Amine Arm Research Articles

An efficient method for the construction of phenolic compounds incorporating pendant amine arms

A new series of tripodal and linear phenolic-amines as well as 1,4,7,10-tetrakis(2,4-dialky-1-hydroxy-6-benzyl)-1,4,7,10-tetraazacyclododecane were efficiently synthesized in excellent to reasonably moderate yields. The one-pot reactions were performed in methanol solution through the commercially available 2,4-disubstited-phenols and dialkyldiamines or the macrocycles 1,4,7,10-tetraazacyclododecane (cyclen) and 1,4,8,11-tetraazacyclotetradecane (cyclam) in the presence of aqueous 37 % HCHO and Et3N. All the isolated compounds were spectroscopically characterized and, in some cases, structurally determined by single crystal- X-ray crystallography.

Synthesis, Solvatochromism and Fluorescence Quenching Studies of Naphthalene Diimide Dye by Nano graphene oxide.

A naphthalene diimide dye with two side amine arm was prepared. Uv-Vis and fluorescence spectroscopic techniques are used for their photophysical and solvatochromic characteristics in different solvents. The Lippert-Mataga plot for naphthalene diimide demonstrated a negative linear dependence by increasing polarity. Results showed naphthalene diimide is more polar in the ground than in the excited state. A quenching study was conducted for interacting the naphthalene diimide as a fluorophore and graphene oxide as a quencher. Fluorescence quenching-based platforms in nanoscale have been used in sensing systems. Raman, FTIR, Uv-Vis and fluorescence spectroscopic techniques were used to study the quenching mechanism. The results indicated that graphene plays an effective quencher against the naphthalene diimide, with a quenching efficiency 91%. The Stern-Volmer analysis results show a mix of static and dynamic quenching mechanisms. The binding constant of the quencher-fluorophore and the number of binding sites have been reported. Thermodynamic parameters of their interaction were evaluated. The negative values of the Gibbs free energy confirm that the complexation process is spontaneous. Meanwhile, the positive entropy value confirms that the favorable pathway process.

Titanium ONN-(phenolate) Alkoxide Complexes: Unique Reaction Kinetics for Ring-Opening Polymerization of Cyclic Esters.

The synthesis, characterization, and polymerization kinetics of four new titanium ONN-(phenolate) alkoxide catalysts were studied. Each catalyst is fluxional at room temperature, suggesting the ligand amine arm may be labile, but adopts a fac geometry in solution at low temperature (223 K) and in the solid state. All catalysts are active for the ring-opening polymerization of both ε-caprolactone (CL) and rac-lactide (LA). GPC analysis indicates that the well-known coordination-insertion mechanism is being followed. However, whereas the typical first-order dependence on monomer concentration is observed in CL, an unexpected zeroth-order dependence is observed with LA. This suggests that, in the case of LA, catalyst saturation occurs and a Michaelis-Menten model can be used to explain the kinetics. An initial mechanism is discussed within this model that proposes CL polymerization proceeds by a 7-coordinate intermediate, whereas LA polymerization adopts a 6-coordinate intermediate, facilitated by the ligand amine arm. Attempts to isolate catalyst-monomer intermediates are ongoing.

Double-Carrousel Mechanism for Mn-Catalyzed Dehydrogenative Amide Synthesis from Alcohols and Amines

We study with density functional theory calculations the mechanism of the original example of a base-metal-catalyzed synthesis of amides from alcohols and amines. A preliminary proposal of the mechanism of this reaction was experimentally reported by Milstein and co-workers. Instead of the proposed reaction mechanism with a hemilabile pincer amine arm, our DFT calculations describe a facile protocol, where the catalyst only produces aldehydes from alcohols. Once formaldehyde is formed from methanol, it reacts with the amine to form a second alcohol. This new alcohol undergoes the same procedure as methanol and creates the desired amide through a double-carrousel mechanism. The rate-determining step in the catalytic aldehyde synthesis corresponds to the H2 formation. However, in the nonmetal-catalyzed part of the mechanism, the interaction of formaldehyde with the amine is also quite kinetically demanding.

