Synthesis of Homo- and Heteronuclear Rare-Earth Metal Complexes

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Cite This: Inorg. Chem. 2019, 58, 8775−8786

Synthesis of Homo- and Heteronuclear Rare-Earth Metal Complexes Stabilized by Ethanolamine-Bridged Bis(phenolato) Ligands and Their Application in Catalyzing Reactions of CO2 and Epoxides Linyan Hua,† Baoxia Li,† Cuiting Han,† Pengfei Gao,† Yaorong Wang,† Dan Yuan,*,† and Yingming Yao*,†,‡

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†

Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Dushu Lake Campus, Soochow University, Suzhou 215123, People’s Republic of China ‡ State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China S Supporting Information *

ABSTRACT: A series of homonuclear rare-earth (RE) metal complexes (1Y, 2Yb, 3Nd, and 4La) and heteronuclear RE−Zn complexes (1Y−Zn, 3Nd−Zn, and 5Sm−Zn) stabilized by ethanolamine-bridged bis(phenolato) ligands was prepared and structurally characterized. Heteronuclear complexes are assembled through bridging acetate ligands, and their formation and characterization add to the diversity of 3d−4f complexes. Their activities in mediating reactions of CO2 and epoxides were evaluated and compared. Heteronuclear RE−Zn complexes found application in the copolymerization of cyclohexene oxide and CO2, giving rise to acetate-group-capped copolymers. Homonuclear complexes showed good activity in catalyzing the cycloaddition of variously monosubstituted epoxides and CO2 (1 bar), generating cyclic carbonates in 65−96% yield. For sterically hindered disubstituted epoxides, good yields of 60−91% were achieved in the presence of 10 bar CO2.

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INTRODUCTION Carbon dioxide (CO2) is a desirable C1 building block because it is abundant in nature and is nontoxic. The reaction of CO2 with epoxides is an intriguing and 100% atom-efficient method to transform CO2 into value-added compounds. Cyclic carbonates and polycarbonate are two possible products, both of which find important applications (Scheme 1).1,2 Cyclic carbonates may be used as engineering plastics, electrolytes, solvents, fuel additives, and precursors to fine chemicals. Polycarbonates are durable, moldable, transparent, and light- and shatter-resistant and have attracted much interest in the biomedical field due to their biocompatibility and biodegradability.3

Many catalysts have been developed to promote reactions of CO2 with epoxides, including organocatalysts4 and metal-based catalysts of main-group (mainly Al)5 and transition metals (e.g., chromium,6 zinc,7 cobalt,8 iron,9 rare-earth (RE) metal10). Among them, RE metal catalysts have shown, in general, good activity due to the oxyphilic and highly Lewis acidic nature of RE metal centers.10 A recent study proved that RE-containing heteronuclear complexes, namely, multinuclear complexes of different metal centers, are reported to outperform homonuclear complexes in catalyzing reactions of epoxides and CO2. Liu et al. developed RE−Zn heterometallic helicates that catalyzed the cycloaddition of epoxides and CO2 under mild conditions.10a−c For copolymerization, our group disclosed heteronuclear complexes of RE−Zn stabilized by ophenylenediamine-bridged tri(phenolato) ligand.11 Recently, Okuda and Mashima et al. reported heteronuclear complexes of RE−Zn supported by macrocyclic tris(salen)-based ligand and acetato ligands.12 In these reports, different metal centers

Scheme 1. Reaction of CO2 with Epoxides

Received: April 22, 2019 Published: June 13, 2019 © 2019 American Chemical Society

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DOI: 10.1021/acs.inorgchem.9b01169 Inorg. Chem. 2019, 58, 8775−8786

Article

Inorganic Chemistry Scheme 2. Synthesis of Homonuclear Complexes

Scheme 3. Synthesis of Heteronuclear Complexes

carrying ethanolamine-bridged bis(phenolato) ligands revealed that they are highly active in catalyzing the cycloaddition of epoxides and CO2 under ambient pressure.14a We herein report the synthesis and characterization of homonuclear RE complexes and heteronuclear RE metal−zinc complexes stabilized by an ethanolamine-bridged bis(phenolato) ligand. Their activity in catalyzing cyclic carbonate and polycarbonate formation has been investigated.

are proposed to activate epoxides and CO2 separately, giving rise to highly efficient or selective catalysts. Amine-bridged poly(phenolato) ligands are a privileged group of ligands that have been intensively studied, especially in the field of early transition-metal and main-group chemistry, because they not only well stabilize metal centers but also give rise to mono/multinuclear complexes of diverse structures.13 Multidentate ligands derived from ethanolamine-bridged bis(phenol) have been reported to form a trinuclear complex of magnesium, dinuclear complexes of copper, iron, vanadium, and aluminum, and mononuclear complexes of titanium, uranyl, and molybdenum.14 However, the synthesis of RE metal complexes stabilized by this type of multidentate ligand has not been reported. In addition, although this multidentate ligand framework should allow the introduction of different metal centers, the report on heterometallic complexes is limited. The only example in literature is Ti−Al heterometallic complexes reported by Nomura et al., which found application in ethylene polymerization.14e Our group has been devoted to exploring the application of RE metal complexes in catalyzing transformations of CO2 into cyclic carbonates, polycarbonates, oxazolidinones, and carboxylic acids.10a,e,11,14a,15 A recent study on aluminum complexes

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RESULTS AND DISCUSSION Ethanolamine-bridged bis(phenol) LH3 was treated with Cp3RE(THF) [RE = Y, Yb, Nd, La], which produced RE metal complexes in 45−56% yield (Scheme 2).16 Complexes 1Y and 2Yb of small ionic radii formed trinuclear structures, whereas complexes 3Nd and 4La of large ionic radii are dinuclear complexes.17 All four complexes show, in general, poor solubility in common organic solvents, for example, hexane, toluene, and benzene. Nuclear magnetic resonance (NMR) spectra of diamagnetic complexes 1Y and 4La were recorded in THF-d8. In both spectra, one set of signals corresponding to ligand L was observed, demonstrating that they are both symmetric structures. Broad signals corresponding to methylene groups were observed in the range of 4.2 to 8776


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Inorganic Chemistry 2.5 ppm, suggesting the fluxionality of the ligand backbone, which is similar to that of the Al complex bearing the same ligand.14a The 1H,1H−COSY spectrum of complex 1Y revealed the correlation between signals resonating at 2.51 and 4.17 ppm, which are assigned to protons of the ethanolamine bridge. Corresponding resonances of carbon atoms were determined to be at 56.7 and 61.8 ppm, respectively, as indicated in the 1H,13C-HSQC spectrum (Figures S3 and S4). Multidentate ethanolamine-bridged bis(phenolate) ligand L was used to construct heterometallic complexes through a onepot, two-step strategy (Scheme 3). The addition of 0.5 equiv of Zn(OAc)2 to a solution of LH3 and Cp3RE(THF) in THF gave rise to heterometallic RE−Zn complexes in 43−56% yield. Complex 1Y−Zn is hexanuclear, consisting of four yttrium and two zinc centers. Bridging bis(phenolato) and acetato ligands facilitate the assembly of the hexanuclear structure. The reaction of homonuclear complex 1Y with Zn(OAc)2 also generated 1Y−Zn. Apparently, ligand exchange and redistribution occurred during the formation of 1Y−Zn. Nd−Zn complex 3Nd−Zn and Sm−Zn complex 5Sm−Zn were isolated as trinuclear complexes, with acetato ligands and the alkoxylate group of ligand L bridging two metal centers. No ytterbium or lanthanum analogue was isolated from either the one-pot reaction or the reaction of the respective homonuclear complex and Zn(OAc)2. The methyl group of acetato groups in the 1H NMR spectrum of heteronuclear complex 1Y−Zn appears at 1.83 ppm, which is consistent with reported data,18 supporting the incorporation of acetato groups in the heterometallic complex. Splitting signals of tert-butyl and methylene groups indicate the restricted rotation of C−C bonds upon the formation of the heterometallic structure. The 1H DOSY spectrum reveals that acetate protons diffuse at the same rate of those of ligand L (diffusion coefficient Dt determined as 5.90 × 10−10 m2/s, Figure S11), proving that both ligands are incorporated in the same complex in THF-d8. All complexes were also characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction analysis, and power X-ray diffraction analysis. Because there are only a few reports of heteronuclear RE−Zn complexes bearing acetato ligands,12,19 the isolation of 1Y−Zn, 3Nd−Zn, and 5Sm−Zn adds to the diversity of structurally characterized RE−Zn acetate complexes. Solid-state structures of complexes 1Y, 4La, 1Y−Zn, and 3Nd−Zn are depicted in Figures 1−4, and the others are presented in the Supporting Information (Figures S12−S14). Complexes 1Y and 2Yb are isostructural, and the structure of Y 1 is described as a representative (Figure 1). Complex 1Y is a trinuclear complex of the formula Y3L3(THF)2, with one multidentate ligand L stabilizing one yttrium center each. All three yttrium centers are six-coordinate and adopt octahedron geometries; however, the coordination environment of each yttrium center is different. In addition to ligand L and one THF molecule, Y1 and Y3 are also bound by another ligand L through the phenolate (Y1) or alkoxylate group (Y3). Y2 is coordinated by one ligand L and two alkoxylate groups from two other ligands. The three ligands hold three yttrium atoms together to form the trinuclear complex. The solid-state structure of complex 4La consists of two ligand L and two lanthanum atoms. Each La atom is bound by ligand L, one alkoxylate group of another L, and two THF molecules. Oxygen atoms of the alkoxylate group bridge two lanthanum atoms. The coordination geometry lanthanum atoms can be described as distorted pentagonal bipyramid.

Figure 1. Molecular structure of complex 1Y·2hex in thermal ellipsoids drawn at the 30% probability level. Aryl groups and coordinating THF molecules are drawn in the form of wireframe. All hydrogen atoms and solvent molecules are omitted for clarity.

Figure 2. Molecular structure of complex 4La·2THF in thermal ellipsoids drawn at the 30% probability level. Aryl groups and coordinating THF molecules are drawn in the form of wireframe. All hydrogen atoms and solvent molecules are omitted for clarity.

