Next Article in Journal
Photonic Crystals for Plasmonic Photocatalysis
Previous Article in Journal
Catalytic Pyrolysis as a Technology to Dispose of Herbal Medicine Waste
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Catalysts
Volume 10
Issue 8
10.3390/catal10080825
catalysts-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Metal Complexes Bearing Sulfur-Containing Ligands as Catalysts in the Reaction of CO2 with Epoxides

by
Veronica Paradiso
,
Vito Capaccio
,
David Hermann Lamparelli
and
Carmine Capacchione
*
Dipartimento di Chimica e Biologia “A. Zambelli”, Università degli Studi di Salerno, Via Giovanni Paolo II n°132, 84184 Fisciano, Italy
*
Author to whom correspondence should be addressed.
Catalysts 2020, 10(8), 825; https://doi.org/10.3390/catal10080825
Submission received: 24 June 2020 / Revised: 20 July 2020 / Accepted: 21 July 2020 / Published: 23 July 2020
(This article belongs to the Special Issue Catalysts for CO2 Utilization)
Browse Figures
Versions Notes

Abstract

:
Coupling of CO2 with epoxides is a green emerging alternative for the synthesis of cyclic organic carbonates (COC) and aliphatic polycarbonates (APC). The scope of this work is to provide a comprehensive overview of metal complexes having sulfur-containing ligands as homogeneous catalytic systems able to efficiently promote this transformation with a concise discussion of the most significant results. The crucial role of sulfur as the hemilabile ligand and its influence on the catalytic activity are highlighted as well.

1. Introduction

Homogeneous catalysis is one of the most fast-developing areas of chemistry because of the possibility to finely tune the course of a given reaction by rational design of the catalyst architecture. Indeed, compared to heterogeneous catalysis, mechanisms governing the activity and selectivity are easier to be understood and therefore the overall performances can be consequentially greatly improved. In particular, the use of soluble transition-metal complexes in catalysis opened unprecedented possibilities to control the product features by a judicious modification of the electronic and steric properties of the ancillary ligand. Inspired by this simple concept, chemists have unfolded countless stereoselective reactions encompassing all families of chemical transformations (oxidations, cross-coupling reactions, polymerizations, etc.) [1,2,3].
Parallel to this trend, in the last two decades, the use of renewable feedstocks has gained momentum because of the growing demand for more sustainable chemical processes. In particular, carbon dioxide utilization (CDU) has emerged as an important tool for the transition to a carbon-neutral society because of the possibility to close, through the use of renewable energies, an anthropogenic carbon cycle avoiding net emission of greenhouse gases. Besides, CO2 displays evident advantages in terms of toxicity, flammability, and the possibility of storage with respect to other C1 feedstocks (such as phosgene and carbon monoxide) that render the implementation of industrial processes based on this molecule quite promising [4,5,6,7,8,9].
Among the possible products obtainable from CO2, cyclic organic carbonates (COCs) and aliphatic polycarbonates (APCs) have received considerable attention because of their wide range of application and straightforward synthetic pathway starting from the corresponding epoxides [10,11,12,13,14,15,16,17,18,19]. The coupling between CO2 and an epoxide can result in the formation of the cyclic product or of the polymeric one depending on many factors such as the nature of the substrate, the reaction conditions, and the catalytic system. Notwithstanding the efforts to develop efficient metal-free catalysts, most of the active systems are based on the combination of a metal complex activated by a suitable nucleophile, often added as ammonium or phosphonium salt. The basic reaction mechanism can be exemplified following the steps depicted in Scheme 1: (i) The coordination of the epoxide to the metal center; (ii) the ring-opening of the activated epoxide by the nucleophilic attack and the formation of the metal-alkoxo bond; (iii) the insertion of CO2. At this stage, the intermediate can give an intramolecular ring-closing with the formation of the COC (path A) or the alternating insertion of epoxide and CO2 with the formation of the APC (path B). Since two consecutive insertions of the epoxide are possible as well (path C), often the resulting polymer also contains some polyether linkages [20].
The metal complexes successfully employed as catalysts in this reaction can be based both on main group metals such as Al, Mg, Ca [21,22,23] and on transition metals such as Ti, Cr, Fe, Co, Nb, La, and Zn [17,18,20,24,25,26,27,28]. Some examples of highly active catalysts for the formation of cyclic carbonates are given in Figure 1 [22,25,29,30].
As for other metal-mediated catalytic transformations, also in this case the Lewis acidic metal center requires to be wrapped by a suitable ligand environment in order to reach good performances in terms of activity and selectivity. Indeed, the most active catalysts developed for the alternating copolymerization of CO2 with epoxides bear well-known structural motifs as the ligand framework, modified, in some cases, to allow obtaining binuclear complexes [31,32,33,34,35,36,37]. Some of the most efficient systems are reported in Figure 2.
At first glance, it is evident that the nitrogen-based macrocycles, multidentate nitrogen framework, and Salen-type ligands, or in general, combination of phenoxo units with neutral nitrogen donors have played the main role in this kind of catalysis. In most cases, these ligands had been already developed to promote other catalytic transformations (polymerizations, oxidations, etc.,) and therefore offer the possibility to be easily synthesized and modified. Salen ligands, for example, represent one of the most successful examples, owing to the possibility to finely tune the steric and electronic properties of the aromatic substituents and modify the bridge between the two imino nitrogen atoms. This also provided the opportunity to obtain chiral, enantiopure ligands for asymmetric transformations (Figure 3) [38].
However, in these species, the strength of the interaction between the metal center and the donor atoms can be scarcely modulated because of the hard nature of nitrogen as a Lewis base. On this basis, it was thought that the introduction in the ligand of a soft donor, such as sulfur, can be advantageous because of the possibility to tune the Lewis acidity of the metal center by using the weaker metal–donor interaction. Indeed, many successful examples of catalysts having sulfur-containing ligands have been reported to date in the field of olefin polymerization [39,40,41,42,43,44,45,46], ring-opening polymerization of cyclic esters [47,48,49], hydroamination [50] and hydrosilylation [51] with various metal centers (Figure 4). In this context, theoretical and experimental studies have shown the crucial role of the hemilabile sulfur atom in determining the catalytic activity and selectivity [52,53].
Despite these findings, the use of sulfur-based ligands in the CO2/epoxide coupling has been neglected until recently. In this review, we cover the recent progress in the use of the corresponding metal complexes in the cycloaddition and copolymerization of CO2 and epoxides, evidencing the fundamental role played by the ligand framework in modulating the catalytic efficiency.

