@article {48708, title = {Metal-catalyzed plastic depolymerization}, journal = {Cell Reports Physical Science}, volume = {4}, year = {2023}, month = {MAY}, pages = {101341}, type = {Review}, abstract = {

Polymers have become an indispensable part of our daily lives, and today we produce around 370 MT of plastic per year. Only about 20\% of it is being recycled, and the rest, 80\%, is unleashed into the environment without appropriate treatment. This calls forth the evaluation of strategies available for mitigating the menace of {\textquoteleft}{\textquoteleft}after-use{\textquoteright}{\textquoteright}plastic waste. Various approaches have evolved over a decade and are at different levels of development. Plastic depolymerization and upcycling are considered some of the most prominent and long-term solutions. The metal-catalyzed depolymerization of plastic waste to chemical feedstocks has emerged as one of the promising ways to address global plastic pollution. Therefore, this review aims to examine the available metal-catalyzed depolymerization methods, notify recent progress, pinpoint current gaps, and gauge the potential of this strategy. Both homogeneous and heterogeneous catalysts have been reported to depolymerize various polymers over the last decade. Considerable advances have been reported in the metal-mediated depolymerization of polyolefins, polyesters, polycarbonates, polyurethanes, polyamides, and polyethers. The depolymerization of the above polymers produces the monomers or intermediates, which can be used again for polymerization and thus brings the waste polymers back into circularity. The overview debates the usage of high temperaagents, etc., in metal-catalyzed depolymerization. Thus, this review summarizes the current understanding of the fundamental science of metal-catalyzed plastic depolymerization, the remaining scientific challenges, and the potential opportunities.

}, doi = {10.1016/j.xcrp.2023.101341}, author = {Khopade, Kishor V. and Chikkali, Samir H. and Barsu, Nagaraju} } @article {49291, title = {Depolymerization of waste polyethylene to linear alkenes via sequential dehydrogenation and metathesis}, journal = {Green Chemistry}, volume = {26}, year = {2024}, month = {OCT}, pages = {10558-10566}, type = {Article}, abstract = {

Polyethylene (PE) is the most abundantly sourced plastic and significant efforts are needed for its end-of-life management. The deconstruction of PE is an uphill task and requires the breaking of highly stable C-C bonds. Here we demonstrate that PE can be deconstructed to value-added dodecene, along with other long-chain alkenes. The PCP-iridium complex catalyzes the dehydrogenation of commercial and post-consumer polyethylene waste to produce dehydrogenated polyethylene (DHP) with 0.5-1.0\% unsaturation. The DHP was subjected to an ethylene cross-metathesis reaction in the presence of suitable catalysts. Through meticulous optimization of reaction parameters, 63\% selectivity toward dodecene, with 26\% overall yield, was achieved. The practical significance of our method has been demonstrated by subjecting post-consumer plastic waste to dehydrogenation followed by ethylene metathesis to produce dodecene as a major product, together with long-chain alkenes. The PE deconstruction has been confirmed by recording molar mass before and after depolymerization using high-temperature gel permeation chromatography. The existence of dodecene has been unambiguously ascertained using GC, GC-MS, NMR, and IR spectroscopy. Thus, these results demonstrate the conversion of waste PE to value-added dodecene and long-chain alkenes under mild reaction conditions.

}, issn = {1463-9262}, doi = {10.1039/d4gc03646h}, author = {Khopade, Kishor V. and Rajput, Nikhita S. and Rangappa, Raghavendrakumar and Barsu, Nagaraju and Chikkali, Samir H.} } @article {49427, title = {Hybrid silylene-Pd catalyst: efficient C-N cross-coupling of sterically bulky amines and chiral amines}, journal = {Chemical Communications}, volume = {60}, year = {2024}, month = {SEP }, pages = {9958-9961}, type = {Article}, abstract = {

Herein, we report a catalytic system with N-heterocyclic silylene (NHSi)-phosphine-based hybrid bidentate ligands [PhC(NtBu)2SiN(PR2)(2,6-iPr2-C6H3)] and Pd(dba)2, which serves as an effective catalyst for C-N cross-coupling of a wide range of sterically bulky amines and optically active amines, which is challenging otherwise. Herein, we report a hybrid silylene-based bidentate ligand (SiNP)-Pd(0) catalytic system, which performs the C-N coupling of difficult substrates, e.g., sterically bulky amines and chiral amines.

}, issn = {1359-7345}, doi = {10.1039/d4cc03108c}, author = {Kaulage, Sandeep H. and Parvin, Nasrina and Khopade, Kishor V. and Khan, Shabana} }