Two lanthanum centers are separated by 4.0648(13) Å, which is comparable to reported values.20 Single-crystal X-ray diffraction analysis reveals that complex 1Y−Zn is a hexanuclear structure, which is composed of four ligands L, four κ2-acetato ligands, four yttrium centers, and two zinc centers. Each zinc center is five-coordinated, adopting a tetragonal pyramid geometry. Four yttrium centers can be divided into two groups: two (Y2 and Y2′) of them are bound by ligand L, adopting a pentagonal bipyramid geometry, and the other two (Y1 and Y1′) are stabilized by acetato ligands, adopting a triangular prism configuration. Zinc and yttrium centers are bridged by the alkoxylate group of ligand L, whereas yttrium centers are bridged by acetato ligands. From X-ray crystallography data, the crystalline radius of complex 1Y−Zn was determined to be 8.8 ± 0.5 Å, assuming a spherical molecule, whereas the hydrodynamic radius rh was determined to be 7.9 ± 0.5 Å.21,22 A conclusion can thus be reached that the crystalline radius and the hydrodynamic radius roughly agree with each other. 8777


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single crystals (Figure 5 and Figure S17). Experimental and simulated data are found to be consistent, which proved that the single crystal is representative of the bulk.

Figure 3. Molecular structure of complex 1Y−Zn·4THF·hex. Aromatic substituents and coordinated THF are in the form of wireframe, whereas the other atoms are in thermal ellipsoids drawn at the 30% probability level. All hydrogen atoms and solvent molecules are omitted for clarity.

Figure 5. PXRD spectra of complex 4La.

Copolymerization Study. The application of homonuclear RE complexes and heterobimetallic RE metal−zinc complexes was evaluated in the copolymerization of cyclohexene oxide and 30 bar CO2 (Table 1, Scheme 4). RE metal complexes have shown negligible activity (Table 1, entries 1− 4), whereas heterometallic complexes were much more effective (Table 1, entries 5−7).23 The lack of an efficient initiating group in the former may be the reason for their low activity (vide infra).10j Complex 1Y−Zn showed higher activity than complexes 3Nd−Zn and 5Sm−Zn at 70 °C (Table 1, entries 5−7); however, all three complexes showed moderate selectivity for copolymerization, as the percentage of polycarbonate was determined to be ca. 59%. In comparison, Zn(OAc)2 showed moderate activity but better selectivity than heterometallic complexes (Table 1, entry 18). Condition screening revealed that the yields of polymers increased as the temperature was raised from 50 to 90 °C. The best yield of 88% was obtained at 90 °C in the presence of complex 1Y−Zn, whereas a lower yield of 43% was detected at 110 °C (Table 4, entries 8−10). The low yield at elevated temperatures deserves further comment, as the 1H NMR spectrum of reaction mixtures revealed 95% conversion of monomer at 110 °C (Figure S18). This observation may be attributed to the degradation of poly(cyclohexene carbonate) (PCHC) in the presence of complex 1Y−Zn, which became obvious at elevated temperatures. To verify this hypothesis, the polymer and complex 1Y−Zn were heated in toluene to 110 °C under 30 bar. GPC analysis revealed the appearance of substances of small molecular weight (Figure S22). Similar observation has been reported with the heterometallic Nd−Zn complex.11 Lowering the CO2 pressure to 20 bar gave rise to a reduced yield of 75%, and no polycarbonate formed under 1 bar of

Figure 4. Molecular structure of complex 3Nd−Zn·4THF. Aromatic substituents and coordinated THF are in the form of wireframe, whereas the other atoms are in thermal ellipsoids drawn at the 30% probability level. All hydrogen atoms and solvent molecules are omitted for clarity.

Heterometallic complexes 3Nd−Zn and 5Sm−Zn are trinuclear structures, consisting of two RE metal centers and one zinc center. Each RE center is coordinated by seven donors: tetradentate ligand L, one bridging acetato ligand, and two THF molecules, which adopt a twisted pentagonal bipyramid configuration. The geometry of the zinc center is a distorted tetrahedron. Acetato ligands and the alkoxylate group of ligand L bridge the RE metal center and the zinc center, resulting in the distances of Sm−Zn and Nd−Zn being ca. 3.82 and 3.84 Å, respectively. All complexes and ligands have similar infrared absorption. IR spectra of Zn(OAC)2, and heterometallic complexes were compared (Figure S16). Zn(OAc)2 exhibits bending vibration at 1538 cm−1, whereas bending vibration is observed at 1559 cm−1 for complexes 3Nd−Zn and 5Sm−Zn and 1594 cm−1 for complex 1Y−Zn. The powder X-ray diffraction (PXRD) analysis of complexes 1−5 was conducted and compared with simulated spectra from 8778


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Inorganic Chemistry Table 1. Copolymerization of Cyclohexene Oxide and CO2 Initiated by Complexes 1−5a entry 1 2 3 4 5 6 7 8 9 10 11e 12f 13 14 15g 16 17h 18

complex Y

1 2Yb 3Nd 4La 1Y−Zn 3Nd−Zn 5Sm−Zn 1Y−Zn 1Y−Zn 1Y−Zn 1Y−Zn 1Y−Zn 1Y−Zn 1Y−Zn 1Y−Zn 1Y−Zn 1Y−Zn Zn(OAc)2

[monomer]/[RE]

time (h)

T (°C)

yield (%)b

polycarbonate (%)c

Mn (× 103)d

Đd

125 125 125 125 125 125 125 125 125 125 125 125 250 500 250 250 250 125

24 24 24 24 24 24 24 24 24 24 24 24 24 24 24 40 24 24

70 70 70 70 70 70 70 50 90 110 90 90 90 90 90 90 90 70

9 5 7 9 71 42 58 34 88 43 75 16 83 36 66 94 42 44

75 60 90 93 56 59 59 35 53 41 53 0 68 70 69 75 53 80

2.5 2.5 4.1 4.2 4.3 3.1 6.4 4.0 6.4 3.9 5.2 6.8 3.1 4.3

9.50 8.72 8.42 13.44 12.79 3.16 6.47 1.22 6.91 8.98 9.86 8.78 1.34 4.66

a

Conditions: VTol/Vmonomer = 1:1, 30 bar CO2. bIsolated yield. cDetermined by 1H NMR spectroscopy. dDetermined by GPC versus polystyrene standards. eP = 20 bar. fP = 1 bar. gVTol/VCHO = 3:2. hWith the addition of BnOH. [monomer]/[RE]/[BnOH] = 250:1:1.

which explains the broad PDI and low Mn values.11,27 In addition, ether linkages in the polymer were also observed, which is consistent with 1H NMR spectra. The 1H NMR spectrum (Figure S21, Table 1, entry 13) of polymers revealed signals for the methine groups of carbonate linkages (4.64 ppm) and ether linkages (3.42 ppm) and for the capping 2hydroxyl cyclohexyl group (3.75 ppm).28 Thermal properties of polymers were studied by differential scanning calorimetry (DSC) (Figure S23). The glass-transition temperature (Tg) was determined to be 115.8 °C, which is comparable to the previously reported value of 114.9 °C.29 Cycloaddition of Epoxides and CO2. Homo- and heteronuclear complexes were also evaluated in catalyzing the formation of cyclic carbonates through the cycloaddition of epoxides and 1 bar CO2. In the presence of complex 3Nd (0.4 mol %) and cocatalyst tetrabutylammonium iodide (TBAI) (0.4 mol %), different reaction conditions were screened, and temperature was found to largely influence the reaction outcome (Table 2, entries 1−3). A good yield of 91% was obtained after 18 h of reaction at 100 °C (Table 2, entry 4). Different cocatalysts, that is, TBAI, tetrabutylammonium bromide (TBAB), tetra-n-octylammonium bromide (TOAB), and bis(triphenylphosphine)iminium chloride (PPNCl), were studied, and the best yield of 95% was obtained in the presence of TBAB (Table 2, entries 4−7). A good balance of nucleophilicity and leaving ability of the Br anion accounts for the good performance of TBAB.30 The yield of cyclic carbonate remained as the catalyst loading was halved (Table 2, entry 8). Under optimal conditions, RE metal complexes of different ionic radii showed differences in catalytic activities (Table 2, entries 9−11). Complex 4La of large ionic radius was most active, possibly due to the larger space for substrates to bind (Table 2, entry 11). Comparing heterometallic RE metal−zinc complexes with homonuclear RE complexes, the former were less efficient, which may also be attributed to their crowded coordination environment. Control experiments were conducted with TBAB, complex 4La, Zn(OAc)2, and Y(OAc)3, which all

Scheme 4. Copolymerization of Cyclohexene Oxide and CO2

pressure (Table 1, entries 11 and 12). Furthermore, decreasing the loading of the catalyst to 250−500:1 resulted in lower yields but improved selectivity for polycarbonate (ca. 70%) (Table 1, entries 9, 13, and 14). In an attempt to further increase the selectivity, the amount of toluene was increased, as it is reported that the presence of toluene suppressed homopolymerization;24 however, a yield drop was observed, whereas the selectivity remained (Table 1, entry 15). The overall optimal result (94% yield, 75% selectivity) was obtained in the monomer to complex 1Y−Zn ratio of 250:1 at 90 °C after 40 h of reaction (Table 1, entry 16). Polydispersity indices (PDIs) are, in general, broad for polymers, which may be ascribed to the degradation (vide supra), both cyclic and linear polymer formation (vide infra), and homopolymerization of CHO. The PDI became significantly narrower (1.34) after the addition of benzyl alcohol as the chain transfer agent (Table 1, entry 17).25 Compared with heteronuclear RE−Zn acetate complexes reported by Okuda and Mashima et al.,12 complexes in this Article showed a lower selectivity for polycarbonate. Their performance is not as good as that of the o-phenylenediaminebridged tri(phenolato) ligand-stabilized Nd−Zn benzyloxy complex either,11 emphasizing the influence of the ligand structure on the catalytic performance. MALDI-TOF mass spectrometry shows a few sets of signals with intervals of 142.07, corresponding to carbonate units (Figure 6). Moreover, the polymer chain is capped by the acetate group, which explains the poor performance of homometallic RE complexes (vide supra).26 Another possibility that cannot be ruled out is that a cyclic polymer may also form (having the same weight as that of OAc-capped linear polymer), resulting from intramolecular transesterification, 8779