Porous silicon-based fluorescent nanoprobe for the detection of anthrax biomarker and its practical sensing applications

Anthrax is an infection caused by bacterium Bacillus anthracis (B. anthracis), and is an old disease that poses a new threat to humans as a biological weapon. Gram-staining and polymerase chain reaction (PCR)-based assays of specimens are standard diagnostic tools for anthrax, but it is time-consuming and limited for the on-site application. In this study, we disclose a porous silicon-based nanoprobe for the detection of dipicolinic acid (DPA), which is a crucial biomarker of the anthrax spore, and its practical sensing applications. The surface of the porous silicon nanoparticles (pSiNPs) was functionalized with multiple amine arms, via a ring-opening click amination and was grafted with terbium ion (Tb3+). A double antenna effect from DPA and pSiNPs to Tb3+ was appeared dramatically and was accompanied by a significant fluorescence enhancement that had high selectivity, sensitivity, and fast response time. The resulting pSiNPs-Tb formulation was used to detect DPA in real water samples and the stimulated Bacillus subtilis (B. subtilis) spores. Besides, the DPA sensing application on the cellulose-based paper was successfully demonstrated as a real-time on-site sensing kit. We believe the demonstrations in this study could encourage further applications throughout a wide variety of fields.

Synthesis and catalytic activity of cationic dinuclear palladium (II) complexes supported by thioether ligands containing two di-(2-picolyl) amine arms

The design, synthesis and characterization of a series of dithioether ligands featuring two di-(2-picolyl)amine arms (2a–2d) and their corresponding cationic dinuclear palladium (II) complexes (3a–d) are reported. Crystal structures of ligand 2b and complexes 3b and 3d were determined by X-ray diffraction studies. The molecular structures of 3b and 3d display each of the two di-(2-picolyl)amine fragments coordinated to one palladium(II) atom in a (κ3-N,N,N) tridentate fashion and with the cationic metal centers displaying square-planar geometries. Weak interactions between the metal centers and the thioether fragments are observed. All bimetallic complexes 3a–d were tested as catalytic precursors in the Suzuki couplings of different o- or p-substituted iodo- or bromoaryls with boronic acids. The overall catalytic results indicate that complex 3b is the best precursor of the series demonstrating even more efficient performance compared to commercial palladium sources such as Pd(OAc)2 and the Nájera Catalysts.

Ligand Identity-Induced Generation of Enhanced Oxidative Hydrogen Atom Transfer Reactivity for a CuII2(O2•-) Complex Driven by Formation of a CuII2(-OOH) Compound with a Strong O-H Bond.

A superoxide-bridged dicopper(II) complex, [CuII2(XYLO)(O2•-)]2+ (1) (XYLO = binucleating m-xylyl derivative with a bridging phenolate ligand donor and two bis(2-{2-pyridyl}ethyl)amine arms), was generated from chemical oxidation of the peroxide-bridged dicopper(II) complex [CuII2(XYLO)(O22-)]+ (2), using ferrocenium (Fc+) derivatives, in 2-methyltetrahydrofuran (MeTHF) at -125 °C. Using Me10Fc+, a 1 ⇆ 2 equilibrium was established, allowing for calculation of the reduction potential of 1 as -0.525 ± 0.01 V vs Fc+/0. Addition of 1 equiv of strong acid to 2 afforded the hydroperoxide-bridged dicopper(II) species [CuII2(XYLO)(OOH)]2+ (3). An acid-base equilibrium between 3 and 2 was achieved through spectral titrations using a derivatized phosphazene base. The pKa of 3 was thus determined to be 24 ± 0.6 in MeTHF at -125 °C. Using a thermodynamic square scheme and the Bordwell relationship, the hydroperoxo complex (3) O-H bond dissociation free energy (BDFE) was calculated as 81.8 ± 1.5 (BDE = 86.8) kcal/mol. The observed oxidizing capability of [CuII2(XYLO)(O2•-)]2+ (1), as demonstrated in H atom abstraction reactions with certain phenolic ArO-H and hydrocarbon C-H substrates, provides direct support for this experimentally determined O-H BDFE. A kinetic study reveals a very fast reaction of TEMPO-H with 1 in MeTHF, with k (-100 °C) = 5.6 M-1 s-1. Density functional theory (DFT) calculations reveal how the structure of 1 may minimize stabilization of the superoxide moiety, resulting in its enhanced reactivity. The thermodynamic insights obtained herein highlight the importance of the interplay between ligand design and the generation and properties of copper (or other metal ion) bound O2-derived reduced species, such as pKa, reduction potential, and BDFE; these may be relevant to the capabilities (i.e., oxidizing power) of reactive oxygen intermediates in metalloenzyme chemical system mediated oxidative processes.

