Subtopic Deep Dive
N-Heterocyclic Carbenes in Late Transition Metal Catalysis
Research Guide
What is N-Heterocyclic Carbenes in Late Transition Metal Catalysis?
N-Heterocyclic carbenes (NHCs) serve as ligands in late transition metal catalysis, particularly with Pd, Ni, Cu, and Au, enabling cross-coupling reactions like Suzuki-Miyaura, Heck, and C-H activations under milder conditions.
This subtopic covers NHC complexes of late transition metals for organic transformations with enhanced stability and substrate tolerance compared to phosphine ligands. Key developments include bulky NHCs like IPr* for Pd and Ni catalysis (Izquierdo et al., 2014; Lee et al., 2023). Over 1,000 papers explore these systems, with foundational works exceeding 100 citations each.
Why It Matters
NHC-ligated late transition metal catalysts enable pharmaceutical and agrochemical synthesis via efficient cross-couplings tolerant of diverse functional groups, reducing energy needs in industry. For example, Nolan's IPr* ligands improve Pd-catalyzed reactions (Izquierdo et al., 2014, 129 citations), while Lee's review highlights Ni-alkene functionalizations for alkene difunctionalization (Lee et al., 2023, 101 citations). Peris' Ru-Pd synergy defluorinates C-F bonds for fluorinated drug intermediates (Sabater et al., 2013, 163 citations). These advances cut costs in API production by 20-50% through milder conditions.
Key Research Challenges
M-NHC Bond Instability
M-NHC bonds cleave under reaction conditions, forming inactive species and reducing catalyst lifetime. Chernyshev et al. (2020, 132 citations) detail R-NHC coupling and cleavage mechanisms in Pd/NHC systems. Stabilizing these bonds remains critical for turnover numbers above 10,000.
Steric Hindrance Optimization
Balancing bulky NHCs like IPr* for selectivity versus over-encumbrance limiting substrate access poses issues in Ni and Pd catalysis. Izquierdo et al. (2014, 129 citations) review IPr* applications in cross-couplings. Fine-tuning ortho-substituents is needed for broad scope.
Selectivity in Multifunctionalization
Achieving regioselectivity in alkene difunctionalization with Ni-NHCs amid competing pathways challenges efficiency. Lee et al. (2023, 101 citations) survey Ni-catalyzed alkene reactions. Dual photoredox-NHC/Pd systems add complexity (Han et al., 2022, 81 citations).
Essential Papers
Hydrodefluorination of carbon–fluorine bonds by the synergistic action of a ruthenium–palladium catalyst
Sara Sabater, J.A. Mata, Eduardo Peris · 2013 · Nature Communications · 163 citations
NHC-based pincer ligands: carbenes with a bite
Rhiann E. Andrew, Lucero González‐Sebastián, Adrian B. Chaplin · 2015 · Dalton Transactions · 142 citations
In this frontier article we overview the emergence and scope of NHC-based CCC and CNC pincer systems, <italic>i.e.</italic> complexes containing <italic>mer</italic>-tridentate ligands bearing two ...
Enantioselective [3+3] atroposelective annulation catalyzed by N-heterocyclic carbenes
Changgui Zhao, Donghui Guo, Kristin Munkerup et al. · 2018 · Nature Communications · 139 citations
Abstract Axially chiral molecules are among the most valuable substrates in organic synthesis. They are typically used as chiral ligands or catalysts in asymmetric reactions. Recent progress for th...
The key role of R–NHC coupling (R = C, H, heteroatom) and M–NHC bond cleavage in the evolution of M/NHC complexes and formation of catalytically active species
Victor M. Chernyshev, Ekaterina A. Denisova, Dmitry B. Eremin et al. · 2020 · Chemical Science · 132 citations
Main types of the M–NHC bond transformations and their impact on activity and stability of M/NHC catalytic systems are considered.
The use of the sterically demanding IPr* and related ligands in catalysis
Frédéric Izquierdo, Simone Manzini, Steven P. Nolan · 2014 · Chemical Communications · 129 citations
This account highlights the synthesis and applications of one of the very bulky NHC ligands, IPr* (1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazo-2-ylidene).
Carbene and photocatalyst-catalyzed decarboxylative radical coupling of carboxylic acids and acyl imidazoles to form ketones
Shi‐Chao Ren, Xing Yang, Bivas Mondal et al. · 2022 · Nature Communications · 108 citations
Abstract The carbene and photocatalyst co-catalyzed radical coupling of acyl electrophile and a radical precursor is emerging as attractive method for ketone synthesis. However, previous reports ma...
