Controlled polymerization of lactides at ambient temperature using [5-Cl-salen]AlOMe

Abstract

SUMMARY:The Schiff-base aluminium complex [5-Cl-salen]AlOMe (2) is shown to be a room temperature initiator for controlled ring-opening polymerization of D,L-and L-lactides; the molecular structure of the precursor [5-Cl-salen]AlMe (1) reveals a distorted trigonal bipyramidal geometry.

Study of ligand substituent effects on the rate and stereoselectivity of lactide polymerization using aluminum salen-type initiators

“…With a view to assessing whether any underlying geometrical effect imposed by the tetradentate ligand might account for the polymerization activities and selectivities, crystal structure determinations were carried out on selected complexes from Groups B, D, E, G, and H; a number of examples from Group A were available from the literature (4,31,32). Table 1).…”

“…catalysis ͉ polyesters I n recent years, Al(salen) complexes [where salen is N,NЈ-bis(salicylaldimine)-1,2-ethylenediamine] have been widely investigated for their ability to initiate the stereocontrolled polymerization of lactide (LA) (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) to give a material, polylactide (PLA), which has a range of biomedical, pharmaceutical, and agricultural applications (18)(19)(20)(21). A convenient synthetic route to PLA is the ring-opening polymerization (ROP) of LA, the cyclic diester of lactic acid, which is derivable from renewable resources such as corn starch, sugars, and dairy produce.…”

“…With regard to the productivities of (salen)Al systems, in the rather limited number of studies to date it has been found that the rate of polymerization is enhanced by appending electronwithdrawing substituents to the phenoxide donor (4). Enhanced activities also have been observed by using a salicylketimine derivative containing neither bulky nor electron-withdrawing substituents on the phenoxide donor (5).…”

Aluminum Alkyl Complexes Bearing Salicylaldiminato Ligands: Versatile Initiators in the Ring-Opening Polymerization of Cyclic Esters

“…These species have the potential to function as active catalysts because of their less coordinatively saturated nature. Interestingly, "half-SALEN" salicylaldiminato aluminum complexes (Figure 1b) Aluminum complexes bearing tetradentate salicilaldiminato ligands (SALEN, Figure 1a) have been largely studied and used in many catalytic reactions [14][15][16][17][18][19][20]. After the discovery of the stereoselective polymerization of racemic lactides by chiral binaphthyl Schiff base aluminum complex [21], a large synthetic effort has been devoted to the preparation of five-coordinate SALEN aluminum complexes and their use in the ROP of lactones and lactides.…”

Dimethyl-Aluminium Complexes Bearing Naphthyl-Substituted Pyridine-Alkylamides as Pro-Initiators for the Efficient ROP of ε-Caprolactone

“…As the catalytic properties of the aluminum species employed are greatly influenced by the ancillary ligand (both electronically and sterically), a wide variety of multidentate ligand architectures have been developed and investigated in this field. While early reports focused on dianionic tetradentate ligands [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], more recent studies have highlighted the considerable potential of using tridentate [21][22][23][24][25][26][27][28][29] and bidentate [20,[30][31][32][33][34][35][36][37][38][39][40][41][42] ligand sets as monoanionic ancillaries for potent and well-behaved AlR2-based (R = alkyl) pro-initiators.…”