Efficient Production of Poly(Cyclohexene Carbonate) via ROCOP of Cyclohexene Oxide and CO2 Mediated by NNO-Scorpionate Zinc Complexes

Abstract

New mono- and dinuclear chiral alkoxide/thioalkoxide NNO-scorpinate zinc complexes were easily synthesized in very high yields, and characterized by spectroscopic methods. X-ray diffraction analysis unambiguously confirmed the different nuclearity of the new complexes as well as the variety of coordination modes of the scorpionate ligands. Scorpionate zinc complexes 2, 4 and 6 were assessed as catalysts for polycarbonate production from epoxide and carbon dioxide with no need for a co-catalyst or activator under mild conditions. Interestingly, at 70 °C, 10 bar of CO2 pressure and 1 mol % of loading, the dinuclear thioaryloxide [Zn(bpzaepe)2{Zn(SAr)2}] (4) behaves as an efficient and selective one-component initiator for the synthesis of poly(cyclohexene carbonate) via ring-opening copolymerization of cyclohexene oxide (CHO) and CO2, affording polycarbonate materials with narrow dispersity values.

Recent Developments in Ring-Opening Copolymerization of Epoxides With CO2 and Cyclic Anhydrides for Biomedical Applications

“…Among them, catalyst 2e showed the highest catalytic activity [89% conversion, turnover frequency (TOF) up to 5.56 h −1 ], carbonate linkage content (99%), and polycarbonate selectivity (90%). After that, in 2020, another type of dinuclear zinc catalysts based on chiral/thioalkoxide NNO-scorpionate ligand was synthesized (Sobrino et al, 2020). The difference from the previous study is that in catalysts 4-5, the heteroscorpionate ligand is connected to the zinc center through two nitrogen atoms on the pyrazole rings, and the oxygen atom on the alkoxy group is connected to the two zinc by κ 2 -NNµ-O coordination mode.…”

Coordination from Heteroscorpionate Ligand Towards Pd(II) via Pd⋅⋅⋅Hδ−C(sp3) Interaction: Structural and Catalytic Studies

“…Complexes 2 and 3 catalyzed the coupling of aryl bromides (Table 3, entries 5-14), with conversions from 70 to 91 % having phenyl boronic acid as coupling partner. The coupling of electron-poor substrates (4-bromobenzaldehyde, 4-bromoacetophenone and 4-nitrobromobenzene) with phenyl boronic acid delivered yields from 80 to 91 % (Table 3, entries 5-10) and with electron-rich substrates (4-bromoanisole and 4-bromobenzene) the cross-coupling product reached 70-82 % conversions (Table 3, entries [11][12][13][14].…”

“…Subsequently, the effect of the alkene as substrate in the Heck reactions was also examined using less activated olefin such as styrene. The Heck coupling was performed with a series of aryl bromides and styrene (Table 5, entries [10][11][12][13][14]. In all cases, the reaction proved regioselective, yielding the psubstituted stilbene product and only traces of the corresponding gem-isomer were detected in less than 5 % detected by NMR spectroscopy.…”

“…[3][4][5][6][7][8][9][10] Bis(pyrazol-1-yl)methane-based NNO-donor scorpionate ligands are widely desired due their ability to coordinate different metal centers via two coordination mode, with or without the deprotonation of the OH group; a) where the two nitrogen and the oxygen atoms link the metal center via a coordination bonds and b) where the metal center is coordinatively binded to two nitrogen and covalently bound to the oxygen atom (Figure 1). [11][12][13][14][15][16][17][18][19][20] On the other hand, intramolecular CÀ H•••M agostic or anagostic interactions were described as responsible for favoring the coordination chemistry of CÀ H bonds. This important interaction in organometallic chemistry can stabilize complexes that are implicated in several catalytic reactions and represent an opportunity to gain insight into transition-metalmediated CÀ H bond activation reactions.…”

“…Bis(pyrazol‐1‐yl)methane‐based NNO‐donor scorpionate ligands are widely desired due their ability to coordinate different metal centers via two coordination mode, with or without the deprotonation of the OH group; a ) where the two nitrogen and the oxygen atoms link the metal center via a coordination bonds and b ) where the metal center is coordinatively binded to two nitrogen and covalently bound to the oxygen atom (Figure 1). [11–20] …”