2. Metal Complexes Bearing Sulfur-Containing Ligands Active in the Coupling of CO2 and Epoxides

2.1. Chromium-Based Systems

Chromium Salen complexes are among the most studied coordination compounds in catalysis. Indeed, in the last years, their chemistry had been deeply investigated because of their unique properties in the oxidation, even in the enantioselective version, of various substrates [38]. The easy synthesis and the possibility to design chiral metal species sparked the interest in using these complexes also in the CO2/epoxide coupling. In this context, Darensbourg and Nguyen separately reported the use of chromium Salen complexes for the coupling of cyclohexene oxide (CHO) or propylene oxide (PO) with CO2 for the formation of polycyclohexene carbonate (PCHC) and propylene carbonate (PC), respectively (Figure 5) [54,55].
After these first reports, many mononuclear and dinuclear chromium Salen complexes have been developed for the copolymerization of epoxides with CO2 allowing the synthesis, with high activity, of new copolymer microstructures (Figure 6) [56,57].
In the search of alternative ligands for the CO2/epoxide chemistry, the first example of chromium catalysts bearing a soft donor atom in the ligand skeleton was reported by Duchateau and coworkers only in 2014 and regarded the utilization of two chromium(III) complexes having an aminophosphine bidentate ligand (Figure 7) [58]. These catalysts showed moderate catalytic activity in the copolymerization of CO2 with CHO affording low molecular weight PCHC (Mn up to 1930 g mol−1).
In this field, the choice of sulfur as the soft Lewis base is even more recent. In 2015, the tetradentate [OSSO]-type chromium complexes (1–4) were developed by Liu and coworkers for the copolymerization of various epoxides with phthalic anhydride and subsequently used for the copolymerization of CO2 with vinylcyclohexeneoxide (VCHO) (Figure 8) [59].
Complexes 1–4, activated by bis(triphenylphosphoranylidene) ammonium chloride (PPNCl) are all active catalysts in the CO2/VCHO coupling by using a [VCHO]/[[OSSO]CrX]/[PPNCl] ratio of 1000/1/2 at 90 °C and high pressure (pCO2 = 3.0 MPa). Activity and chemoselectivity toward the APC vis a vis COC depended on the catalyst structure. Indeed, the complexes 1–3 with a cyclohexyl or an ethyl carbon bridge showed better performances compared to the phenylene analogue 4. Selected results are reported in Table 1.
In addition, 4 also produced a low molecular weight polymer, in comparison to the other complexes, albeit with a narrow dispersity (Ð = 1.24–1.49). For the most active catalyst 1, the authors also explored the use of different co-catalysts, such as bis(triphenylphosphoranylidene)ammonium azide, (PPNN3), tetrabutylammonium chloride (TBAC), and 4-dimethylaminopyridine (DMAP) obtaining the best compromise between activity and selectivity toward the polymeric product by using 2 equivalents, with respect to the metal, of PPNCl. Notably, by adjusting the [VCHO]/[1]/[PPNCl] ratio to 500/1/2, the activity reached the value of 134 h−1 with 76% of selectivity for the polymeric product at 90 °C and with a CO2 pressure of 3.0 MPa. 13C NMR analysis showed that the resulting polymer is atactic in all cases. The reaction of terminal epoxides such as PO or epichlorohydrine (EPC) invariably resulted in the formation of the corresponding COC.
Starting from the observation that 2 equivalents of cocatalyst (PPNCl or PPNN3) are needed to reach the best catalytic performances, the authors speculated about interaction of the onium salt with the metal center enhancing the catalytic performance. This idea was supported by IR experiments that revealed an interaction between the N 3 − anion or DMAP with the metal center that leads to the formation of a six-coordinated chromium atom. Based on these experiments, it was proposed a mechanism in which the true catalytic species was formed by the interaction of the nucleophile with the precatalyst. The presence of a protic compound such H2O lead to a chain transfer with the formation of hydroxyl-terminated polymeric chains that were observed in the 1H NMR spectrum (Scheme 2).
Almost simultaneously, Darensbourg and coworkers reported the synthesis of four new imine-thioether-bridged bis(phenolate) [ONSO]-type chromium(III) complexes 5–8 and their use as catalysts for the CO2/CHO copolymerization (Figure 9) [60].
Also in this case, in analogy with the abovementioned [OSSO]-type chromium complexes reported by Liu, the best cocatalysts are PPNCl and PPNN3 in a 2/1 molar ratio with respect to the chromium complex. These nucleophile sources performed better than the more hygroscopic TBAC giving the polymeric product with good selectivity (72–77%) at 80 °C and with a CO2 pressure of 3.0 MPa. Complexes 7 and 8 bearing a phenylene-bridged ligand were the most active catalysts reaching a TOF up to 71 h−1 with the azide-derivative 8 slightly better performing with respect to the chloro-derivative 7. The PCHC obtained was atactic in nature under all the reaction conditions explored and displayed narrow dispersity (Ð = 1.23–1.28). As expected, the selectivity toward the polymer is negatively affected by an increase of the reaction temperature although the catalytic activity increased (TOF up to 100 h−1 at 110 °C). An in situ IR spectroscopy study showed that, in the early stages, only the COC was formed by complexes 5 and 6, whereas the production of the APC started after 50 min. These results were rationalized proposing a mechanism in which the backbiting reaction initially predominated, leading to the COC. However, once the alternating CHO/CO2 insertion began, the backbiting of the alkyl carbonate became less favored with respect to the polymerization process. Differently, by using the less electron-rich Cr(III) complex 7 the production of the polymer immediately started.
Liu and Darensbourg both explained the observed lower activity and selectivity for the formation of the polymeric product of the sulfur-containing Cr(III) complexes when compared to the corresponding Salan analogues by the fact that the electron-releasing sulfur atoms in the ligand skeleton render the chromium atom more electron-rich, thus favoring the displacement of the growing polymeric chain from the metal center and the formation of the cyclic product.
Recently, our group reported the synthesis of the new [OSSO]-type Cr(III) complex 9 (Figure 10) [61]. This complex contained the ligand developed by Okuda and coworkers for group 4-based complexes which differed from the ligands used for the foregoing complexes 1–8 for the absence of the methylene spacer between the sulfur atoms and the aromatic rings. It was expected that this design would render the sulfur atoms electron poorer, weakening their electron-releasing character and consequently enhancing the Lewis acidity of the metal center. When activated by TBAC, complex 9 under 1.0 MPa of CO2 pressure produced a mixture of polymeric and cyclic products by using PO as the substrate ([PO]/[9]]/[TBAC] ratio of 1000/1/1). The selectivity strongly depends on the reaction temperature with a maximum (45%) for the polypropylene carbonate (PPC) at 45 °C and with the almost exclusive formation of the PC at higher temperatures (80 °C) (Figure 10).
Changing the onium salt to PPNCl, reducing the [9]/[PPNCl] ratio to 1/0.5, and increasing the CO2 pressure to 2.0 MPa, both the activity and the selectivity increased, reaching a TOF of 35 h−1 and a selectivity of 93% for the polymer. The PPC produced was atactic but highly regioregular (up to 90% of head to tail enchainment) with no polyether linkages detectable. The molecular weight was high (Mn up to 36 kDa) with a bimodal distribution due to the presence of traces of water that acted as a chain transfer agent. The same system also promoted the copolymerization of CO2 with CHO, 1-hexene oxide (HO) and styrene oxide (SO). In the case of CHO, activity was lower to those observed by using PO (TOF up to 19 h−1) but the selectivity reached the value of 99%. Notably, HO was copolymerized with good selectivity (up to 92%) albeit with low activity (TOF up to 16 h−1). Moreover even SO that, because of its electronic features, it is usually less prone to copolymerize, giving 32% of polystyrene carbonate (PSC).
The high versatility of complex 9 in promoting the copolymerization of CO2 with various epoxides was further confirmed by the obtaining of PO/CHO/CO2 and PO/HO/CO2 terpolymers. The resulting polycarbonates had high content of carbonate linkages (87–93%) and narrow dispersity (Ð = 1.16–1.27) with thermal and 13C NMR analyses suggesting a block microstructure for these materials.
DFT calculation, carried out for the coupling involving PO as the substrate, displayed that the activation energies for cyclization and copolymerization are quite close in value (Scheme 3). This was coherent with the experimental observation that the course of the reaction can be driven to the formation of PC or PPC by a proper choice of the reaction conditions.

