Chelating Ring Research Articles

Iodide-enhanced palladium catalysis via formation of iodide-bridged binuclear palladium complex

The prevalence of metalloenzymes with multinuclear metal complexes in their active sites inspires chemists’ interest in the development of multinuclear catalysts. Studies in this area commonly focus on binuclear catalysts containing either metal-metal bond or electronically discrete, conformationally advantageous metal centres connected by multidentate ligands, while in many multinuclear metalloenzymes the metal centres are bridged through μ2-ligands without a metal-metal bond. We report herein a μ2-iodide-bridged binuclear palladium catalyst which accelerates the C-H nitrosation/annulation reaction and significantly enhances its yield compared with palladium acetate catalyst. The superior activity of this binuclear palladium catalyst is attributed to the trans effect-relay through the iodide bridge from one palladium sphere to the other palladium sphere, which facilitates dissociation of the stable six-membered chelating ring in palladium intermediate and accelerates the catalytic cycle. Such a trans effect-relay represents a bimetallic cooperation mode and may open an avenue to design and develop multinuclear catalysts.

NHC-phosphane rhodium complexes and their reaction with oxygen

The new homoleptic square planar Rh+I complexes [Rh(NHC-PPh2)2][X] (cis-2[X] and trans-2[X], X = Cl, PF6) with chelating phosphane N-heterocyclic carbene ligands were synthesized by reaction of [Rh(μ-Cl)(COD)]2 with the free ligand {1-[2-(diphenylphosphino)ethyl)]-3-ethylimidazol-2-ylidene)}. The ligand precursor was obtained by deprotonation of the imidazolium salts 1 {1-[2-(diphenylphosphino)ethyl)]-3-ethyl-imidazoliumiodide} 1[I] or hexafluorophosphate 1[PF6], respectively, with KN(SiMe3)2 in THF. Cis-2[Cl] and trans-2[Cl] coexist in a dynamic equilibrium which has been studied by temperature-dependent 31P NMR spectroscopy. cis-2[Cl] and trans-2[Cl] react with O2 at ambient temperature to afford the new cis and trans peroxo Rh+III complexes [Rh(η2-O2)(NHC-PPh2)2]Cl (cis-3[Cl] and trans-3b[Cl]). 31P NMR spectra prove that the bonding of O2 to cis-2[Cl] is reversible. In solution, cis-3[Cl] shows a fluxional behaviour as evidenced by 31P NMR spectra. The fluxionality is attributed to the flexibility of the chelating rings formed by the ligand and the metal centre. Cis-2[PF6] reacts with S8 to give the novel Rh+III complex [Rh(η2-S2)(NHC-PPh2)2][PF6] (cis-4[PF6]). Contrary to the analogous peroxo complex cis-3[Cl], no fluxionality could be observed in this case. All complexes have been characterised by 31P, 1H, 13C NMR spectroscopy and single-crystal X-ray analysis.

Ru(II)‐PBTNNXN complex bearing functional 2‐(pyridin‐2‐yl)benzo[d]thiazole ligand catalyzed α‐alkylation of nitriles with alcohols

Six tridentate NNN ligand precursors derived from 2‐(pyridin‐2‐yl)benzo[d]thiazole(PBT) with different linkers, PBTNNXN (X = NH, NMe, O, S) (1a–1f), have been successfully prepared. The electronic properties of PBTNNXN ligands are well tunable by differing linkers between PBT skeleton and the pyridine ring, and/or by introducing electron‐donating/withdrawing groups on the pyridine ring (R = OMe or F). The ligand precursors and representative complexes Ru (PBTNNNHN)Cl2(PPh3) (2a), Ru (PBTNNNMeN)Cl2(PPh3) (2b), and Ru (PBTNNSN)Cl2(PPh3) (2f) have been characterized by NMR spectroscopy, high‐resolution mass spectroscopy, and Fourier transform infrared (FT‐IR). The molecular structures of 1f, 2a, and 2f have been determined by X‐ray diffraction study. The results indicate that PBTNNNHN ligand in the complex presented coplanar with two five‐membered chelating rings. It should be noted that 2a featuring a NH group exhibits superior performance compared to those with other linkers (such as NMe, O, or S). A variety of heterocyclic and aromatic nitriles with aromatic and aliphatic alcohols have been explored in α‐alkylation for good to excellent yields. Based on kinetic experiments and mechanistic studies, a proposed mechanism was put forward. Ru‐H species and benzaldehyde, which was oxidized from benzyl alcohol, were detected in the catalytic cycle.

