Subtopic Deep Dive
Steric and Electronic Properties of N-Heterocyclic Carbenes
Research Guide
What is Steric and Electronic Properties of N-Heterocyclic Carbenes?
Steric and electronic properties of N-heterocyclic carbenes (NHCs) refer to the quantification of their donor ability, π-acidity, and steric bulk using metrics like Tolman Electronic Parameter (TEP), %V_Bur, and buried volume.
Researchers measure these properties through iridium carbonyl complexes for TEP and computational models for %V_Bur (Gómez-Suárez et al., 2017, 365 citations). Electronic parameters assess σ-donation and π-backbonding, while steric metrics evaluate ligand congestion around the metal center. Over 1,000 papers explore structure-property relationships for NHC ligand design.
Why It Matters
Quantifying steric and electronic properties enables rational NHC ligand design for catalysis, as shown in Nolan's work on steric quantification guiding catalyst optimization (Gómez-Suárez et al., 2017). In hydrosilylation, Pt-NHC complexes with tuned %V_Bur enhance selectivity (Maliszewski et al., 2023). Ghadwal's iMIC study links donor strengths to reactivity trends (Merschel et al., 2020), accelerating applications in cross-coupling and C-H activation.
Key Research Challenges
Accurate Steric Quantification
Varied NHC substituents complicate %V_Bur and SAMPI measurements across backbones (Gómez-Suárez et al., 2017). Computational models often overestimate buried volume for bulky aryl groups. Standardizing protocols remains unresolved.
Electronic Parameter Variability
TEP values fluctuate with metal and coligands, hindering direct comparisons (Merschel et al., 2020). π-acidity assessment lacks unified metrics beyond CO stretching frequencies. Distinguishing σ-donation from π-effects challenges prediction.
Structure-Property Prediction
Predicting ligand performance from substituent patterns requires advanced QSAR models (Twycross et al., 2021). Mesoionic carbenes like iMICs show anomalous profiles needing new frameworks (Merschel et al., 2020). Integrating steric-electronic data for catalysis design persists as a gap.
Essential Papers
Quantifying and understanding the steric properties of N-heterocyclic carbenes
Adrián Gómez‐Suárez, David J. Nelson, Steven P. Nolan · 2017 · Chemical Communications · 365 citations
This Feature Article presents and discusses the use of different methods to quantify and explore the steric impact of N-heterocyclic carbene (NHC) ligands.
The “weak base route” leading to transition metal–N-heterocyclic carbene complexes
Ekaterina A. Martynova, Nikolaos V. Tzouras, Gianmarco Pisanò et al. · 2021 · Chemical Communications · 100 citations
N-Heterocyclic carbenes (NHCs) are nowadays ubiquitous in organometallic chemistry and catalysis. A simple synthetic route to these is presented.
Quantifying the Electronic and Steric Properties of 1,3-Imidazole-Based Mesoionic Carbenes (iMICs)
Arne Merschel, Dennis Rottschäfer, Beate Neumann et al. · 2020 · Organometallics · 57 citations
1,3-Imidazole-based mesoionic carbenes (iMICs) are a very promising class of carbon-donor ligands in synthesis and catalysis. However, a systematic study of the quantification of stereoelectronic p...
Unusual NHC–Iridium(I) Complexes and Their Use in the Intramolecular Hydroamination of Unactivated Aminoalkenes
Gellért Sipos, Arnold Ou, Brian W. Skelton et al. · 2016 · Chemistry - A European Journal · 48 citations
Abstract N‐heterocyclic carbene (NHC) ligands with naphthyl side chains were employed for the synthesis of unsaturated, yet isolable [(NHC)Ir(cod)] + (cod=1,5‐cyclooctadiene) complexes. These compo...
Hybrids of cationic [4]helicene and N-heterocyclic carbene as ligands for complexes exhibiting (chir)optical properties in the far red spectral window
Robert Tarrieu, I. Hernández Delgado, Francesco Zinna et al. · 2021 · Chemical Communications · 20 citations
A cationic Helicene-NHC hybrid is readily prepared and used for the construction of Rh<sup>I</sup>, Au<sup>I</sup> and Au<sup>III</sup> complexes. Ligand controlled chiroptical properties in the fa...
Pt<sup>II</sup>−N‐Heterocyclic Carbene Complexes in Solvent‐Free Alkene Hydrosilylation
Benon P. Maliszewski, Tahani A. C. A. Bayrakdar, Perrine Lambert et al. · 2023 · Chemistry - A European Journal · 16 citations
Abstract Herein, we report the catalytic activity of a series of platinum(II) pre‐catalysts, bearing N ‐heterocyclic carbene (NHC) ligands, in the alkene hydrosilylation reaction. Their structural ...