2.2. Iron-Based Systems

Despite the abundance of this metal on the Earth-crust, the use of iron in homogeneous catalysis has been longtime neglected and only in the last two decades emerged as a viable alternative to catalysts based on rare/precious metals. In this trend, the development of iron catalysts for the reaction of CO2 with epoxides was not an exception, with only few examples of complexes that showed significant activity in the cycloaddition of CO2 to epoxide or in the alternating copolymerization [18,62,63,64,65]. As for other metals, the structural motifs of choice were based on macrocyclic or polydentate ligands having oxygen and nitrogen as donor atoms. In particular, the complexes developed by Williams and Nozaki [62,63], depicted in Figure 11, were the first examples of iron catalysts able to promote the copolymerization of CO2 with CHO and PO, respectively. The iron complexes developed by Kleij [64,65] (Figure 11), efficiently produced cyclic carbonates from a variety of terminal and internal epoxides.
The first example of sulfur-containing ligand for iron complexes active in the reaction of CO2 with epoxides was reported by Abu-Surrah and coworkers in 2013 (10, Figure 12) [66]. This thiophenaldimine Fe(II) complex, activated by TBAB, at 130 °C and 0.5 MPa of CO2 pressure, promoted the formation of styrene carbonate (SC) with low activity (TON = 799; TOF = 33.3 h−1).
In 2015, our group reported on the synthesis of a new air-stable dinuclear iron(III) complex (11, Figure 13) bearing a bis-thioether-triphenolate ligand [67,68,69]. These complexes were stable in solution, and when activated by TBAB (11/TBAB = 1/2), were able to promote the transformation of various terminal or internal epoxides to the corresponding COCs with good activity and selectivity. In particular, PO was converted to PC reaching a TOF of 580 h−1 at 100 °C with a CO2 pressure of 2.0 MPa, and with a [PO]/[11]/[TBAB] ratio of 4000/1/5. Furthermore, this catalyst showed to be also highly stereoselective affording exclusively the cis-COC by using CHO as the substrate regardless the TBAB/[11] ratio. Moreover, by using the enantiopure SO as the epoxide (ee = 94%) the corresponding SC was gained with a good degree of stereoretention (ee = 74%).
An enlargement of the catalysts’ family and an optimization of the reaction conditions led to a further improvement of the catalytic activity. In particular, complex 16, bearing methyl substituents on the phenol ring, displayed the highest activity so far reported for an iron catalyst with a TOF of 5200 and 7000 h−1 in the conversion of PO and EPC, respectively, in the corresponding COCs at 120 °C with a CO2 pressure of 2.0 MPa and a [PO]/[16]/[TBAB] ratio of 10000/1/10. Conversely, the introduction of bulkier substituents in catalyst 12 and electron-withdrawing groups in catalyst 14 resulted in a lowering of the catalyst activity.
In order to shed more light on the reaction mechanism, DFT calculations were performed and highlighted three important features regarding the formation of COCs promoted by these catalysts: (i) The coordination of the epoxide to the iron(III) center requires the detachment of a sulfur atom from the coordination sphere; (ii) the insertion of CO2 is not mediated by the second iron center; (iii) the ring-closure of the COCs is the rate-limiting step (Figure 14). As a matter of fact, the hemilability of the sulfur atoms plays a fundamental role in determining the catalytic activity. This was also confirmed by the worse performances of catalyst 14, which were reasonably caused by a stronger sulfur-iron interaction which, in turn, was caused by the presence of electron-withdrawing substituents on the phenoxo rings.
Later on, we moved to the development of iron(III) mononuclear complexes bearing [OSSO]-type ligands 17–20 (Figure 15) [52].
Notably, when activated by TBAB, these catalysts efficiently performed in the cycloaddition of CO2 to terminal and internal epoxides giving the corresponding COC under mild reaction conditions (35 °C; pCO2 = 0.1 MPa) and, by using catalyst 20, reaching a TOF of 290 h−1 in the case of PO with a [PO]/[20]/[TBAB] ratio of 1000/1/5. Substituents on the ligand framework had a negligible influence on the catalytic activity. In analogy with the bis-thiother-triphenolate complexes 11–16, the reaction occurred with a high degree of stereoretention (98%) in the case of internal epoxides such as 2-buteneoxide. More importantly, when the substrate was CHO, only the alternating PCHC was observed. In this case, the best cocatalyst was TBAC and the activity order was 18 > 20 ≈ 17 > 19.
A thorough kinetic investigation of the formation of PC was performed by means of ATR-IR spectroscopy. This study evidenced that reaction followed a second-order dependence in 20. Furthermore, this behavior was observed exclusively when 2 equivalents of TBAB were used, suggesting that only under these conditions the true catalytic species was formed. As a further confirmation, UV-vis spectra detected the formation of a new ferrate species when an excess of TBAB was added to the catalyst’s solution. These findings were rationalized by DFT calculations showing that the rate-limiting step was the ring-opening of the epoxide that took place in the presence of two iron centers: one acted as the Lewis acid and the other one, as metallate, furnished the nucleophile (Figure 16).
The ferrate species 21 was also isolated and characterized both starting from the chloro-derivative 20 and the bromo-derivative 22 by reaction with two and one equivalent of TBAB, respectively (Figure 17) [70]. Complex 21 was used as single-component catalyst in couplings of various terminal and internal epoxides showing good performances under mild reaction conditions (35 °C; pCO2 = 0.1 MPa, [PO]/[21] = 100) and reached a TOF of 54 h−1.
Lately, we also developed a new family of tridentate bisthioether phenolate ligands that supported both Fe(II) and Fe(III) centers [71]. It is worth noting that the both Fe(II) and Fe(III) complexes existed in solution as mononuclear or dinuclear species depending on the steric bulk of the ligand (Figure 18).
The cycloaddition reaction of CO2 to HO was used as the benchmark reaction to test the catalytic activity of these complexes: on one hand, for the Fe(II) complexes the activity depended on the complex structure, with 26 being the most active (TOF = 36 h−1), on the other hand all the Fe(III) species showed comparable activities (TOF = 32 h−1). This different behavior was explained by supposing that the Fe(III) complexes reacted with TBAB forming the corresponding ferrate, in analogy to what was observed for the [OSSO]-type Fe(III) complexes. In contrast, the formation of such anionic species does not occur in the case of the Fe(II) complexes. This mechanistic picture was supported by UV-vis experiments treating the precatalysts with an excess of TBAB.
More recently, Jones and coworkers reported on the synthesis of a wide family of imine-thioether-bridged bis(phenolate) ([ONSO]-type) Fe(III) complexes 29–34 (Figure 19) [72].
These complexes, when activated by TBAC at 80 °C, with a CO2 pressure of 1.0 MPa and a [CHO]/[Fe]/[TBAB] ratio of 1250/1/8 performed as active catalysts (TOF = 22–31 h−1) for the cycloaddition of CO2 to CHO with excellent selectivity toward the formation of cis-CHC (>99%). The most active catalytic system, complex 33, could reach a TOF of 156 h−1 by increasing the temperature to 120 °C. However, under this condition, a lower selectivity was detected, because of the simultaneous production of the polyether product. A reduction of the [TBAC]/[33] ratio down to 2, resulted in a lower selectivity as well, with the formation of polycyclohexeneoxide (PCHO) and, in lower amounts, of the trans-CHC. In this publication, the use of other terminal epoxides was also explored. By using PO, a higher activity with respect to the case of CHO was detected (TOFs of 42 h−1 versus 31 h−1). As a matter of fact, Thiolen Fe(III) compounds showed to be more active if compared to the corresponding Salen Fe(III) complexes demonstrating, once again, the beneficial effect of sulfur on catalytic activity.

