Balancing between Heterogeneity and Reactivity in Porphyrin Chromium-Cobaltate Catalyzed Ring Expansion Carbonylation of Epoxide into β-Lactone

Abstract

The synthesis of a unique heterogeneous catalyst that combines the functionality of a homogeneous catalyst and the advantages of a heterogeneous catalytic process is a continuing goal in various industrially applicable reactions. Here, we report heterogenization of homogeneous catalyst for lactone production from epoxide carbonylation through a facile polymerization using Friedel–Crafts reaction. A correlation between reactivity and degree of heterogeneity has been deduced by synthesizing different sized polymeric catalysts. The partially polymerized catalyst showed a remarkable initial turnover frequency of 400 h–1, and the fully polymerized catalyst displayed excellent selectivity during recycling with a total turnover number of 4100.

Direct Heterogenization of Salphen Coordination Complexes to Porous Organic Polymers: Catalysts for Ring-Expansion Carbonylation of Epoxides

“…18,39−41 Direct heterogenization of active catalysts by covalently linking the aromatic rings of homogeneous catalysts using FCR has gained widespread interest, as it provides a simple, rapid, inexpensive, and scalable one-pot method for generating highly porous solid material networks. 10,27,37,38,42,43 As a first attempt to heterogenize metallosalphen using FCR knitting linkages, we synthesized the salphenAl(III)Cl monomer (1). This monomer was used as a model complex to study and optimize heterogenization conditions (Scheme 1).…”

“…44 On the basis of these preliminary results, we report a facile synthetic strategy for the direct heterogenization of metallosalphen complexes to generate highly porous organic polymers using FDA as an external cross-linker. 37,42,44 Metallosalphen-containing porous organic polymers were constructed by FCR using metallosalphen chlorides [salphenM(III)Cl, where M = Al (1) or Cr (4)] as monomers. FCR conditions were optimized using various cross-linkers and Lewis acidic metal catalysts to produce highly porous metallosalphen-containing organic polymers.…”

“…The obtained polymeric material was dried under high vacuum at 80 °C for 24 h to yield dark orange and dark red solids for 2 and 5, respectively (see the Supporting Information for the detailed procedure). 10,37,42,44 The porosities of the obtained polymers were investigated in detail by adsorption− desorption measurements performed at 77 K using N 2 as the sorbate. The polymers exhibited typical type I and type IV isotherms (according to the IUPAC classification of adsorption isotherms), as shown in Figure S5.…”

“…Before recycling, the heterogeneity of the catalyst was validated by a hot filtration test; a suspension of catalyst 3 or 6 in DME was heated to 60 °C for 6 h, and the catalyst was isolated by filtration. 37 The acquired filtrate and filtered solid catalyst were tested separately using the reaction conditions for PO carbonylation (2 mol % to PO, 60 °C, 60 bar of CO, and 6 h reaction time). The solid catalyst promoted the full conversion of propylene oxide to lactone, whereas no lactone conversion was observed with the filtrate.…”

“…In this regard, ring-expansion carbonylation of epoxides is an attractive direct one-pot method for the production of β-lactones from the commercially available epoxides. In recent times, tetraphenylporphyrinatoaluminum­(III)­Cl and tetraphenylporphyrinatochromium­(III)Cl (TPPAlCl and TPPCrCl, respectively) monomers were directly heterogenized by hyper-cross-linking using FCR. , The cross-linked polymers were incorporated with tetracarbonylcobaltate anions to produce a Lewis acid–base pair bimetallic heterogeneous catalyst for the ring-expansion carbonylation of epoxides with excellent reactivity and selectivity . Similarly, an aluminumphthalocyanine-based picket fence-type POP was constructed using solvent knitting FCR to generate a robust network with good chemical stability and carbonylation activity …”