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Figure 6. MALDI-TOF mass spectrum of polymer (sample prepared under the conditions stated in Table 1, entry 9).

a

(Table 3). Various monosubstituted epoxides bearing chloromethyl, phenyl, and butenyl group were converted into cyclic carbonates 7b−7d in excellent yield (93−95%) (Table 3, entries 1−3). It is noteworthy that epoxides substituted by the oxygen-containing group (i.e., ether and ester groups) reacted straightforwardly with CO2 and generated cyclic carbonates 7e−7i in 81−96% yield without an interfering interaction of epoxide with metal centers (Table 3, entries 4−8). The reaction of glycidol with CO2 proceeded sluggishly and generated cyclic carbonate 7j in 65% yield (Table 3, entry 9). Morpholine-substituted cyclic carbonate 7k was obtained in 82% yield (Table 3, entry 10). For sterically hindered disubstituted epoxides, increasing the pressure of CO2 to 10 bar and prolonging the reaction time to 40 h lead to cyclic carbonate formation in good yield of 60− 91% (Table 4). For 1,2-disubstituted epoxides, configuration retention was observed, proving that the reaction proceeds via two consecutive SN2 steps.9f,31 It is noteworthy that a mixture of cis- and trans-cyclic carbonate, polyether, and polycarbonate has been reported to form from the reaction of cis-configured cyclohexene oxide and CO2,14a,32 whereas in this study, cisconfigured cyclohexene oxide was converted almost exclusively to cis-cyclic carbonate 7n in a good yield of 86%.

showed inferior activity to that of 4La + TBAB (Table 2, entries 15−18). To study the scope of the cycloaddition reaction, a series of terminal epoxides was tested under optimized conditions

CONCLUSIONS We report the synthesis and structural characterization of homonuclear RE metal complexes (1Y, 2Yb, 3Nd, and 4La) and heteronuclear RE−Zn complexes (1Y−Zn, 3Nd−Zn, and 5Sm−Zn) stabilized by ethanolamine-bridged bis(phenolato) ligand. Because examples of RE−Zn acetate complexes are limited

Table 2. Reaction of CO2 and 1,2-Epoxyhexane (6a) Catalyzed by Complexes 1−5a entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

catalyst (mol %)a Nd

3 (0.4) 3Nd (0.4) 3Nd (0.4) 3Nd (0.4) 3Nd (0.4) 3Nd (0.4) 3Nd (0.4) 3Nd (0.2) 1Y (0.2) 2Yb (0.2) 4La (0.2) 1Y−Zn (0.2) 5Sm−Zn (0.2) 3Nd−Zn (0.2) 4La (0.2) Zn(OAc)2 (0.2) Y(OAc)3 (0.2)

cocatalyst (mol %)

T (°C)

t (h)

conversionc

TBAI (0.4) TBAI (0.4) TBAI (0.4) TBAI (0.4) TOAB (0.4) TBAB (0.4) PPNCl (0.4) TBAB (0.4) TBAB (0.4) TBAB (0.4) TBAB (0.4) TBAB (0.4) TBAB (0.4) TBAB (0.4) TBAB (0.4)

70 85 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100

12 12 12 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18

33 70 80 91 90 95 60 93 70 76 95 72 55 65 18 0 80 27

TBAB (0.4) TBAB (0.4)

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Reaction conditions: 1,2-epoxyhexane (10 mol), 1 bar CO2 (balloon), neat. bBased on rare-earth metal center. cDetermined by 1 H NMR spectroscopy.

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Inorganic Chemistry Table 3. Cycloaddition of Terminal Epoxides and CO2 Catalyzed by Complex 4La and TBABa

a Reaction conditions: 0.2 mol % catalyst 4La, 0.4 mol % TBAB, 18 h, 1 bar CO2 (balloon), 100 °C, neat. bIsolated yield. cSelectivities for the cyclic carbonate were all >99%.

in the literature, the isolation of complexes 1Y−Zn, 3Nd−Zn, and 5Sm−Zn, which are assembled through bridging acetate ligands, adds to the diversity of heteronuclear complexes. The activities of all seven complexes in catalyzing reactions of CO2 and epoxides were evaluated and compared. Heteronuclear RE−Zn complexes found application in the copolymerization of cyclohexene oxide and CO2, giving rise to acetate-groupcapped copolymers. Homonuclear complexes showed good activity in catalyzing the cycloaddition of variously monosubstituted epoxides and CO2 (1 bar) as well as sterically hindered disubstituted epoxides and CO2 (10 bar). Further study of the development of RE metal-based catalysts for CO2 transformation is ongoing in our laboratory.

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DD2-600 spectrometer. Crystal data were collected on Gemini Atlas and Japan Rigaku Saturn 724+ X-ray diffractometers (Mo Kα radiation). Structures were solved by direct methods and refined by a full-matrix least-squares technique based on F2 using the SHELXL program. All of the non-hydrogen atoms were refined anisotropically. Hydrogen atoms were generated geometrically. The molecular weight and PDI of polycarbonate were determined by gel permeation chromatography (GPC), which was performed on a TOSOH HLC8320GPC instrument at 40 °C with a flow of 0.35 mL/min and with THF as the eluent, calibrated with polystyrene standards. The MALDI-TOF mass for polymer studies was carried out by using a BRUKER Autoflex matrix-assisted laser desorption−ionization timeof-flight mass spectrometer. trans-2-[3-(4-tert-Butylphenyl)-2-methyl2-propenylidene]malononitrile was used as a matrix. CH3COONa was added for ion formation. DSC experiments were performed using a TA Instruments DSC 2010 analyzer by cycling between 0 and 200 °C with heating/cooling rates of 20 °C/min under a N2 atmosphere, and the data were analyzed by Universal Analysis 2000 software. PXRD was conducted by X’Pert-Pro MPD. Experimental Procedure. Synthesis of Ligand Precursor. The ligand precursor N,N-bis(2-hydroxy-3,5-di-tert-buthylbenzyl)-2-aminoethanol (LH3) was synthesized according to the literature procedure.16 1H NMR (CDCl3,400 MHz): δ 7.22 (d, J = 2.3 Hz, 2H, Ar-H), 6.90 (d, J = 2.3 Hz, 2H, Ar-H), 3.88 (t, J = 5.3 Hz, 2H, OCH2CH2N), 3.76 (s, 4H, NCH2Ar), 2.74 (t, J = 5.3 Hz, 2H, OCH2CH2N), 1.40 (s, 18H, C(CH3)3), 1.27 (s, 18H, C(CH3)3).

EXPERIMENTAL SECTION

General Considerations. All manipulations involving air- and moisture-sensitive compounds were carried out in a glovebox or using standard Schlenk techniques under argon. Solvents (tetrahydrofuran (THF), toluene, hexane) were dried by refluxing with sodium or CaH2. Epoxides were dried over CaH2. All solid starting materials were dried at 50 °C under vacuum. Elemental analysis was recorded on an Elementar Vario EL III analyzer. Infrared spectra were recorded on a ThermoFisher Nicolet 6700 spectrometer in the 400−4000 cm−1 region. 1H NMR spectra were recorded on a Bruker Ascend 400 spectrometer or an Agilent 8781