2.3. Bismuth-Based Systems

Among the possible Lewis acidic metal centers in catalysis, the last two decades have witnessed a rising interest in the use of bismuth. Indeed, bismuth is cheap and low-toxic and therefore the implementation of catalytic processes based on this metal are an active task of research in green chemistry [73,74,75,76].
Actually, the use in CO2/epoxide reactions was barely explored and only recently received more attention [77,78]. In this field, one of the most efficient catalytic systems was developed by Shimada e Yin in 2009 [79]. In this study, the synthesis of Bi(III) compounds 35 and 36, bearing a sulfur bridged bis(phenolato) ligand, was reported (Figure 20).
In the presence of iodide as the nucleophile, by using sources such as Ph3PI, tetrabutylammonium iodide (TBAI), NaI or LiI, these compounds were found to be active catalysts for the conversion of PO to PC under mild reaction conditions (RT; pCO2 = 0.1 MPa; [PO]/[Bi]/[I−] = 820/1/4) reaching a TOF of 34 h−1. More recently, Wong, Au, and coworkers reported that the dinuclear sulfide-bridged complexes 37–40 (Figure 21) performed as active catalysts for the conversion of EPC to the corresponding carbonate at 140 °C and a CO2 pressure of 3.0 MPa ([EPC]/[Bi]/[TBAI] = 200/1/0.2) reaching TOFs up to 25 h−1 [80]. Complexes 37–39 are also among the few air-stable organobismuth compounds reported so far.

3. Conclusions

The use of sulfur-containing ligands to support metal ions in the reaction between CO2 and epoxides has attracted an increasing interest in the past years. In many cases, the presence of sulfur in the ligand backbone imparts unique properties in terms of activity, selectivity, and stability of the catalyst precursor. Furthermore, both cyclic carbonates and polycarbonates were obtained with good activity and selectivity for a wide range of substrates showing a high potential for further development. In particular, the use of these ligands can be extended to a major variety of metal centers, allowing an increase in the catalytic performances and expanding the portfolio of possible products. Finally, the design and the synthesis of new structural motifs containing sulfur atoms in the ligand backbone is another important objective for a possible expansion of the catalytic applications.

