Recent advances in ruthenium-based olefin metathesis

Inflammation-Responsive Micellar Nanoparticles from Degradable Polyphosphoramidates for Targeted Delivery to Myocardial Infarction

Nanoparticles that undergo a localized morphology change to target areas of inflammation have been previously developed but are limited by their lack of biodegradability. In this paper, we describe a low-ring-strain cyclic olefin monomer, 1,3-dimethyl-2-phenoxy-1,3,4,7-tetrahydro-1,3,2-diazaphosphepine 2-oxide (MePTDO), that rapidly polymerizes via ring-opening metathesis polymerization at room temperature to generate well-defined degradable polyphosphoramidates with high monomer conversion (>84%). Efficient MePTDO copolymerizations with norbornene-based monomers are demonstrated, including a norbornenyl monomer functionalized with a peptide substrate for inflammation-associated matrix metalloproteinases (MMPs). The resulting amphiphilic peptide brush copolymers self-assembled in aqueous solution to generate micellar nanoparticles (30 nm in diameter) which exhibit excellent cyto- and hemocompatibility and undergo MMP-induced assembly into micron-scale aggregates. As MMPs are upregulated in the heart postmyocardial infarction (MI), the MMP-responsive micelles were applied to target and accumulate in the infarcted heart following intravenous administration in a rat model of MI. These particles displayed a distinct biodistribution and clearance pattern in comparison to nondegradable analogues. Specifically, accumulation at the site of MI competed with elimination predominantly through the kidney rather than the liver. Together, these results suggest this as a promising new biodegradable platform for inflammation targeted delivery.

Palladium-catalyzed regioselective decarboxylative hydroarylation of alkynyl carboxylic acids with arylboronic acids

The synthesis of (deuterated) 1,1-disubstituted alkenes via Pd-catalyzed decarboxylative hydroarylation of alkynyl carboxylic acids with arylboronic acids has been developed. The reaction features excellent regioselectivity, a broad substrate scope and gram-scale synthetic ability and offers a general synthetic method to synthesize 1,1-dideuterio olefins. Preliminary mechanism investigations indicate that 1,1-disubstituted alkenes are formed by hydroarylation of terminal alkynes generated by in situ decarboxylation of alkynyl carboxylic acids.

Catalytic Olefin-Imine Metathesis: Cobalt-Enabled Amidine Olefination with Enaminones

Organic metathesis reactions allow for expedient assembly of diverse molecular skeletons and appendages through the exchange of molecular fragments. The olefin-imine variant of this process, in particular, can expand the synthetic toolbox for manipulating carbon-carbon and carbon-nitrogen bonds but has thus far been achieved only on a stoichiometric metal-mediated basis. Herein, we report the development of a catalytic olefin-imine metathesis reaction, featuring cobalt-catalyzed amidine olefination with enaminones and a versatile product synthon enabling further structural diversification.

Aldehyde Olefination with Arylboroxines Enabled by Binary Rhodium Catalysis

A rhodium-catalyzed olefination of aliphatic aldehydes with arylboroxines is described. The simple rhodium(I) complex [Rh(cod)OH]₂ without any external ligands or additives is able to catalyze the reaction in air and neutral conditions, allowing the construction of aryl olefins in an efficient manner with a good functional group tolerance. The mechanistic investigation illustrates that the binary rhodium catalysis is the key for the transformation, which involves a Rh(I)-catalyzed 1,2-addition and a Rh(III)-catalyzed elimination.

Carbene Radicals in Transition-Metal-Catalyzed Reactions

Discovered as organometallic curiosities in the 1970s, carbene radicals have become a staple in modern-day homogeneous catalysis. Carbene radicals exhibit nucleophilic radical-type reactivity orthogonal to classical electrophilic diamagnetic Fischer carbenes. Their successful catalytic application has led to the synthesis of a myriad of carbo- and heterocycles, ranging from simple cyclopropanes to more challenging eight-membered rings. The field has matured to employ densely functionalized chiral porphyrin-based platforms that exhibit high enantio-, regio-, and stereoselectivity. Thus far the focus has largely been on cobalt-based systems, but interest has been growing for the past few years to expand the application of carbene radicals to other transition metals. This Perspective covers the advances made since 2011 and gives an overview on the coordination chemistry, reactivity, and catalytic application of carbene radical species using transition metal complexes and catalysts.