Synthesis and properties of heteroaromatic carbenes of the imidazole and triazole series and their fused analogues
Н. И. Коротких, Alan H. Cowley, Jason A. C. Clyburne et al. · 2017 · ARKIVOC · 15 citations
The present review deals with the syntheses and properties of individual heteroaromatic carbenes of the imidazole, 1,2,4-and 1,2,3-triazole series, their fused analogs and mesoionic carbenes includ...
Reading Guide
Foundational Papers
Start with Gómez-Suárez et al. (2017) for comprehensive steric metrics overview (365 citations), as it standardizes %V_Bur and TEP usage across NHC classes.
Recent Advances
Study Merschel et al. (2020) on iMIC quantification and Maliszewski et al. (2023) for Pt-NHC applications linking properties to catalysis.
Core Methods
Core techniques: TEP from IR spectroscopy of Ir carbonyls, %V_Bur via SambVca software on X-ray structures, Tolman cone angle for classic comparison.
How PapersFlow Helps You Research Steric and Electronic Properties of N-Heterocyclic Carbenes
Discover & Search
Research Agent uses searchPapers with query 'NHC steric %V_Bur TEP' to retrieve Gómez-Suárez et al. (2017), then citationGraph maps 365 citing works and findSimilarPapers uncovers Merschel et al. (2020) on iMICs. exaSearch drills into 'buried volume NHC iridium complexes' for 50+ metrics-focused papers.
Analyze & Verify
Analysis Agent applies readPaperContent on Gómez-Suárez et al. (2017) to extract TEP tables, then runPythonAnalysis plots %V_Bur vs. substituent size using NumPy/pandas. verifyResponse with CoVe cross-checks claims against Nolan's dataset, while GRADE assigns A-grade to verified steric trends and flags B-grade for unconfirmed π-acidity.
Synthesize & Write
Synthesis Agent detects gaps in TEP-%V_Bur correlations across iMICs vs. classic NHCs, flagging contradictions in donor ability. Writing Agent uses latexEditText to draft property comparison tables, latexSyncCitations for 10 papers, and latexCompile for publication-ready review; exportMermaid generates ligand steric diagrams.
Use Cases
"Compare %V_Bur values for bulky NHCs in Nolan's 2017 paper vs. recent terphenyl variants"
Research Agent → searchPapers + readPaperContent (Gómez-Suárez 2017, Twycross 2021) → Analysis Agent → runPythonAnalysis (pandas scatter plot of %V_Bur data) → researcher gets CSV-exported comparison chart with statistical R² fit.
"Draft LaTeX section on TEP trends for Pt-NHC hydrosilylation catalysts"
Synthesis Agent → gap detection (Maliszewski 2023) → Writing Agent → latexGenerateFigure (TEP vs. yield plot) + latexSyncCitations (5 papers) + latexCompile → researcher gets compiled PDF section with synced refs and figure.
"Find Python code for NHC buried volume calculations from related repos"
Research Agent → paperExtractUrls (Twycross 2021) → Code Discovery → paperFindGithubRepo + githubRepoInspect → researcher gets inspected repo with %V_Bur script, runPythonAnalysis verifies output against paper data.
Automated Workflows
Deep Research workflow scans 50+ NHC papers via searchPapers → citationGraph, producing structured report with TEP/%V_Bur meta-analysis. DeepScan's 7-step chain verifies steric claims in Merschel et al. (2020) using CoVe checkpoints and GRADE scoring. Theorizer generates hypotheses on iMIC electronic tuning from Gómez-Suárez (2017) + Maliszewski (2023) trends.
Frequently Asked Questions
What defines steric properties of NHCs?
Steric properties are quantified by %V_Bur from iridium complex models and SAMPI, measuring ligand bulk (Gómez-Suárez et al., 2017).
How are electronic properties measured?
TEP uses ν(CO) in (NHC)Ir(CO)₂Cl complexes; lower TEP indicates stronger σ-donation (Merschel et al., 2020).
What are key papers on NHC metrics?
Gómez-Suárez et al. (2017, 365 citations) covers steric methods; Merschel et al. (2020) quantifies iMICs (57 citations).
What open problems exist?
Standardizing π-acidity metrics and predictive QSAR for mixed steric-electronic effects remain unsolved (Twycross et al., 2021).
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