Funding

Financial Support from Ministero dell’Istruzione dell’Università e della Ricerca (MIUR, Roma, PRIN 2017—CO2 as only source of carbons for monomers and polymers: a step forwards circular economy—CO2 only) and Università degli Studi di Salerno are gratefully acknowledged.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Cornils, B.; Herrmann, W.A.; Beller, M.; Paciello, R. (Eds.) Applied Homogeneous Catalysis with Organometallic Compounds: A Comprehensive Handbook in Four Volumes, 3rd ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2018; ISBN 978-3-527-32897-0. [Google Scholar]
  2. Bhaduri, S.; Mukesh, D. Homogeneous Catalysis: Mechanisms and Industrial Applications, 2nd ed.; Wiley: Hoboken, NJ, USA, 2014; ISBN 978-1-118-87251-2. [Google Scholar]
  3. van Leeuwen, P.W.N.M. Homogeneous Catalysis: Understanding the Art; Springer Netherlands: Dordrecht, The Netherlands, 2004; ISBN 978-1-4020-3176-2. [Google Scholar]
  4. Aresta, M.; Dibenedetto, A. Utilisation of CO2 as a chemical feedstock: Opportunities and challenges. Dalton Trans. 2007, 28, 2975–2992. [Google Scholar] [CrossRef] [PubMed]
  5. Burkart, M.D.; Hazari, N.; Tway, C.L.; Zeitler, E.L. Opportunities and challenges for catalysis in carbon dioxide utilization. ACS Catal. 2019, 9, 7937–7956. [Google Scholar] [CrossRef]
  6. Zhang, Z.; Pan, S.-Y.; Li, H.; Cai, J.; Olabi, A.G.; Anthony, E.J.; Manovic, V. Recent advances in carbon dioxide utilization. Renew. Sustain. Energy Rev. 2020, 125, 109799. [Google Scholar] [CrossRef]
  7. Aresta, M.; Dibenedetto, A.; Angelini, A. Catalysis for the valorization of exhaust carbon: From CO2 to chemicals, materials, and fuels. Technological use of CO2. Chem. Rev. 2014, 114, 1709–1742. [Google Scholar] [CrossRef] [PubMed]
  8. Cokoja, M.; Bruckmeier, C.; Rieger, B.; Herrmann, W.A.; Kühn, F.E. Transformation of carbon dioxide with homogeneous transition-metal catalysts: A molecular solution to a global challenge? Angew. Chem. Int. Ed. 2011, 50, 8510–8537. [Google Scholar] [CrossRef]
  9. Hepburn, C.; Adlen, E.; Beddington, J.; Carter, E.A.; Fuss, S.; Mac Dowell, N.; Minx, J.C.; Smith, P.; Williams, C.K. The technological and economic prospects for CO2 utilization and removal. Nature 2019, 575, 87–97. [Google Scholar] [CrossRef] [Green Version]
  10. Dai, W.-L.; Luo, S.-L.; Yin, S.-F.; Au, C.-T. The direct transformation of carbon dioxide to organic carbonates over heterogeneous catalysts. Appl. Catal. A Gen. 2009, 366, 2–12. [Google Scholar] [CrossRef]
  11. Decortes, A.; Castilla, A.M.; Kleij, A.W. Salen-complex-mediated formation of cyclic carbonates by cycloaddition of CO2 to epoxides. Angew. Chem. Int. Ed. 2010, 49, 9822–9837. [Google Scholar] [CrossRef]
  12. North, M.; Pasquale, R.; Young, C. Synthesis of cyclic carbonates from epoxides and CO2. Green Chem. 2010, 12, 1514. [Google Scholar] [CrossRef]
  13. Darensbourg, D.J.; Wilson, S.J. What’s new with CO2? Recent advances in its copolymerization with oxiranes. Green Chem. 2012, 14, 2665. [Google Scholar] [CrossRef]
  14. Pescarmona, P.P.; Taherimehr, M. Challenges in the catalytic synthesis of cyclic and polymeric carbonates from epoxides and CO2. Catal. Sci. Technol. 2012, 2, 2169. [Google Scholar] [CrossRef]
  15. Sakakura, T.; Kohno, K. The synthesis of organic carbonates from carbon dioxide. Chem. Commun. 2009, 1312. [Google Scholar] [CrossRef]
  16. Coates, G.W.; Moore, D.R. Discrete Metal-based catalysts for the copolymerization of CO2 and epoxides: Discovery, reactivity, optimization, and mechanism. Angew. Chem. Int. Ed. 2004, 43, 6618–6639. [Google Scholar] [CrossRef] [PubMed]
  17. 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, 1462–1484. [Google Scholar] [CrossRef] [PubMed]
  18. Della Monica, F.; Buonerba, A.; Capacchione, C. Homogeneous iron catalysts in the reaction of epoxides with carbon dioxide. Adv. Synth. Catal. 2019, 361, 265–282. [Google Scholar] [CrossRef]
  19. Poland, S.J.; Darensbourg, D.J. A quest for polycarbonates provided via sustainable epoxide/CO2 copolymerization processes. Green Chem. 2017, 19, 4990–5011. [Google Scholar] [CrossRef]
  20. Della Monica, F.; Kleij, A.W. Mechanistic guidelines in nonreductive conversion of CO2: The case of cyclic carbonates. Catal. Sci. Technol. 2020, 10, 3483–3501. [Google Scholar] [CrossRef]
  21. Whiteoak, C.J.; Kielland, N.; Laserna, V.; Castro-Gómez, F.; Martin, E.; Escudero-Adán, E.C.; Bo, C.; Kleij, A.W. Highly active aluminium catalysts for the formation of organic carbonates from CO2 and oxiranes. Chem. Eur. J. 2014, 20, 2264–2275. [Google Scholar] [CrossRef] [PubMed]
  22. Maeda, C.; Miyazaki, Y.; Ema, T. Recent progress in catalytic conversions of carbon dioxide. Catal. Sci. Technol. 2014, 4, 1482. [Google Scholar] [CrossRef] [Green Version]
  23. Liu, X.; Zhang, S.; Song, Q.-W.; Liu, X.-F.; Ma, R.; He, L.-N. Cooperative calcium-based catalysis with 1,8-diazabicyclo[5.4.0]-undec-7-ene for the cycloaddition of epoxides with CO2 at atmospheric pressure. Green Chem. 2016, 18, 2871–2876. [Google Scholar] [CrossRef]
  24. Comerford, J.W.; Ingram, I.D.V.; North, M.; Wu, X. Sustainable metal-based catalysts for the synthesis of cyclic carbonates containing five-membered rings. Green Chem. 2015, 17, 1966–1987. [Google Scholar] [CrossRef]
  25. Martínez, J.; Fernández-Baeza, J.; Sánchez-Barba, L.F.; Castro-Osma, J.A.; Lara-Sánchez, A.; Otero, A. An efficient and versatile lanthanum heteroscorpionate catalyst for carbon dioxide fixation into cyclic carbonates. ChemSusChem 2017, 10, 2886–2890. [Google Scholar] [CrossRef]
  26. Chen, A.; Chen, C.; Xiu, Y.; Liu, X.; Chen, J.; Guo, L.; Zhang, R.; Hou, Z. Niobate salts of organic base catalyzed chemical fixation of carbon dioxide with epoxides to form cyclic carbonates. Green Chem. 2015, 17, 1842–1852. [Google Scholar] [CrossRef]
  27. Chen, F.; Liu, N.; Dai, B. Iron(II) bis-cnn pincer complex-catalyzed cyclic carbonate synthesis at room temperature. ACS Sustain. Chem. Eng. 2017, 5, 9065–9075. [Google Scholar] [CrossRef]
  28. Wang, Y.; Qin, Y.; Wang, X.; Wang, F. Coupling reaction between CO2 and cyclohexene oxide: Selective control from cyclic carbonate to polycarbonate by ligand design of salen/salalen titanium complexes. Catal. Sci. Technol. 2014, 4, 3964–3972. [Google Scholar] [CrossRef]
  29. Sheng, X.; Qiao, L.; Qin, Y.; Wang, X.; Wang, F. Highly efficient and quantitative synthesis of a cyclic carbonate by iron complex catalysts. Polyhedron 2014, 74, 129–133. [Google Scholar] [CrossRef]
  30. Whiteoak, C.J.; Kielland, N.; Laserna, V.; Escudero-Adán, E.C.; Martin, E.; Kleij, A.W. A powerful aluminum catalyst for the synthesis of highly functional organic carbonates. J. Am. Chem. Soc. 2013, 135, 1228–1231. [Google Scholar] [CrossRef] [PubMed]
  31. Moore, D.R.; Cheng, M.; Lobkovsky, E.B.; Coates, G.W. Electronic and steric effects on catalysts for CO2/epoxide polymerization: Subtle modifications resulting in superior activities. Angew. Chem. Int. Ed. 2002, 41, 2599–2602. [Google Scholar] [CrossRef]
  32. Cheng, M.; Lobkovsky, E.B.; Coates, G.W. Catalytic reactions involving C1 feedstocks: New high-activity zn(ii)-based catalysts for the alternating copolymerization of carbon dioxide and epoxides. J. Am. Chem. Soc. 1998, 120, 11018–11019. [Google Scholar] [CrossRef]
  33. 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, 11911–11924. [Google Scholar] [CrossRef]
  34. Kissling, S.; Lehenmeier, M.W.; Altenbuchner, P.T.; Kronast, A.; Reiter, M.; Deglmann, P.; Seemann, U.B.; Rieger, B. Dinuclear zinc catalysts with unprecedented activities for the copolymerization of cyclohexene oxide and CO2. Chem. Commun. 2015, 51, 4579–4582. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  35. Trott, G.; Garden, J.A.; Williams, C.K. Heterodinuclear zinc and magnesium catalysts for epoxide/CO2 ring opening copolymerizations. Chem. Sci. 2019, 10, 4618–4627. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  36. Darensbourg, D.J.; Mackiewicz, R.M.; Billodeaux, D.R. Pressure dependence of the carbon dioxide/cyclohexene oxide coupling reaction catalyzed by chromium salen complexes. optimization of the comonomer-alternating enchainment pathway. Organometallics 2005, 24, 144–148. [Google Scholar] [CrossRef]
  37. Ren, W.-M.; Liu, Z.-W.; Wen, Y.-Q.; Zhang, R.; Lu, X.-B. Mechanistic aspects of the copolymerization of CO2 with epoxides using a thermally stable single-site cobalt(III) catalyst. J. Am. Chem. Soc. 2009, 131, 11509–11518. [Google Scholar] [CrossRef]
  38. Bellemin-Laponnaz, S.; Dagorne, S. Coordination chemistry and applications of salen, salan and salalen metal complexes. In PATAI’S Chemistry of Functional Groups; Rappoport, Z., Ed.; John Wiley & Sons, Ltd.: Chichester, UK, 2012; p. pat0611. ISBN 978-0-470-68253-1. [Google Scholar]