Ring-closing C-O/C-O metathesis of ethers with primary aliphatic alcohols

In canonical organic chemistry textbooks, the widely adopted mechanism for the classic transetherifications between ethers and alcohols starts with the activation of the ether in order to weaken the C-O bond, followed by the nucleophilic attack by the alcohol hydroxy group, resulting in a net C-O/O-H σ-bond metathesis. In this manuscript, our experimental and computational investigation of a Re₂O₇ mediated ring-closing transetherification challenges the fundamental tenets of the traditional transetherification mechanism. Instead of ether activation, the alternative activation of the hydroxy group followed by nucleophilic attack of ether is realized by commercially available Re₂O₇ through the formation of perrhenate ester intermediate in hexafluoroisopropanol (HFIP), which results in an unusual C-O/C-O σ-bond metathesis. Due to the preference for the activation of alcohol rather than ether, this intramolecular transetherification reaction is therefore suitable for substrates bearing multiple ether moieties, unparalleled by any previous methods.

On the Edge of the Known: Extremely Electron-Rich (Di)Carboranyl Phosphines

The syntheses of the first B9-connected carboranylphosphines (B9-Phos) featuring two carboranyl moieties as well as access to B9-Phos ligands with bulky electron-donating substituents, previously deemed unattainable, is reported. The electrochemical properties of the B9-Phos ligands were investigated, revealing the ability of the mesityl derivatives to form stabilized phosphoniumyl radical cations. The B9-Phos ligands display an extremely electron-releasing character surpassing that of alkyl phosphines and commonly used N-heterocyclic carbenes. This is demonstrated by their very small Tolman electronic parameters (TEPs) as well as extremely low P-Se coupling constants. Cone angles and buried volumes attest to the high steric demand exerted by the (di)carboranyl phosphines. The dicarboranyl phosphine Au^I complexes show superior catalytic performance in the hydroamination of alkynes compared to the monocarboranyl phosphine analogs.

Biological Activities of Ruthenium NHC Complexes: An Update

Ruthenium N-heterocyclic carbene (NHC) complexes have unique physico-chemical properties as catalysts and a huge potential in medicinal chemistry and pharmacology, exhibiting a variety of notable biological activities. In this review, the most recent studies on ruthenium NHC complexes are summarized, focusing specifically on antimicrobial and antiproliferative activities. Ruthenium NHC complexes are generally active against Gram-positive bacteria, such as Bacillus subtilis, Staphylococcus aureus, Micrococcus luteus, Listeria monocytogenes and are seldom active against Gram-negative bacteria, including Salmonella typhimurium, Pseudomonas aeruginosa and Escherichia coli and fungal strains of Candida albicans. The antiproliferative activity was tested against cancer cell lines of human colon, breast, cervix, epidermis, liver and rat glioblastoma cell lines. Ruthenium NHC complexes generally demonstrated cytotoxicity higher than standard anticancer drugs. Further studies are needed to explore the mechanism of action of these interesting compounds.

Palladium-Catalyzed Cyclization Coupling with Cyclobutanone-Derived N-Tosylhydrazones: Synthesis of Benzofuran-3-Cyclobutylidenes and Spirocyclobutanes

A palladium-catalyzed cyclization coupling of iodoarene-tethered alkynes with cyclobutanone-derived N-tosylhydrazones is reported, providing a convenient and efficient approach to benzofuran-3-cyclobutylidenes. On this basis, spirocyclobutanes can be generated smoothly in an efficient cascade manner by the addition of dienophiles. Good yields and scalability are demonstrated. Sequential intramolecular carbopalladation, palladium-carbene migratory insertion, δ-hydride elimination, and cycloaddition processes are involved.