A theoretical study on the electronic structure and phosphorescence properties of two series of iridium(iii) complexes with a four-membered Ir–S–C–S chelating ring

The electronic structure and photophysical properties of two series of iridium(iii) complexes with a four-membered Ir–S–C–S chelating ring have been theoretically studied using the DFT and TDDFT method.

Synthesis, Structure, and Biological Assays of Novel Trifluoromethyldiazepine–Metal Complexes

A new series of CuII, NiII, CoII, and MnIII complexes have been synthesised from the (6Z)-6-(7-trifluoromethyl-1,2,3,4-tetrahydro-5H-1,4-diazepin-5-ylidene)cyclohexa-2,4-dien-1-one (HDZP) ligand. These complexes were characterised by elemental, spectroscopic (IR and UV-vis), and thermal analysis. The crystal structure of Cu-DZP was solved by X-ray diffraction methods. The complex crystallises in the monoclinic P21/c space group, with two molecules per unit cell. The crystal lattice is stabilised by different intra and intermolecular interactions. Hirshfeld surface analysis was employed to obtain additional information about interactions that are responsible for the crystal packing. Quantitative examination of the fingerprint plots indicated the dominant contribution of H⋯H and H⋯X (X=O, F) interactions in the crystal packing. In addition, C–H⋯chelate ring (CR) and C–H⋯π interactions are described in detail and evaluated using DFT calculations. The antibacterial properties and the mechanism of inhibition of the main bacterial resistant mechanism, the biofilm, of the metal complexes and free ligand were investigated. [Mn(DZP)3]·2H2O was the most active complex against the Pseudomonas aeruginosa biofilm formation with an inhibition of 40%. However, none of the complexes inhibit more than 25% of the Gram negative bacteria microbial development. The most meaningful result was the bactericidal effect of [Co(DZP)2(H2O)2]·2H2O against the Gram positive bacteria, Staphylococcus aureus, which inhibits the bacterial development and significantly reduces the biofilm formation at low concentration.

Importance of π-Interactions Involving Chelate Rings in Addition to the Tetrel Bonds in Crystal Engineering: A Combined Experimental and Theoretical Study on a Series of Hemi- and Holodirected Nickel(II)/Lead(II) Complexes

Five heteronuclear nickel(II)/lead(II) complexes with two compartmental reduced Schiff base ligands were prepared and characterized. Their structures were confirmed by single crystal X-ray diffract...

Highly Selective Aluminum(III) Ion Sensing with Luminescent Iridium(III) Complexes Bearing a Distorted 2,2'-Bipyridine-3,3'-diol Moiety Utilizing a Rigidified Seven-Membered Chelate Ring.

To create an ion sensor utilizing a rigidified seven-membered chelate ring, we developed two Ir(III) complexes with 2,2'-bipyridine-3,3'-diol (bpy(OH)2, bpydL) ligands as reaction centers, namely Ir1 ([Ir(ppy)2{bpy(O-)(OH)}], ppy = 2-phenylpyridine) and Ir2 ([Ir(bzq)2{bpy(O-)(OH)}], bzq = benzo[h]quinoline), and evaluated their reactivities toward metal ions by spectrophotometry. When they are reacted with Al3+, these complexes exhibit dramatic enhancements in emission intensity (775-fold for Ir1 and 51.0-fold for Ir2) and distinct orange to green changes in emission color. The reactions of Ir1 and Ir2 with Al3+ were found to barely be affected by nearly all common metal ions. We conclude that these high selectivities arise from the high affinities of the (O,O) atoms in bpydL for hard metal ions and the increased strain of the seven-membered chelate ring due to the coordination of bpydL to the Ir(III) center in each complex, which excludes large metal ions out of the chelate ring.