  39. Kakugo, M.; Miyatake, T.; Mizunuma, K. Polymerization of styrene and copolymerization of styrene with olefin in the presence of soluble ziegler-natta catalysts. In Studies in Surface Science and Catalysis; Elsevier: Tokyo, Japan, 1990; Volume 56, pp. 517–529. ISBN 978-0-444-98747-1. [Google Scholar]
  40. Song, T.; He, J.; Liang, L.; Liu, N.; Li, F.; Tong, X.; Mu, X.; Mu, Y. Titanium and zirconium complexes bearing new tridentate [OSO] bisphenolato-based ligands: Synthesis, characterization and catalytic properties for alkene polymerization. Dalton Trans. 2019, 48, 13719–13731. [Google Scholar] [CrossRef]
  41. Nakata, N.; Toda, T.; Ishii, A. Recent advances in the chemistry of Group 4 metal complexes incorporating [OSSO]-type bis(phenolato) ligands as post-metallocene catalysts. Polym. Chem. 2011, 2, 1597. [Google Scholar] [CrossRef]
  42. Miyatake, T.; Mizunuma, K.; Seki, Y.; Kakugo, M. 2,2′-thiobis(6-tert-butyl-4-methylphenoxy)titanium or zirconium complex-methylalumoxane catalysts for polymerization of olefins. Makromol. Chem. Rapid Commun. 1989, 10, 349–352. [Google Scholar] [CrossRef]
  43. Capacchione, C.; Proto, A.; Ebeling, H.; Mülhaupt, R.; Möller, K.; Spaniol, T.P.; Okuda, J. Ancillary ligand effect on single-site styrene polymerization: Isospecificity of group 4 metal bis(phenolate) catalysts. J. Am. Chem. Soc. 2003, 125, 4964–4965. [Google Scholar] [CrossRef]
  44. Meppelder, G.-J.M.; Fan, H.-T.; Spaniol, T.P.; Okuda, J. Synthesis, structure, and olefin polymerization activity of titanium complexes bearing asymmetric tetradentate [OSNO]-type bis(phenolato) ligands. Inorg. Chem. 2009, 48, 7378–7388. [Google Scholar] [CrossRef]
  45. Mella, M.; Izzo, L.; Capacchione, C. Role of the metal center in the ethylene polymerization promoted by group 4 complexes supported by a tetradentate [OSSO]-type bis(phenolato) ligand. ACS Catal. 2011, 1, 1460–1468. [Google Scholar] [CrossRef]
  46. Buonerba, A.; Fienga, M.; Milione, S.; Cuomo, C.; Grassi, A.; Proto, A.; Capacchione, C. Binary copolymerization of p-Methylstyrene with butadiene and isoprene catalyzed by titanium compounds showing different stereoselectivity. Macromolecules 2013, 46, 8449–8457. [Google Scholar] [CrossRef]
  47. Ma, H.; Spaniol, T.P.; Okuda, J. Rare earth metal complexes supported by 1,ω-dithiaalkanediyl-bridged bis(phenolato) ligands: Synthesis, characterization and ring-opening polymerization catalysis of l-lactide. Dalton Trans. 2003, 4770–4780. [Google Scholar] [CrossRef]
  48. Meppelder, G.-J.M.; Halbach, T.S.; Spaniol, T.P.; Mülhaupt, R.; Okuda, J. A vanadium(V) complex with a tetradentate [OSSO]-type bis(phenolato) ligand: Synthesis, structure, and ethylene polymerization activity. J. Organomet. Chem. 2009, 694, 1235–1237. [Google Scholar] [CrossRef]
  49. Della Monica, F.; Luciano, E.; Buonerba, A.; Grassi, A.; Milione, S.; Capacchione, C. Poly(lactide-co-ε-caprolactone) copolymers prepared using bis-thioetherphenolate group 4 metal complexes: Synthesis, characterization and morphology. RSC Adv. 2014, 4, 51262–51267. [Google Scholar] [CrossRef]
  50. Lian, B.; Spaniol, T.P.; Horrillo-Martínez, P.; Hultzsch, K.C.; Okuda, J. Imido and amido titanium complexes that contain a [OSSO]-type bis(phenolato) ligand: Synthesis, structures, and hydroamination catalysis. Eur. J. Inorg. Chem. 2009, 2009, 429–434. [Google Scholar] [CrossRef]
  51. Konkol, M.; Kondracka, M.; Voth, P.; Spaniol, T.P.; Okuda, J. Rare-Earth metal alkyl and hydrido complexes containing a thioether-functionalized bis(phenolato) ligand: Efficient Catalysts for olefin hydrosilylation. Organometallics 2008, 27, 3774–3784. [Google Scholar] [CrossRef]
  52. Della Monica, F.; Maity, B.; Pehl, T.; Buonerba, A.; De Nisi, A.; Monari, M.; Grassi, A.; Rieger, B.; Cavallo, L.; Capacchione, C. [OSSO]-type iron(III) complexes for the low-pressure reaction of carbon dioxide with epoxides: Catalytic activity, reaction kinetics, and computational study. ACS Catal. 2018, 8, 6882–6893. [Google Scholar] [CrossRef]
  53. Della Monica, F.; Luciano, E.; Roviello, G.; Grassi, A.; Milione, S.; Capacchione, C. Group 4 metal complexes bearing thioetherphenolate ligands. coordination chemistry and ring-opening polymerization catalysis. Macromolecules 2014, 47, 2830–2841. [Google Scholar] [CrossRef]
  54. Darensbourg, D.J.; Mackiewicz, R.M.; Rodgers, J.L.; Fang, C.C.; Billodeaux, D.R.; Reibenspies, J.H. Cyclohexene Oxide/CO2 copolymerization catalyzed by chromium(iii) salen complexes and n-methylimidazole: Effects of varying salen ligand substituents and relative cocatalyst loading. Inorg. Chem. 2004, 43, 6024–6034. [Google Scholar] [CrossRef]
  55. Paddock, R.L.; Nguyen, S.T. Chemical CO2 fixation: Cr(III) Salen complexes as highly efficient catalysts for the coupling of CO2 and epoxides. J. Am. Chem. Soc. 2001, 123, 11498–11499. [Google Scholar] [CrossRef]
  56. Vagin, S.I.; Reichardt, R.; Klaus, S.; Rieger, B. Conformationally flexible dimeric salphen complexes for bifunctional catalysis. J. Am. Chem. Soc. 2010, 132, 14367–14369. [Google Scholar] [CrossRef] [PubMed]
  57. Wang, Y.; Darensbourg, D.J. Carbon dioxide-based functional polycarbonates: Metal catalyzed copolymerization of CO2 and epoxides. Coord. Chem. Rev. 2018, 372, 85–100. [Google Scholar] [CrossRef]
  58. Gurnham, J.; Gambarotta, S.; Korobkov, I.; Jasinska-Walc, L.; Duchateau, R. Chromium-catalyzed CO2–epoxide copolymerization. Organometallics 2014, 33, 4401–4409. [Google Scholar] [CrossRef]
  59. Si, G.; Zhang, L.; Han, B.; Zhang, H.; Li, X.; Liu, B. Chromium complexes containing a tetradentate [OSSO]-type bisphenolate ligand as a novel family of catalysts for the copolymerization of carbon dioxide and 4-vinylcyclohexene oxide. RSC Adv. 2016, 6, 22821–22826. [Google Scholar] [CrossRef]
  60. Han, B.; Zhang, L.; Kyran, S.J.; Liu, B.; Duan, Z.; Darensbourg, D.J. Copolymerization of carbon dioxide and cyclohexene oxide catalyzed by chromium complexes bearing semirigid [ONSO]-type ligands. J. Polym. Sci. Part A Polym. Chem. 2016, 54, 1938–1944. [Google Scholar] [CrossRef]
  61. Della Monica, F.; Paradiso, V.; Grassi, A.; Milione, S.; Cavallo, L.; Capacchione, C. A novel [OSSO]-type chromium(III) complex as a versatile catalyst for copolymerization of carbon dioxide with epoxides. Chem. Eur. J. 2020, 26, 5347–5353. [Google Scholar] [CrossRef]
  62. 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, 8456–8459. [Google Scholar] [CrossRef]
  63. Buchard, A.; Kember, M.R.; Sandeman, K.G.; Williams, C.K. A bimetallic iron(III) catalyst for CO2/epoxide coupling. Chem. Commun. 2011, 47, 212–214. [Google Scholar] [CrossRef] [Green Version]
  64. 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 scaffolds. Angew. Chem. Int. Ed. 2014, 53, 10416–10419. [Google Scholar] [CrossRef]
  65. Whiteoak, C.J.; Martin, E.; Belmonte, M.M.; Benet-Buchholz, J.; Kleij, A.W. An Efficient iron catalyst for the synthesis of five- and six-membered organic carbonates under mild conditions. Adv. Synth. Catal. 2012, 354, 469–476. [Google Scholar] [CrossRef]
  66. Sunjuk, M.; Abu-Surrah, A.S.; Al-Ramahi, E.; Qaroush, A.K.; Saleh, A. Selective coupling of carbon dioxide and epoxystyrene via salicylaldimine-, thiophenaldimine-, and quinolinaldimine-iron(II), iron(III), chromium(III), and cobalt(III)/Lewis base catalysts. Transit. Met. Chem. 2013, 38, 253–257. [Google Scholar] [CrossRef]
  67. Buonerba, A.; De Nisi, A.; Grassi, A.; Milione, S.; Capacchione, C.; Vagin, S.; Rieger, B. Novel iron(III) catalyst for the efficient and selective coupling of carbon dioxide and epoxides to form cyclic carbonates. Catal. Sci. Technol. 2015, 5, 118–123. [Google Scholar] [CrossRef]
  68. Della Monica, F.; Vummaleti, S.V.C.; Buonerba, A.; Nisi, A.D.; Monari, M.; Milione, S.; Grassi, A.; Cavallo, L.; Capacchione, C. Coupling of carbon dioxide with epoxides efficiently catalyzed by thioether-triphenolate bimetallic iron(III) complexes: Catalyst structure-reactivity relationship and mechanistic DFT study. Adv. Synth. Catal. 2016, 358, 3231–3243. [Google Scholar] [CrossRef]
  69. Buonerba, A.; Della Monica, F.; De Nisi, A.; Luciano, E.; Milione, S.; Grassi, A.; Capacchione, C.; Rieger, B. Thioether-triphenolate bimetallic Iron(III) complexes as robust and highly efficient catalysts for cycloaddition of carbon dioxide to epoxides. Faraday Discuss. 2015, 183, 83–95. [Google Scholar] [CrossRef] [PubMed]
  70. Della Monica, F.; Buonerba, A.; Paradiso, V.; Milione, S.; Grassi, A.; Capacchione, C. [OSSO]-type Fe(III) metallate as single-component catalyst for the CO2 cycloaddition to epoxides Adv. Synth. Catal. 2019, 361, 283–288. [Google Scholar] [CrossRef]
  71. Della Monica, F.; Leone, M.; Buonerba, A.; Grassi, A.; Milione, S.; Capacchione, C. CO2 cycloaddition to epoxides promoted by bis-thioether-phenolate Fe(II) and Fe(III) complexes. Mol. Catal. 2018, 460, 46–52. [Google Scholar] [CrossRef]
  72. Driscoll, O.J.; Stewart, J.A.; McKeown, P.; Jones, M.D. Salalen vs. thiolen: In the ring(-opening of epoxide and cyclic carbonate formation). New J. Chem. 2020, 44, 6063–6067. [Google Scholar] [CrossRef] [Green Version]