Article

Inorganic Chemistry

8.41; N, 1.78. IR (selected absorbance, cm−1): 2955 (−CH3), 2902 (CH2−), 2858 (−CH2−), 1473 (−CH2−), 1167 (C−N), 1064 (Ar), 1035 (−CH2−), 874 (Ar), 807 (Ar), 740 (Ar). 1H NMR (THF-d8, 400 MHz) δ 7.12 (s, 6H, ArH), 6.90 (s, 6H, ArH), 4.23 (s, 4H, CH2O), 3.54 (br, 8H, ArCH2N), 2.58 (br, 4H, CH2N), 1.36 (s, 36H, C(CH3)), 1.28 (s, 36H, C(CH3)). 13C NMR (THF-d8, 101 MHz) δ 134.6 (ArC), 134.3 (ArC), 125.7 (ArC), 124.2 (ArC), 122.6 (ArC), 61.8 (OCH2), 59.3 (NCH2Ar), 58.2 (NCH2), 34.6 (C(CH3)), 33.5 (C(CH3)), 31.4 (C(CH3)), 29.5 (C(CH3)). General Procedure for the Synthesis of Heteronuclear RE−Zn Complexes. After the reaction mixture of Cp3RE(THF) (1.5 mmol) and LH3 (0.73 g, 1.5 mmol) was stirred in THF for 12 h, Zn(OAc)2 (0.14 g, 0.75 mmol) was added and heated to 50 °C for 3 days. After the reaction, the solvent was removed in vacuo. The crude produce was washed with hexane (3 × 10 mL) and dissolved in THF and hexane. Crystals formed upon standing of solution. L4Y4Zn2(OAc)4(THF)2 (1Y−Zn). The compound was prepared from Cp3Y(THF) (0.66 g, 1.5 mmol) following the general procedure. Colorless crystals were obtained from the solution of 5 mL of THF and 5 mL of hexane at −12 °C (0.47 g, 43%). Anal. Calcd for C144H220N4O22Y4Zn2·2C6H14·2C4H8O: C, 62.29; H, 8.42; N, 1.77. Found: C, 62.27; H, 8.32; N, 1.68. IR (selected absorbance, cm−1): 2951 (−CH2−), 2868 (−CH2−), 1594 (CO), 1473 (−CH2−), 1167 (C−N), 1053 (C−O), 872 (Ar), 805 (Ar), 743 (Ar). 1H NMR (THF-d8, 400 MHz) δ 7.00 (s, 4H, ArH), 6.66 (s, 4H, ArH), 5.79 (ddd, J = 22.7, 5.7, 3.0 Hz, 2H, ArCH2N), 5.32 (ddd, J = 18.3, 5.8, 2.4 Hz, 2H, ArCH2N), 3.70 (br, 4H, CH2O), 2.73 (s, 2H, ArCH2N), 2.63 (s, 2H, ArCH2N), 2.54 (br, 4H, NCH2), 1.83 (s, 6H, CH3), 1.31− 1.27 (m, 32H, C(CH3)), 1.17−1.12 (s, 32H, C(CH3)). 13C NMR (THF-d8, 101 MHz) δ 136.83 (ArCH2N), 135.83 (ArCH2N), 133.13 (ArCH2N), 132.73 (Ar CH2N), 126.5 (ArC), 126.1 (ArC), 123.9 (ArC), 123.6 (ArC), 56.0 (OCH2), 47.3 (ArCH2N), 46.3 (ArCH2N), 42.4 (NCH2), 36.0 (C(CH3)3), 35.8 (C(CH3)3), 35.5 (C(CH3)3), 34.7 (C(CH3)3), 34.6 (C(CH3)3), 32.7 (C(CH3)3), 32.5 (C(CH3)3), 30.7 (C(CH3)3), 30.4 (C(CH3)3), 23.7 (CH3). L2Sm2Zn(OAc)2(THF)4 (5Sm−Zn). The compound was prepared from Cp3Sm(THF) (0.63 g, 1.5 mmol) following the general procedure. Orange crystals were obtained from the solution of 5 mL of THF and 3 mL of hexane at room temperature (0.69 g, 52%). Anal. Calcd for C84H134N2O14Sm2Zn·C6H14·C4H8O: C, 58.79; H, 8.19; N, 1.46. Found: C, 58.41; H, 8.04; N, 1.34. IR (selected absorbance, cm−1): 2953 (−CH2−), 2865 (−CH2−), 1559 (CO), 1459 (−CH2−), 1167 (C−N), 1038 (C−O), 875 (Ar), 806 (Ar), 743 (Ar). L2Nd2Zn(OAc)2(THF)4 (3Nd−Zn). The compound was prepared from Cp3Nd(THF) (0.62 g, 1.5 mmol) following the general procedure. Colorless crystals were obtained from the solution of 20 mL of THF and 1 mL of hexane at room temperature (0.73 g, 56%). Anal. Calcd for C84H134N2O14Nd2Zn·C6H14·C4H8O: C, 59.17; H, 8.24; N, 1.47. Found: C, 58.97; H, 8.17; N, 1.34. IR (selected absorbance, cm−1): 2953 (−CH2−), 2865 (−CH2−), 1559 (CO), 1459 (−CH2−), 1166 (C−N), 1038 (C−O), 877 (Ar), 803 (Ar), 742 (Ar). General Procedure for Synthesis of Polycarbonate under 30 bar CO2. Experiments were conducted in a 100 mL stainless-steel Parr reactor. The complex 1Y−Zn (60.7 mg, 0.08 mmol) and cyclohexene oxide (2.03 mL, 20.0 mmol) were dissolved in 2.03 mL of toluene. The mixture was transferred into the reactor preheated to 90 °C. The reactor was pressurized to 30 bar with CO2. After 40 h, the reactor was cooled in an ice bath, and the resulting mixture was analyzed by 1 H NMR spectroscopy to determine the yield and selectivity. The product was dissolved in 2 mL of CH2Cl2, and the polymer precipitated after the addition of 10 mL of ethanol. The product was isolated, dried in vacuo to constant weight, and analyzed. Polycarbonate.28a,b 1H NMR (CDCl3, 400 MHz, Table 1, entry 13): δ 4.64 (br, 2H, CHCH O P C H C ), 2.13 (br, 2H, OCH2(CH2)2CH2OCO), 1.73 (br, 4H, O(CH2)4OCO), 1.38 (br, CH2(CH2)2CH2). Polyether.28c 1H NMR (CDCl3, 400 MHz, Table 1, entry 13): δ 3.75 (s, 1H, CHCHOH), 3.45 (br, 2H, CHCHO), 1.89 (br, 2H, OCH 2 (CH 2 ) 2 CH 2 O), 1.63 (br, 4H, O(CH 2 ) 4 O), 1.28 (br, CH2(CH2)2CH2).

Table 4. Reaction of Disubstituted Epoxides and CO2 Catalyzed by Complex 4La and TBABa

a

Reaction conditions: 0.2 mol % catalyst 4La, 0.4 mol % TBAB, 40 h, 10 bar CO2, 100 °C. bIsolated yield. cSelectivities for the cyclic carbonate were all >99%. dcis/trans-6o = 22:78, cis/trans-7o = 21:79. General Procedure for the Synthesis of Homonuclear Rare-Earth Metal Complexes. Cp3RE(THF) (1.5 mmol) was treated with LH3 (0.73 g, 1.5 mmol) in THF (20 mL) at room temperature for 12 h. After the reaction, the solvent was removed in vacuo. The crude product was washed with hexane (3 × 10 mL) and dissolved in THF and hexane. Crystals formed upon standing of solution. L3Y3(THF)2 (1Y). The compound was prepared from Cp3Y(THF) (0.66 g, 1.5 mmol) following the general procedure. Colorless crystals were obtained from the solution of 10 mL of THF and 12 mL of hexane at −12 °C (0.47 g, 50%). Anal. Calcd for C104H160N3O11Y3· C6H14: C, 66.68; H, 8.85; N, 2.12. Found: C, 66.46; H, 8.10; N, 2.10. IR (selected absorbance, cm−1): 2955 (−CH3), 2926 (−CH2−), 2902 (−CH2−), 2858 (−CH2−), 1474 (−CH2−), 1167 (C−N), 1059 (C−O), 878 (Ar), 804 (Ar), 741 (Ar). 1H NMR (THF-d8, 400 MHz) δ 7.14 (s, 6H, ArH), 6.89 (s, 6H, ArH), 4.17 (s, 6H, CH2O), 3.49 (br, 12H, ArCH2N), 2.51 (br, 6H, CH2N), 1.33 (s, 54H, C(CH3)), 1.30 (s, 54H, C(CH3)). 13C NMR (THF-d8, 101 MHz) δ 161.1 (ArC), 135.1 (ArC), 134.7 (ArC), 125.0 (ArC), 123.8 (ArC), 122.7 (ArC), 61.8 (OCH2), 59.7 (NCH2Ar), 56.7 (NCH2), 34.6 (C(CH3)), 33.5 (C(CH3)), 31.6 (C(CH3)), 31.4 (C(CH3)). L3Yb3(THF)2 (2Yb). The compound was prepared from Cp3Yb(THF) (0.53 g, 1.5 mmol) following the general procedure. Colorless crystals were obtained from the solution of 3 mL of THF and 10 mL of hexane at −12 °C (0.60 g, 56%). Anal. Calcd for C104H160N3O11Yb3·2C6H14: C, 60.06; H, 8.17; N, 1.81. Found: C, 60.67; H, 7.94; N, 1.86. IR (selected absorbance, cm−1): 2955 (−CH3), 2926 (−CH2−), 2902 (−CH2−), 2858 (−CH2−), 1474 (−CH2−), 1167 (C−N), 1059 (C−O), 878 (Ar), 804 (Ar), 741 (Ar). L2Nd2(THF)4 (3Nd). The compound was prepared from Cp3Nd(THF)4 (0.62 g, 1.5 mmol) following the general procedure. Blue crystals were obtained from the solution of 15 mL of THF and 2 mL of hexane at room temperature (0.53 g, 45%). Anal. Calcd for C80H128N2O10Nd2: C, 61.34; H, 8.24; N, 1.79. Found: C, 61.59; H, 8.37; N, 1.78. IR (selected absorbance, cm−1): 2955 (−CH3), 2902 (−CH2−), 2858 (−CH2−), 1474 (−CH2−), 1167 (C−N), 1064 (Ar), 1035 (−CH2−), 878 (Ar), 804 (Ar), 741 (Ar). L2La2(THF)4 (4La). The compound was prepared from Cp3La(THF) (0.61 g, 1.5 mmol) following the general procedure. Colorless crystals were obtained from the solution of 18 mL of THF and 2 mL of hexane at room temperature (0.56 g, 48%). Anal. Calcd for C80H128N2O10La2: C, 61.76; H, 8.29; N, 1.80. Found: C, 61.94; H, 8782


Article

Inorganic Chemistry

cis-Tetrahydro-furo[3,4-d]-1,3-dioxolan-2-one (cis-7m).30 1H NMR (CDCl3, 400 MHz): δ 5.18 (m, 2H, OCH), 4.24−4.20 (m, 2H, OCH2), 3.55−3.52 (m, 2H, OCH2). cis-1,2-Cyclohexane Carbonate (cis-7n).30 1H NMR (CDCl3, 400 MHz): δ 4.70−4.69 (m, 2H, OCHCH2), 1.91−1.89 (m, 4H, OCHCH2), 1.65−1.61 (m, 2H, CH2), 1.45−1.44 (m, 2H, CH2). trans-4,5-Dimethyl-1,3-dioxolan-2-one (trans-7o).30 1H NMR (CDCl3, 400 MHz): δ 4.386−4.80 (m, 2H, CH), 1.37−1.35 (m, 6H, CH3). cis-4,5-Dimethyl-1,3-dioxolan-2-one (cis-7o). 30 1 H NMR (CDCl3, 400 MHz): δ 4.35−4.33 (m, 2H, CH), 1.45−1.40 (m, 6H, CH3). 4,4-Dimethyl-1,3-dioxolan-2-one (7p).30 1H NMR (CDCl3, 400 MHz): δ 4.12 (s, 2H, CH2), 1.49 (s, 6H, CH3).