Activation of the Cyano Group at Imidazole via Copper Stimulated Alcoholysis

Reactions of 4,5-dicyano-1-methylimidazole with CuX2 (X = Cl, Br) in alcohol solvents (ethanol and methanol) resulted in the formation of Cu(II) carboximidate complexes [CuCl2(5- cyano-4-C(OEt)N-1-methylimidazole)(EtOH)] (1), [Cu2(µ-Cl)2Cl2(5-cyano-4-C(OMe)N-1-methylimidazole)2] (2), [Cu2(µ-Br)2Br2(5-cyano-4-C(OMe)N-1-methylimidazole)2] (3), and [Cu2(µ-Br)2Br2(5-cyano-4-C(OEt)N-1-methylimidazole)2] (4). The structures were determined by the X-ray crystallographic method, and further spectroscopic and computational methods were employed to explain the structural features. The solvent contributed to the alcoholysis reaction of the cyano group, as the result of which the ligand coordinated to the metal center in bidentate mode forming a five-membered chelating ring. In 1, the solvent also acts as an additional ligand, which coordinates to the metal center of a monomeric complex. In compounds 2–4, two halogen ligands link the metal atoms forming dihalo-bridged copper dimers. The infrared absorption characteristics were verified by simulation of the infrared spectra at the density functional theory level. In addition, the electronic absorption characteristics were explained by simulation of the UV–Vis spectra using the TD-DFT method. Molecular modelling at the DFT level was performed to study the effects of halogen type and steric hindrance of the alkoxy groups in forming the copper(II) complexes.

MoS2/ZnO-Heterostructures-Based Label-Free, Visible-Light-Excited Photoelectrochemical Sensor for Sensitive and Selective Determination of Synthetic Antioxidant Propyl Gallate

Propyl gallate (PG) as one of the important synthetic antioxidants is widely used in the prevention of oxidative deterioration of oils during processing and storage. Determination of PG has received extensive concern because of its possible toxic effects on human health. Herein, we report a photoelectrochemical (PEC) sensor based on ZnO nanorods and MoS2 flakes with a vertically constructed p-n heterojunction. In this system, the n-type ZnO and p-type MoS2 heterostructures exhibited much better optoelectronic behaviors than their individual materials. Under an open circuit potential (zero potential) and visible light excitation (470 nm), the PEC sensor exhibited extraordinary response for PG determination, as well as excellent anti-inference properties and good reproducibility. The PEC sensor showed a wide linear range from 1.25 × 10-7 to 1.47 × 10-3 mol L-1 with a detection limit as low as 1.2 × 10-8 mol L-1. MoS2/ZnO heterostructure with proper band level between MoS2 and ZnO could make the photogenerated electrons and holes separated more easily, which eventually results in great improvement of sensitivity. On the other hand, formation of a five membered chelating ring structure of Zn(II) with adjacent oxygen atoms of PG played significant roles for selective detection of PG. Moreover, the PEC sensor was successfully used for PG analysis in different samples of edible oils. It demonstrated the ability and reliability of the MoS2/ZnO-based PEC sensor for PG detection in real samples, which is beneficial for food quality monitoring and reducing the risk of overuse of PG in foods.