Advances in the Synthesis of Chemically Recyclable Polymers

The development of modern society is closely related to polymer materials. However, the accumulation of polymer materials and their evolution in the environment causes not only serious environmental problems, but also waste of resources. Although physical processing can be used to reuse polymers, the properties of the resulting polymers are significantly degraded. Chemically recyclable polymers, a type of polymer that degrades into monomers, can be an effective solution to the degradation of polymer properties caused by physical recycling of polymers. The ideal chemical recycling of polymers, i. e., quantitative conversion of the polymer to monomers at low energy consumption and repolymerization of the formed monomers into polymers with comparable properties to the original, is an attractive research goal. In recent years, significant progress has been made in the design of recyclable polymers, enabling the regulation of the "polymerization-depolymerization" equilibrium and closed-loop recycling under mild conditions. This review will focus on the following aspects of closed-loop recycling of poly(sulfur) esters, polycarbonates, polyacetals, polyolefins, and poly(disulfide) polymer, illustrate the challenges in this area, and provide an outlook on future directions.

Synthesis of polynorbornadienes by ring-opening metathesis polymerization and their saturated derivatives bearing various ester groups and carboxyl groups

Various symmetric and non-symmetric polynorbornadienes having a variety of ester groups and carboxyl groups were synthesized by ring-opening metathesis polymerization (ROMP) with Grubbs' third generation catalyst (G3 or [Ru]-III catalyst) in a controlled living manner from half-esters prepared by the selective monohydrolysis of symmetric diesters that we previously reported. The half-esters thus obtained can be directly submitted to ROMP with the G3 catalyst, leading to mostly the trans structure and narrow polydispersity indexes. The subsequent hydrogenation yielded saturated polymers, improving the thermostabilities according to the T ⁵ _d results. Our selective monohydrolysis reactions combined with ROMP initiated by the G3 catalyst have proven to be an efficient tool for the production of a variety of homopolymers with well-controlled structures in a living manner.

Catalytic Living Ring-Opening Metathesis Polymerization Using Vinyl Ethers as Effective Chain-Transfer Agents

A catalytic living ring-opening metathesis copolymerization (ROMP) method is described that relies on a degenerative, reversible and regioselective exchange of propagating Fischer-carbenes. All characteristics of a living polymerization such as narrow dispersity, excellent molar mass control and the ability to form block copolymers are achieved by this method. The method allows the use of up to 200 times less ruthenium complex than traditional living ROMP. We demonstrate the synthesis of ROMP-ROMP diblock copolymers, ATRP from a ROMP macro-initiator and living ROMP from a PEG-based macro chain transfer agent. The cost-effective, sustainable and environmentally friendly synthesis of degradable polymers and block copolymers enabled by this strategy will find various applications in biomedicine, materials science, and technology.

Total Synthesis of Sanctolide A and Formal Synthesis of (2S)-Sanctolide A

Two synthetic strategies employing phosphate tether-mediated one-pot sequential protocols for the total synthesis of the polyketide nonribosomal peptide macrolide, sanctolide A, and the formal synthesis of the (2S)-epimer of sanctolide A are reported. In this work, a phosphate tether-mediated one-pot sequential ring-closing metathesis/cross metathesis/substrate-controlled "H2"/tether removal approach was developed to accomplish the total synthesis of the natural product sanctolide A.

Expanding the Synthetic Toolbox through Metal-Enzyme Cascade Reactions

The combination of metal-, photo-, enzyme-, and/or organocatalysis provides multiple synthetic solutions, especially when the creation of chiral centers is involved. Historically, enzymes and transition metal species have been exploited simultaneously through dynamic kinetic resolutions of racemates. However, more recently, linear cascades have appeared as elegant solutions for the preparation of valuable organic molecules combining multiple bioprocesses and metal-catalyzed transformations. Many advantages are derived from this symbiosis, although there are still bottlenecks to be addressed including the successful coexistence of both catalyst types, the need for compatible reaction media and mild conditions, or the minimization of cross-reactivities. Therefore, solutions are here also provided by means of catalyst coimmobilization, compartmentalization strategies, flow chemistry, etc. A comprehensive review is presented focusing on the period 2015 to early 2022, which has been divided into two main sections that comprise first the use of metals and enzymes as independent catalysts but working in an orchestral or sequential manner, and later their application as bionanohybrid materials through their coimmobilization in adequate supports. Each part has been classified into different subheadings, the first part based on the reaction catalyzed by the metal catalyst, while the development of nonasymmetric or stereoselective processes was considered for the bionanohybrid section.