General Procedure for Synthesis of Cyclic Carbonate under 1 bar CO2. The 1,2-epoxyhexane (1.20 mL, 10.0 mmol), complex 4La (15.5 mg, 0.2 mol %), and TBAB (12.9 mg, 0.4 mol %) were placed in a 5 mL flask. A CO2 balloon was connected to the flask. The reaction mixture was heated to 100 °C for 18 h. The conversion of epoxide to cyclic carbonate was determined by 1H NMR spectroscopy. The product was purified by flash chromatography (hexane and ethylene acetate). General Procedure for Synthesis of Cyclic Carbonate under 10 bar CO2. Experiments were conducted in a 100 mL stainless-steel Parr reactor. Complex 4La (15.5 mg, 0.2 mol %) and TBAB (12.9 mg, 0.4 mol %) were dissolved in cyclohexene oxide (1.02 mL, 10.0 mmol). The mixture was transferred to the reactor preheated to 100 °C. The reactor was pressurized to 10 bar with CO2. After 40 h, the reactor was cooled in an ice bath, and the resulting mixture was analyzed by 1 H NMR spectroscopy to determine the yield and selectivity. The product was purified by flash chromatography (hexane and ethylene acetate) and confirmed by comparison with literature data. 4-Butyl-1,3-dioxolan-2-one (7a).30 1H NMR (CDCl3, 400 MHz) δ 4.72−4.64 (m, 1H, CHO), 4.53 (t, J = 8.8 Hz, 1H, OCH2), 4.07 (t, J = 8.2 Hz, 1H, OCH2), 1.86−1.76 (m, 1H, CH2), 1.70−1.63 (m, 1H, CH2), 1.37−1.29 (m, 4H, CH2), 0.92 (t, J = 6.8 Hz, 3H, CH3). 4-Chloromethyl-1,3-dioxolan-2-one (7b).30 1H NMR (CDCl3, 400 MHz): δ 4.98−4.93 (m, 1H, OCH), 4.55 (t, J = 8.3 Hz, 1H, OCH2), 4.36 (m, 1H, OCH2), 3.75−3.67 (m, 2H, ClCH2). 4-Phenyl-1,3-dioxolan-2-one (7c).30 1H NMR (CDCl3, 400 MHz): δ 7.34−7.40 (m, 5H, ArH), 5.65 (t, J = 8.2 Hz, 1H, OCH), 4.77 (t, J = 8.6 Hz, 1H, OCH2), 4.31 (t, J = 8.4 Hz, 1H, OCH2). 4-(3-Butenyl)-1,3-dioxolan-2-one (7d).10a 1H NMR (CDCl3, 400 MHz): δ 5.71−5.79 (m, 1H, CHCH2), 5.02−5.08 (m, 2H, CH CH2), 4.67−4.71 (m, 1H, OCH), 4.48−4.52 (t, J = 8.0 Hz, 1H, OCH2), 4.04−4.08 (t, J = 8.3 Hz, 1H, OCH2), 2.19 (m, 2H, CH2), 1.75−2.29 (m, 4H, CH2). 4-Phenoxymethyl-1,3-dioxolan-2-one (7e).10a 1H NMR (CDCl3, 400 MHz): δ 7.28 (t, J = 7.9 Hz, 2H, ArH), 6.99 (t, J = 7.3 Hz, 1H, ArH), 6.90 (d, J = 8.2 Hz, 2H, ArH), 4.99−5.00 (m, 1H, OCH), 4.57−4.51 (m, 2H, OCH2), 4.22−4.08 (m, 2H, OCH2). 4-Methoxymethyl-1,3-dioxolan-2-one (7f).10a 1H NMR (CDCl3, 400 MHz): δ 4.80−4.74 (m, 1H, OCH), 4.45 (t, J = 8.5 Hz, 1H, OCH2), 4.32 (m, 1H, OCH2), 3.61−3.49 (m, 2H, OCH2), 3.37 (s, 3H, OCH3). 4-Allyoxymethyl-1,3-dioxolan-2-one (7g).30 1H NMR (CDCl3, 400 MHz): δ 5.88−5.75 (m, 1H, CHCH2), 5.19−5.12 (m, 2H, CHCH2), 4.81−4.77 (m, 1H, OCH), 4.47 (t, J = 8.4 Hz, 1H, OCH2), 4.36 (m, 1H, OCH2), 4.01−4.00 (m, 2H, OCH2), 3.64−3.49 (m, 2H, OCH2). 4-Butoxymethyl-1,3-dioxolan-2-one (7h).30 1H NMR (CDCl3, 400 MHz): δ 4.80−4.75 (m, 1H, OCH), 4.46 (t, J = 8.0 Hz, 1H, OCH2), 4.35−4.34 (m, 1H, OCH2), 3.62−3.58 (m, 2H, OCH2CH), 3.48 (t, J = 6.4 Hz, 2H, OCH2CH2), 1.52−1.40 (m, 2H, CH2), 1.38− 1.30 (m, 2H, CH2), 0.88 (t, 3H, CH3). 4-tert-Butyl-benzoic Acid 2-Oxo-[1,3]dioxolan-4-ylmethyl Ester (7i).30 1H NMR (CDCl3, 400 MHz): δ 7.91 (d, J = 8.6 Hz, 2H, ArH), 7.44 (d, J = 8.5 Hz, 2H, ArH), 5.01 (m, 1H, OCH), 4.57−4.62 (m, 1H, OCH2), 4.56−4.46 (m, 2H, OCH2), 4.41−4.37 (m, 1H, OCH2), 1.31 (s, 9H, C(CH3)3). 4-Hydroxymethyl-1,3-dioxolan-2-one (7j).30 1H NMR (CDCl3, 400 MHz): δ 4.80−4.76 (m, 1H, OCH), 4.50 (m, 1H, OCH2), 4.43 (m, 1H, OCH2), 3.99−3.96 (m, 1H, CH2OH), 3.72−3.69 (m, 1H, CH2OH). 4-(Morpholinomethyl)-1,3-dioxolan-2-one (7k).30 1H NMR (CDCl3, 400 MHz): δ 4.84−4.77 (m, 2H, CH), 4.50 (t, J = 8 Hz, 1H, OCH2), 4.20 (t, J = 8 Hz, 1H, OCH2), 3.66 (t, J = 4.6 Hz, 4H, OCHCH2N), 2.66−2.65 (m, 2H, OCH2CH2N), 2.55−2.52 (m, 4H, OCH2CH2N). cis-1,2-Cyclopentene Carbonate (cis-7l).30 1H NMR (CDCl3, 400 MHz): δ 5.07−5.03 (m, 2H, OCHCH2), 2.10−2.08 (m, 2H, CH2), 1.77−1.65 (m, 4H, CH2).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b01169. NMR, IR, and PXRD spectra and solid-state structures of complexes. Characterization data of polymers and cyclic carbonates (PDF) Accession Codes

CCDC 1893126, 1893682−1893684, and 1893686−1893688 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc. cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (D.Y.). *E-mail: [email protected] (Y.Y.). ORCID

Dan Yuan: 0000-0002-4816-0842 Yingming Yao: 0000-0001-9841-3169 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the National Natural Science Foundation of China (grants 21871198 and 21674070), the Project of Scientific and Technologic Infrastructure of Suzhou (SZS201708), the Open Research Fund of State Key Laboratory of Polymer Physics and Chemistry (CIAC), and PAPD. Professor Marc Henry from University of Strasbourg is thanked for suggestions.

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REFERENCES

(1) (a) Sakakura, T.; Kohno, K. The synthesis of organic carbonates from carbon dioxide. Chem. Commun. 2009, 1312. (b) Guo, W.; Gómez, J. E.; Cristòfol, À .; Xie, Ji; Kleij, A. W. Catalytic transformations of functionalized cyclic organic carbonates. Angew. Chem., Int. Ed. 2018, 57, 13735. (2) (a) Fukuoka, S.; Kawamura, M.; Komiya, K.; Tojo, M.; Hachiya, H.; Hasegawa, K.; Aminaka, M.; Okamoto, H.; Fukawa, I.; Konno, S. A novel non-phosgene polycarbonate production process using byproduct CO2 as starting material. Green Chem. 2003, 5, 497. (b) Luinstra, G. A. Poly(propylene carbonate), old copolymers of propylene oxide and carbon dioxide with new interests: catalysis and material properties. Polym. Rev. 2008, 48, 192. 8783