Synthesis and characterization of copper complexes with a series of tripodal amine ligands

A series of copper complexes with tripodal amine ligands was synthesized and structurally characterized. The copper(I) complexes of this series were investigated in regard to their reactivity towards dioxygen using stopped-flow techniques. For most complexes no “dioxygen adduct” complexes as intermediates could be detected. During the course of our investigations it was observed that the copper(II) complex with the ligand 3,3′-dimethylaminopropyl-(2-methylenpyridyl)-amine (Me4-p33) crystallized as a dinuclear complex, [Cu(Me4-p3H3)OH]2(ClO4)4, that could be structurally characterized. Interestingly, it turned out that in crystalline form the two bridging hydroxide ions were intact while two of the amine arms of the two ligands were protonated. DFT calculations were performed to get a better understanding of the behavior of this complex system in solution. Further protonation of two more amine ligand arms in solution was possible, still keeping the bridging hydroxide ions in place in the solid state. A related copper(II) complex system could be crystallized that contained a coordinated carbonate anion together with a protonated amine arm.

A Route toward (Aminomethyl)cyclopentadienide Ligands and Their Group 4 Metal Complexes

A new method is described, by which N‐functionalized cyclopentadienide ligands are synthesized via the nucleophilic substitution of sodium cyclopentadienide onto Katritzky's (benzotriazolyl) compounds. This route enables the introduction of bulky and basic amines, separated from the cyclopentadienyl ring by a methylene spacer. The method thus represents a valuable alternative to the general fulvene route. The resulting ligands have been coordinated to titanium and zirconium, producing a series of discrete metallocene derivatives with a pendant amine arm. These complexes are extremely sensitive towards moisture, but they can easily be converted into benchtop‐stable ammonium chloride derivatives. The ligands and their complexes have been fully characterized by NMR and IR spectroscopy, elemental analysis and/or high resolution ESI‐MS. The solid‐state structures of ten complexes have been established by single‐crystal X‐ray diffraction analysis.

Template Synthesis of an Iron(II) Complex with a New Tridentate Macrocyclic Ligand Containing an Additional Pendant Arm

The reaction of acetone with tris(2‐aminoethyl)amine (tren) in the presence of iron(II) chloride led to formation of a new tridentate macrocyclic imine ligand with a pendant amine arm, 2‐[(E)‐8,10,10‐trimethyl‐1,2,3,4,5,6,9,10‐octahydro‐1,4,7‐triazecin‐4‐yl]‐ethylamine (L). The complex [Fe(L)Cl2] could be structurally characterized. The iron(II) complex reacts with dioxygen, however in a sluggish way and no intermediates could be spectroscopically detected. Efforts to isolate the imine ligand or to reduce it to the corresponding amine so far failed. If iron(II) triflate was used instead of iron(II) chloride in the synthesis only the iron(II)‐tren complex, [Fe(tren)CH3CN](OTf)2, was obtained.

Macrocyclic mononuclear Ni(II) and macroacyclic tetranuclear Cu(II) complexes: Dimerization of binuclear Cu(II) complexes with help of perchlorate anions

New macroacyclic Cu(II) and macrocyclic Ni(II) complexes, [Cu2L1(ClO4)2]2 (1) and [NiClL2]ClO4 (2), respectively, have been synthesized (H2L1 and H2L2 = Schiff bases). The Schiff bases H2L1and H2L2 were prepared by the reaction of 2-[3-(formyl phenoxy)-2-hydroxy propoxy]benzaldehyde and propanol amine and propylene diamine respectively. Single crystal X-ray structure analysis of 1 showed that the complex is tetranuclear, with two binuclear Cu(II) units connected through coordination of deprotonated OH groups of one of the propanol amine arms of each unit to the other one. In the structure of each binuclear fragment, none of the donor atoms of the potentially heptadentate (N2O5) ligand remained uncoordinated, and one oxygen atom is bridged between the two Cu(II) ions. In addition, the crystal structure analysis shows that two perchlorate ions are coordinated to the Cu(II) metal centers. DFT studies show that the coordinated perchlorate anions have the key role in the dimerization of the binuclear Cu(II) species that give rise to complex 1. X-ray structure analysis of 2 shows that it is a macrocyclic complex where all nitrogen and oxygen atoms of the potentially pentadentate (N2O3) ligand are coordinated to the Ni(II) central ion. In addition to the macrocyclic Schiff base ligand, a chloride ion is also coordinated to the Ni(II) ion.

