One of the most direct methods for synthesizing internal alkenes is the isomerization of terminal alkenes. Currently, noble metal catalysts are the most commonly used for alkene isomerization. However, the high cost and limited availability of late transition metals have prompted growing interest in replacing these precious metals with more readily available, earth-abundant alternatives. Herein, we report an iron-catalyzed alkene isomerization conducted in absence of solvent. A well-defined mononuclear Fe(II) complex, [HFe(CO)4SiPh3] ([Fe-1]), efficiently catalyzes the isomerization of terminal alkenes to internal alkenes under mild conditions. To demonstrate the synthetic utility of this transformation, gram-scale isomerization reactions were successfully performed. Kinetic investigations reveal that the reaction follows approximately first-order kinetics with respect to the iron catalyst, with an initial reaction rate of 7.08 × 10-3 Mmin-1. Furthermore, the tandem functionalization of terminal alkenes to aldehyde products was achieved via sequential isomerizing-ozonolysis and isomerizing-hydroformylation reactions. The complementarity of the two catalysts (Fe and Rh) was conclusively demonstrated through mechanistic investigations and control experiments.

Phosphine-phosphite (P-OP) ligands constitute a privileged class of chiral ligands in asymmetric catalysis owing to their modular structures and tunable steric and electronic properties. Herein, we report a direct, one-pot, synthesis of a new flexible P-OP ligand (L) derived from BINOL-PCl and its in situ complexation with rhodium (Rh) for catalytic evaluation. The resulting Rh/L system efficiently hydrogenates a diverse library of 19 functionalized olefins under mild conditions, delivering moderate to excellent enantioselectivities, with ee values reaching up to 99%. Several of the hydrogenated products correspond to valuable chiral building blocks relevant to pharmaceutical synthesis, underscoring the practical utility of flexible P-OP ligand architectures in asymmetric hydrogenation.

The electron-withdrawing pentafluorophenyl phenoxy-imine-derived titanium complexes are known to produce ultrahigh molecular weight polyethylene (UHMWPE). However, cyclohexyl phenoxy-imine-derived zirconium complexes have been reported to produce low molecular weight polyethylene. The disparity between the two types of polyethylenes and the two types of catalysts can be bridged if a titanium complex bearing sterically bulky groups is made to produce UHMWPE. We report steric bulk-directed cyclohexyl phenoxy-imine titaniumcatalyzed synthesis of UHMWPE in a disentangled state. The influence of steric bulk in a phenoxy-imine-cyclohexyl ligand framework on titanium complex formation and subsequent ethylene polymerization was investigated through a combined computational and experimental approach. Density functional theory (DFT) and buried volume analyses indicated that increasing steric demand from -H to -Me to -tert-Bu substituents enhances the buried volume around the metal center, potentially favoring high molecular weight polyethylene formation. Guided by these insights, three ligands, L1-L3, were synthesized in excellent yields and fully characterized, including by single-crystal X-ray diffraction. Treatment of L1-L3 with a titanium precursor produced respective complexes, Cat.1-Cat.3, in good yields. These were characterized by NMR, IR, MS, and single-crystal X-ray diffraction. Upon activation with various co-catalysts [methyl aluminoxane (MMAO), triisobutylaluminum (TIBA), and tetrakis (pentafluoro phenyl) borate (BT)], these complexes initiated ethylene polymerizations. The catalytic activity increased from Cat.1 to Cat.2 with growing steric bulk, but decreased for the highly hindered Cat.3, likely due to restricted monomer access to the active site. Among the three, Cat.2, in combination with MMAO, showed the best performance under optimized conditions and produced ultrahigh molecular weight polyethylene (UHMWPE, Mw = 2.75 & times; 106 g/mol). Differential scanning calorimetry (DSC) revealed different melting transitions (143 degrees C first heating; 137 degrees C second heating), indicating the formation of disentangled UHMWPE, suitable for melt processing. The findings of this work provide valuable insights into the intricate interplay between steric effects, catalytic activity, and polymer molecular weight, offering considerations for the rational design of efficient catalysts for ethylene polymerization.