Article

Inorganic Chemistry

Gonzalez, M. D.; Cuesta-Aluja, L.; Castilla, J.; Orejon, A.; El Guemmout, F.; Masdeu-Bulto, A. M. Chromium complexes with tridentate NN’O Schiff base ligands as catalysts for the coupling of CO2 and epoxides. J. Mol. Catal. A: Chem. 2014, 383, 143. (f) Gurnham, J.; Gambarotta, S.; Korobkov, I.; Jasinska-Walc, L.; Duchateau, R. Chromium-catalyzed CO2-epoxide copolymerization. Organometallics 2014, 33, 4401. (g) Elmas, S.; Subhani, M. A.; Harrer, M.; Leitner, W.; Sundermeyer, J.; Muller, T. E. Highly active Cr(III) catalysts for the reaction of CO2 with epoxides. Catal. Sci. Technol. 2014, 4, 1652. (h) Darensbourg, D. J.; Mackiewicz, R. M. Role of the cocatalyst in the copolymerization of CO2 and cyclohexene oxide utilizing chromium salen complexes. J. Am. Chem. Soc. 2005, 127, 14026. (7) (a) Ma, R.; He, L.-N.; Zhou, Y.-B. An efficient and recyclable tetraoxo-coordinated zinc catalyst for the cycloaddition of epoxides with carbon dioxide at atmospheric pressure. Green Chem. 2016, 18, 226. (b) Hu, J.; Ma, J.; Zhu, Q.; Qian, Q.; Han, H.; Mei, Q.; Han, B. Zinc(II)-catalyzed reactions of carbon dioxide and propargylic alcohols to carbonates at room temperature. Green Chem. 2016, 18, 382. (c) Reiter, M.; Vagin, S.; Kronast, A.; Jandl, C.; Rieger, B. A Lewis acid β-diiminato-zinc-complex as all-rounder for co- and terpolymerisation of various epoxides with carbon dioxide. Chem. Sci. 2017, 8, 1876. (d) Kernbichl, S.; Reiter, M.; Adams, F.; Vagin, S.; Rieger, B. CO2-controlled one-pot synthesis of AB, ABA Block, and statistical terpolymers from β-butyrolactone, epoxides, and CO2. J. Am. Chem. Soc. 2017, 139, 6787. (e) Moore, D. R.; Cheng, M.; Lobkovsky, E. B.; Coates, G. W. Mechanism of the alternating copolymerization of epoxides and CO2 using β-diiminate zinc catalysts: Evidence for a bimetallic epoxide enchainment. J. Am. Chem. Soc. 2003, 125, 11911. (f) Xiao, Y. L.; Wang, Z.; Ding, K. L. Copolymerization of cyclohexene oxide with CO2 by using intramolecular dinuclear zinc catalysts. Chem. - Eur. J. 2005, 11, 3668. (8) (a) Lu, X.-B.; Darensbourg, D. J. Cobalt catalysts for the coupling of CO2 and epoxides to provide polycarbonates and cyclic carbonates. Chem. Soc. Rev. 2012, 41, 1462. (b) Ren, W.-M.; Liu, Y.; Wu, G.-P.; Liu, J.; Lu, X.-B. Stereoregular polycarbonate synthesis: Alternating copolymerization of CO2 with aliphatic terminal epoxides catalyzed by multichiral cobalt(III) complexes. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 4894. (c) Viciano, M.; Munoz, B. K.; Godard, C.; Castillon, S.; Reyes, M. L.; Garcia-Ruiz, M.; Claver, C. Salcynaphthalene cobalt complexes as catalysts for the synthesis of high molecular weight polycarbonates. ChemCatChem 2017, 9, 3974. (d) Hošt’álek, Z.; Mundil, R.; Císařová, I.; Trhlíková, O.; Grau, E.; Peruch, F.; Cramail, H.; Merna, J. Salphen-Co(III) complexes catalyzed copolymerization of epoxides with CO2. Polymer 2015, 63, 52. (e) Hatazawa, M.; Nakabayashi, K.; Ohkoshi, S.; Nozaki, K. In situ generation of CoIII−salen complexes for copolymerization of propylene oxide and CO2. Chem. - Eur. J. 2016, 22, 13677. (f) Anderson, C. E.; Vagin, S. I.; Xia, W.; Jin, H.; Rieger, B. Cobalt oporphyrin-catalyzed CO2/epoxide copolymerization: selectivity control by molecular design. Macromolecules 2012, 45, 6840. (g) Reiter, M.; Altenbuchner, P. T.; Kissling, S.; Herdtweck, E.; Rieger, B. Amine-bis(phenolato)cobalt(II) catalysts for the formation of organic carbonates from carbon dioxide and epoxides. Eur. J. Inorg. Chem. 2015, 2015, 1766. (h) Qin, Z.; Thomas, C. M.; Lee, S.; Coates, G. W. Cobalt-based complexes for the copolymerization of propylene oxide and CO2: active and selective catalysts for polycarbonate synthesis. Angew. Chem., Int. Ed. 2003, 42, 5484. (i) Sugimoto, H.; Kuroda, K. The cobalt porphyrin-Lewis base system: a highly selective catalyst for alternating copolymerization of CO2 and epoxide under mild conditions. Macromolecules 2008, 41, 312. (j) Liu, Y.; He, K.; Ren, W.; Li, R.; Lu, X. Adjustable crystalline stereocomplexes from enantiopure gradient polycarbonates. Sci. China: Chem. 2016, 59, 1415. (9) (a) Nakano, K.; Kobayashi, K.; Ohkawara, T.; Imoto, H.; Nozaki, K. Copolymerization of epoxides with carbon dioxide catalyzed by iron-corrole complexes: Synthesis of a crystalline copolymer. J. Am. Chem. Soc. 2013, 135, 8456. (b) Taherimehr, M.; Al-Amsyar, S. M.; Whiteoak, C. J.; Kleij, A. W.; Pescarmona, P. P.

(3) (a) Zhang, H.; Grinstaff, M. W. Synthesis of a tactic and isotactic poly(1,2-glycerol carbonate)s: degradable polymers for biomedical and pharmaceutical applications. J. Am. Chem. Soc. 2013, 135, 6806. (b) Paul, S.; Romain, C.; Shaw, J.; Williams, C. K. Sequence selective polymerization catalysis: A new route to ABA block copoly(ester-bcarbonate-b-ester). Macromolecules 2015, 48, 6047. (4) (a) Maeda, C.; Taniguchi, T.; Ogawa, K.; Ema, T. Bifunctional catalysts based on m-phenylene-bridged porphyrin dimer and trimer platforms: synthesis of cyclic carbonates from carbon dioxide and epoxides. Angew. Chem., Int. Ed. 2015, 54, 134. (b) Wang, L.; Zhang, G.; Kodama, K.; Hirose, T. An efficient metal- and solvent-free organocatalytic system for chemical fixation of CO2 into cyclic carbonates under mild conditions. Green Chem. 2016, 18, 1229. (c) Liu, N.; Xie, Y.-F.; Wang, C.; Li, S.-J.; Wei, D.; Li, M.; Dai, B. Cooperative multifunctional organocatalysts for ambient conversion of carbon dioxide into cyclic carbonates. ACS Catal. 2018, 8, 9945. (d) Tanaka, S.; Nakashima, T.; Maeda, T.; Ratanasak, M.; Hasegawa, J. Y.; Kon, Y.; Tamura, M.; Sato, K. ACS Catal. 2018, 8, 1097. (e) Hu, J.; Ma, J.; Liu, H.; Qian, Q.; Xie, C.; Han, B. Dual-ionic liquid system: an efficient catalyst for chemical fixation of CO2 to cyclic carbonates under mild conditions. Green Chem. 2018, 20, 2990. (f) Ding, M.; Jiang, H.-L. Incorporation of imidazolium-based poly(ionic liquid)s into a metal-organic framework for CO2 capture and conversion. ACS Catal. 2018, 8, 3194. (g) Fiorani, G.; Guo, W.; Kleij, A. W. Sustainable conversion of carbon dioxide: the advent of organocatalysis. Green Chem. 2015, 17, 1375. (h) Maisonneuve, L.; Lamarzelle, O.; Rix, E.; Grau, E.; Cramail, H. Isocyanate-free routes to polyurethanes and poly(hydroxy urethane)s. Chem. Rev. 2015, 115, 12407. (i) Yuan, G.; Zhao, Y.; Wu, Y.; Li, R.; Chen, Y.; Xu, D.; Liu, Z. Cooperative effect from cation and anion of pyridine-containing anion-based ionic liquids for catalysing CO2 transformation at ambient conditions. Sci. China: Chem. 2017, 60, 958. (5) (a) Kindermann, N.; Cristofol, A.; Kleij, A. W. Access to biorenewable polycarbonates with unusual glass-transition temperature (Tg) modulation. ACS Catal. 2017, 7, 3860. (b) Wang, Y.; Zhao, Y. J.; Ye, Y. S.; Peng, H. Y.; Zhou, X. P.; Xie, X. L.; Wang, X. H.; Wang, F. S. A one-step route to CO2-based block copolymers by simultaneous ROCOP of CO2/epoxides and RAFT polymerization of vinyl monomers. Angew. Chem., Int. Ed. 2018, 57, 3593. (c) Sheng, X. F.; Wang, Y.; Qin, Y. S.; Wang, X. H.; Wang, F. S. Aluminum porphyrin complexes via delicate ligand design: emerging efficient catalysts for high molecular weight poly(propylene carbonate). RSC Adv. 2014, 4, 54043. (d) Wu, W.; Sheng, X. F.; Qin, Y. S.; Qiao, L. J.; Miao, Y. Y.; Wang, X. H.; Wang, F. S. Bifunctional aluminum porphyrin complex: Soil tolerant catalyst for copolymerization of CO2 and propylene oxide. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2346. (e) Fuchs, M. A.; Altesleben, C.; Zevaco, T. A.; Dinjus, E. An efficient homogeneous chloro−aluminum−[N2O2] catalyst for the coupling of epoxides with carbon dioxide. Eur. J. Inorg. Chem. 2013, 2013, 4541. (f) Yamaguchi, K.; Ebitani, K.; Yoshida, T.; Yoshida, H.; Kaneda, K. Mg−Al mixed oxides as highly active acid−base catalysts for cycloaddition of carbon dioxide to epoxides. J. Am. Chem. Soc. 1999, 121, 4526. (g) Luo, R.; Yang, Z.; Zhang, W.; Zhou, X.; Ji, H. Recyclable bifunctional aluminum salen catalyst for CO2 fixation: the efficient formation of five-membered heterocyclic compounds. Sci. China: Chem. 2017, 60, 979. (6) (a) Castro-Osma, J. A.; Lamb, K. J.; North, M. Cr(salophen) complex catalyzed cyclic carbonate synthesis at ambient temperature and pressure. ACS Catal. 2016, 6, 5012. (b) Ni, K.; Kozak, C. M. Kinetic studies of copolymerization of cyclohexene oxide with CO2 by a diamino-bis(phenolate) chromium(III) complex. Inorg. Chem. 2018, 57, 3097. (c) Darensbourg, D. J.; Chung, W. C.; Yeung, A. D.; Luna, M. Dramatic behavioral differences of the copolymerization reactions of 1,4-cyclohexadiene and 1,3-cyclohexadiene oxides with carbon dioxide. Macromolecules 2015, 48, 1679. (d) Cuesta-Aluja, L.; Djoufak, M.; Aghmiz, A.; Rivas, R.; Christ, L.; Masdeu-Bulto, A. M. Novel chromium (III) complexes with N4-donor ligands as catalysts for the coupling of CO2 and epoxides in supercritical CO2. J. Mol. Catal. A: Chem. 2014, 381, 161. (e) Iksi, S.; Aghmiz, A.; Rivas, R.; 8784


