Yusheng Qin

An aluminum porphyrin complex with high activity and selectivity for cyclic carbonate synthesis

An aluminum porphyrin complex with a quaternary ammonium salt cocatalyst exhibits high activity (i.e., a turnover frequency as high as 1.85 × 105 h−1) and selectivity (>99%) for cyclic carbonates synthesis from CO2 and epoxides; the catalyst can be reused at least 4 times with only a slight loss in activity.

Quantitative synthesis of bis(cyclic carbonate)s by iron catalyst for non-isocyanate polyurethane synthesis

Bis(cyclic carbonate)s were quantitatively prepared with high efficiency via the coupling reaction of carbon dioxide (CO2) with diglycidyl ethers by a [Fe(BPMCDAC)]/TBAB catalytic system, where glycol diglycidyl ether (1a) could be completely converted to the corresponding bis(cyclic carbonate) (2a) with a turnover number of 1000 at 100 °C and 3 MPa in 4 h. The obtained bis(cyclic carbonate) (2a) could be used to prepare hydroxyl-functional polyurethanes via reaction with diamines, which may be one alternative for obtaining conventional polyurethanes without the use of toxic phosgene or isocyanates. The number-average molecular weights of the obtained non-isocyanate polyurethanes (NIPUs) were up to 25.4–30.2 kg mol−1, and the polydispersity indexes (PDIs) were relatively narrow between 1.18 and 1.22. A typical NIPU showed a glass transition temperature of 9 °C and an initial degradation temperature (Td 5%) of 206 °C.

A novel metalloporphyrin-based conjugated microporous polymer for capture and conversion of CO2

A novel conjugated microporous polymer was solvothermally synthesized using an aluminum porphyrin as a main building block, which had a high Brunauer–Emmett–Teller specific surface area up to 839 m2 g−1 and a pore volume of 2.14 cm3 g−1. The polymer displayed excellent capacity to capture carbon dioxide (4.3 wt%) at 273 K and 1 bar, and good catalytic activity for cyclic carbonate synthesis with TOF up to 364 h−1.

Coupling reaction between CO2 and cyclohexene oxide: selective control from cyclic carbonate to polycarbonate by ligand design of salen/salalen titanium complexes

Based on the mechanistic features of metal salen catalysis systems, titanium(IV) complexes from salen (salen-H2 = N,N-bis(3,5-di-tert-butylsalicylidene)-1,2-benzenediamine) and its half saturated form salalen have been prepared, which were used as catalysts in conjugation with bis(triphenylphosphino)iminium chloride ([PPN]Cl) for the coupling reaction of CO2 and cyclohexene oxide (CHO). The salen titanium complex (salen)Ti(IV)Cl2 showed moderate activity, producing a unique cis-isomer of cyclic carbonate with high conversion up to 100% in 8 h, however, it could not catalyze the copolymerization reaction. Meanwhile, the salalen titanium complex (salalen)Ti(IV)Cl was effective for the copolymerization of CO2 and CHO, where only one chain grew on Ti during the chain propagation reaction, yielding completely alternating copolymers with –OH and –Cl as terminal groups. Moreover, the nearly complete conversion of CHO indicated that (salalen)Ti(IV)Cl might be used to synthesize multiblock poly(cyclohexene carbonate)s with controllable sequences.

One-pot controllable synthesis of oligo(carbonate-ether) triol using a Zn-Co-DMC catalyst: the special role of trimesic acid as an initiation-transfer agent

A one-pot synthesis of oligo(carbonate-ether) triol was realized by the copolymerization of CO2 and propylene oxide (PO) using a zinc-cobalt double metal cyanide (Zn-Co-DMC) catalyst in the presence of 1,3,5-benzenetricarboxylic (trimesic) acid (TMA). The catalytic activity ranged from 0.3 to 1.0 kg g−1 DMC under various copolymerization conditions. The structure of the oligo(carbonate-ether) triol was clearly confirmed, providing sound evidence for the special role played by the TMA, i.e., that it acted as an initiation-transfer agent. In the first stage the TMA initiated PO homo-polymerization to afford oligo-ether triol via a core-first approach in the presence of Zn-Co-DMC. After all of the TMA was consumed, the in situ formed oligo-ether triol acted as new chain transfer agent to participate in the copolymerization, forming carbonate-ether segments and therefore the oligo(carbonate-ether) triol. Since every molecule of TMA participated in initiation and propagation steps, the molecular weight of the triol depended on the amount of TMA used rather than the amount of Zn-Co-DMC. Consequently, the number average molecular weight (Mn) of the oligo(carbonate-ether) triol could be well controlled from 1400 to 3800 g mol−1 with a relatively narrow polydispersity index (PDI) (1.15–1.45), and its carbonate unit content (CU) could be adjusted between 20% and 54%.

A novel 2,5-furandicarboxylic acid-based bis(cyclic carbonate) for the synthesis of biobased non-isocyanate polyurethanes

This paper describes the synthesis of a new biobased bis(cyclic carbonate) derived from 2,5-furandicarboxylic acid (FDCA) with the incorporation of CO2. The bis(cyclic carbonate) was then used to synthesize non-isocyanate polyurethanes (NIPUs) via polyaddition reactions with a series of diamines. The chemical structures of the bis(cyclic carbonate) and the NIPUs were characterized by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). The number-average molecular weights (Mn) of the NIPUs were between 3900 g mol−1 and 7000 g mol−1 as determined by gel permeation chromatography (GPC). The thermal properties of the NIPUs were investigated by differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA). The results showed that the NIPUs synthesized in this study had a degradation temperature for 5% weight loss (T5%) in the range of 240 °C and 279 °C, indicating good thermal stability. The NIPUs were also found to be fully amorphous with a broad range of glass transition temperatures (Tg) from 63 °C to 113 °C, depending on the chemical structures of the diamines used. The rigid chemical moiety of cycloaliphatic diamine led to a higher Tg of the NIPUs than the flexible carbon chains of linear aliphatic diamines. This study demonstrated a new method for the synthesis of biobased NIPUs, with satisfactory properties, from FDCA, which is an important platform chemical derived from cellulosic biomass.