Chlorinated polymers have made enormous contributions to materials science and are commercially produced on a large scale. These chlorinated polymers could be recycled as chlorine sources to efficiently produce valuable chlorinated compounds owing to their facile release of HCl. Although the thermal stability of PVDC is low compared to PVC, this can be advantageous in terms of easy and fast dehydrochlorination. Herein, we report an efficient electrochemical chlorination using poly(vinylidene chloride) (PVDC) as a chlorine source that works in an undivided cell and applies to a good number of examples. This method works on commodity polymers such as waste PVDC-PVC pharma blister film, PVDC-PO multilayer food packaging, and compression molded sheets of Ixan PVDC (with heat stabilizer) with similar efficiency. Furthermore, this method also provides the dechlorination of PVDC up to 98 %, leading to unsaturated dechlorinated material. Converting PVDC into more stable unsaturated compounds, the release of harmful chlorine-containing gases during incineration can be minimized. Additionally, this method is not only restricted to batch processes but an electroflow process for PVDC dechlorination and electrosynthesis has also been demonstrated.

The conversion of waste polyethylene into valuable long-chain functional molecules offers a contemporary solution to the global plastic waste challenge. This study presents a two-step catalytic approach, comprising of polyethylene (PE) dehydrogenation followed by cross-metathesis with renewable resource-derived functional olefins, catalyzed by the Grubbs-II catalyst (G-II). A dehydrogenated polyethylene (DHP) was subjected to a tandem catalytic cross-alkene metathesis with functional olefins under mild conditions to achieve approximately 36% conversion of DHP into valuable long-chain building blocks with controlled product distribution. Comprehensive characterization of intermediates and products was performed using NMR, GC, GC-MS, GPC, and DSC. In the alkene cross-metathesis with methyl-10-undecenoate, the product distribution consisted of 23% lower alkenes (C8-C14), 40% unsaturated long-chain mono-esters (C12-C18), and 37% unsaturated di-esters. In the case of 10-undecen-1-ol, the distribution included 20% lower alkenes (C8-C11), 32% unsaturated long-chain (C12-C18) mono-alcohols, and 48% unsaturated di-alcohols. This strategy opens up new opportunities for converting waste polyethylene into high-value chemical intermediates, enabling resource recovery and delivering environmental benefits.

Synthesis of value-added products from post-consumer waste polyolefins is fascinating as well as challenging. Here we report ruthenium-catalyzed up-cycling of the polyethylene to long-chain alkene derivatives. The developed methodology mainly involves two steps i.e., dehydrogenation of polyethylene through hydrogen atom transfer and its metathesis using the HG-II catalyst. The dehydrogenation of polyethylene using ruthenium catalysis derived up to 3.38 %, of double bonds; with 90 % of the recovered polyolefin material. The obtained unsaturated polyethylene was subjected to cross-metathesis with ethylene using HG-II catalytic system. This resulted in the synthesis of predominantly dodecene (C12) derivatives, with 58 % selectivity, along with other derivatives of varying chain lengths. The overall reaction produced terminal and internal olefins in the ratio 1:0.8 respectively. The dehydrogenation of polyethylene and its deconstruction was confirmed by NMR spectroscopy, Gel Permeation Chromatography (GPC) and Differential Scanning Calorimetry (DSC). The origin of C12 selectivity has been demonstrated by control experiments. The scope of the methodology was extended to post-consumer waste polyethylene which gave high conversion to value-added dodecene derivatives as a major product.

Renewable feedstocks pave the way to reduce the demand for petroleum-derived chemicals. Castor oil is one such plant-based raw material that can be used to synthesize chemicals and materials with diverse applications. Herein, we report the synthesis of a novel monomer, 18-methoxy-18-oxooctadec-9-en-7-yl methyl oxalate (3), from castor oil-derived ricinoleic acid. The identity of the monomer 3 has been unambiguously ascertained using 1-2D NMR spectroscopic analysis. Monomer 3 was then subjected to condensation polymerization with potentially bio-renewable long-chain aliphatic diols to yield degradable linear polyoxalates having molecular weights in the range of 8000-22,000 g/mol. The polymerization reactions were performed using pTSA and [Sn(Oct)2] as catalysts, and the polymerization conditions were optimized. The structure of the polymer was confirmed by 1-2D NMR spectroscopy, IR spectroscopy, and GPC analysis. The thermal characterizations of the polyoxalates were carried out by DSC and TGA analysis. The polyoxalates were found to degrade in acidic media. These renewable polyoxalates were further reacted with thiols by "thiol-ene" click reaction to produce a cross-linked rubbery polymer, which retained degradability.