Synthesis and Anti-Proliferative Evaluation of Arctigenin Analogues with C-9' Derivatisation

Dibenzylbutyrolactone lignans (DBLs) are a class of natural products with a wide variety of biological activities. Due to their potential for the development of human therapeutic agents, DBLs have been subjected to various SAR studies in order to optimise activity. Previous reports have mainly considered changes on the aromatic rings and at the benzylic carbons of the compounds, whilst the effects of substituents in the lactone, at the C-9' position, have been relatively unexplored. This position has an unexploited potential for the development of novel dibenzyl butyrolactone derivatives, with previous preliminary findings revealing C-9'-hydroxymethyl analogues inducing programmed cell cycle death. Using the core structure of the bioactive natural product arctigenin, C-9' derivatives were synthesised using various synthetic pathways and with prepared derivatives providing more potent anti-proliferative activity than the C-9'-hydroxymethyl lead compound.

The Story of the Little Blue Box: A Tribute to Siegfried Hünig

The tetracationic cyclophane, cyclobis(paraquat-p-phenylene), also known as the little blue box, constitutes a modular receptor that has facilitated the discovery of many host-guest complexes and mechanically interlocked molecules during the past 35 years. Its versatility in binding small π-donors in its tetracationic state, as well as forming trisradical tricationic complexes with viologen radical cations in its doubly reduced bisradical dicationic state, renders it valuable for the construction of various stimuli-responsive materials. Since the first reports in 1988, the little blue box has been featured in over 500 publications in the literature. All this research activity would not have been possible without the seminal contributions carried out by Siegfried Hünig, who not only pioneered the syntheses of viologen-containing cyclophanes, but also revealed their rich redox chemistry in addition to their ability to undergo intramolecular π-dimerization. This Review describes how his pioneering research led to the design and synthesis of the little blue box, and how this redox-active host evolved into the key component of molecular shuttles, switches, and machines.

Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series

Terpene compounds probably represent the most diversified class of secondary metabolites. Some classes of terpenes, mainly diterpenes (C20) and sesterterpenes (C25) and to a lesser extent sesquiterpenes (C15), share a common bicyclo[3.6.0]undecane core which is characterized by the presence of a cyclooctane ring fused to a cyclopentane ring, i.e., a [5-8] bicyclic ring system. This review focuses on the different strategies elaborated to construct this [5-8] bicyclic ring system and their application in the total synthesis of terpenes over the last two decades. The overall approaches involve the construction of the 8-membered ring from an appropriate cyclopentane precursor. The proposed strategies include metathesis, Nozaki-Hiyama-Kishi (NHK) cyclization, Pd-mediated cyclization, radical cyclization, Pauson-Khand reaction, Lewis acid-promoted cyclization, rearrangement, cycloaddition and biocatalysis.

Nickel-catalyzed desulfonylative olefination of β-hydroxysulfones

A Ni-catalyzed C–O bond activation is used to access alkenes directly from β-hydroxysulfones.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Alternating Ring-Opening Metathesis Polymerization Promoted by Ruthenium Catalysts Bearing Unsymmetrical NHC Ligands

In this paper, Grubbs- and Hoveyda–Grubbs-type olefin metathesis catalysts featuring N-cyclopentyl/N’-mesityl backbone-substituted N-heterocyclic carbene (NHC) ligands were synthesized. Their propensity to promote the alternating ring-opening metathesis copolymerization (ROMP) of norbornene (NBE) with cyclooctene (COE) or cyclopentene (CPE) was evaluated and compared to that shown by analogous N-cyclohexyl complexes. High degrees of chemoselectivity were achieved in both copolymerizations. The presence of the N-cyclopentyl substituent allowed for the achievement of up to 98% and 97% of alternating diads for NBE-COE and NBE-CPE copolymers, respectively, at low comonomer ratios. Density functional theory (DFT) studies showed that both the sterical and electronic effects of NHC ligands influence catalyst selectivity.

