Cobalt‐Catalyzed Carbonylative Copolymerization of N‐Alkylazetidines and Tetrahydrofuran

Abstract

The metal-catalyzed carbonylative polymerization of heterocycles (COPH) has received much attention in the last few years as a novel method for the synthesis of polyamides and polyesters. [1][2][3][4][5][6][7] Motivation for these research activities is the practical demand for polymers with heteroatom-containing backbones that are susceptible to hydrolytic and/or enzymatic attack in biological or ecological environments. [8,9] We are interested in the development of COPH using an approach based on single-site catalysts, under the idea that well-defined molecular catalysts would allow rational design and control of the chemical composition, molecular weight, and microstructure of the polymer product.Herein, we report the carbonylative polymerization of azetidines catalyzed by [Co(CH 3 CO)(CO) 3 P(o-tol) 3 ] (1; tol = tolyl), and the participation of the tetrahydrofuran (THF) solvent in the polymerization to give ester units in the polymer products. The use of LiI as a cocatalyst eliminates the g-lactam by-product and influences both the amount and distribution of the ester units in the polymer backbone. The well-controlled distribution of the ester units and the living character of the polymerization have allowed the synthesis of polymers with alternating amide blocks and ester segments, which undergo two-stage degradation. [10] Herein, N-n-butylazetidine (2) and Nisobutylazetidine (3) are used as representative monomers. The polymerization was carried out in THF under CO (1000 psi) at 60-80 8C (Table 1). For 2, in addition to the major carbonylative enchainment that resulted in the amide units, a simple ring-opening enchainment without carbonylation was also observed, which resulted in amine units in the polymer chain (entries 1 and 2).[7c] For the sterically bulkier and less nucleophilic 3, selective carbonylative enchainment occurred, as assessed by NMR spectroscopy (entries 3-8).[11] Somewhat surprisingly, carbonylative enchainment of THF also took place and resulted in d-oxyvaleroyl ester units in the polymer products.[12] Thus, the reactions of 2 and 3 in THF produced poly(amide-co-amine-co-ester)s (PAAEs) and poly(amideco-ester)s (PAEs), respectively [Table 1, Eqs. (1) and (2)].The extent of THF carbonylative enchainment differed when 2 and 3 were used as the monomer: twofold as many ester units were incorporated with 3 than with 2 (entries 1 vs. 3, and 2 vs. 4).The ester abundance, which is defined as the number of ester units divided by the total number of all monomer units, was also a function of the initial monomer-to-catalyst ratio. Higher monomer loadings resulted in a lower degree of ester incorporation (entries 3-8), which suggests that the reaction of THF was favored when the azetidine concentration was low. Directly monitoring the amide and ester growth by in situ IR spectroscopy confirmed that the ester abundance in the Table 1: Carbonylative polymerization of azetidine and THF (CO pressure 1000 psi). [a] Entry THF[mL]Azetidine Azetidine/1 (molar ratio)Cocatalyst Selectivity [b] Ester abun...

Metal‐Catalyzed Synthesis of Alternating Copolymers

“…[77f] Also, Liu and Jia have reported the carbonylative polymerization of azetidines catalyzed by [(CH 3 CO)Co(CO) 3 P(otol) 3 ] (o-tol ¼ ortho-tolyl) 29, and the participation of the tetrahydrofuran solvent in the polymerization to give ester units in the polymer products. [78] The use of LiI as a cocatalyst eliminates the g-lactam by-product and influences both the amount and distribution of the ester units in the polymer backbone. The acyl-cobalt catalyst, when combined with the appropriate cocatalyst, is capable of producing polyamides with M n values up to 14 900 g Á mol À1 and M w =M n values as low as 1.23.…”

Zwitterionic Design Principle of Nickel(II) Catalysts for Carbonylative Polymerization of Cyclic Ethers

“…[1] Since it can be easily obtained by CO 2 reduction, CO is ar aw materials with low carbon footprint. [9][10][11][12][13][14][15][16] Cobalt was the metal of choice to catalyze the COPs of, for example,e poxides,a ziridines and imines. [2] Among the COPs,C O-olefin copolymerization is well-studied, [3][4][5][6][7][8] while the COPs of heteroatom-containing comonomers (for example,e poxides, aziridines,imines,etc.)…”

“…Among the products,p olyketones are photodegradable,a nd polyesters are hydrolytically degradable.T hese features make COP an attractive platform for producing sustainable polymers for av ariety of applications. [11][12][13][14][15][16] Acyl-Co-(CO) 4 is likely ubiquitously involved as the catalytically active species.The mechanisms for the enchainment of the polar comonomers have much commonalities among themselves but are different from the coordinative insertion mechanism of olefin enchainment. only experienced amodest amount of research interest.…”

“…[2] Among the COPs,C O-olefin copolymerization is well-studied, [3][4][5][6][7][8] while the COPs of heteroatom-containing comonomers (for example,e poxides, aziridines,imines,etc.) [11,16] Cyclic ethers,primarily epoxides,require the presence of apyridine derivative as the co-catalyst to undergo COP. [9][10][11][12][13][14][15][16] Cobalt was the metal of choice to catalyze the COPs of, for example,e poxides,a ziridines and imines.…”

Zwitterionic Design Principle of Nickel(II) Catalysts for Carbonylative Polymerization of Cyclic Ethers

“…[9][10][11][12][13][14][15][16] Cobalt was the metal of choice to catalyze the COPs of, for example,e poxides,a ziridines and imines. [11][12][13][14][15][16] Acyl-Co-(CO) 4 is likely ubiquitously involved as the catalytically active species.The mechanisms for the enchainment of the polar comonomers have much commonalities among themselves but are different from the coordinative insertion mechanism of olefin enchainment. Thee lectrophilic acyl group is the reactive site for the nucleophilic co-monomers instead of the Co center.T he COPs of cyclic amines and imines,w hich are good nucleophiles,a re relatively fast, give polyamides in high yields,a nd often display living characters.…”