Side Arm Twist on Zn-Catalyzed Hydrosilylative Reduction of CO2 to Formate and Methanol Equivalents with High Selectivity and Activity

Reductive hydrosilylation of CO2 by catalysts based on environmentally benign metals such as zinc still presents an unmet challenge in terms of catalyst selectivity and activity. Here we show that tetra-coordinated neutral zinc siloxide complexes supported by the β-diketiminato ligand bearing a pendant amine arm exhibit unprecedentedly high catalytic activity toward the selective reduction of CO2 by a hydrosilane to silyl formate. More significantly, this zinc catalyst system can also effectively catalyze the subsequent reduction of silyl formate into methoxysilane in quantitative yield. To understand the mechanism of the CO2 hydrosilylation and the influence of the side arm, a series of catalytic active species (or intermediates), zinc hydrides, and formates, has been synthesized and structurally characterized; the relevant stoichiometric reactions and kinetic study were performed. DFT calculations were also carried out to determine the reaction profiles for the CO2 hydrosilylation and to explain the rel...

Push–Pull‐Type Polychlorotriphenylmethyl Radicals: New Two‐Photon Absorbers and Dyes for Generation of Photo‐Charges

Tri(4-iodo-2,3,5,6-tetrachlorophenyl)methane (2) is reported as a general building block for the synthesis of various π-conjugated polychlorotriphenylmethyl (PTM) radicals. Three push-pull-type triphenylamine-substituted PTM radicals with different substitution patterns were prepared and all exhibited intense inter-valence charge-transfer bands and large two-photon absorption (TPA) cross sections. Moreover, increase of solvent polarity also resulted in improved TPA response. The charge-transfer character of the relevant excited states provoked the efficient photo-generation of charges, anions in the PTM and cations in the amine arms, driven by the amphoteric redox character and the small coupling between donor and acceptor.

From imine to amine: an unexpected left turn. Cis-β iron(ii) PNNP' precatalysts for the asymmetric transfer hydrogenation of acetophenone.

A novel PNN ligand bearing an orthophenylene group and a primary amine was synthesized with the aid of a palladium-catalyzed amination and reacted with phosphonium dimers [-PR2CH2CH(OH)-]2[Br]2 R = Et, iPr, Cy, Ph, xylyl, and o-Tol, and [Fe(OH2)6]2+ to produce a new series of cis-β iron(ii) PNNP' precatalysts cis-β-[Fe(Br)(CO)(PNNP')]BPh4 as a pair of diastereomers. The more stable orthophenylene amido group was chosen to imitate and replace the enamido moiety of a highly active iron precatalyst for the asymmetric transfer hydrogenation (ATH) of ketones in an attempt to prevent its deactivation caused by reduction of the enamido group. This objective was partially achieved using the complex with a PEt2 group which catalyzed the transfer hydrogenation in isopropanol of 150 000 equivalents of acetophenone to racemic 1-phenylethanol. With a low acetophenone to catalyst ratio of 500 to 1, the catalytic activity was moderate and the enantiomeric excess (ee) of the product 1-phenylethanol ranged surprisingly from 94% (R) to 95% (S) depending on the nature of PR2 and whether the precatalyst contained an imine or amine donor. The amine precatalyst with a PEt2-group produced a more stable hydride species when activated, allowing the reaction mixture to be heated to 75 °C to obtain a TON of 8821 for acetophenone while retaining the high ee of 95% (S). The activation pathway in basic isopropanol (iPrOH) was studied for three precatalysts to elucidate that the cis-β precatalysts rearrange to form trans hydride complexes. The study suggests that the enantioselectivity of these complexes is determined by from which side of the PNNP' plane the hydride transfer occurs.

Enzyme-Inspired Axially Chiral Pyridoxamines Armed with a Cooperative Lateral Amine Chain for Enantioselective Biomimetic Transamination.

Enzymatic transamination is catalyzed by pyridoxal/pyridoxamine, and it involves remarkable cooperative catalysis of a Lys residue in the transaminase. Inspired by transaminases, we developed a class of axially chiral pyridoxamines 11 bearing a lateral amine arm. The pyridoxamines exhibited high catalytic activity and excellent enantioselectivity in asymmetric transamination of α-keto acids, to give various α-amino acids in 67-99% yields with 83-94% ee's. The lateral amine arm likely participates in cooperative catalysis as the Lys residue does in biological transamination and has an important impact on the transamination in terms of activity and enantioselectivity.

