Ethyl 2-hydroxy-2-methylpropanoate derivatives of magnesium and zinc. The effect of chelation on the homo- and copolymerization of lactide and ε-caprolactone

Abstract

The preparation, single crystal and molecular structures of the compounds (BDI)Mg(OCMe2COOEt)(L) are described where BDI = 2-[(2,6-diisopropylphenyl)amino]-4-[(2,6-diisopropylphenyl)imino]pent-2-ene and L = pyridine (py) and 4-dimethylaminopyridine (DMAP). In the solid-state the molecules have five coordinate Mg(2+) ions that may be considered as derived from a trigonal bipyramid where the chelating BDI and OCMe2COOEt ligands span equatorial-axial sites. IR spectroscopic data obtained in CH2Cl2 indicate that the chelating nature of the OCMe2COOEt ligand is maintained in solution and variable temperature NMR studies reveal that the ligands py or DMAP undergo a rapid reversible dissociation in toluene-d8 and especially in THF-d8. This leads to a facile exchange involving coordinated and free L upon the addition of L and evidence is presented to support the view that this occurs exclusively by a dissociative interchange mechanism. Zinc forms a related complex (BDI)Zn(OCMe2COOEt) lacking additional coordination of L but maintaining the chelating nature of the OCMe2COOEt ligand and undergoing reversible coordination of L in the presence of added ligands L. The magnesium and zinc complexes will initiate and sustain the living polymerization of lactide (L- or rac-LA) but not the ring-opening polymerization of ε-caprolactone.

Block Copolymers of “PE-Like” Poly(pentadecalactone) and Poly(l-lactide): Synthesis, Properties, and Compatibilization of Polyethylene/Poly(l-lactide) Blends

“…This is in agreement with results found for the copolymerization of LLA and CL using Zn and Mg complexes, where the chelating effect of the lactate unit was shown to be responsible for the inability of these complexes to facilitate copolymerization, while both monomers were efficiently homopolymerized. 28,29 Since the PLLA growing chain showed no reactivity toward PDL and the ROP of a strainless cyclic ester such as PDL resembles the transesterification of a linear chain, it was assumed that a growing PLLA chain would not be able to undergo transesterification with a PPDL chain either. Therefore, in an attempt to produce a poly(PDL-block-LLA) copolymer, a sequential feed approach was applied in which first PDL was allowed to polymerize to >94% monomer conversion using 2′ ([PDL]/[2′] = 50), after which varying amounts of lactide (as hot p-xylene solutions) were added.…”

BDI∗MgX(L) where X = Bu and O Bu and L = THF, py and DMAP. The rates of kinetic exchange of L where BDI∗= CH{C( Bu)N-2,6- Pr2C6H3}2

“…the rate of PLA that is formed is $80% but when L = py or DMAP the conversion is only $30%. We note that in DCM the binding of L toward to the catalytic center suppress the rate of polymerization [5]. In DCM the % of heterotactic (isi, sis) PLA is close to 50%.…”

“…In the ground state the two i Pr groups are equivalent if we obtain a three-coordinate (I) and in a five-coordinate (II) complex as shown in Fig. 1 [3][4][5]. In the four-coordinated metal the i Pr ligands are inequivalent.…”

Imino(phenoxide) compounds of magnesium: Synthesis, structural characterization, and polymerization studies

“…Here we observed that our catalyst showed more catalytic activity towards the ROP and taken less time for complete conversion. [47][48][49][50][51][52][53][54][55][56][57][58][59] M n of the PLA was found much higher and narrow MWDs than literature reported magnesium catalysts [47][48][49][50][51]55 but tacticity (P r ) of the PLA was found to be comparatively less than the few other recently reported magnesium catalysts. [47][48][49]58 The variation of M n and MWDs with [M] o /[C] o ratio for the polymerization of rac-LA and L-LA using 1, 5, and 6 were studied next.…”