Organoaluminium Complexes Derived from Anilines or Schiff Bases for the Ring‐Opening Polymerization of ε‐Caprolactone, δ‐Valerolactone and rac‐Lactide

Abstract

Reaction of R 1 R 2 CHN=CH(3,5-tBu 2 C 6 H 2 -OH-2) (R 1 = R 2 = Me L 1 H; R 1 = Me, R 2 = Ph L 2 H; R 1 = R 2 = Ph L 3 H) with slightly greater than one equivalent of R 3 3 Al (R 3 = Me, Et) afforded the complexes [(L 1-3 )AlR 3 2 ] (L 1 , R 3 = Me 1, R 3 = Et 2; L 2 , R 3 = Me 3, R 3 = Et 4; L 3 R 3 = Me 5, R 3 = Et 6); complex 1 has been previously reported. Use of the N,O-ligand derived from 2,2′-diphenylglycine afforded either 5 or the byproduct [Ph 2 NCH 2 (3,5-tBu 2 C 6 H 2 -O-2)AlMe 2 ] (7). The known Schiff base complex [2-Ph 2 PC 6 H 4 CH 2 (3,5-tBu 2 C 6 H 2 -O-2)AlMe 2 ] (8) and the product of the reaction of 2-diphenylphosphinoaniline 1-NH 2 ,2-PPh 2 C 6 H 4 with Me 3 Al, namely {Ph 2 PC 6 H 4 N[(Me 2 Al) 2 μ-Me]-(μ-Me 2 Al)} (9), were also isolated. For structural and catalytic comparisons, complexes resulting from the interaction of Me 3 Al with diphenylamine (or benzhydrylamine), namely {Ph 2 N[(Me 2 Al) 2 μ-Me]} (10) and [Ph 2 CHNH(μ-Me 2 Al)] 2 ·MeCN (11), were prepared. The molecular structures of the Schiff proligands derived from Ph 2 CHNH 2 and 2,2′-Ph 2 C(CO 2 H)(NH 2 ), together with those of complexes 5, 7 and 9-11·MeCN were determined; 5 contains a chelating imino/phenoxide ligand, whereas 7 contains the imino function outside of the metallocyclic ring. Complex 9 contains three nitrogen-bound Al centres, two of which are linked by a methyl bridge, whilst the [a] Scheme 1. Compounds (proligands) employed herein. Scheme 2. Complexes studied herein.1952 tBu 2 C 6 H 2 -O-2)AlR 3 2 ] (R 1 = R 2 = R 3 = Me 1; R 1 = R 2 = R 3 = Et 2; R 1 = R 3 = Me, R 2 = Ph 3; R 1 = Me, R 2 = Ph, R 3 = Et 4; R 1 = R 2 = Ph, R 3 = Me 5; R 1 = R 2 = Ph, R 3 = Et 6) and compare their behaviour against organoaluminium complexes derived from the amine component only (i.e., minus the phenoxy-containing 3,5-di-tert-butylsalicyl motif, see Schemes 1 and 2). We note that Nomura and colleagues have previously investigated the effect of the imino substituent on the ROP of ε-caprolactone (CL) and observed greatly enhanced activity for aryl substituents (C 6 F 5 , 2,6-iPr 2 C 6 H 3 ) versus aliphatic substituents (adamantyl, tert-butyl). [7] Herein, we initially targeted diphenylglycine (dpg) and derivatives thereof given the tendency of related motifs to form highly crystalline products. [9] However, the loss of CO 2 during the formation L 3 H(dpg), see discussion below, led us to explore the family of proligands with both aliphatic and aromatic substituents bound to the N-bound CH group.

Synthesis of Biodegradable Polymers: A Review on the Use of Schiff-Base Metal Complexes as Catalysts for the Ring Opening Polymerization (ROP) of Cyclic Esters

“…Over the past 2 decades, our group have been contributing to the development of the field. Simple arylimino compound 188 ( Figure 34) proved inactive in the ROP of ε-CL [109], while the 2,4-t Bu-salicylaldehyde derivatives 189-196 exhibited interesting activity towards the polymerization of different monomers [110]. In the presence of BnOH as co-activator, complexes 189 and 195 were the most performing catalysts in the ROP of ε-CL, leading to complete monomer conversion at 80 • C within 3 and 1 h for the former and the latter, respectively.…”

Low temperature splinting activity and catalytic behavior of nano Ag doped sulphamicacid bridged diblock copolymer

“…The catalysts and initiators used for the ROP of CL are discussed below. Organo aluminium complexes derived from anilines were used for the ROP of CL . In 2018, Jiang et al reported a novel catalyst for the ROP of CL .…”

“…Organo aluminium complexes derived from anilines were used for the ROP of CL. 1 In 2018, Jiang et al reported a novel catalyst for the ROP of CL. 2 Galia and co-workers 3 studied the ROP of CL using wet β-cyclodextrin as a novel catalyst.…”

Synthesis and Characterization of Niobium and Tantalum Complexes with Bidentate Ligand and its use in Ring Opening Polymerization of e-Caprolactone

“…According to the literature a few papers published on these metals complexes as catalysts toward polymerization of lactide, lactone or ethylene [3][4][5][6]. The use of Schiff base ligation has received more interest because of easy to prepare [7] and versatile applications of Schiff base and their complexes as biological activity, antifungal properties, anticancer properties, application in modern technologies, application in synthesis and chemical analysis [8][9][10][11][12][13].…”