Catalytic carbon-carbon bond cleavage and carbon-element bond formation give new life for polyolefins as biodegradable surfactants

Uddhav Kanbur,Guiyan Zang,Alexander L Paterson,Puranjan Chatterjee,Ryan A Hackler,Massimiliano Delferro,Igor I Slowing,Frédéric A Perras,Pingping Sun,Aaron D Sadow

doi:10.1016/j.chempr.2021.03.007

Uddhav Kanbur, Guiyan Zang + Show 8 more

Open Access

https://doi.org/10.1016/j.chempr.2021.03.007

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Abstract

Summary Catalytic methods that introduce functional groups via carbon–carbon bond cleavage steps have typically been limited to moieties activated by strain or by directing groups, with few transformations engaging the bonds of only sp 3 -hybridized carbon atoms in saturated hydrocarbons. Here, we report the conversion of catenated carbon chains in polyolefins, which currently represent >50% of discarded plastics, into shorter aliphatic alkylaluminum species via a sequence of zirconation via C–H bond activation, β-alkyl elimination for carbon–carbon bond cleavage, and heterobimetallic alkyl group exchange for carbon–aluminum bond formation. The versatility of aliphatic alkylaluminum species is exemplified by their subsequent conversion into high-value fatty acids or alcohols, which have applications as biodegradable surfactants and detergents. A technoeconomic analysis indicates that fatty alcohols produced from discarded polyolefins are cost competitive with conventional syntheses. Thus, this process could ameliorate economic and environmental challenges of the plastic-waste crisis.

Highlights

C–H bond metalations, in which a hydrogen atom is replaced by a metal center, have revolutionized syntheses by reducing or eliminating requirements for specific and limiting chemical functional groups.[1,2,3] In these metalations, the carbon-based molecular framework of the organic reactants is preserved in the functionalized products
The surface species contains an average of two neopentyl groups per zirconium center, as determined by elemental analysis using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and protonolytic titration
Effects of aluminum reagents On the basis of these initial results, and leveraging the analytical methods adapted to characterize the composition and structure of a distributions of functionalized chains, we investigated the effects of aluminum reagents on catalytic carbon– carbon bond cleavage and alumination in conversions of polyethylene

Summary

Introduction

C–H bond metalations, in which a hydrogen atom is replaced by a metal center, have revolutionized syntheses by reducing or eliminating requirements for specific and limiting chemical functional groups.[1,2,3] In these metalations, the carbon-based molecular framework of the organic reactants is preserved in the functionalized products. An even wider range of starting materials could be leveraged by methods that concurrently alter the carbon-based skeleton of organic molecules and introduce new functional groups. With such transformations, for example, natural resources that contain structural components of the desired products would become available for chemical manufacturing, or framework reconstructions could increase late-stage structural diversification during multistep syntheses. Current methods that install a metal center by breaking a carbon–carbon bond, are limited to positions activated either by thermodynamically weakened bonds or directing functional groups (Figure 1A).[4,5,6,7] On the other hand, established C–C bond cleavages involving only sp3-hybridized carbon centers generally do not provide new carbon–heteroatom bonds. Alkane metathesis (Figure 1B) alters chain lengths without introducing new functional groups.[8,9] Likewise, hydrogenolysis of carbon–carbon bonds in hydrocarbons, catalyzed by heterogeneous platinum-group nanoparticles[10,11] or air-sensitive early transition metal hydrides,[12,13] provides shorter alkane products

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