Bimetallic Anilido-Aldimine Zinc Complexes for Epoxide/CO₂ Copolymerization

Abstract

Acyclic o-phenylene-bridged bis(anilido-aldimine) compounds, o-C(6)H(4){C(6)H(2)R(2)N=CH-C(6)H(4)-(H)N(C(6)H(3)R'(2))}(2) and related 30-membered macrocyclic compounds, o-C(6)H(4){C(6)H(2)R'(2)N=CH-C(6)H(4)-(H)N-C(6)H(2)R(2)}(2) (o-C(6)H(4)) are prepared. Successive additions of Me(2)Zn and SO(2) gas to the bis(anilido-aldimine) compounds afford quantitatively dinuclear mu-methylsulfinato zinc complexes, o-C(6)H(4){(C(6)H(2)R(2)N=CH-C(6)H(4)-N(C(6)H(3)R'(2))-kappa(2)-N,N)Zn(mu-OS(O)Me)}(2) (R = iPr and R' = iPr, 29; R = Et and R' = Et, 30; R = Me and R'= Me, 31; R = Me and R' = iPr, 32; R = Et and R' = Me, 33; R = Et and R' = iPr, 34; R = iPr and R' = Et, 35) and o-C(6)H(4){C(6)H(2)R'(2)N=CH-C(6)H(4)-N-C(6)H(2)R(2)-kappa(2)-N,N)Zn(mu-OS(O)Me)}(2) (o-C(6)H(4)) (R = Et and R'= Et, 36; R = Me and R' = Me, 37; R = iPr and R' = Me, 38; R = Et and R' = Me, 39; R = Me and R'= iPr, 40). Molecular structures of 34 and 40 are confirmed by X-ray crystallography. Complexes 30-35 show high activity for cyclohexene oxide/CO(2) copolymerization at low [Zn]/[monomer] ratio (1:5600), whereas the complex of mononucleating beta-diketiminate {[(C(6)H(3)Et(2))N=C(Me)CH=C(Me)N(C(6)H(3)Et(2))]Zn(mu-OS(O)Et)}(2) shows negligible activity in the same condition. Activity is sensitive to the N-aryl ortho substituents and the highest activity is observed with 32. Turnover number up to 2980 and molecular weight (M(n)) up to 284 000 are attained with 32 at such a highly diluted condition as [Zn]/[monomer] = 1:17 400. Macrocyclic complexes 36-40 show negligible activity for copolymerization.

Alternating Copolymerization of Carbon Dioxide and Cyclohexene Oxide and Their Terpolymerization with Lactide Catalyzed by Zinc Complexes of N,N Ligands

“…For the CO 2 /epoxide copolymerization, tetradentate derivatives of this ligand have been developed to bind rare earth metals [23] as well as to form a rigid bimetallic zinc acetate complex. [24] As a new alternative to the classic b-diketimines, new aminoimidoacrylate (AIA) ligands and their zinc acetate complexes, which showed high activities in the CO 2 /cyclo-hexene oxide copolymerization, have been reported by our group. [25] In this paper we present new derivatives of this group of ligands, their catalytic behavior, some insight into the CO 2 /epoxide copolymerization and first results in the terpolymerization of CO 2 , cyclohexene oxide and lactide (Scheme 1).…”

Differences in Reactivity of Epoxides in the Copolymerisation with Carbon Dioxide by Zinc‐Based Catalysts: Propylene Oxide versus Cyclohexene Oxide

“…[33,34] In 2005 and 2006, Lee et al reported on anilido-aldimine ligands for the preparation of dinuclear zinc catalysts 5. [35,36] Due to the bimetallic nature of the complexes, activities were retained even under high dilution. Limberg, Hultzsch and co-workers as well as Harder and co-workers focussed on a BDI-like structure in their dinuclear catalysts 6 and 7.…”

Mechanistic Aspects of a Highly Active Dinuclear Zinc Catalyst for the Co‐polymerization of Epoxides and CO2

“…[34] So far,this complex represents the only homogeneous zinc catalyst for co-polymerization of propylene oxide and CO 2 .O ther homogeneous zinc-based systems for,f or example,c yclohexeneo xide/CO 2 co-polymerization have not been reported to be active for the synthesis of poly(propylene carbonate). [17,21,25,29,30] Previous catalyst research in our group was focused on heterogeneous zinc(II)glutarates for the co-polymerizationo fp ropylene oxide and CO 2 .I nt he course of these investigations, the experimental and theoretical results corroboratedt he necessity of two cooperating metal centers for any activity with heterogeneous zinc dicarboxylates. However,t he activities with such catalysts are restricted due to restrained surface area and diffusion limitations.…”

“…[19,21,[24][25][26][27][28][29][30][31] One major breakthrough was the synthesis of b-diketiminato (BDI) zinc complexes by Coates et al [19,32,33] Already minor steric and electronic variations in the ligand framework led to dramatic changes in catalytic behavior.I ntroducing electronwithdrawing groups enabled the formation of poly(propylene carbonate). [34] So far,this complex represents the only homogeneous zinc catalyst for co-polymerization of propylene oxide and CO 2 .O ther homogeneous zinc-based systems for,f or example,c yclohexeneo xide/CO 2 co-polymerization have not been reported to be active for the synthesis of poly(propylene carbonate).…”