Khamphee Phomphrai

Lactide polymerization by well-defined calcium coordination complexes: comparisons with related magnesium and zinc chemistry.

Amide and alkoxide coordination complexes of calcium supported by beta-diiminato and bulky trispyrazolylborate complexes are reported together with their activity in lactide ring-opening polymerization; some are amongst the most active systems discovered to date.

Conformational effects in β-diiminate ligated magnesium and zinc amides. Solution dynamics and lactide polymerization

Abstract The preparation of the compounds LMg(N i Pr 2 )(THF) ( 1 ); and LZnN i Pr 2 ( 2 ), are reported for L=the bulky β-diiminate ligand, CH(CMeN-2- t BuC 6 H 4 ) 2 . In solution compound 2 is shown to exist as a mixture of syn - and anti -rotamers that do not interconvert significantly. Compound 1 readily and reversibly dissociates THF in benzene-d 6 or toluene-d 8 from a site where THF is syn to the t Bu group of L. Both 1 and 2 are catalyst precursors for the ring-opening polymerization of lactides and it is shown that the syn -conformer of 2 reacts much faster than the anti . Polymerization of rac -lactide employing 2 in benzene or CH 2 Cl 2 or 1 in THF yield approximately 90% heterotactic PLA ( isi + sis ). These results are compared with related work by Coates [J. Am. Chem. Soc. 123 (2001) 3229]; and us [J. Chem. Soc., Dalton Trans. (2001) 222] and us employing the symmetric β-diiminate ligand CH(CMeN-2,6- i Pr 2 C 6 H 3 ) 2 .

Monomeric metal alkoxides and trialkyl siloxides: (BDI)Mg(OtBu)(THF) and (BDI)Zn(OSiPh3)(THF). Comments on single site catalysts for ring-opening polymerization of lactides

The monomeric alkoxide (BDI)Mg(OtBu)(THF) and triphenylsiloxide (BDI)Zn(OSiPh3)(THF) have been prepared and characterized and shown to reversibly dissociate THF in solution on the NMR time scale; both compounds are active precursors for the ring-opening polymerization of lactide and the rate of polymerization is notably faster for the magnesium complex though in the polymerization of rac-lactide only the zinc complex shows selectivity for heterotactic tetrads.

Effects of appended hydroxyl groups and ligand chain length on copper coordination and oxidation activity

Treatment of a series of (imino)pyridine ligands bearing appended hydroxyl groups 2-((pyridin-2-ylmethylene)amino)phenol (Hpyph), 2-((pyridin-2-ylmethylene)amino)ethanol (Hpyet), and 3-((pyridin-2-ylmethylene)amino)propanol (Hpypr) with one equiv. of CuCl2·2H2O afforded the corresponding Cu(II) complexes in low to moderate yields. The crystal structure of (μ-Cl)2[CuCl(κ2-N,N-Hpyet)]2 reveals a symmetric dinuclear structure with the bidentate N,N-coordination mode of (imino)pyridine with no Cu–OH interaction. On the other hand, the dinuclear Cu(II) complex of the related propyl ligand Hpypr possesses a significantly different crystal structure involving nucleophilic addition of the hydroxyl group to the aldehyde group of 2-pyridinecarboxaldehyde. The Cu complex/Cu0/TEMPO/Na2CO3 (TEMPO = 2,2,6,6-tetramethylpiperidinyl-1-oxyl) catalyst system generally exhibited good activity for aerobic oxidation of benzyl alcohol to benzaldehyde in H2O at room temperature. The dinuclear Cu(II) complex (μ-Cl)2[CuCl(κ2-N,N-Hpyet)]2 was demonstrated as an effective catalyst toward aerobic oxidation of various benzyl alcohol derivatives, cinnamyl alcohol, and 2-thiophenemethanol.

Synthesis and characterization of neutral and cationic aluminum complexes supported by a furfuryl-containing aminophenolate ligand for ring-opening polymerization of ε-caprolactone

The synthesis, structural characterization and reactivity of aluminum complexes supported by a novel tetradentate aminophenolate ligand containing furfuryl groups (LH), LAlMe2 (1), LAlMeCl (2) and LAlMeOtBu (3), are described. The molecular structures of ligand LH and complexes 1–3 are determined by X-ray structural analysis. Complexes 1–3 contain a four-coordinated mononuclear aluminum center. Activation of complex 1 with either B(C6F5)3 or [Ph3C][B(C6F5)4] afforded the corresponding cationic complex, [LAlMe][MeB(C6F5)3] or [LAlMe][B(C6F5)4], respectively. All cationic complexes were stable at room temperature in the absence of an external Lewis base over a week. The cationic complex [LAlMe][MeB(C6F5)3] decomposed upon heating at 70 °C, giving a neutral LAlMe(C6F5) complex. Complexes 1–3 were inactive for the ring-opening polymerization (ROP) of e-caprolactone (CL) at room temperature. However, only the cationic aluminum complex [LAlMe][MeB(C6F5)3] in the presence of benzyl alcohol was found to be active in the ROP of CL at room temperature in a well-behaved manner, giving a first-order reaction with respect to [CL].

Polymerization of ε-Caprolactone Using Bis(phenoxy)-amine Aluminum Complex: Deactivation by Lactide

Polymerizations of biodegradable lactide and lactones have been the subjects of intense research during the past decade. They can be polymerized/copolymerized effectively by several catalyst systems. With bis(phenolate)-amine aluminum complex, we have shown for the first time that lactide monomer can deactivate the aluminum complex during the ongoing polymerization of ε-caprolactone to a complete stop. After hours of dormant state, the aluminum complex can be reactivated again by heating at 100 °C without the addition of any external chemicals still giving polymer with narrow dispersity. Studies using NMR, in situ FTIR, and single-crystal X-ray crystallography indicated that the coordination of the carbonyl group in lactyl unit was responsible for the unusual behavior of lactide. In addition, the unusual methyl-migration from methyl lactate ligand to the amine side chain of the aluminum complex was observed through intermolecular nucleophilic-attack mechanism.