Chemoselective hydrosilylation of unsaturated imines is challenging as the two double bonds compete for the reaction. Here in, we report an iron‐catalyzed chemoselective hydrosilylation of enimines leading to the generation of allyl amines in the presence of phosphine ligand. A low‐valent Fe(0) complex [(BDA)Fe(CO)3] catalyzed the hydrosilylation of enimine at room temperature and exhibited broad substrate scope including a variety of enimine (cinnamylimine, allylimine) and ketimine. Mechanistic investigations revealed that the reaction proceeds through an oxidative addition of the silane compound, leading to the formation of an iron hydride intermediate. Subsequently, a two‐electron pathway facilitates the hydrosilylation of the enimine substrate. This has been supported by preparing a well‐defined Fe(II)‐silane complex and using it as a catalyst control. Based on experimental and computational investigations, a plausible Chalk‐Harrod‐type mechanism is proposed.

One approach to mitigate the crisis of plastic waste is “chemical upcycling”, in which waste plastic is converted into products with higher economic value. Towards this goal, several metal-catalyzed post-functionalization of polymers have been reported, with variable success, mostly on account of lack of selectivity, use of harsh reaction conditions, and use of environmentally unfriendly solvents. In this work, we demonstrate selective hydroxylation of the backbone 3° C-H bonds in polyolefin macromolecules using in-house developed (Et4N)2[FeIII-(Ph,Me-bTAML)] (3) complex and solid Na2CO3.1.5 H2O2 (SPC; Sodium percarbonate) under solvent-free mechanochemical conditions. The reaction condition only employs simple mechanochemical grinding at room tempera-ture. The polar functional group -OH was successfully incorporated into the polymer backbone without any chain degradation and crosslinking. The same reaction conditions were also employed to selectively hydroxylate small organic molecules including com-plex natural products. The rate and selectivity of the reaction towards 3° C-H bonds far exceed that performed under homogene-ous conditions. Mechanistic investigation indicates the formation of the well-characterized oxoiron(V) intermediate upon mechani-cal grinding of 3 and SPC. The high selectivity observed under solvent-free conditions is due to the elimination of solvent-induced side-reaction of this intermediate. This represents a very sustainable process since it uses environmentally benign reagents (iron complex, “oxygen bleach”), thus eliminating the use of hazardous solvents. The workup protocol involves simple washing with water where both the spent catalyst and the oxidant are soluble.

The enantioselective synthesis of P-stereogenic compounds has emerged as a central focus in modern asymmetric catalysis, driven by their pivotal roles as ligands (Ls), organocatalysts, and bioactive molecules. Over the past decade, significant advances have been made in developing catalytic strategies that enable precise control over phosphorus stereochemistry, expanding both the structural diversity and synthetic utility of these scaffolds. This review highlights recent progress in two key areas: direct P-C bond formation and desymmetrization. P-C bond-forming approaches include cross-coupling reactions of secondary phosphines or their oxides with aryl, alkyl, or benzyl halides, as well as hydrophosphination of alkenes and alkynes. Desymmetrization strategies encompass nucleophilic substitution at P(V) centers, cyclization, C-H activation (CHA), phenolic -OH activation, and P-O alkylation/arylation. Mechanistic insights into these transformations have been discussed, along with the derivatization of P-chiral products and their applications in catalysis, L design, and bioactive molecule synthesis. This comprehensive overview shall serve as a valuable resource for researchers working in asymmetric organophosphorus chemistry.