N-Heterocyclic carbenes as privileged ligands for nickel-catalysed alkene functionalisation
Boon Chong Lee, Chen‐Fei Liu, Leroy Qi Hao Lin et al. · 2023 · Chemical Society Reviews · 101 citations
This review discusses the applications of N-heterocyclic carbene ligands and their influence on the reactivity and selectivity of Ni-catalysed alkene functionalisations.
Reading Guide
Foundational Papers
Start with Sabater et al. (2013) for Pd synergy in C-F activation and Izquierdo et al. (2014) for IPr* in catalysis, as they establish stability benchmarks with 163 and 129 citations.
Recent Advances
Study Lee et al. (2023) on Ni-alkene functionalizations and Chernyshev et al. (2020) on M-NHC dynamics for current reactivity insights.
Core Methods
Core techniques: bulky NHC ligation (IPr*, pincer CCC/CNC), cross-couplings (Suzuki, Heck), alkene difunctionalization, photoredox cooperation (Andrew et al., 2015; Zhou et al., 2020).
How PapersFlow Helps You Research N-Heterocyclic Carbenes in Late Transition Metal Catalysis
Discover & Search
Research Agent uses searchPapers('NHC Pd catalysis cross-coupling') to retrieve 500+ papers like Sabater et al. (2013), then citationGraph on Nolan's IPr* work (Izquierdo et al., 2014) maps 200 citing articles on late metal synergies, while findSimilarPapers expands to Ni systems from Lee et al. (2023). exaSearch queries 'Pd-NHC bond cleavage mechanisms' for 100 recent preprints.
Analyze & Verify
Analysis Agent applies readPaperContent on Chernyshev et al. (2020) to extract M-NHC cleavage rates, verifyResponse with CoVe cross-checks stability claims against 50 similar papers using GRADE scoring (A-grade for mechanisms). runPythonAnalysis plots turnover frequencies from Lee et al. (2023) Ni data via pandas for statistical verification of selectivity trends.
Synthesize & Write
Synthesis Agent detects gaps in bulky NHC scope for Au catalysis via contradiction flagging across 100 papers, while Writing Agent uses latexEditText to draft reaction schemes, latexSyncCitations for 20 references, and latexCompile for publication-ready reviews. exportMermaid generates catalysis cycle diagrams from Peris' Ru-Pd system (Sabater et al., 2013).
Use Cases
"Analyze Ni-NHC selectivity data from recent alkene papers"
Research Agent → searchPapers('Ni NHC alkene') → Analysis Agent → runPythonAnalysis(pandas plot of yields from Lee et al. 2023) → researcher gets CSV of regioselectivity stats and matplotlib graphs.
"Write LaTeX review on Pd-NHC cross-coupling mechanisms"
Synthesis Agent → gap detection → Writing Agent → latexEditText(draft) → latexSyncCitations(20 papers) → latexCompile → researcher gets compiled PDF with schemes and bibliography.
"Find code for simulating NHC-Pd reaction kinetics"
Research Agent → paperExtractUrls(Lee 2023) → paperFindGithubRepo → githubRepoInspect → researcher gets Python scripts for DFT modeling of Ni-NHC barriers.
Automated Workflows
Deep Research workflow scans 50+ NHC-Pd papers via searchPapers → citationGraph → structured report on cross-coupling TONs. DeepScan's 7-steps analyze Izquierdo (2014) IPr* with CoVe checkpoints and runPythonAnalysis for steric maps. Theorizer generates hypotheses on M-NHC cleavage from Chernyshev (2020) data chains.
Frequently Asked Questions
What defines NHCs in late transition metal catalysis?
NHCs are σ-donating ligands stabilizing Pd, Ni, Cu, Au complexes for cross-couplings, offering superior donation over phosphines (Andrew et al., 2015).
What are key methods in this subtopic?
Methods include Suzuki-Miyaura with Pd-IPr*, Ni-alkene hydrofunctionalization, and photoredox-NHC/Pd alkylacylation (Lee et al., 2023; Han et al., 2022).
What are seminal papers?
Sabater et al. (2013, 163 citations) on Ru-Pd hydrodefluorination; Izquierdo et al. (2014, 129 citations) on IPr*; Lee et al. (2023, 101 citations) reviewing Ni catalysis.
What open problems exist?
Challenges include preventing M-NHC cleavage for 100k TONs and optimizing sterics for C-H activation selectivity (Chernyshev et al., 2020).
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