[Zinc(II)(Pyridine‐Containing Ligand)] Complexes as Single‐Component Efficient Catalyst for Chemical Fixation of CO₂ with Epoxides

Abstract

Dedicated to Professor Franco Cozzi on the occasion of his 70 th birthday. "Senatores boni viri, senatus mala bestia"The reaction between epoxides and CO 2 to yield cyclic carbonates is efficiently promoted under solvent-free and relatively mild reaction conditions (0.5 mol % catalyst loading, 0.8 MPa, 125°C) by zinc(II) complexes of pyridine containing macrocyclic ligands (PcÀ L pyridinophanes). The zinc complexes have been fully characterized, including X-ray structural determination. The [Zn(II)X(PcÀ L)]X complexes showed good solubility in several polar solvents, including cyclic carbonates. The scope of the reaction under solvent-free conditions has been studied and good to quantitative conversions with excellent selectivities have been obtained, starting from terminal epoxides. When solvent-free conditions were not possible (solid epoxides or low solubility of the catalyst in the oxirane) the use of cyclic carbonates as solvents has been successfully investigated. The remarkable stability of the catalytic system has been demonstrated by a series of consecutive runs.

Synthesis, characterization and application of oxovanadium(iv) complexes with [NNO] donor ligands: X-ray structures of their corresponding dioxovanadium(v) complexes

“…Catalytic cycloaddition of CO 2 with epoxides to yield cyclic carbonates using both homogeneous and heterogeneous catalyst systems that encompass metal complexes, [31][32][33][34][35][36][37][38][39][50][51][52][53][54][55][56] ionic liquids, 40,41 metal organic frameworks (MOFs), 42,57 covalent organic frameworks (COFs), 43 porous organic polymers (POPs), 44 organo-catalysts, 45 bi-functional catalysts, 46 alkali metal salts, 47,48 and metal oxides 49 have been demonstrated by various research groups. Currently, vanadium complexes have gained considerable attention from scientic community to be used as catalyst in the CO 2 cycloaddition with epoxides due to the Lewis acidic nature of high-valent V V and V IV centers, suitable for activating epoxides as well as relatively non-toxic nature of naturally abundant vanadium metal.…”

“…17–21 Of many important CO 2 transformation reactions, 22 cycloaddition of CO 2 with epoxides to form cyclic carbonates stands out to be a very attractive transformation process. 23–57 The process is 100% atom economic and the resulting cyclic carbonate products are commercially important chemicals which can be used as electrolytes in lithium-ion battery, 58 polar aprotic solvents, 59 functionalized building blocks for synthesizing valuable organic products, 60 monomers for polycarbonates 61 and isocyanate-free polyurethanes, 62 intermediates for pharmaceuticals and fine chemicals. 63 Interestingly, cyclic carbonate moieties are also seen in some natural products 64–66 thereby making the CO 2 transformation reaction to cyclic carbonate a very significant and naturally relevant reaction.…”

Ammonium zincates as suitable catalyst for the room temperature cycloaddition of CO2 to epoxides

“…The most promising catalyst resulted to be the [TBA] 2 [ZnBr 4 ] complex, that in just 1 h of reaction converted 98% of starting 1a with 96% selectivity in 2a (entry 8, Table 2). As we already noticed in the case of [Zn(II)pyclen] complexes reported recently as efficient catalysts for the chemical fixation of CO 2 with epoxides (Cavalleri et al, 2021), the chloro-zincate salt was the less active one. Among the three zincates, the activity increased in the order X = Cl − < I − < Br − (compare entries 7, 8 and 9, Table 2) and this trend can be rationalized considering the following considerations regarding the overall catalytic activity: 1) lability of the halide from the zincate anion (vide supra, ESI(-)-HRMS analyses); 2) the nucleophilicity of the halide in the ring opening of the epoxide; and 3) the halide leaving group ability, in order to promote the cyclic carbonate formation in the ring closing step (Kamphuis et al, 2019a).…”

Recent progress in the chemistry of 12-membered pyridine-containing tetraazamacrocycles: from synthesis to catalysis

“…In this regard, Caselli and coworkers have recently disclosed that well-defined cationic Zn II –pyclen complexes were a competent catalyst for utilization of CO 2 in cycloaddition reactions with terminal epoxides (Scheme 31). 111 In particular, zinc– pyclen complexes XZn II –pyclen (X = Cl, Br, I) were easily prepared form zinc halide salts in very good yields and they could be fully characterized. X-ray diffraction analysis of zinc cationic complexes revealed a distorted square pyramidal zinc environment, which provides a free coordination site on the zinc and might eventually make use of the outer-sphere anion.…”