Efficient synthesis and stabilization of poly(propylene carbonate) from delicately designed bifunctional aluminum porphyrin complexes

Bifunctional aluminum porphyrin complexes were designed to synthesize poly(propylene carbonate) (PPC) by copolymerization of propylene oxide and carbon dioxide. The catalytic performance is adjustable via delicate control of the electronic environment of the central Al by the number of methoxy groups in the ligand framework as well as the length of the alkyl chain in the quaternary ammonium cation. The optimal catalyst having six methoxy groups in the ligand framework, two trihexylammonium cations linked to benzene via a six-methylene spacer, and NO3− as the axial ligand and quaternary ammonium anions exhibited a TOF of 1320 h−1 at 80 °C and 3 MPa, and a PPC selectivity of 93%, and the TOF even reached 2824 h−1 at 90 °C and 3 MPa, while the PPC selectivity remained at 89%, the highest recorded in aluminum porphyrin complexes to date. In another concern, even though the bifunctional aluminum porphyrin complex has a soil-compostable feature and can be left in PPC without separation, the depolymerization was very rapid even at 25 °C under an ambient atmosphere, and over a 50% decrease in number average molecular weight was observed in 8 days, which could be stabilized by treatment with aqueous HCl solution.

Controllable synthesis of a narrow polydispersity CO2-based oligo(carbonate-ether) tetraol

A CO2-based oligo(carbonate-ether) tetraol was synthesized in a controlled manner by immortal copolymerization of carbon dioxide (CO2) and propylene oxide (PO) in the presence of 1,2,4,5-benzenetetracarboxylic acid (btcH4) catalyzed by using a zinc–cobalt double metal cyanide (Zn–Co–DMC) catalyst. The number average molecular weight (Mn) of the tetraol was in a good linear relationship with the molar ratio of PO and btcH4 (PO/btcH4), and hence can be precisely controlled. Besides, the rapid chain transfer in immortal copolymerization afforded the tetraol with a narrow polydispersity index (PDI) of 1.08 at a Mn of 1400 g mol−1. Notably, the weight fraction of the byproduct propylene carbonate (WPC) was reduced to as low as 4.0 wt%, which is the lowest Wpc ever reported for the synthesis of branched polyols. The structure of the oligo(carbonate-ether) tetraol was confirmed, providing new evidence for the effect of the acidity (pKa1 value) of the chain transfer agent (CTA) on the initial catalytic mechanism. The acid only acts as the CTA directly participating in the copolymerization via the chain transfer reaction when its pKa1 value is higher than that of adipic acid (pKa1 = 4.43). However, when its pKa1 value is lower than that of succinic acid (pKa1 = 4.2), it acts as the initiate-transfer agent, which first initiates PO homopolymerization to an oligo-ether polyol, and then the in situ formed polyol acts as a new CTA for the copolymerization.

COPOLYMERIZATION OF CARBON DIOXIDE AND CYCLOHEXENE OXIDE CATALYZED BY ALUMINUM PORPHYRIN-QUATERNARY AMMONIUM SALT IN THE PRESENCE OF BULKY LEWIS ACID

Chloro(5,10,15,20-tetraphenyl-porphyrinato)-aluminum/tetraethylammonium bromide (Et4NBr) in combination with bulky Lewis acid was used for the copolymerization of CO2 and cyclohexene oxide (CHO). Bulky Lewis acid having substituents at the ortho positions of the phenolate ligands, like methylaluminum bis(2,6-di-tert-butyl-4-methylphenolate), significantly shortened the induction period and raised the catalytic activity, the corresponding turnover frequency reached 44.9 h-1 in 9 h, which was 23.8% higher than that from (TPP)AlCl/Et4NBr binary catalyst. The resulting polycarbonate has carbonate linkage over 93% with number average molecular weight of (4.5–6.5) × 103 and polydispersity index below 1.10.

Aluminum porphyrin complexes via delicate ligand design: emerging efficient catalysts for high molecular weight poly(propylene carbonate)

Due to the deep concern over residual, toxic cobalt or chromium from catalysts in biodegradable poly(propylene carbonate) (PPC), bifunctional aluminum porphyrin complexes with quaternary ammonium salts anchored on the ligand framework were prepared, and a delicate design of the porphyrin ligand was obtained. An optimized catalyst was complex 6b, which had two para-bromine benzenes and two quaternary ammonium cations linked to benzene via a six-methylene spacer in the meso-position of the porphyrin framework and NO3− as axial ligand and quaternary ammonium anion, showed TOF of 560 h−1 at 80 °C and 3 MPa to yield PPC with 94% carbonate linkage and number average molecular weight of 96 kg mol−1. The PPC selectivity reached 93%, which was the highest record in this copolymerization for aluminum porphyrin complexes. The soil tolerant bifunctional aluminum porphyrin complexes are becoming increasingly competitive catalysts, since they can be left with the plastics without any extra separation.