Lithium complexes supported by amine bis-phenolate ligands as efficient catalysts for ring-opening polymerization of l-lactide

Abstract

Lithium complexes bearing dianionic amine bis(phenolate) ligands are described. Reactions of ligand precursors H(2)O(2)NN(Me), H(2)O(2)NN(Py) or H(2)O(2)NO(Me) [H(2)O(2)NN(Me)=Me(2)NCH(2)CH(2)N-(CH(2)-2-HO-3,5-C(6)H(2)((t)Bu)(2))(2); H(2)O(2)NN(Py)=(2-C(5)H(4)N)CH(2)N-(CH(2)-2-HO-3,5-C(6)H(2)((t)Bu)(2))(2); H(2)O(2)NO(Me)=MeOCH(2)CH(2)N-(CH(2)-2-HO-3,5-C(6)H(2)((t)Bu)(2))(2)] with 2.2 molar equivalents of (n)BuLi in diethylether afford (Li(2)O(2)NN(Me))(2) (1), (Li(2)O(2)NN(Py))(2) (2) and (Li(2)O(2)NO(Me))(2) (3) as tetra-nuclear lithium complexes. The crystalline solids of partially hydrolyzed product, (LiO(HO)NN(Py)) (4), were obtained from recrystallization of 2 in diethylether solution for three months. The synthesis of (LiO(HO)NO(Me))(2) (5) was carried out at ambient temperature by carefully layering a solution of water in hexane on top of a solution of 3 in Et(2)O. Crystalline solids of were obtained after two months. Molecular structures are reported for compounds 1, 3, 4 and 5. Compounds 1-3 show excellent catalytic activities toward the ring-opening polymerization of L-lactide in the presence of benzyl alcohol.

Ring-opening polymerization of ε-caprolactone by lithium piperazinyl-aminephenolate complexes: synthesis, characterization and kinetic studies

“…The use of alcohols as activators has been reported to be necessary for ROPs of cyclic esters. 2,4,6 In the current study, the polymerization time required in the absence of benzyl alcohol was longer than in the presence of benzyl alcohol as shown in 6, 18, and 19). The polydispersity of all the polymerization reactions at or above 40°C was high (>1.5), which suggests that transesterification had occurred.…”

“…[2][3][4][5][34][35][36] This contrasts with related mono-anionic aminephenolate lithium complexes that still remain relatively unexplored. 6 Furthermore, it has been established that lithium phenolates usually contain square Li 2 39 Following our recently reported work on zinc compounds of piperazinyl aminephenolate ligands, 18 which efficiently initiated the ring-opening polymerization of rac-lactide and ε-caprolactone in a controlled manner, we decided to study the chemistry of related Li complexes.…”

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

“…Various ligands of this type have been used in main group and early transition metal chemistry (including lithium, [2][3] magnesium, [4][5][6][7][8][9][10] calcium, [11] rare-earths, [12,13] , zinc, [1,[14][15][16][17]19] aluminum, [18,20] zirconium [21,22] and titanium. [23] ) Many of these complexes have been reported to be excellent initiators for ring-opening polymerization (ROP) of cyclic esters such as rac-lactide.…”

Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

“…Thus, amine-phenolate and related ligands possessing a mixed set of N-and O-donor atoms have emerged as attractive candidates due to their ability to stabilize a wide range of metal centers and the ease of systematic steric manipulation by variation of the backbone and phenol substituents. 9 A number of main-group and transition metal complexes including lithium, [10][11][12][13][14][15][16] magnesium, [17][18][19][20][21][22][23] larger alkaline earths, 24 rare-earths, 25,26 zinc, [27][28][29][30][31][32][33][34][35][36] aluminum, [37][38][39][40][41][42][43][44] , tin, 45 zirconium 46,47 and titanium 48 complexes stabilized by these and related ligands have been prepared and some are effective initiators for ROP of cyclic esters such as lactide and ε-caprolactone (e.g., I-IV, Figure 1). Among the catalysts/initiators studied, aluminum complexes with N,O-chelate and related ligands have attracted much attention due to their high activity and good polymer molecular weight control.…”

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Abstract:A series of aluminum methyl and chloride complexes bearing 2(N-piperazinyl-N′-methyl)-2-methylene-4-R′-6-R-phenolate or 2(N-morpholinyl)-2-methylene-4-R′-6-R-phenolate ([ONE R1,R2 ]-) {[ R 1 = t Bu, R 2 = Me, E = NMe (L1); R 1 = R 2 = t Bu, E = NMe (L2); R 1 = R 2 = t Bu, 1 E = O (L3)} ligands were synthesized and characterized through elemental analysis, 1 H, 13 The catalytic activity of complexes 1-3 toward ring-opening polymerization (ROP) of ε-caprolactone was assessed. These complexes are more active than analogous Zn complexes for this reaction but less active than the Zn analogs for ROP of rac-lactide.

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