  73. Ollevier, T. New trends in bismuth-catalyzed synthetic transformations. Org. Biomol. Chem. 2013, 11, 2740. [Google Scholar] [CrossRef] [Green Version]
  74. Ollevier, T. (Ed.) Bismuth-Mediated Organic Reactions; Topics in Current Chemistry; Springer: Berlin/Heidelberg, Germany, 2012; Volume 311, ISBN 978-3-642-27238-7. [Google Scholar]
  75. Yamamoto, H.; Ishihara, K. (Eds.) Acid Catalysis in Modern Organic Synthesis; WILEY-VCH: Weinheim, Germany, 2008; ISBN 978-3-527-31724-0. [Google Scholar]
  76. Salvador, J.A.R.; Silvestre, S.M.; Pinto, R.M.A. Bismuth(III) reagents in steroid and terpene chemistry. Molecules 2011, 16, 2884–2913. [Google Scholar] [CrossRef] [Green Version]
  77. Chen, Y.; Qiu, R.; Xu, X.; Au, C.-T.; Yin, S.-F. Organoantimony and organobismuth complexes for CO2 fixation. RSC Adv. 2014, 4, 11907–11918. [Google Scholar] [CrossRef]
  78. Zhang, X.; Dai, W.; Yin, S.; Luo, S.; Au, C.-T. Cationic organobismuth complex as an effective catalyst for conversion of CO2 into cyclic carbonates. Front. Environ. Sci. Eng. China 2009, 3, 32–37. [Google Scholar] [CrossRef] [Green Version]
  79. Yin, S.-F.; Shimada, S. Synthesis and structure of bismuth compounds bearing a sulfur-bridged bis(phenolato) ligand and their catalytic application to the solvent-free synthesis of propylene carbonate from CO2 and propylene oxide. Chem. Commun. 2009, 1136. [Google Scholar] [CrossRef] [PubMed]
  80. Qiu, R.; Meng, Z.; Yin, S.; Song, X.; Tan, N.; Zhou, Y.; Yu, K.; Xu, X.; Luo, S.; Au, C.-T.; et al. Synthesis and structure of binuclear o/s-bridged organobismuth complexes and their cooperative catalytic effect on CO2 fixation. ChemPlusChem 2012, 77, 404–410. [Google Scholar] [CrossRef]
Catalysts 10 00825 sch001 550
Scheme 1. Mechanism of the coupling of CO2 with epoxides [20].
Scheme 1. Mechanism of the coupling of CO2 with epoxides [20].
Catalysts 10 00825 sch001
Catalysts 10 00825 g001 550
Figure 1. Selected catalytic systems for the synthesis of cyclic organic carbonates (COC) from CO2 and epoxides [22,25,29,30].
Figure 1. Selected catalytic systems for the synthesis of cyclic organic carbonates (COC) from CO2 and epoxides [22,25,29,30].
Catalysts 10 00825 g001
Catalysts 10 00825 g002 550
Figure 2. Representative catalytic systems for the synthesis of aliphatic polycarbonates (APC) from CO2 and epoxides [33,34,35,36,37].
Figure 2. Representative catalytic systems for the synthesis of aliphatic polycarbonates (APC) from CO2 and epoxides [33,34,35,36,37].
Catalysts 10 00825 g002
Catalysts 10 00825 g003 550
Figure 3. Selected examples of metal complexes containing a chiral Salen ligand and their applications [38].
Figure 3. Selected examples of metal complexes containing a chiral Salen ligand and their applications [38].
Catalysts 10 00825 g003
Catalysts 10 00825 g004 550
Figure 4. Representative examples of complexes bearing [OSO], [OSSO], or [OS]-ligands [39,41,43,47,49,50,51].
Figure 4. Representative examples of complexes bearing [OSO], [OSSO], or [OS]-ligands [39,41,43,47,49,50,51].
Catalysts 10 00825 g004
Catalysts 10 00825 g005 550
Figure 5. Chromium(III) Salen complexes for the reaction of CO2 with CHO or propylene oxide (PO) [54,55].
Figure 5. Chromium(III) Salen complexes for the reaction of CO2 with CHO or propylene oxide (PO) [54,55].
Catalysts 10 00825 g005
Catalysts 10 00825 g006 550
Figure 6. Bimetallic chromium(III) Salen complex developed by Rieger for the coupling of CO2 with PO [56].
Figure 6. Bimetallic chromium(III) Salen complex developed by Rieger for the coupling of CO2 with PO [56].
Catalysts 10 00825 g006
Catalysts 10 00825 g007 550
Figure 7. Chromium(III)-Aminophosphine complexes developed by Duchateau for the coupling of CO2 with CHO [58].
Figure 7. Chromium(III)-Aminophosphine complexes developed by Duchateau for the coupling of CO2 with CHO [58].
Catalysts 10 00825 g007
Catalysts 10 00825 g008 550
Figure 8. Chromium(III)-[OSSO] catalysts 1–4 [59].
Figure 8. Chromium(III)-[OSSO] catalysts 1–4 [59].
Catalysts 10 00825 g008
Catalysts 10 00825 sch002 550
Scheme 2. Proposed mechanism for the copolymerization of VCHO and CO2. X = Cl−, N 3 − [59].
Scheme 2. Proposed mechanism for the copolymerization of VCHO and CO2. X = Cl−, N 3 − [59].
Catalysts 10 00825 sch002
Catalysts 10 00825 g009 550
Figure 9. Chromium(III)-[ONSO] catalysts 5–8 [60].
Figure 9. Chromium(III)-[ONSO] catalysts 5–8 [60].
Catalysts 10 00825 g009
Catalysts 10 00825 g010 550
Figure 10. Coupling of PO and CO2 catalyzed by the chromium(III)-[OSSO] catalyst 9 [61]. Reprinted with permission from ref. 61. Copyright (2020) John Wiley and Sons.
Figure 10. Coupling of PO and CO2 catalyzed by the chromium(III)-[OSSO] catalyst 9 [61]. Reprinted with permission from ref. 61. Copyright (2020) John Wiley and Sons.
Catalysts 10 00825 g010
Catalysts 10 00825 sch003 550
Scheme 3. Free energy profile evaluating the cyclization versus polymerization paths for the coupling of PO and CO2 promoted by complex 9 [61]. Reprinted with permission from ref. 61. Copyright (2020) John Wiley and Sons.
Scheme 3. Free energy profile evaluating the cyclization versus polymerization paths for the coupling of PO and CO2 promoted by complex 9 [61]. Reprinted with permission from ref. 61. Copyright (2020) John Wiley and Sons.
Catalysts 10 00825 sch003
Catalysts 10 00825 g011 550
Figure 11. Representative examples of iron-based complexes active in the coupling of CO2 with epoxides [18,62,63,64,65].
Figure 11. Representative examples of iron-based complexes active in the coupling of CO2 with epoxides [18,62,63,64,65].
Catalysts 10 00825 g011
Catalysts 10 00825 g012 550
Figure 12. Coupling of styrene oxide (SO) and CO2 promoted by the iron(II) thiophenaldimine complex 10 [66].
Figure 12. Coupling of styrene oxide (SO) and CO2 promoted by the iron(II) thiophenaldimine complex 10 [66].
Catalysts 10 00825 g012
Catalysts 10 00825 g013 550
Figure 13. Dinuclear iron(III) complexes 11–16 containing a bis-thioether-triphenolate ligand [67,68].
Figure 13. Dinuclear iron(III) complexes 11–16 containing a bis-thioether-triphenolate ligand [67,68].
Catalysts 10 00825 g013
Catalysts 10 00825 g014 550
Figure 14. Free energy profile for the coupling of PO and CO2 promoted by complex 16 [68]. Reprinted with permission from ref. 68. Copyright (2020) John Wiley and Sons.
Figure 14. Free energy profile for the coupling of PO and CO2 promoted by complex 16 [68]. Reprinted with permission from ref. 68. Copyright (2020) John Wiley and Sons.
Catalysts 10 00825 g014
Catalysts 10 00825 g015 550
Figure 15. Iron(III)-[OSSO] complexes 17–20 [52].
Figure 15. Iron(III)-[OSSO] complexes 17–20 [52].
Catalysts 10 00825 g015
Catalysts 10 00825 g016 550
Figure 16. Free energy profile for the coupling of PO and CO2 promoted by complex 20 [52]. Reprinted with permission from ref. 52. Copyright (2020) American Chemical Society.
Figure 16. Free energy profile for the coupling of PO and CO2 promoted by complex 20 [52]. Reprinted with permission from ref. 52. Copyright (2020) American Chemical Society.
Catalysts 10 00825 g016
Catalysts 10 00825 g017 550
Figure 17. Synthesis of the ferrate species 21 from complexes 20 or 22 through reaction with two or one equivalents of TBAB, respectively [70].
Figure 17. Synthesis of the ferrate species 21 from complexes 20 or 22 through reaction with two or one equivalents of TBAB, respectively [70].
Catalysts 10 00825 g017
Catalysts 10 00825 g018 550
Figure 18. Bisthioether phenolate Fe(II) and Fe(III) complexes 23–28 [71].
Figure 18. Bisthioether phenolate Fe(II) and Fe(III) complexes 23–28 [71].
Catalysts 10 00825 g018
Catalysts 10 00825 g019 550
Figure 19. ([ONSO]-type) Fe(III) complexes 29–34 [72].
Figure 19. ([ONSO]-type) Fe(III) complexes 29–34 [72].
Catalysts 10 00825 g019
Catalysts 10 00825 g020 550
Figure 20. Bi(III) complexes 35–36 containing an [OSO]-bisphenolate ligand [79].
Figure 20. Bi(III) complexes 35–36 containing an [OSO]-bisphenolate ligand [79].
Catalysts 10 00825 g020
Catalysts 10 00825 g021 550
Figure 21. Dinuclear sulfide-bridged complexes 37–40 [80].
Figure 21. Dinuclear sulfide-bridged complexes 37–40 [80].
Catalysts 10 00825 g021
Table
Table 1. Complexes 1–4 in the copolymerization of vinylcyclohexeneoxide (VCHO) and CO2 [59].
Table 1. Complexes 1–4 in the copolymerization of vinylcyclohexeneoxide (VCHO) and CO2 [59].
ComplexTOF a (h−1)Selectivity b (%) (Polymer-Carbonate Linkages)Mnc (KDa)Ðc
17473–97.5151.30
28268–98.0201.35
37871–99.0191.27
41344–95.561.26
Reaction conditions: [VCHO]/[[OSSO]CrX]/[PPNCl] = 1000/1/2; T = 90 °C, pCO2 = 3.0 MPa; time = 6 h. a Turnover frequency (TOF) for the copolymer calculated as mole of VCHO consumed per mole of catalyst per hour. b Selectivity of PVCHC estimated by IR spectroscopy; selectivity toward polycarbonate linkages calculated through 1H NMR spectroscopy. c Determined by GPC.