Antimicrobial photodynamic inactivation with decacationic functionalized fullerenes: Oxygen-independent photokilling in presence of azide and new mechanistic insights

Functionalized fullerenes are gaining wide interest for mediating photodynamic therapy (PDT) of diseases such as cancers and infections. We recently reported the synthesis of two new decacationic fullerene monoadducts: C60[>M(C3N6+C3)2]–(I−)10(LC14) and its derivative with a light-harvesting antenna conjugated as a C60[>CPAF–(MN6+C3)2]–(I−)10 nanostructure (LC15). We studied the ability of these compounds to mediate PDT of human cancer cells in vitro when excited by UVA light or by white light. Here we report the synthesis of a new fullerene derivative C60[>M(C3N6+C3)2][>M(C3N6C3)2]–(I−)10 (LC16 derived from LC14), as a malonate bisadduct containing a covalently bound decatertiary amine arm. We investigated the relative abilities of the three compounds to generate singlet oxygen (1O2), hydroxyl radicals (HO·), and hydrogen peroxide (H2O2) after excitation by UVA or by white light. We used three different classes of pathogenic microbial cells (Gram-positive bacterium, methicillin-resistant Staphylococcus aureus (MRSA), Gram-negative bacterium Escherichia coli, and fungal yeast Candida albicans). LC15 was the most powerful broad spectrum antimicrobial fullerenyl photosensitizer (FPS) followed by LC16, and LC14 was least powerful. Killing depended on both fullerene monoadduct concentration and light fluence. UVA was five times more effective than white light for killing, but not for generation of ROS and relative absorption was greater in white spectral region. Bacterial killing was not much inhibited by addition of azide anions and in some cases was potentiated. In the absence of oxygen, microbial photokilling was highly potentiated (up to 5 logs) by the addition of azide anions. We conclude that molecular functional addends that encourage a type I electron-transfer mechanism increase the ability of photoactivated fullerene monoadducts to kill microbial cells. Oxygen-independent photokilling is possible with fullerene monoadducts in the presence of azide anions, probably mediated by azidyl radicals. UVA excitation may kill bacteria partly by an electron-transfer mechanism directly into bacteria as well as by ROS.

Rational Design of Rhodium Complexes Featuring κ4‐N,N,N,N‐ and κ5‐N,N,N,P,P‐Bis(imino)pyridine Ligands

AbstractThe addition of aminoalkyl‐substituted 2,6‐bis(imino)pyridine (or pyridine diimine, PDI) ligands to [(COD)RhCl]2 (COD = 1,5‐cyclooctadiene) resulted in the formation of rhodium monochloride complexes with the general formula (NPDI)RhCl (NPDI = iPr2NEtPDI or Me2NPrPDI). The investigation of (iPr2NEtPDI)RhCl and (Me2NPrPDI)RhCl by single‐crystal X‐ray diffraction verified the absence of amine arm coordination and a pseudo square‐planar geometry about rhodium. Replacement of the chloride ligand with an outer‐sphere anion was achieved by adding AgBF4 directly to (iPr2NEtPDI)RhCl to form [(iPr2NEtPDI)Rh][BF4]. Alternatively, this complex was prepared by chelate addition following the salt metathesis reaction between AgBF4 and [(COD)RhCl]2. Using the latter method, both [(NPDI)Rh][BF4] complexes were isolated and found to exhibit κ4‐N,N,N,N‐PDI coordination regardless of arm length or steric bulk. In contrast, the metallation of PPDI chelates featuring alkylphosphane imine substituents (PPDI = Ph2PEtPDI or Ph2PPrPDI) resulted in the formation of cationic complexes featuring κ5‐N,N,N,P,P‐PDI coordination in all instances, [(PPDI)Rh][X] (X = Cl, BF4). Adjusting the metallation stoichiometry allowed the preparation of [(Ph2PPrPDI)Rh][(COD)RhCl2], as validated by multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction.