Chiral Polymers from Norbornenes Based on Renewable Chemical Feedstocks

Optically active polymers are of great interest as materials for dense enantioselective membranes, as well as chiral stationary phases for gas and liquid chromatography. Combining the versatility of norbornene chemistry and the advantages of chiral natural terpenes in one molecule will open up a facile route toward the synthesis of diverse optically active polymers. Herein, we prepared a set of new chiral monomers from cis-5-norbornene-2,3-dicarboxylic anhydride and chiral alcohols of various natures. Alcohols based on cyclic terpenes ((-)-menthol, (-)-borneol and pinanol), as well as commercially available alcohols (S-(-)-2-methylbutanol-1, S-(+)-3-octanol), were used. All the synthesized monomers were successfully involved in ring-opening metathesis polymerization, affording polymers in high yields (up to 96%) and with molecular weights in the range of 1.9 × 10⁵-5.8 × 10⁵ (M_w). The properties of the metathesis polymers obtained were studied by TGA and DSC analysis, WAXD, and circular dichroism spectroscopy. The polymers exhibited high thermal stability and good film-forming properties. Glass transition temperatures for the prepared polymers varied from -30 °C to +139 °C and, therefore, the state of the polymers changed from rubbery to glassy. The prepared polymers represent a new attractive platform of chiral polymeric materials for enantioselective membrane separation and chiral stationary phases for chromatography.

Electrophilicity of Hoveyda-Grubbs Olefin Metathesis Catalysts as the Driving Force that Controls Initiation Rates

The dissociative mechanism of initiation for a series of Hoveyda-Grubbs type metathesis catalysts modified at the para and meta positions in the isopropoxybenzylidene ligand is investigated by means of DFT calculations. The electron donating/withdrawing capacity of the ligand was screened through the incorporation of various substituents such as halogens, nitro, alkoxides, ketones, esters, amines, and amides. Variations in structural parameters, energy barriers for the Ru-O bond dissociation, and Ru-O bond strength were examined as a function of the Hammett constant. It was found that electronic properties of the catalysts such as chemical potential, hardness, and electrophilicity correlate linearly with the dissociative energy barriers. These findings enable a systematic rationalization and prediction of rate of precatalyst initiation through the calculation of only the HOMO-LUMO gap of catalysts, as the faster the initiation, the more electrophilic the catalyst.

Functionalized Chromans from ortho-Quinone Methides and Arylallenes

ortho-Quinone methides (o-QMs) underwent formal [4 + 2]-cycloaddition reactions with arylallenes regioselectively at the styrenyl olefin to furnish the corresponding 3-methylene-2-arylchromans in moderate to good yields (up to 88%). When R ≠ H, the reactions also proceeded with moderate stereoselectivity (up to 5:1) which was governed by the nature of the R group. The 3-methylene-2-arylchromans could serve as common intermediates for further functionalization including epoxidation, oxidative cleavage/Baeyer-Villiger oxidation, Riley oxidation, acid-catalyzed rearrangement, and Pd-catalyzed cross-coupling reactions to furnish the corresponding derivatives in moderate to good yields.

A symmetry-driven approach toward the total synthesis of dodecahedrane

Herein, we describe our progress toward the total synthesis of dodecahedrane, a complex and highly symmetrical hydrocarbon that bears twelve fused rings arranged in a cage-like architecture. Central to our approach is a late-stage [2+2+2+2+2] polyene cyclization cascade, which is expected to construct five new bonds and ten new rings in a single transformation. Toward this end, we describe efforts to synthesize key monomeric fragments, along with successful dimerization studies using a pinacol coupling approach. Subsequent studies include an attempted olefin metathesis rearrangement cascade in addition to a successful intramolecular photochemical [2+2] reaction. Although attempts to elaborate the photocycloaddition product were unsuccessful, our studies provide access to complex dimeric scaffolds and are expected to help guide our future total synthesis studies.

Chain transfer agents for the catalytic ring opening metathesis polymerization of norbornenes

Here, we present a detailed study of the metathesis activity of conjugated 1,3 diene derivatives in ring opening metathesis polymerization (ROMP) using Grubbs' 3rd generation catalyst (G3). A comprehensive screening of those derivatives revealed that monosubstituted 1,3 dienes show similar reactivities towards G3-alkylidenes as norbornene derivatives. Therefore, they represent perfect candidates for chain transfer agents in a kinetically controlled catalytic ROMP. This unprecedented reactivity allowed us to catalytically synthesize mono-end-functional poly(norborneneimide)s on the gram scale. Much more complex architectures such as star-shaped polymers could also be synthesized catalytically for the very first time via ROMP. This inexpensive and greener route to produce telechelic ROMP polymers was further utilized to synthesize ROMP block copolymers using bifunctional ROMP and ATRP/NCL initiators. Finally, the regioselective reaction of G3 with 1,3 diene derivatives was also exploited in the synthesis of a ROMP-PEG diblock copolymer initiated from a PEG macroinitiator.