Article

Inorganic Chemistry

(11) Qin, J.; Xu, B.; Zhang, Y.; Yuan, D.; Yao, Y. Cooperative rare earth metal−zinc based heterometallic catalysts for copolymerization of CO2 and cyclohexene oxide. Green Chem. 2016, 18, 4270. (12) Nagae, H.; Aoki, R.; Akutagawa, S.; Kleemann, J.; Tagawa, R.; Schindler, T.; Choi, G.; Spaniol, T. P.; Tsurugi, H.; Okuda, J.; Mashima, K. Lanthanide complexes supported by a trizinc crown ether as catalysts for alternating copolymerization of epoxide and CO2: telomerization controlled by carboxylate anions. Angew. Chem., Int. Ed. 2018, 57, 2492. (13) (a) Carpentier, J.-F. Rare-earth complexes supported by tripodal tetradentate bis(phenolate) ligands: a privileged class of catalysts for ring-opening polymerization of cyclic esters. Organometallics 2015, 34, 4175. (b) Ouyang, H.; Nie, K.; Yuan, D.; Zhang, Y.; Cui, D.; Yao, Y. A convenient method to prepare random LA/CL copolymers from poly(L-lactide) and ε-caprolactone. Sci. China: Chem. 2018, 61, 708. (c) Sun, Q.; Chen, P.; Wang, Y.; Luo, Y.; Yuan, D.; Yao, Y. Addition of C−H bonds of pyridine derivatives to alkenes catalyzed by zirconium complexes bearing amine-bridged bis(phenolato) ligands. Inorg. Chem. 2018, 57, 11788. (14) (a) Gao, P.; Zhao, Z.; Chen, L.; Yuan, D.; Yao, Y. Dinuclear Aluminum poly(phenolate) complexes as efficient catalysts for cyclic carbonate synthesis. Organometallics 2016, 35, 1707. (b) Safaei, E.; Rasouli, M.; Weyhermüller, T.; Bill, E. Synthesis and characterization of binuclear [ONXO]-type amine-bis(phenolate) copper(II) complexes. Inorg. Chim. Acta 2011, 375, 158. (c) Yu, G.; Chen, J.-Y.; Cai, Z.-M.; Zhan, S.-Z. Synthesis, Structures, and Magnetic Behavior of Two Binuclear Fe(III) Complexes of N-(1-ethanol)-N,N-bis(3,5-ditert-butyl-2-hydroxybenxyl)amine and N-(3-amino-1- propanol)-N,Nbis(3,5-di-tert-butyl-2-hydroxybenxyl)amine. Synth. React. Inorg., Met.Org., Nano-Met. Chem. 2014, 44, 48. (d) Laurén, E.; Kivelä, H.; Hänninen, M.; Lehtonen, A. Oxidomolybdenum(VI) complexes with atrane-type [O3N] ligands. Polyhedron 2009, 28, 4051. (e) Padmanabhan, S.; Katao, S.; Nomura, K. Synthesis and Structure of Titanatranes Containing Tetradentate Trianionic Donor Ligands of the Type [(O-2,4-R2C6H2-6-CH2)2(OCH2CH2)]N3− and their use in catalysis for ethylene polymerization. Organometallics 2007, 26, 1616. (f) Ghosh, S.; Antharjanam, P. K. S.; Chakraborty, D. Magnesium complexes of the N, O polydentate scaffold: synthesis, structural characterization and polymerization studies. Polymer 2015, 70, 38. (g) Wichmann, O.; Sopo, H.; Lehtonen, A.; Sillanpää, R. Oxidovanadium(V) complexes with aminoethanol bis(phenolate) [O,N,O,O’] ligands: preparations, structures, n-dealkylation and condensation reactions. Eur. J. Inorg. Chem. 2011, 2011, 1283. (15) (a) Cheng, H.; Zhao, B.; Yao, Y.; Lu, C. Carboxylation of terminal alkynes with CO2 catalyzed by bis(amidate) rare-earth metal amides. Green Chem. 2015, 17, 1675. (b) Xu, B.; Wang, P.; Lv, M.; Yuan, D.; Yao, Y. Transformation of carbon dioxide into oxazolidinones and cyclic carbonates catalyzed by rare-earth-metal phenolates. ChemCatChem 2016, 8, 2466. (c) Zhao, Z.; Qin, J.; Zhang, C.; Wang, Y.; Yuan, D.; Yao, Y. Recyclable single-component rare-earth metal catalysts for cycloaddition of CO2 and epoxides at atmospheric pressure. Inorg. Chem. 2017, 56, 4568. (d) Xu, Y.; Yuan, D.; Wang, Y.; Yao, Y. Aluminum complexes derived from a hexadentate salen-type Schiff base: synthesis, structure, and catalysis for cyclic carbonate synthesis. Dalton Trans. 2017, 46, 5848. (e) Xie, Y.; Lu, C.; Zhao, B.; Wang, Q.; Yao, Y. Cycloaddition of aziridine with CO2/CS2 catalyzed by amidato divalent lanthanide complexes. J. Org. Chem. 2019, 84, 1951. (16) Sopo, H.; Sviili, J.; Valkonen, A.; Sillanpäa,̈ R. Uranyl ion complexes with aminoalcoholbis(phenolate) [O,N,O,O′] donor ligands. Polyhedron 2006, 25, 1223. (17) Pan, L.; Huang, X.; Li, J.; Wu, Y.; Zheng, N. Novel single- and double-layer and three-dimensional structures of rare-earth metal coordination polymers: the effect of lanthanide contraction and acidity control in crystal structure formation. Angew. Chem., Int. Ed. 2000, 39, 527. (18) (a) Yoshidomi, T.; Fukushima, T.; Itami, K.; Segawa, Y. Synthesis, structure, and electrochemical property of a bimetallic bis2-pyridylidene palladium acetate complex. Chem. Lett. 2017, 46, 587.

High activity and switchable selectivity in the synthesis of cyclic and polymeric cyclohexene carbonates with iron amino triphenolate catalysts. Green Chem. 2013, 15, 3083. (c) Taherimehr, M.; Serta, J.; Kleij, A. W.; Whiteoak, C. J.; Pescarmona, P. P. New iron pyridylamino-bis(phenolate) catalyst for converting CO2 into cyclic carbonates and cross-linked polycarbonates. ChemSusChem 2015, 8, 1034. (d) Adolph, M.; Zevaco, T. A.; Walter, O.; Dinjus, E.; Doring, M. Easy-to-handle ionic transition metal complexes in the formation of carbonates from epoxides and CO2: a N4-ligand system based on N,N-bis(2-pyridinecarboxamide)-1,2-benzene. Polyhedron 2012, 48, 92. (e) Gu, G.-G.; Yue, T.-J.; Wan, Z.-Q.; Zhang, R.; Lu, X.-B.; Ren, W.-M. A single-site iron(III)-salan catalyst for converting COS to sulfur-containing polymers. Polymers 2017, 9, 515. (f) Buchard, A.; Kember, M. R.; Sandeman, K. G.; Williams, C. K. A bimetallic iron(III) catalyst for CO2/epoxide coupling. Chem. Commun. 2011, 47, 212. (10) (a) Wang, L.; Xu, C.; Han, Q.; Tang, X.; Zhou, P.; Zhang, R.; Gao, G.; Xu, B.; Qin, W.; Liu, W. Ambient chemical fixation of CO2 using a highly efficient heterometallic helicate catalyst system. Chem. Commun. 2018, 54, 2212. (b) Wang, G.; Xu, C.; Wang, L.; Liu, W. Highly efficient 3d/4d-4f coordination polymer catalysts for carbon dioxide fixation into cyclic carbonates. Dalton Trans. 2018, 47, 12711. (c) Wang, L.; Zhang, R.; Han, Q.; Xu, C.; Chen, W.; Yang, H.; Gao, G.; Qin, W.; Liu, W. Amide-functionalized heterometallic helicate cages as highly efficient catalysts for CO2 conversion under mild conditions. Green Chem. 2018, 20, 5311. (d) Xu, H.; Zhai, B.; Cao, C.-S.; Zhao, B. A bifunctional Europium-organic framework with chemical fixation of CO2 and Luminescent detection of Al3+. Inorg. Chem. 2016, 55, 9671. (e) Qin, J.; Wang, P.; Li, Q.; Zhang, Y.; Yuan, D.; Yao, Y. Catalytic production of cyclic carbonates mediated by lanthanide phenolates under mild conditions. Chem. Commun. 2014, 50, 10952. (f) Das, S. K.; Chatterjee, S.; Bhunia, S.; Mondal, A.; Mitra, P.; Kumari, V.; Pradhan, A.; Bhaumik, A. A new strongly paramagnetic cerium-containing microporous MOF for CO2 fixation under ambient conditions. Dalton Trans. 2017, 46, 13783. (g) Wei, N.; Zuo, R.-X.; Zhang, Y.-Y.; Han, Z.-B.; Gu, X.-J. Robust highconnected rare-earth MOFs as efficient heterogeneous catalysts for CO2 conversion. Chem. Commun. 2017, 53, 3224. (h) Lazarov, B. B.; Hampel, F.; Hultzsch, K. C. Z. Synthesis and structural characterization of β-diketiminato yttrium complexes and their application in epoxide/CO2-copolymerization. Z. Anorg. Allg. Chem. 2007, 633, 2367. (i) Zhang, Z.; Cui, D.; Liu, X. Alternating copolymerization of cyclohexene oxide and carbon dioxide catalyzed by noncyclopentadienyl rare-earth metal bis(alkyl) complexes. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 6810. (j) Decortes, A.; Haak, R. M.; Martín, C.; Belmonte, M. M.; Martin, E.; Benet-Buchholz, J.; Kleij, A. W. Copolymerization of CO2 and cyclohexene oxide mediated by Yb(salen)-based complexes. Macromolecules 2015, 48, 8197. (k) Chen, X.; Shen, Z.; Zhang, Y. New catalytic systems for the fixation of carbon dioxide. 1. copolymerization of carbon dioxide and propylene oxide with new rare-earth catalysts-RE(P204)3-Al(i-Bu)3R(OH)n. Macromolecules 1991, 24, 5305. (l) Tan, C.-S.; Hsu, T.-J. Alternating copolymerization of carbon dioxide and propylene oxide with a rare-earth-metal coordination catalyst. Macromolecules 1997, 30, 3147. (m) Hsu, T.-J.; Tan, C.-S. Synthesis of polyethercarbonate from carbon dioxide and cyclohexene oxide by yttrium-metal coordination catalyst. Polymer 2001, 42, 5143. (n) Guo, J.-T.; Wang, X.-Y.; Xu, Y.-S.; Sun, J.-W. Copolymerizations of carbon dioxide and epoxides in the presence of rare earth coordinate catalyst. J. Appl. Polym. Sci. 2003, 87, 2356. (o) Quan, Z.; Wang, X.; Zhao, X.; Wang, F. Copolymerization of CO2 and propylene oxide under rare earth ternary catalyst: design of ligand in yttrium complex. Polymer 2003, 44, 5605. (p) Cui, D.; Nishiura, M.; Hou, Z. Alternating copolymerization of cyclohexene oxide and carbon dioxide catalyzed by organo rare earth metal complexes. Macromolecules 2005, 38, 4089. (q) Cui, D.; Nishiura, M.; Tardif, O.; Hou, Z. Rare-earth-metal mixed hydride/aryloxide complexes bearing mono(cyclopentadienyl) ligands. synthesis, CO2 fixation, and catalysis on copolymerization of CO2 with cyclohexene oxide. Organometallics 2008, 27, 2428. 8785


