 mm). In comparison, the 60PVA:40CMC:AA film showed better results in terms of high mechanical strength, uniform morphology, higher soil burial degradation, and lower water vapor transmission rate. Therefore, the prepared film could be used as a promising candidate in the food packaging industry.

Structural and Luminescence Properties of Eu-Doped PMO Films with Ethylene Bridge and Methyl Terminal Groups

Eu-doped periodic mesoporous organosilicate (PMO) films with terminal methyl and ethylene bridging groups have been synthesized using sol-gel technology and spin-coating, employing evaporation-induced self-assembly (EISA), on silicon wafers. Eu doping is achieved by the dissolution of Eu(NO3)3·6H2O in the precursor solution. The deposited films are characterized using Fourier transform infrared (FTIR) spectroscopy, ellipsometric porosimetry (EP), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy. It is observed that Eu doping reduces the concentration of terminal methyl groups, makes the films more hydrophilic and reduces the pore size and open porosity. The reduction reaction Eu3+ → Eu2+ occurs in the pores of organosilicate glass (OSG) films, which was confirmed by the depth profiling XPS. Eu3+ was still present on the top surface of the films. The presence of Eu3+ and Eu2+ gives luminescence emission in the range of 600–630 nm (Eu3+) and 290–400 nm (Eu2+). The Eu2+/Eu3+ concentrations ratio depends on CH3 groups concentration in the films. The concentration of Eu2+ ions in the pores can be reduced by exposure to inductively coupled (ICP) oxygen plasma. The observed shift in the luminescence spectra towards the UV region, in comparison to previously reported Eu-doped organosilicate films, can be attributed to the energy transfer occurring between the host material and Eu2+ ions.

Antibiotic Potential of the Ambigol Cyanobacterial Natural Product Class and Simplified Synthetic Analogs.

The ambigols are cyanobacterial natural products characterized by three polychlorinated aromatic building blocks connected by biaryl and biaryl ether bridges. All ambigols known to date possess promising biological activities. Most significantly, ambigol A was reported to have antibacterial activity against Gram-positive bacteria, such as Bacillus megaterium and B. subtilis. We established a diverse compound library for in-depth biological evaluation building on our previous bio- and total synthetic research on this natural product family. To explore the antimicrobial potential in detail and to determine initial structure-activity relationships of this product class, a large set of dimeric and trimeric compounds were screened against selected bacterial and Candida target strains. Our results reveal exceptional antibiotic activity of the ambigols, especially against challenging clinical isolates.

Temperature evolution of organosilicate glass films with organic bridges

Thin porous sol–gel organosilicate glass (OSG) films containing methylene (Me-OSG), ethylene (Et-OSG), or phenylene (Ph-OSG) bridges between Si atoms, along with terminal methyl groups, were spin-coated onto Si wafers. Porosity was generated using the Brij® L4 template. The investigation focused on examining the effects of annealing (200–1000 °C, 30 min) on the properties of the micro/mesoporous films. The changes in the properties of the films during the annealing process at different temperatures are impacted by the evaporation of solvents, condensation reactions, and destruction of the porogen (200–400 °C). Additionally, the degradation of terminal and bridging organic groups has been observed to occur within the temperature range of 200–600 °C. Finally, the films undergo densification through subsequent condensation and viscous sintering within a temperature range of 700–1000 °C. Ph-OSG films demonstrate remarkable resistance to temperatures of ∼400 °C. Additionally, these films exhibit the highest Young's Modulus (YM) and the smallest pore radius (YM ≈ 6.7 GPa and R ≈ 1 nm after 400 °C annealing). It is important to acknowledge that these materials exhibit a relatively hydrophilic nature, significant shrinkage, and higher refractive index (RI) and dielectric constant (k) compared to the Me-OSG and Et-OSG films. Me-OSG films demonstrate the highest hydrophobicity and porosity, along with minimal shrinkage, RI, and k. However, they also possess the largest pore radius (R = 1.7–2.2 nm after undergoing annealing at 400–550 °C). Modeling the concentrations of different species reveals that the predicted changes in concentrations are strongly dependent on the number of hydroxyl groups present on the surface of the pore walls. The decrease in the number and/or polarizability of OH groups leads to an increased impact of other species on the dielectric constant, resulting in higher computed values.