Thiol-ene synthesis of thioether/carboxyl-functionalized polymers for selective adsorption of silver (I) ions

In this study, a novel adsorbent (TCP) for the selective adsorption of Ag (I) was synthesized by thiol-ene polymerization of dimercaptosuccinic acid and 1,3,5-triallyl-1,3,5-triazine-2,4,6-trione. Element analysis, FT-IR and NMR spectroscopy confirmed that TCP was a functional-group-dense polymer with abundant thioether/carboxyl groups. The results of batch adsorption experiments revealed that the maximum adsorption capacity for Ag (I) by TCP at pH 4 was 5.2 mmol g−1, which was much higher than that at pH 2. Moreover, the adsorption isotherm of Ag (I) on TCP at pH 4 followed the Langmuir model better. However, the isothermal adsorption behavior at pH 2 fitted the Freundlich model well. The kinetic study demonstrated that both chemical adsorption and internal diffusion might be involved in the Ag (I) adsorption process. Furthermore, TCP showed much higher selectivity for Ag (I) in the presence of multiple interfering ions at pH 2 than that at pH 4. However, if the initial concentration of Ag (I) ions was high enough, TCP still exhibited good selectivity for Ag (I) in the presence of Cu (II) over a wide pH range: the selectivity coefficient (KAg/Cu) fluctuated between 40 and 60 in the pH range of 0.5–5. FT-IR spectroscopy and XPS analysis evidenced that the carboxyl and thioether groups in TCP could have synergistic effects on the adsorption of Ag (I), which might form five-membered or six-membered chelated rings, thereby inhibiting the combination of the carboxylic groups with other interfering ions. In addition, TCP showed high adsorption capacity and selectivity for Ag (I) in the treatment of simulated industrial effluent at pH 2.

Synthesis of intramolecularly coordinated heteroleptic diorganotellurides and diorganotelluroxides: Isolation of monomeric diorganotelluroxide [{2,6-(Me2NCH2)2C6H3}2TeO] and diorganohydroxytelluronium chloride [{2,6-(Me2NCH2)2C6H3}2Te(OH)]Cl

A series of heteroleptic diorganotellurides (2-NMe2CH2C6H4)(R)Te, where R = C6H5 (5), 2-MeC6H4 (6), 2,6-MeC6H3 (7) and 2,6-iPrC6H3 (8) was synthesised from N,N-dimethylbenzylamine via the ortho-lithiation route. Reactions of 5–8 with SO2Cl2 followed by alkaline hydrolysis afforded diorganotelluroxides (2-NMe2CH2C6H4)(R)TeO, where R = C6H5 (10), 2-MeC6H4 (11), 2,6-MeC6H3 (12) and 2,6-iPrC6H3 (13) respectively. A similar alkaline hydrolysis of homoleptic diorganotellurides, {2,6-(Me2NCH2)2C6H3}2Te (9), afforded a co-crystal of [{2,6-(Me2NCH2)2C6H3}2TeO] (14a) and disordered [{2,6-(Me2NCH2)2C6H3}2Te(OH)]Cl (14b) or a completely ordered diorganohydroxytelluronium chloride [{2,6-(Me2NCH2)2C6H3}2Te(OH)]Cl (14c). Heteroleptic diorganotellurides 7–8 and telluroxides 10–14a-b and diorganohydroxytelluronium chloride 14c were characterised by single crystal X-ray diffraction studies. In the molecular structures, the N-donor substituent made five membered chelating ring with the tellurium atom via Te⋯N secondary bonding interactions. Diorganotelluroxide 10 existed in dimeric form exhibiting both intramolecular Te⋯N and intermolecular Te⋯O secondary interactions. Due to the strong intramolecular Te⋯N secondary bonding interactions from the three N-donor substituents, diorganotelluroxide 14a was stabilised in the monomeric form. This is, in fact, the only second example of a discrete monomeric diorganotelluroxide. Again, because of the presence of intramolecular Te⋯N secondary bonding interactions, the diorganotelluroxides 10–14a-b and diorganohydroxytelluronium chloride 14c exhibited downfield 125Te NMR chemical shift as compared with the earlier reported oligomeric or polymeric diorganotelluroxides.

