Wan-Jung Chuang

Characterization of A New Copper(I)-Nitrito Complex That Evolves Nitric Oxide

The complexes [Cu(kappa(2)-Ph(2)PC(6)H(4)(o-OMe))(2)(CH(3)CN)](BF(4)) (1) and [CuCl(Ph(2)PC(6)H(4)(o-OMe))(2)] (2) have been prepared by treating [Cu(CH(3)CN)(4)](BF(4)) or CuCl with two equivalents o-(diphenylphosphino)anisole (Ph(2)PC(6)H(4)(o-OMe)) at room temperature, respectively. The reaction of 1 and (PPN)(NO(2)) in acetonitrile solution affords a neutral compound [Cu(Ph(2)PC(6)H(4)(o-OMe))(2)(ONO)] (3). In contrast to the synthesis of 3, mixing NaNO(2) and 1 in MeOH yielded a unique dicopper(I) cationic species, [((Ph(2)PC(6)H(4)(o-OMe))(2)Cu)(2)(mu-NO(2))](+) (4) after ether/CH(2)Cl(2) crystallization. The molecular structures of 1-4 have been determined by an X-ray diffraction study. The copper(I)-nitrito adduct 3 containing phosphine-ether ligands forms nitric oxide gas from the reaction with acetic acid, suggesting the first example and model compound in the asymmetric O-bound copper(I) nitrite intermediate microenvironment of copper nitrite reductases (Cu-NIRs).

Synthesis of Sodium Complexes Supported with NNO-Tridentate Schiff Base Ligands and Their Applications in the Ring-Opening Polymerization of l-Lactide

A series of sodium complexes bearing NNO-tridentate Schiff base ligands with an N-pendant arm were synthesized and used as catalysts for the ring-opening polymerization of L-lactide (L-LA). Electronic effects of ancillary ligands coordinated by sodium complexes substantially influence the catalysis, and ligands with electron-donating groups increase the catalytic activity of the sodium complexes for catalyzing L-LA polymerization. In particular, a sodium complex bearing a 4-methoxy group has the highest activity with conversion up to 95% within 30 s at 0 °C and a low polydispersity index of 1.13, whereas the 4-bromo group showed the poorest performance with regard to the catalytic rate of L-LA polymerization in the presence of benzyl alcohol (BnOH). (1)H NMR pulsed-gradient spin-echo diffusion experiments and single-crystal X-ray analyses showed that sodium complexes [L(H)Na(THF)]2 and [L(4-Cl)Na(THF)]2 were dinuclear species in both solution and the solid state. The kinetic results indicated a first-order dependence on each of [[L(4-Cl)Na]2], [l-LA], and [BnOH].

Copper(I) nitro complex with an anionic [HB(3,5-Me2Pz)3]− ligand: a synthetic model for the copper nitrite reductase active site.

The new copper(I) nitro complex [(Ph(3)P)(2)N][Cu(HB(3,5-Me(2)Pz)(3))(NO(2))] (2), containing the anionic hydrotris(3,5-dimethylpyrazolyl)borate ligand, was synthesized, and its structural features were probed using X-ray crystallography. Complex 2 was found to cocrystallize with a water molecule, and X-ray crystallographic analysis showed that the resulting molecule had the structure [(Ph(3)P)(2)N][Cu(HB(3,5-Me(2)Pz)(3))(NO(2))]·H(2)O (3), containing a water hydrogen bonded to an oxygen of the nitrite moiety. This complex represents the first example in the solid state of an analogue of the nitrous acid intermediate (CuNO(2)H). A comparison of the nitrite reduction reactivity of the electron-rich ligand containing the CuNO(2) complex 2 with that of the known neutral ligand containing the CuNO(2) complex [Cu(HC(3,5-Me(2)Pz)(3))(NO(2))] (1) shows that reactivity is significantly influenced by the electron density around the copper and nitrite centers. The detailed mechanisms of nitrite reduction reactions of 1 and 2 with acetic acid were explored by using density functional theory calculations. Overall, the results of this effort show that synthetic models, based on neutral HC(3,5-Me(2)Pz)(3) and anionic [HB(3,5-Me(2)Pz)(3)](-) ligands, mimic the electronic influence of (His)(3) ligands in the environment of the type II copper center of copper nitrite reductases (Cu-NIRs).