Dynamic and Persistent Cyclochirality in Hydrogen-Bonded Derivatives of Medium-Ring Triamines.

Cyclic triureas derived from 1,4,7-triazacyclononane (TACN) were synthesized; X-ray crystallography showed a chiral bowl-like conformation with each urea hydrogen-bonded to its neighbor with uniform directionality, forming a "cyclochiral" closed loop of hydrogen bonds. Variable-temperature 1H NMR, 1H-1H exchange spectroscopy, Eyring analysis, computational modeling, and studies in various solvents revealed that cyclochirality is dynamic (ΔG‡25°C = 63-71 kJ mol-1 in noncoordinating solvents), exchanging between enantiomers by two mechanisms: bowl inversion and directionality reversal, with the former subject to a slightly smaller enantiomerization barrier. The enantiomerization rate substantially increased in the presence of hydrogen-bonding solvents. Population of only one of the two cyclochiral hydrogen-bond directionalities could be induced by annulating one ethylene bridge with a trans-cyclohexane. Alternatively, enantiomerization could be inhibited by annulating one ethylene bridge with a cis-cyclohexane (preventing bowl inversion) and replacing one urea function with a formamide (preventing directionality reversal). Combining these structural modifications resulted in an enantiomerization barrier of ΔG‡25°C = 93 kJ mol-1, furnishing a planar-chiral, atropisomeric bowl-shaped structure whose stereochemical stability arises solely from its hydrogen-bonding network.

CO2 adsorption by ethane periodic mesoporous organosilica at low temperatures and high pressure

In this work, the maximum CO2 adsorption capacity of an ordered mesoporous organosilica with ethylene bridges (PMO-Ethane) was studied. The maximum capture capacity was achieved for the sample at 0 °C and 34 atm (827.8 mg·g-1). This result was better than that obtained by most of the studies on other mesoporous materials found in the literature. Approximately 0.33 g of PMO-Ethane would be sufficient to shrink the concentration of atmospheric CO2 by 1 m3 to preindustrial levels. A study of successive adsorption-desorption cycles has demonstrated the material's potential for use in reversible multicycle CO2 capture processes. The CO2 adsorption curves were fitted using mathematical models: Langmuir, Freundlich, Sips, Toth, DubininRadushkevich and Temkin. Previously, several techniques were used to characterize the material: X-Ray diffraction (XRD), surface area (SBET) and porosity, thermogravimetric and differential thermal analysis (TGA-DTA), particle size, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). These results contribute to the development and use of new materials in GHG capture technologies.

Antiproliferative and Tubulin-Destabilising Effects of 3-(Prop-1-en-2-yl)azetidin-2-Ones and Related Compounds in MCF-7 and MDA-MB-231 Breast Cancer Cells.

A series of novel 3-(prop-1-en-2-yl)azetidin-2-one, 3-allylazetidin-2-one and 3-(buta-1,3-dien-1-yl)azetidin-2-one analogues of combretastatin A-4 (CA-4) were designed and synthesised as colchicine-binding site inhibitors (CBSI) in which the ethylene bridge of CA-4 was replaced with a β-lactam (2-azetidinone) scaffold. These compounds, together with related prodrugs, were evaluated for their antiproliferative activity, cell cycle effects and ability to inhibit tubulin assembly. The compounds demonstrated significant in vitro antiproliferative activities in MCF-7 breast cancer cells, particularly for compounds 9h, 9q, 9r, 10p, 10r and 11h, with IC50 values in the range 10-33 nM. These compounds were also potent in the triple-negative breast cancer (TBNC) cell line MDA-MB-231, with IC50 values in the range 23-33 nM, and were comparable with the activity of CA-4. The compounds inhibited the polymerisation of tubulin in vitro, with significant reduction in tubulin polymerization, and were shown to interact at the colchicine-binding site on tubulin. Flow cytometry demonstrated that compound 9q arrested MCF-7 cells in the G2/M phase and resulted in cellular apoptosis. The antimitotic properties of 9q in MCF-7 human breast cancer cells were also evaluated, and the effect on the organization of microtubules in the cells after treatment with compound 9q was observed using confocal microscopy. The immunofluorescence results confirm that β-lactam 9q is targeting tubulin and resulted in mitotic catastrophe in MCF-7 cells. In silico molecular docking supports the hypothesis that the compounds interact with the colchicine-binding domain of tubulin. Compound 9q is a novel potent microtubule-destabilising agent with potential as a promising lead compound for the development of new antitumour agents.