Toward the Synthesis of Indenyl Molybdenum Compound [(η3-Ind)(η5-Cp)Mo(CO)2]: Modified Compounds and Structure of a Previously Unrecognized Intermediate

The mechanism of synthesis of [(η3-Ind′)(η5-Cp)Mo(CO)2] was studied on methyl-substituted derivatives (Ind′ = 2-MeC9H6; 4,7-Me2C9H5). It was observed that the initial step involving reaction with HCl gives dimeric chloride species [{(η5-Ind′)Mo(CO)2(μ-Cl)}2]. This outcome differs from the structure suggested in the literature. Furthermore, it was demonstrated by various examples that compounds of the formula [{(η5-Ind′)Mo(CO)2(μ-Cl)}2] are convenient starting materials giving [(η3-Ind′)(η5-Cp′)Mo(CO)2] through the reaction with appropriate cyclopentadienides. The variability of this method was demonstrated on several examples including weakly donating Cp ligands bearing strong electron-withdrawing functional groups [C5H4COOMe, (1,2-MeOCO)2C5H3, and 1,2-(tBuNHCO)2C5H3] as well as Cp ligands bearing a pendant amine arm (C5H4CH2CH2NMe2). Similar η3-indenyl complexes are formed when using other univalent six-electron ligands such as carbaborane (9-Me2S-7,8-nido-C2B9H10) or scorpionate (Tp, Tp*). The attempts to synthesize [(η3-Ind)(η5-Cp)Mo(CO)2] from [(η3-C3H5)(η5-Cp)Mo(CO)2] have failed because the initial reaction with HCl does not give the expected [{(η5-Cp)Mo(CO)2(μ-Cl)}2] but trivial [(η5-Cp)Mo(CO)3Cl].

Synthesis and Characterization of Positively Charged Pentacationic [60]Fullerene Monoadducts for Antimicrobial Photodynamic Inactivation

We designed and synthesized two analogous pentacationic [60]fullerenyl monoadducts, C60(>ME1N6+C3) (1) and C60(>ME3N6+C3) (2), with variation of the methoxyethyleneglycol length. Each of these derivatives bears a well-defined number of cationic charges aimed to enhance and control their ability to target pathogenic Gram-positive and Gram-negative bacterial cells for allowing photodynamic inactivation. The synthesis was achieved by the use of a common synthon of pentacationic N,N′,N,N,N,N-hexapropyl-hexa(aminoethyl)amine arm (C3N6+) having six attached propyl groups, instead of methyl or ethyl groups, to provide a well-balanced hydrophobicity–hydrophilicity character to pentacationic precursor intermediates and better compatibility with the highly hydrophobic C60 cage moiety. We demonstrated two plausible synthetic routes for the preparation of 1 and 2 with the product characterization via various spectroscopic methods.

Zinc complexes supported by claw-type aminophenolate ligands: synthesis, characterization and catalysis in the ring-opening polymerization of rac-lactide

A series of zinc silylamido complexes bearing claw-type multidentate aminophenolate ligands, [LZnN(SiMe(3))(2)] (L = -OAr(1)-CH(2)N[(CH(2))(n)NR(2)]CH(2)Ar(2), n = 2 or 3; R = Me or Et (1a-3a, 5a, 7a and 8a); L = -OC(6)H(2)-4,6-(t)Bu(2)-2-CH(2)N[(CH(2))(2)OMe](2) (9a)), have been synthesized via the reaction of Zn[N(SiMe(3))(2)](2) and 1 equiv. of corresponding aminophenol. The reaction of Zn[N(SiMe(3))(2)](2) with the proligand L(6)H (2-{N-(2-methoxybenzyl)-N-[3-(N',N'-dimethylamino)propyl]aminomethyl}-4-methyl-6-tritylphenol) resulted in the formation of bisphenolate zinc complex 6 regardless of the stoichiometric ratio of the two starting materials. Complex 4b with an initiating group of 3-tert-butyl-2-methoxy-5- methylbenzyloxy was obtained and further studied via the X-ray diffraction method to be monomeric. Zinc ethyl complex 2c was also prepared from the reaction of ZnEt(2) and 1 equiv. of proligand L(2)H as the representative complex with an alkyl initiating group. All zinc silylamido complexes efficiently initiated the ring-opening polymerization of rac-lactide in the presence or absence of isopropanol at ambient temperature. The steric and electronic characteristics of the ancillary ligands significantly influenced the polymerization performance of the corresponding zinc complexes. The introduction of bulky ortho- substituents on the phenoxy moiety resulted in an apparent decrease of catalytic activity while a slightly enhanced isotactic selectivity. Meanwhile, the elongation of the pendant amine arm to three-carbon-atom linkage led to significant decline of the catalytic activity in the absence of isopropanol. The zinc ethyl complex 2c was not such an efficient initiator as the silylamido ones, but the alkoxy complex 4b gave an obviously faster and better controlled polymerization when compared to the zinc silylamido complexes.