The ring-opening polymerization of ε-caprolactone and L-lactide using aluminum complexes bearing benzothiazole ligands as catalysts

A series of aluminum complexes bearing benzothiazole ligands was synthesized and the ring-opening polymerization of e-caprolactone (CL) and L-lactide (LA) using these aluminum complexes as catalysts was studied. The polymerization results revealed that the electron withdrawing groups increased the polymerization rate of the CL and LA polymerization. Steric bulky groups increased the polymerization rate of the CL polymerization but reduced the rate of the LA polymerization. The results also revealed that PLA-gradual-PCL that included PLA-(random-PLA-PCL)-PCL was synthesized by a one-pot synthesis, although the rate of the CL polymerization was higher than that of the LA polymerization. In addition, the results demonstrated that the catalytic activity of the Al complexes bearing benzothiazole ligands was higher than that of other Al complexes bearing heterocyclic amine ligands.

Anion Reduction Dominated Cathodic Limit of Metal-Free Ionic Liquid: Experimental and Theoretical Proofs

The cathodic limit of the electrochemical window in the second-generation ionic liquids (composed of air- and water-stable metal-free cations and anions) is traditionally believed to be determined by the reduction of the cation. More and more exceptions, however, were found in various ionic liquids. In this study, the cathodic limit of the electrochemical window in 1-butyl-1-methylpyrrolidinium salicylate ionic liquid (BMP-SAL IL) was studied. It has been found that the cathodic limit of BMP-SAL is determined by the reduction of SAL(-) anion rather than the reduction of BMP(+) cation. The cyclic voltammetric behavior, NMR spectra, and MALDI-TOF MS spectra of BMP-SAL recorded before and after the IL was electrolyzed at the cathodic limit provide sufficient evidence that the major reaction at the cathodic limit of BMP-SAL is the reduction of SAL(-) anion. The theoretical calculations support the experimental data, and the results indicate that anion reduction dominated cathodic limit should be a common phenomenon in ionic liquids.

Synthesis, characterization, and catalytic activity of sodium ketminiate complexes toward the ring-opening polymerization of l -lactide

Studies of the ring-opening polymerization of L-lactide (LA) using Na complexes with Schiff base ligands as catalysts have revealed high catalytic activity but poor controllability of the polymer molecular weight. In this study, Na complexes bearing ketiminate ligands instead of Schiff base ligands were synthesized and their application in LA polymerization was tested. The polymerization results revealed that the catalytic activity of Na complexes bearing ketiminate ligands was higher than that of Na complexes bearing Schiff base ligands, but the poor controllability of polymer molecular weight was still a drawback. However, the poor controllability could be improved by means of using a high concentration of initiators in the polymerization system at 0 °C for 1 min. LPy–Na revealed the excellent controllability of polymer molecular weight depending on the ratio of [LA]/[initiator] (the molar averages of the number from 4500 to 35 000) with narrow polydispersity indexes, ranging from 1.29 to 1.35.

Steric and chelating ring concerns on the L-lactide polymerization by asymmetric β-diketiminato zinc complexes

A series of new asymmetrical N-aryl-N′-alkyl β-diketimines bearing a pendant pyridyl group (L1H–L4H) were synthesized in a two steps reaction from acetylacetone and the corresponding appropriate amines. The reaction of these β-diketimines (LH) with ZnEt2 afforded the corresponding ethyl zinc complexes. The ethyl zinc complexes were characterized by NMR spectroscopy and single crystal X-ray diffraction to confirm their structure and ligand binding mode. Diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY) experiments yielded diffusion coefficients suggesting that all ethyl zinc complexes are monomeric in solution. All these zinc complexes demonstrate catalytic capabilities towards the ring-opening polymerization of L-lactide. The rate of polymerization depended heavily on the ligand favoring steric bulky aryl substituents (1,3,5-trimethylphenyl) and short pendant arms (pyridylmethyl).