Expedient Synthesis and Ring-Opening Metathesis Polymerization of Pyridinonorbornenes

Pyridine-containing polymers are promising materials for a variety of applications from the capture of contaminants to the self-assembly of block copolymers. However, the innate Lewis basicity of the pyridine motif often hampers living polymerization catalyzed by transition-metal complexes. Herein, we report the expedient synthesis of pyridinonorbornene monomers via a [4+2] cycloaddition between 2,3-pyridynes and cyclopentadiene. Well-controlled ring-opening metathesis polymerization was enabled by careful structural design of the monomer. Polypyridinonorbornenes exhibited high Tg and Td, a promising feature for high-temperature applications. Investigation of the polymerization kinetics and of the reactivity of the chain ends shed light on the influence of nitrogen coordination on the chain-growth mechanism.

Protocol for olefin metathesis reactions of hydrophobic substrates performed in aqueous emulsion with mechanical stirring or with microwaves support

In the presented protocol, we describe the olefin metathesis of hydrophobic substrates in water emulsions using ruthenium catalysts in the presence of air. We detail the testing of mechanical foaming for emulsification and the use of microwave heating to optimize metathesis reaction efficiency. By utilizing relatively low catalyst loading and ensuring simple product isolation, the steps outlined in this protocol extend known methods for the aqueous metathesis techniques. For complete details on the use and execution of this protocol, please refer to Tyszka-Gumkowska et al. (2022).

Photocatalytic E → Z Contra ‐Thermodynamic Isomerization of Vinyl Silanes with Lewis Base

Herein, we disclosed the contra‐thermodynamic E→Z isomerization of alkenyl silanes, according to the in situ formation of a chromophoric species, in the presence of rac‐BINAP as the catalyst. The reaction carried out in DMSO or CH₃CN under irradiation at 405 nm allowed the interconversion of the E‐isomers into the Z‐congeners in good to excellent yields and outstanding Z/E selectivities, on 18 examples. Finally, the mechanism of this E→Z isomerization was studied to get insight into the reaction mechanism.

Exporting Homogeneous Transition Metal Catalysts to Biological Habitats

The possibility of performing designed transition-metal catalyzed reactions in biological and living contexts can open unprecedented opportunities to interrogate and interfere with biology. However, the task is far from obvious, in part because of the presumed incompatibly between organometallic chemistry and complex aqueous environments. Nonetheless, in the past decade there has been a steady progress in this research area, and several transition-metal (TM)-catalyzed bioorthogonal and biocompatible reactions have been developed. These reactions encompass a wide range of mechanistic profiles, which are very different from those used by natural metalloenzymes. Herein we present a summary of the latest progress in the field of TM-catalyzed bioorthogonal reactions, with a special focus on those triggered by activation of multiple carbon-carbon bonds.

Pd-PEPPSI N-Heterocyclic Carbene Complexes from Caffeine: Application in Suzuki, Heck, and Sonogashira Reactions

The first synthesis of Pd-PEPPSI N-heterocyclic carbene complexes derived from the abundant and renewable natural product caffeine is reported. The catalysts bearing 3-chloro-pyridine, pyridine and N-methylimidazole ancillary ligands were readily prepared from the corresponding N9-Me caffeine imidazolium salt by direct deprotonation and coordination to PdX2 in the presence of N-heterocycles or by ligand displacement of PdX2(Het)2. The model Pd-PEPPSI-caffeine complex has been characterized by x-ray crystallography. The complexes were successfully employed in the Suzuki cross-coupling of aryl bromides, Suzuki cross-coupling of amides, Heck cross-coupling and Sonogashira cross-coupling. Computational studies were employed to determine frontier molecular orbitals and bond order analysis of caffeine derived Pd-PEPPSI complexes. This class of catalysts offers an entry to utilize benign and sustainable biomass-derived Xanthine NHC ligands in the popular Pd-PEPPSI systems in organic synthesis and catalysis.