Mechanism of the Cycloaddition of Carbon Dioxide and Epoxides Catalyzed by Cobalt‐Substituted 12‐Tungstenphosphate

Abstract

Co(II)-substituted α-Keggin-type 12-tungstenphosphate [(n-C(4)H(9))(4)N](4)H[PW(11)Co(H(2)O)O(39)]-(PW(11)Co) is synthesized and used as a single-component, solvent-free catalyst in the cycloaddition reaction of CO(2) and epoxides to form cyclic carbonates. The mechanism of the cycloaddition reaction is investigated using DFT calculations, which provides the first computational study of the catalytic cycle of polyoxometalate-catalyzed CO(2) coupling reactions. The reaction occurs through a single-electron transfer from the doublet Co(II) catalyst to the epoxide and forms a doublet Co(III)-carbon radical intermediate. Subsequent CO(2) addition forms the cyclic carbonate product. The existence of radical intermediates is supported by free-radical termination experiments. Finally, it is exhilarating to observe that the calculated overall reaction barrier (30.5 kcal mol(-1)) is in good agreement with the real reaction rate (83 h(-1)) determined in the present experiments (at 15 °C).

Coordination of Carbon Dioxide to the Lewis Acid Site of a Zinc‐Substituted Polyoxometalate and Formation of an Adduct Using a Polyoxometalate–2,4,6‐Trimethylpyridine Frustrated Lewis Pair

“…At 224 K the clear appearance of an additional set of peaks was observed indicating the presence of an additional compound. DFT calculations carried out in the past on Ru III ‐ and Co II ‐substituted Keggin anions, [Ru III SiW 11 O 39 ] 5– and [Co II PW 11 O 39 ] 5– , showed two plausible coordination modes, a higher energy “end‐on” coordination and a lower energy more stable “side‐on” coordination, Scheme , . The 31 P NMR spectra support the idea of “side‐on” coordination” at room temperature down to ca.…”

Highly efficient conversion of CO2 at atmospheric pressure to cyclic carbonates with in situ-generated homogeneous catalysts from a copper-containing coordination polymer

“…[1][2][3], four reactions were carried out at four different concentrations (n) of BIT-C, respectively. Catalyst and co-catalyst were completely dissolved in 1,2-epoxyoctane before reacting.…”

“…Meanwhile, a large number of homogeneous and heterogeneous catalysts have been reported, such as metal-salen complexes [5], ionic liquids [6], nitrogen-containing polymers [7], metal oxides [8], organocatalysts [9], and metal-organic frameworks (MOFs) [10,11]. In our previous work, the transition metal-substituted polyoxometalates (POMs) were also found to be effective catalysts for CO 2 cycloaddition to epoxides as the single-component catalysts [1,12,13]. Unfortunately, relatively high temperature (>100°C) and high CO 2 pressure (>2.0 MPa) are generally required in most of catalytic systems, which greatly limit practical application.…”

“…Chemical fixation of CO 2 to obtain the valuable chemical materials is of both scientific and practical significance [1]. One of the most promising pathways is the synthesis of cyclic carbonate from CO 2 and epoxide.…”

The effect of ring size on the selective carboxylation of cycloalkene oxides

“…For systems containing redox active metals such as Co in α-Keggin-type structures calculations have also shown that ring opening of the epoxide can occur without the intervention of a nucleophilic agent through electron transfer and oxidation of the metal cente. 24 To realise cyclic carbonate production on a large scale, epoxides themselves will have to be synthesised by the oxidation of alkenes. The direct synthesis of cyclic carbonates from olefins, avoiding additional work-up procedures, would be an interesting and economically feasible route.…”