Cytotoxic pyridine alkaloids from a marine-derived fungus Arthrinium arundinis exhibiting apoptosis-inducing activities against small cell lung cancer

Small cell lung cancer (SCLC) is a kind of high-grade neuroendocrine carcinoma, which is characterized by a higher proliferative rate, earlier metastasis and more poor outcomes compared to non-small cell lung cancer (NSCLC). Under the guidance of MS/MS based molecular networking, three undescribed pyridone alkaloids, namely, arthpyrones M–O (1–3), together with two known pyridone derivatives, arthpyrones C (4) and G (5), were isolated from a sponge-derived Arthrinium arundinis. Their structures were determined through extensive spectroscopic analysis, ECD calculations, and X-ray single-crystal diffraction. Arthpyrone M (1) possessed a novel cage structure bearing an ether bridge functionality rarely reported in this class of metabolites. All isolated compounds were evaluated for their cytotoxicities against five cancer cell lines. As a result, compounds 1–5 showed cytotoxicity against some or all of the five cancer cell lines with IC50 values ranging from 0.26 to 6.43 μM. Among them, arthpyrone O (3) not only exhibited potent efficacy against the proliferative activity of SCLC cells and induced apoptosis in vitro, but also significantly inhibited the growth of xenograft tumor based on SCLC cells in vivo, which indicated 4-hydroxy-2-pyridone alkaloids might been revised as privileged scaffolds in drug discovery.

Effect of solvent quality on covalent bonds cleavage behaviors of lignite during pyrolysis/liquefaction processes

Effect of solvent quality on coal conversion and product distribution during lignite pyrolysis/liquefaction were investigated at the temperatures ranging from 180 to 460 °C, and the covalent bond cleavage behaviors in different solvents were comparatively elucidated. Results showed that at the temperatures below 280 °C, weak covalent bonds, such as methoxy and carboxyl groups, are cleaved to generate a small amount of gaseous products (mainly CO2) and liquefied oil. At the temperatures of 330–380 °C, ether bridges that connecting the aromatic clusters are cleaved and contributed significantly to the production of preasphaltene (PA). Meanwhile, oil yield and coal conversion increased to 27.50% and 64.58% in tetralin. At the temperatures of 430–460 °C, the cleavage of CH2 bridges, alkyl substituent groups and aromatic heterocyclic structures proceeded markedly, and the scission of CH2 bridges and some naphthenic CH2 bonds significantly contributed to oil production. Consequently, oil yield and coal conversion greatly increased to 43.90% and 84.13% in tetralin. Hydrogen donor solvent is conducive to the cleavage of strong covalent bonds, such as Car–O–Car and Car-Cal bonds, to realize the efficient liquefaction of coal.

Mono- and Bimetallic Aluminum Complexes Supported by Thioether-Amide Ligands: Synthesis, Characterization, and Application in the Ring Opening Polymerization of l-Lactide

Mono- and bimetallic aluminum complexes bearing bidentate NS or tetradentate NSSN ligands have been synthesized via reaction of AlMe3 with the corresponding proligand and spectroscopically characterized. In these complexes the aluminum centers are surrounded by anionic nitrogen and neutral sulfur atoms that, together with the carbon atoms of the alkyl groups, produce tetrahedral coordination geometries. In the bimetallic complexes the two metal centers are linked by a thioether-bridge of different lengths. The solid state structure of the complexes featuring the thioethyl or thiopropyl bridge were determined by X-ray diffraction studies. Both mono- and bimetallic aluminum complexes display fluxional behaviors in solution. After proper activation, all complexes were able to promote the ring opening polymerization of l-lactide in toluene solution. The polymerizations were well controlled as testified by the linear increase of the molecular weights with the conversions and the narrow polydispersity indexes. The highest activity was observed for the bimetallic complex bearing the NSSN ligand with the shortest bridge (ethyl bridge) with a turnover frequency of 11.6 molLA·molAl–1·h–1 (toluene, 80 °C). The activity decreased as the distance between the two metal centers increased. Moreover, the activity of the bimetallic complex with the ethyl bridge was higher than those of the monometallic ones. These findings suggest that a cooperative interaction between two aluminum centers is operative in the bimetallic complex with the shortest bridge.