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

Abstract

A series of aluminum salen-type complexes [where salen is N,Nbis(salicylaldimine)-1,2-ethylenediamine] bearing ligands that differ in their steric and electronic properties have been synthesized and investigated for the polymerization of rac-lactide. X-ray crystal structures on key precatalysts reveal metal coordination geometries intermediate between trigonal bipyramidal and square-based pyramidal. Both the phenoxy substituents and the backbone linker have a significant influence over the polymerization. Electronwithdrawing groups attached to the phenoxy donor generally gave an increased polymerization rate, whereas large ortho substituents generally slowed down the polymerization. The vast majority of the initiators afforded polylactide with an isotactic bias; only one exhibited a bias toward heteroselectivity. Isoselectivity generally increases with increased flexibility of the backbone linker, which is presumed to be better able to accommodate any potential steric clashes between the propagating polymer chain, the inserting monomer unit, and the substituents on the phenoxy donor.catalysis ͉ polyesters

Tetrameric Self-Assembly of a Cu(II) Complex Containing Schiff-Base Ligand and Its Unusually High Catecholase-like Activity

“…16 A gold matte powder of Cu 4 L 4 ·4(CH 3 OH) was obtained by adding a methanolic solution of Cu(ClO 4 ) 2 ·6H 2 O into a methanolic solution of H 2 L (Scheme 1). 1.321 and −0.920…”

“…The ligand, H 2 L, was prepared by slight modification of the literature method. 16 A solution of salicylaldehyde (0.75 g, 6.0 mmol) dissolved in 5 mL of dry toluene was added to a magnetically-stirred solution of 2,2'-ethylenedianiline (0.66 g, 3.0 mmol) dissolved in 20 mL of dry toluene. The mixture solution was refluxed for 2 h. Yellow solid products were washed several times with methanol and dried under a vacuum at ambient temperature.…”

Highly Active Polymer‐Supported (Salen)Al Catalysts for the Enantioselective Addition of Cyanide to α,β‐Unsaturated Imides

“…Metallated salen catalysts, first reported by Jacobsen and Katsuki, [1][2][3][4][5][6] are among the most versatile catalysts for the enantioselective synthesis of organic compounds catalyzing a diverse set of organic transformations ranging from 1,4-conjugate additions [7][8][9][10][11] and 1,2-additions [12][13][14] to environmentally benign ones such as the CO 2 addition to epoxides [15][16][17][18] and the formation of polylactide from renewable resources. [19][20][21] The enantioselective 1,4-addition reaction is of particular interest because it is a key transformation in the syntheses of high therapeutic value compounds in the pharmaceutical industry. Furthermore, to obtain high selectivities for this transformation is often not a trivial task.…”

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

“…The results of the catalytic screening are collected in Table 3 (entries [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. At 30 °C, all the systems display moderate to good activity [5] for the polymerization of ε-CL with para-i-Pr-containing 1b/PhCH2OH being the most active reaching 80% conversion to poly(CL) after 2 h (entry 8).…”

“…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.…”