Structural Features of Monomeric Octahedral Monooxo d2-Rhenium(V) Complexes [ReO(Ln)2(Lmono)] with Oxygen Atoms of Bidentate Chelate O, N Ligands (Ln): 2. Complexes with Six-Membered Chelate Rings ReNC3O

Structural Features of Monomeric Octahedral Monooxo d2-Rhenium(V) Complexes [ReO(Ln)2(Lmono)] with Oxygen Atoms of Bidentate Chelate O, N Ligands (Ln): 2. Complexes with Six-Membered Chelate Rings ReNC3O

Synthesis of Pd(II) complexes of unsymmetrical, hybrid selenoether and telluroether ligands: Isolation of tellura-palladacycles by fine tuning of intramolecular chalcogen bonding in hybrid telluroether ligands

Two novel unsymmetrical selenoether ligands namely, N,N-dimethyl-2-(o-tolylselanyl)aniline (10) and 2-((2,6-dimethylphenyl)selanyl)-N,N-dimethylaniline (11) were synthesized from N,N-dimethylbenzylamine via the ortho-lithiation route. When ligands 10 and 11 were treated with Pd(COD)Cl2 (COD = 1,5-cyclooctadiene), the reaction afforded novel Pd(II) complexes of the form Pd(2-NMe2CH2C6H4)(R)SeCl2, where R = 2-MeC6H4 (16) and 2,6-MeC6H3 (17) respectively. Similarly, when unsymmetrical telluroether ligands, N,N-dimethyl-2-(phenyltellanyl)aniline (12), N,N-dimethyl-2-(o-tolyltellanyl)aniline (13), 2-((2,6-dimethylphenyl)tellanyl)-N,N-dimethylaniline (14) and 2-((2,6-diisopropylphenyl)tellanyl)-N,N-dimethylaniline (15), which contain one coordinating group with an sp3 N-donor atom, were treated with Pd(COD)Cl2, the palladium telluroether complexes of the form Pd(2-NMe2CH2C6H4)(R)TeCl2, where R = C6H5 (18), 2-MeC6H4 (19), 2,6-MeC6H3 (20) and 2,6-iPrC6H3 (21) respectively were obtained. The selenoether complexes 16 and 17 and telluroether complexes 18, 20 and 21 were characterized by single crystal X-ray diffraction studies. In the asymmetric unit of complex 18, two molecules are present and due to the presence of weak, intermolecular Te⋯Cl interactions, the two molecules exist as symmetrically related dimer. The N-donor substituents, which were involved in intramolecular chalcogen bonding (IChB) with the chalcogen atoms in the free ligand, made six-membered chelating rings in the complexes. Again, when bis(2-phenylazophenyl-C,N′)selenide 22 was treated with Pd(COD)Cl2, it afforded ortho C–H bond activated cyclopalladated complex 24. However, when bis(2-phenylazophenyl-C,N′)telluride 23 was treated with Pd(COD)Cl2, due to strong IChB from two N-donor substituents, the reaction afforded cleaved product, [2-(phenylazo)phenyl-C,N′]tellurenyl chloride, 25. All the metal complexes exhibited significant downfield chemical shifts in 77Se/125Te NMR spectra as compared to the corresponding free ligands. The downfield shifts in the 77Se/125Te NMR signal in the complexes might be attributed to the coordination of the chalcogen atoms to the electropositive Pd(II) center.

Structural Features of Monomeric Octahedral Monooxo d2-Rhenium(V) Complexes [ReO(Ln)2(Lmono)] with Oxygen Atoms of Bidentate Chelate O,N Ligands (Ln): 1. Complexes with Five-Membered Chelate Rings ReNC2O

The structural features of 24 mononuclear octahedral monooxo d2-Re(V) complexes with single charged oxygen atoms of bidentate chelate (O, N) ligands (Ln) of the general formula [ReO(Ln)2(Lmono)] (where Lmono is a monodentate ligand) containing six-membered chelate rings ReNC3O are discussed. The O(Ln) atoms, with three exception, are in the trans positions to the O(oxo) ligands. In the two complexes, the oxygen atoms of the acido-ligand OMe− occupy the trans positions to the oxo ligands, and in the third, it is occupied by the O atom of the neutral H2O ligand. In the case of complexes [ReO(Ln)2(Lmono)] with five-membered chelate cycles ReNC2O, the structures of three complexes with Lmono ligands in the trans positions to oxo ligands are also known: one with Lmono = Cl− and two with Lmono = OMe−.

