Catalytic Decomposition of Long‐Chain Olefins to Propylene via Isomerization‐Metathesis Using Latent Bicyclic (Alkyl)(Amino)Carbene‐Ruthenium Olefin Metathesis Catalysts

Abstract

One of the most exciting scientific challenges today is the catalytic degradation of non-biodegradable polymers into value-added chemical feedstocks. The mild pyrolysis of polyolefins, including high-density polyethylene (HDPE), results in pyrolysis oils containing long-chain olefins as major products. In this paper, novel bicyclic (alkyl)(amino)carbene ruthenium (BICAACÀ Ru) temperature-activated latent olefin metathesis catalysts, which can be used for catalytic decomposition of long-chain olefins to propylene are reported. These thermally stable catalysts show significantly higher selectivity to propylene at a reaction temperature of 75 °C compared to second generation Hoveyda-Grubbs or CAACÀ Ru catalysts under ethenolysis conditions. The conversion of long-chain olefins (e.g., 1-octadecene or methyl oleate) to propylene via isomerization-metathesis is performed by using a (RuHCl)(CO)(PPh 3 ) 3 isomerization co-catalyst. The reactions can be carried out at a BICAACÀ Ru catalyst loading as low as 1 ppm at elevated reaction temperature (75 °C). The observed turnover number and turnover frequency are as high as 55 000 and 10 000 mol propylene mol catalyst À 1 h À 1 , respectively.

Synthesis and catalytic olefin metathesis activity of amberlyst-15 supported cyclic and bicyclic alkyl amino carbene ruthenium complexes

“…As catalyst 1 and 3 have shown exceptional activity comparing to their bis-carbene anologues (2 and 4) their impregnation to Amberlyst ionexchange resin have been investigated. Catalyst 1 and 3 have been synthesized according to the literature procedure [41,42] and impregnated onto pre-treated Amberlyst resins (Amberlyst 15 yielding 1-AL-15 and 3-AL-15 and Amberlyst-36 resulting in 1-AL-36 and 3-AL-36) via the well-known wet-impregnation method (Scheme 2). Upon impregnation of the complexes to the Amberlyst solid support followed by multiple washing greenish pearls could be obtained (Fig.…”

“…Self-metathesis of 1-octene ( 9) was carried out in hexane solution and in neat, as well (Table 1 Entry 10 and 11), showing as high yields as 44% at low, 0.01% 1-AL-15 catalyst loading. Since homogenous catalyst 3 catalyzes olefin metathesis reaction only over 75 °C [41], the CM reaction of 9 using catalyst 3-AL-15 was carried out at the same temperature. When hexane was used as solvent (Table 1 Entry 12), only the formation of the expected 7-tetradecene (10) was observed as the sole product.…”

“…An emerging, new class of olefin metathesis catalyst bearing cyclic and bicyclic alkyl amino carbene (CAAC and BICAAC) family ligands appeared recently showing superior catalyst activity and stability. In our laboratories new CAAC (1 and 2) and latent BICAAC (3 and 4) ruthenium alkylidene complexes bearing dimethyl amino group have been synthesized recently [41,42], showing exceptional stability and catalytic activity even in protic solvents or at elevated temperature (Scheme 1).…”

Catalytic deconstruction of waste polyethylene with ethylene to form propylene

“…More specifically, dehydrogenation could be used to enable subsequent C–C bond cleavage by a combination of olefin metathesis and isomerization to form propylene (Fig. 1B) ( 19 , 20 ). We show that the combination of dehydrogenation of high-molecular-weight PE having high density (HDPE) or low density (LDPE) and subsequent isomerizing ethenolysis (I/E) of the resulting crude polymer containing internal alkenes converts PE with commercially relevant molecular weights to propene in yields as high as 80%.…”

“…I/E of hydrocarbons is known for the conversion of unsaturated alkylarenes to vinylarenes and for the conversion of 1-octadecene to propylene at low conversions. We sought an I/E that would transform the long-chain PE fragments to propylene in high yield by first seeking conditions for high conversion of 1-octadecene ( 1a ) ( 19 ). Several combinations of complexes known to catalyze either olefin metathesis or isomerization were tested, and the results are summarized in table S1.…”