Polyethylene-grafted layered silsesquioxanes, termed polyethylene-clays (PEC), are nanocomposites comprising polyethylene chains tethered to inorganic sheets with a phyllosilicate-like structure. Here, we report that these nanocomposites show two-stage crystallization on cooling, qualitatively different from previous reports on polyethylene nanocomposites. We employ differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) to study the melting and crystallization of PEC. End tethering of the polyethylene chains to a nanosheet strongly influences the manner in which PEC crystallizes from the melt on cooling. PEC exhibits two-step crystallization, characterized by a sharp high-temperature exotherm, followed by a broader exotherm at lower temperatures, in contrast to a single sharp exotherm for neat polyethylene. SAXS indicates that lamellar stacks form at high temperatures and that the low-temperature exotherm corresponds to the formation of additional lamellae and their insertion within these stacks. PEC exhibits lower peak melting temperature, lower crystallinity, and a wider melting range relative to polyethylene. We show that the progress of crystallization of PEC is determined by its ultraslow relaxation dynamics. In contrast, PEC in xylene solution exhibits a significantly shorter relaxation time than the melt PEC. Such systems exhibited a single exotherm on cooling and SAXS structure factor peaks with peak positions in a ratio of 1:2. We hypothesize that the high melt viscosity inhibits the crystallization-induced decrease in the specific volume of PEC, resulting in tensile internal stresses that determine the observed thermal behavior.

P-chiral supramolecular phosphine ligands are crucial for asymmetric transformations, but their synthesis is tedious. We report a one-step synthesis of thermally stable P-chiral supramolecular phosphines and their performance in the asymmetric hydrogenation of functionalized alkenes. A rational designing and synthesis of (R, R)-QuinoxP* ligated palladium complex (Pd-2) in excellent yield is reported. This Pd-2 catalyzed a direct P-C coupling of 2,3-dihydro-1-H-phosphindole (A1)/1,2,3,4-tetrahydrophosphindoline (A2) with 1-(3-iodophenyl)urea (B1)/2-iodo /6-hydroxy pyridine (B2) and,produced corresponding ligands L1-L3. The P-C coupling between A1 and B2 produced 6-(2,3-dihydro-1H-phosphindol-1-yl)pyridine-2(1H)-one (L2) with an excellent enantiomeric excess of up to 99 %. L2 was found to be remarkably stable even at 150 degrees C and did not oxidize/hydrolyze for at least 24 hours in open air. Such thermal stability and an impediment to oxidation are unprecedented. L2 self-assembled and produced L2-C1 (Pt), L2-C2(Pd), and L2-C3(Rh) assemblies. The utility of the self-assembled P-chiral ligand was demonstrated in the Rh-catalyzed asymmetric hydrogenation (AH) of functionalized olefins. The L2-C3 catalyzed AH of functionalized alkenes and delivered chiral products with excellent enantioselectivity of >99 %. A small library of 16 substrates was subjected to AH using L2-C3 to produce chiral compounds with excellent conversion and ee.

Here we report the syntheses of systematically sterically tailored naphthoxy imine-ligated nickel complexes and, their performance in ethylene polymerization. Sterically less bulky Ni1 and Ni2 produced highly branched (43–54) PE, while the bulkiest Ni3 suppressed branching (only 28).

Although PLA is widely used, melt processing of this polymer is still a challenging task. In our efforts to improve the melt strength and processability of PLA, we report the synthesis of high molecular weight linear PLA ionomers. PLA copolymers (CP1-CP3) with pendant alkyne groups were synthesized by reacting L-lactide with propargylated lactide. The existence of copolymers with alkyne groups was unambiguously demonstrated, and the percentage of alkyne was found to be 3-7%. A click reaction protocol was developed to treat the resultant alkyne functionalized copolymers (CP1-CP3) with mercaptosuccinic acid (MSA) and pendant carboxylic acid group functionalized copolymers (CP1-MSA1 to CP3-MSA3) were obtained. The 1-2D NMR confirmed the formation of a major MSA bis-addition product, along with a minor mono-addition product. In the final step, the MSA functionalized copolymers were treated with sodium hydride (NaH) to obtain the corresponding linear PLA ionomers (CP1-MSA1-Na1 to CP3-MSA3-Na3). Significant improvement in thermal and melt rheological properties was observed in these ionomers, as compared to the precursor copolymer and unmodified PLA, due to the microstructural changes caused by the association of the ionic groups. Storage modulus (G ') and loss modulus (G '') values showed a substantial increase in melt elasticity of the ionomers with G ' > G '', whereas the unmodified PLA melt behaved like a viscoelastic liquid. Detailed investigation reveals that incorporating pendant ionic groups in a high molecular weight linear PLA remarkably enhances the elastic modulus from 10 to 100 000 Pa (four orders of magnitude).