Regioselective Polymerizations of α-Olefins with an α-Diamine Nickel Catalyst

Polymerizations of linear α-olefins (CnH2n, CH2 = CH―R, R = Cn−2) catalyzed by early transition metals typically afford amorphous polymers with alkyl chains (Cn−2), while chain-straightening polymerizations of α-olefins with nickel-based catalysts produce semicrystalline polyolefins. Polymerizations of various α-olefins were carried out using an α-diamine nickel catalyst with a significantly distorted chelating ring. The influences of temperature, monomer concentration, and chain length of α-olefins on polyolefin microstructure were examined in detail. The α-diamine nickel catalyst realized highly regioselective 2,1-insertion of α-olefins regardless of reaction temperature and monomer concentration. Increased chain length of α-olefins led to the formation of more linear polyolefin. Semicrystalline polyolefins with high melting temperatures (Tm) were made from α-olefins through highly regioselective 2,1-insertion and precise chain-straightening.

Prebiotic Iron Originates the Peptidyl Transfer Origin.

The ribosome is responsible for protein synthesis in all living organisms. It is best known to exist around 3.5–3.7 Ga whereat life on Earth inhabited anoxic environment with abundant soluble irons. The RNAs and proteins are the two biopolymers that constitute the ribosome. However, both proteins and RNAs require metal cations to fold and to function. There are four Mg-microcluster (Mg2+-μc) structures conserved in core of large subunit, and the 23S ribosomal RNA (rRNA) was shown to catalyze electron transfer in an anoxic environment in the presence of Fe2+. The Mg2+-μc features two idiosyncratic Mg2+ ions that are chelated and bridged by a common phosphate group and along with that, the adjacent residues of RNA backbone together forming ten-membered chelation ring(s). Here, we utilized four rRNA fragments of the large subunit 23S rRNA of Haloarcula marismortui, that includes the residues that form the four Mg2+-μc’s. These four rRNA fragments are shown competent to assemble with Mg2+. Our results show that when these rRNA fragments fold or assembly in the presence of Fe2+ under anoxic conditions, each Fe2+-microcluster can catalyze electron transfer. We propose that Fe2+-microclusters of the ribosome, which use Fe2+ as a cofactor to regulate electron transfer, are pivotal and primordial and may be an origin in evolution of the ribosome.

Chiral iridium(iii) complexes with four-membered Ir-S-P-S chelating rings for high-performance circularly polarized OLEDs.

Two series of chiral cyclometalated iridium(iii) complexes based on sulfur atom containing enantiopure BINOL derivatives were rapidly synthesized, which are endowed with varied chiroptical properties. Moreover, the circularly polarized OLEDs using enantiomers show a maximum luminance of above 40 000 cd m-2 and an external quantum efficiency of 23.6% with low efficiency roll-off as well as obvious CPEL properties.

Rapid room temperature synthesis of red iridium(iii) complexes containing a four-membered Ir-S-C-S chelating ring for highly efficient OLEDs with EQE over 30.