Article

Inorganic Chemistry (b) Hyslop, J. S.; Boydstun, A. R.; Fereday, T. R.; Rusch, J. R.; Strunk, J. L.; Wall, C. T.; Pena, C. C.; McKibben, N. L.; Harris, J. D.; Thurber, A.; Punnoose, A.; Brotherton, J.; Walker, P.; Lowe, L.; Rapp, B.; Purnell, S.; Knowlton, W. B.; Hubbard, S. M.; Frost, B. J. Synthesis and characterization of [Zn(acetate)2(amine)x] compounds (x = 1 or 2) and their use as precursors to ZnO. Mater. Sci. Semicond. Process. 2015, 38, 278. (19) (a) Akine, S.; Taniguchi, T.; Nabeshima, T. Helical metallohost-guest complexes via site-selective transmetalation of homotrinuclear complexes. J. Am. Chem. Soc. 2006, 128, 15765. (b) Jiang, D.; Yang, X.; Chen, H.; Wang, F.; Wang, S.; Zhu, T.; Zhang, L.; Huang, S. Cation sensing by luminescent high-nuclearity Zn-Eu Schiff base nanoscale complexes: high sensitivity to Ag+ and Cd2+ ions at the ppm level. Dalton Trans. 2019, 48, 2206. (c) Dong, W.-K.; Zheng, S.-S.; Zhang, J.-T.; Zhang, Y.; Sun, Y.-X. Luminescent properties of heterotrinuclear 3d-4f complexes constructed from a naphthalenediol-based acyclic bis(salamo)-type ligand. Spectrochim. Acta, Part A 2017, 184, 141. (d) Ghosh, S.; Hari, N.; Pinkowicz, D.; Fitta, M.; Mohanta, S. Syntheses, crystal structures and magnetic properties of a series of ZnII2LnIII2 compounds (Ln = Gd, Tb, Dy, Ho and Er): contrasting structural and magnetic features. New J. Chem. 2018, 42, 15917. (e) Oyarzabal, I.; Artetxe, B.; Rodríguez-Diéguez, A.; García, J. Á .; Seco, J. M.; Colacio, E. A family of acetato-diphenoxo triply bridged dimetallic ZnIILLnIII complexes: SMM behavior and luminescent properties. Dalton Trans. 2016, 45, 9712. (20) (a) Minyaev, M. E.; Korchagina, S. A.; Tavtorkin, A. N.; Churakov, A. V.; Nifant’ev, I. E. Dinuclear neodymium and lanthanum bis(2,6-diisopropylphenyl) phosphate complexes bearing a hydroxide ligand: catalytic activity of the Nd complex in 1,3-diene polymerization Acta. Acta Crystallogr., Sect. C: Struct. Chem. 2018, 74, 673. (b) Klaus, S.; Lehenmeier, M. W.; Anderson, C. E.; Rieger, B. Recent advances in CO2/epoxide copolymerization-new strategies and cooperative mechanisms. Coord. Chem. Rev. 2011, 255, 1460. (21) Hydrodynamic radius rh (7.9 ± 0.5 Å) was computed from the Stokes−Einstein relationship: Dt = kT/(6πηrh), where k is the Boltzmann constant, T is the temperature (298 K), η is the viscosity of the liquid (THF viscosity η = 0.47 mPa/s), and Dt = 5.90 × 10−10 m2/s. The crystalline radius 8.8 ± 0.5 Å was calculated from the molecular volume of 2805 Å3, determined by the Monte Carlo method. (22) (a) Gill, D. S.; Singh, J.; Ludwig, R.; Zeidler, M. D. Nuclear magnetic resonance relaxation, permittivity, viscosity and ultrasonic velocity measurements in binary mixtures of methanol and tetrahydrofuran. J. Chem. Soc., Faraday Trans. 1993, 89, 3955. (b) Giannetto, A.; Puntoriero, F.; Notti, A.; Parisi, M. F.; Ielo, I.; Nastasi, F.; Bruno, G.; Campagna, S.; Lanza, S. Self-assembly of hexameric macrocycles from PtII/ferrocene dimetallic subunitssynthesis, characterization, chemical reactivity, and oxidation behavior. Eur. J. Inorg. Chem. 2015, 2015, 5730. (c) Weekes, D. M.; Diebold, C.; Mobian, P.; Huguenard, C.; Allouche, L.; Henry, M. A remarkable solvent effect on the nuclearity of neutral Titanium(IV)based helicate assemblies. Chem. - Eur. J. 2014, 20, 5092. (d) Diebold, C.; Mobian, P.; Huguenard, C.; Allouche, L.; Henry, M. Spontaneous symmetry breaking during self-Assembly of a double stranded biphenolate-based Ti(IV)-helicate. Inorg. Chem. 2010, 49, 6369. (23) (a) Saini, P. K.; Romain, C.; Williams, C. K. Dinuclear metal catalysts: improved performance of heterodinuclear mixed catalysts for CO2-epoxide copolymerization. Chem. Commun. 2014, 50, 4164. (b) Garden, J. A.; Saini, P. K.; Williams, C. K. Greater than the sum of its parts: a heterodinuclear polymerization catalyst. J. Am. Chem. Soc. 2015, 137, 15078. (c) Deacy, A. C.; Durr, C. B.; Garden, J. A.; White, A. J. P.; Williams, C. K. Groups 1, 2 and Zn(II) heterodinuclear catalysts for epoxide/CO2 ring-opening copolymerization. Inorg. Chem. 2018, 57, 15575. (d) Trott, G.; Garden, J. A.; Williams, C. K. Heterodinuclear zinc and magnesium catalysts for epoxide/CO2 ring opening copolymerizations. Chem. Sci. 2019, 10, 4618. (24) Sâr bu, T.; Beckman, E. J. Homopolymerization and copolymerization of cyclohexene oxide with carbon dioxide using zinc and aluminum catalysts. Macromolecules 1999, 32, 6904.

(25) (a) Cyriac, A.; Lee, S. H.; Varghese, J. K.; Park, E. S.; Park, J. H.; Lee, B. Y. Immortal CO2/propylene pxide copolymerization: precise control of molecular weight and architecture of various block copolymers. Macromolecules 2010, 43, 7398. (b) Xiao, Y.; Wang, Z.; Ding, K. Macromolecules 2006, 39, 128. (c) Zhang, D.; Boopathi, S. K.; Hadjichristidis, N.; Gnanou, Y.; Feng, X. Metal-Free alternating copolymerization of CO2 with epoxides: fulfilling “green” synthesis and activity. J. Am. Chem. Soc. 2016, 138, 11117. (26) Nakano, K.; Kamada, T.; Nozaki, K. Selective formation of polycarbonate over cyclic carbonate: copolymerization of epoxides with carbon dioxide catalyzed by a cobalt(III) complex with a piperidinium end-capping arm. Angew. Chem., Int. Ed. 2006, 45, 7274. (27) Shaik, M.; Peterson, J.; Du, G. Cyclic and linear polyhydroxylbutyrates from ring-opening polymerization of βbutyrolactone with amido-oxazolinate zinc catalysts. Macromolecules 2019, 52, 157. (28) (a) Inoue, S.; Koinuma, H.; Yokoo, Y.; Tsuruta, T. Stereochemistry of copolymerization of carbon dioxide with epoxycyclohexane. Makromol. Chem. 1971, 143, 97. (b) Super, M.; Berluche, E.; Costello, C.; Beckman, E. Macromolecules 1997, 30, 368. (c) Mandal, M.; Chakraborty, D.; Ramkumar, V. Zr(IV) complexes containing salan-type ligands: synthesis, structural characterization and role as catalysts towards the polymerization of epsiloncaprolactone, rac-lactide, ethylene, homopolymerization and copolymerization of epoxides with CO2. RSC Adv. 2015, 5, 28536. (29) Koning, C.; Wildeson, J.; Parton, R.; Plum, B.; Steeman, P.; Darensbourg, D. J. Synthesis and physical characterization of poly(cyclohexane carbonate), synthesized from CO2 and cyclohexene oxide. Polymer 2001, 42, 3995. (30) Steinbauer, J.; Spannenberg, A.; Werner, T. An in situ formed Ca2+-crown ether complex and its use in CO2-fixation reactions with terminal and internal epoxides. Green Chem. 2017, 19, 3769. (31) (a) Laserna, V.; Fiorani, G.; Whiteoak, C. J.; Martin, E.; Escudero-Adán, E.; Kleij, A. W. Carbon dioxide as a protecting group: highly efficient and selective catalytic access to cyclic cis-diol scaffold. Angew. Chem., Int. Ed. 2014, 53, 10416. (b) Langanke, J.; Greiner, L.; Leitner, W. Substrate dependent synergetic and antagonistic interaction of ammonium halide and polyoxometalate catalysts in the synthesis of cyclic carbonates from oleochemical epoxides and CO2. Green Chem. 2013, 15, 1173. (c) Whiteoak, C. J.; Martin, E.; Escudero-Adán, E.; Kleij, A. W. Stereochemical divergence in the formation of organic carbonates derived from internal epoxides. Adv. Synth. Catal. 2013, 355, 2233. (d) Darensbourg, D. J. Making plastics from carbon dioxide: salen metal complexes as catalysts for the production of polycarbonates from epoxides and CO2. Chem. Rev. 2007, 107, 2388. (32) Ikpo, N.; Saunders, L. N.; Walsh, J. L.; Smith, J. M. B.; Dawe, L. N.; Kerton, F. M. Zinc complexes of piperazinyl-derived aminephenolate ligands: synthesis, characterization and ring-opening polymerization activity. Eur. J. Inorg. Chem. 2011, 2011, 5347.

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