Ligand-Promoted Bifunctional Cobalt-Catalyzed Carbonylation-Polymerization of Epoxides: One Step to Polyhydroxyalkanoates

Abstract

Poly(3-hydroxyalkanoates) (PHAs) are an important category of biodegradable plastics with properties similar to those of conventional ones. The development of a simple and efficient catalytic system for PHAs from the most abundant chemicals is economically important. Now we report an in situ generated bifunctional cobalt-catalyzed direct carbonylation-polymerization of epoxides in high efficiency in the presence of a diphosphine oxide ligand WenPhos oxide, which can be easily made from diphenyl sulfone in three steps with regular reagents. In addition, this ligand can promote the disproportionation of Co2(CO)8 to [Co(CO)4]− and Co(II) which is coordinated with phosphine oxide and sulfone oxide. Mechanistic studies indicate that this reaction is not from the ring-opening polymerization of in situ generated β-lactone. Instead, the phosphine oxide coordinated cobalt cation and [Co(CO)4]− anion pair catalyzed direct carbonylation-polymerization of epoxide was proposed based on previous studies, some control experiments, and X-ray structures of the cobalt complexes.

Synthesis and catalytic activity of well-defined Co(i) complexes based on NHC–phosphane pincer ligands

“…Bifunctional catalysts based on the Lewis base characteristics of the latter have been reported; namely, the cooperative ring opening of epoxides by a Lewis acid metal centre and a [Co(CO) 4 ] − counterion acting as a Lewis base has been proposed as a key step in epoxide functionalization. 43 The heterolytic splitting of the Si–H bond results in the formation of a Co-hydride species and a silyl iminium cation, either directly or via a [Co(CO) 4 ] − shuttle. Finally, hydride transfer furnishes the hydrosilylation product, regenerating the active species.…”

Chloride‐Bridged Dimeric SalphenZr(IV) Cobaltate Catalyst Unleashes the Potential of Base‐Free Carbonylative Polymerization for Biodegradable PHAs†

“…Existing polyolefin production infrastructure can be repurposed to enhance resource efficiency by transitioning to biodegradable PHA production. [ 16 ] The abundant and affordable nature of CO and epoxides ensures a sustainable and economically viable feedstock. [ 17 ] Moreover, the synthesis process would achieve 100% atom economy, minimizing waste generation and promoting overall process sustainability.…”

“…This approach holds significant promise in advancing the field of PHA synthesis, offering environmentally friendly alternatives to conventional plastics. [ 16 ]…”

“…reported an in situ generated bifunctional cobalt ion pair could catalyze the direct carbonylation‐polymerization of epoxides to produce PHAs using WenPhos oxide ligand and Co 2 CO 8 . [ 16 ] However, despite continuous efforts over the past six decades, this direct carbonylative polymerization route still faces limitations such as low monomer conversion, poor selectivity, and low molecular weights (Mn). [ 11,16,18‐19,21‐25 ] Therefore, there is a need for the development of a new, practical, and efficient catalyst for PHA synthesis.…”

“…[ 16 ] However, despite continuous efforts over the past six decades, this direct carbonylative polymerization route still faces limitations such as low monomer conversion, poor selectivity, and low molecular weights (Mn). [ 11,16,18‐19,21‐25 ] Therefore, there is a need for the development of a new, practical, and efficient catalyst for PHA synthesis. [ 16,24‐25 ]…”