Transition metal catalysis plays a pivotal role in chemical synthesis. Noble metals often grab significant attention in organometallic catalysis due to their high reactivity. However, the serious issues associated with these metals such as low abundance, toxicity, geopolitical limitations, and volatile prices are driving the scientific community to discover sustainable alternatives. In this context, iron appears to be the first choice as an alternative metal due to its unique properties, including a range of stable oxidation states, Lewis acidity, high abundance in the earth‘s crust, and low toxicity. Over the past two decades, substantial progress has been made in iron catalysis. This overview examines the recent developments in iron-catalyzed industrially relevant transformations such as hydroformylation, olefin isomerization, hydrosilylation, hydrophosphination, carbonylation, Wacker-type oxidation, and plastic depolymerization. As witnessed throughout this review, the performance of iron can be significantly altered by suitable ligand selection and by tailoring the electronic and steric properties of the iron center. While noble metals remain the industry work-horse, iron is inching closer and with extensive scientific understanding, it may replace noble metals in the near future.

One approach to mitigate the crisis of plastic waste is “chemical upcycling”, in which waste plastic is converted into products with higher economic value. Towards this goal, several metal-catalyzed post-functionalization of polymers have been reported, with variable success, mostly on account of lack of selectivity, use of harsh reaction conditions, and use of environmentally unfriendly solvents. In this work, we demonstrate selective hydroxylation of the backbone 3° C-H bonds in polyolefin macromolecules using in-house developed (Et4N)2[FeIII-(Ph,Me-bTAML)] (3) complex and solid Na2CO3.1.5 H2O2 (SPC; Sodium percarbonate) under solvent-free mechanochemical conditions. The reaction condition only employs simple mechanochemical grinding at room tempera-ture. The polar functional group -OH was successfully incorporated into the polymer backbone without any chain degradation and crosslinking. The same reaction conditions were also employed to selectively hydroxylate small organic molecules including com-plex natural products. The rate and selectivity of the reaction towards 3° C-H bonds far exceed that performed under homogene-ous conditions. Mechanistic investigation indicates the formation of the well-characterized oxoiron(V) intermediate upon mechani-cal grinding of 3 and SPC. The high selectivity observed under solvent-free conditions is due to the elimination of solvent-induced side-reaction of this intermediate. This represents a very sustainable process since it uses environmentally benign reagents (iron complex, “oxygen bleach”), thus eliminating the use of hazardous solvents. The workup protocol involves simple washing with water where both the spent catalyst and the oxidant are soluble.

Iron-catalyzed hydrosilylation of internal alkynes has been rarely reported. Even in these rare cases, additives have been used for the success of the reaction, which often creates a problem for the functional group tolerance of the reaction. Herein, we report an additive-free iron-catalyzed (E)-selective hydrosilylation of internal alkynes in the presence of a phosphine ligand. A low-valent Fe(0) complex [Fe(CO)(3)(BDA)] {[Fe-1]} catalyzed the hydrosilylation of alkynes at 60 to 120 degrees C, exhibited a broad substrate (24 substrates) scope and tolerated different functional groups. The synthetic utility of the reaction was demonstrated by a gram scale experiment, preparing alkenes, and by chemo-selective hydrosilylation. The modus operandi of the reaction has been investigated by i) homogeneity test, ii) radical trapping experiments, iii) X-ray photoelectron spectroscopy, and iv) by preparing a Fe(II) complex as catalyst control. These mechanistic investigations revealed a two-electron pathway for the hydrosilylation of alkynes. In addition, kinetic investigations were undertaken to shed light on the rates of the reaction. Kinetic studies suggest the absence of an induction period, and the reaction is first order with respect to the concentration of iron catalyst [Fe-1] and zeroth order with respect to the substrate (alkyne). The Hammett plot suggests that strongly electron-withdrawing groups on the alkyne favour the hydrosilylation reaction. Meanwhile Eyring analysis suggests that the rate-determining step likely involves an associative pathway. Based on the findings of the mechanistic and kinetic investigation, a plausible Chalk-Harrod-type mechanism is likely to be operative. The proposed mechanism is substantiated by computational investigations, which suggested that the Chalk-Harrod mechanism is kinetically more favored by 15.8 kcal mol(-1) over the modified Chalk-Harrod mechanism.