Three red cyclometalated iridium(iii) complexes (4tfmpq)2Ir(dipdtc), (4tfmpq)2Ir(dpdtc) and (4tfmpq)2Ir(Czdtc) (4tfmpq = 4-(4-(trifluoromethyl)phenyl)quinazoline, dipdtc = N,N-diisopropyl dithiocarbamate, dpdtc = N,N-diphenyl dithiocarbamate, and Czdtc = N-carbazolyl dithiocarbamate) containing the unique four-membered Ir-S-C-S backbone ring were synthesized in five minutes at room temperature with good yields, and the Gibbs free energy calculation results indicate that all reactions are exothermic and thermodynamically favorable processes. The emission colors (λ peak = 641-611 nm), photoluminescence quantum efficiencies (Φ P = 58.3-93.0%) and bipolar properties can be effectively regulated by introducing different electron-donating substituents into the dithiocarbamate ancillary ligands. Employing these emitters, organic light emitting diodes (OLEDs) with double emissive layers exhibit excellent performances with a maximum brightness over 60 000 cd m-2, a maximum current efficiency of 40.68 cd A-1, a maximum external quantum efficiency (EQEmax) of 30.54%, and an EQE of 26.79% at the practical luminance of 1000 cd m-2. These results demonstrate that Ir(iii) complexes with sulfur-containing ligands can be rapidly synthesized at room temperature, which is key to the production of metal luminescent materials for large-scale application in highly efficient OLEDs.

Chelate rings of different sizes with non-innocent ligands

Redox-active unsaturated chelate ligands can be realised with different ring sizes of the resulting metallacycles. An overview is presented, starting from an exposition of non-innocent behaviour and chelate effects. A systematic approach is used to describe the most familiar situation, the metal complexes of 1,4-hetero-1,3-dienes in established forms (e.g. o-quinone, α-dithiolene, and α-diimine ligands) and with less common combinations of O, S, and N heteroatoms. The different steric and electronic conditions in six-membered chelate ring systems derived from the β-diketonate structure will be discussed with examples of substituted and π extended ligands, including 9-oxidophenalenyl, formazanate, and anions derived from indigo or 9,10-anthraquinone. Four-membered chelate rings existing in at least two ligand-based oxidation states are available through steric and electronic stabilisation in amidinate or triazenide complexes. Three-membered and seven-membered chelate ring situations are discussed briefly as further alternatives.

Synthesis and characterization of chromium complexes 2-Me4CpC6H4CH2(R)NHCrCl2 and their catalytic properties in ethylene homo- and co-polymerization.

A series of new half-sandwich secondary amine-coordinated dichlorochromium complexes chelated by 2-(tetramethylcyclopentadienyl)benzylamine ligands, 2-Me4CpC6H4CH2(R)NHCrCl2 [R = iPr (1), Cy (2), Ph (3), 4-MePh (4), 2,6-Me2Ph (5), 2,6-Et2Ph (6)], have been synthesized from the reactions of CrCl3(THF)3 with the dilithium salts of the corresponding ligands in THF, followed by the addition of 1/2 eq. of H2O to the reaction mixtures. The isolated yields of the chromium complexes were found to increase with the increase in the amount of H2O introduced and reach the highest values (66-76%) when 1/2 eq. of H2O is added. Attempts to isolate the 2-(tetramethylcyclopentadienyl)benzylamidochromium complexes, 2-Me4CpC6H4CH2(R)NCrCl, were not successful. The new dichlorochromium complexes were characterized by IR, 1H NMR, EPR, and UV/Vis spectroscopy and elemental analyses, and the molecular structures of complexes 1, 5 and 6 were determined by X-ray crystallography. The X-ray crystallographic analysis reveals that these chromium complexes possess a three-legged piano-stool geometry with the amine N atom in a mitered six-membered chelating ring and the two chloride atoms as the legs. Upon activation with AlR3 and Ph3CB(C6F5)4, complexes 1-6 exhibit reasonable catalytic activity for ethylene polymerization and copolymerization with 1-hexene, producing polyethylenes with moderate to high molecular weights and poly(ethylene-co-1-hexene)s with moderate comonomer incorporation which are typical linear low-density polyethylenes (LLDPE). Complex 4 was found to show higher catalytic activity for ethylene homo- and co-polymerization than other complexes under similar conditions, while complex 3 produced poly(ethylene-co-1-hexene)s with the highest comonomer incorporation.