Share and Cite

MDPI and ACS Style

Paradiso, V.; Capaccio, V.; Lamparelli, D.H.; Capacchione, C. Metal Complexes Bearing Sulfur-Containing Ligands as Catalysts in the Reaction of CO2 with Epoxides. Catalysts 2020, 10, 825. https://doi.org/10.3390/catal10080825

AMA Style

Paradiso V, Capaccio V, Lamparelli DH, Capacchione C. Metal Complexes Bearing Sulfur-Containing Ligands as Catalysts in the Reaction of CO2 with Epoxides. Catalysts. 2020; 10(8):825. https://doi.org/10.3390/catal10080825

Chicago/Turabian Style

Paradiso, Veronica, Vito Capaccio, David Hermann Lamparelli, and Carmine Capacchione. 2020. "Metal Complexes Bearing Sulfur-Containing Ligands as Catalysts in the Reaction of CO2 with Epoxides" Catalysts 10, no. 8: 825. https://doi.org/10.3390/catal10080825

APA Style

Paradiso, V., Capaccio, V., Lamparelli, D. H., & Capacchione, C. (2020). Metal Complexes Bearing Sulfur-Containing Ligands as Catalysts in the Reaction of CO2 with Epoxides. Catalysts, 10(8), 825. https://doi.org/10.3390/catal10080825

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop