Theoretical NMR spectroscopy of N-heterocyclic carbenes and their metal complexes

Falivene, Laura; Cavallo, Luigi

doi:10.1016/j.ccr.2016.12.015

Cited by 30 publications

(22 citation statements)

References 86 publications

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“…Furthermore, the electronic structure of a series of NHB rings stabilized with Lewis bases was evaluated in terms of σ‐donating and π‐accepting properties, as well as ring strain and electron delocalization, thus contributing to understanding the chemical reactivity of borylene complexes [39] . Techniques used for carbenes can be adapted for the assessment of π‐accepting properties of B=X compounds, such as the preparation of carbene phosphinidene or selenoureas [(R 2 N) 2 C=Se] complexes followed by the analysis of the corresponding 31 P and 77 Se NMR shifts, using both experimental [40,41] and theoretical means [42,43] . In this regard, we have already described the electronic properties of 58 B=Se species that are similar to selenoureas in the form of [(A 2 N) 2 B=Se] − in the case of anionic species with neutral substituents A, or [(A’ 2 N) 2 B=Se] for neutral species with only one cationic substituent A’ like imidazolium.…”

Section: Resultsmentioning

confidence: 99%

Structural and Electronic Properties of Boranes Containing Boron‐Chalcogen Multiple Bonds and Stabilized by Amido Imidazoline‐2‐imine Ligands

Martínez

Trzaskowski

2022

Chemistry A European J

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The stabilization of elusive monomeric species containing multiple boron‐chalcogen bonds has motivated the investigation of sophisticated ligand systems in the past few years. Recently, a series of neutral, Lewis acid‐free chalcogenboranes were prepared by incorporation of an amido imidazoline‐2‐imine as the supporting ligand (Frank et al., Angew. Chem. Int. Ed. 2021, 60, 4633), resulting in well‐defined molecular entities with pronounced multiple bond character, B=X (X=O, S, Se, Te). In view of the potential use of N‐heterocyclic boranes (NHB=X) as ligands in catalysis and fine chemistry, we evaluated in this work the bonding properties of the new B=X compounds based on a π‐backdonation model. The electronic properties of systems in question were modulated via systematic modifications of the NHB ring with respect to ligand variation, saturation, size, and heteroatom substitutions. Investigations into the B=X bond length and order, calculated by means of density functional theory methods, reveal enhanced B=X bonding properties for NHB rings with high electron delocalization in the NHB ring and bearing electron‐withdrawing substituents; a fact that was also confirmed by computational assessment of electron interactions of the B=X species with a dicarbonyl manganese complex. We expect that the analysis will contribute to the rational optimization of existing ligands as well as the development of new moieties, which would further allow for exploration of new boron chemistry.

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Section: Resultsmentioning

confidence: 99%

Structural and Electronic Properties of Boranes Containing Boron‐Chalcogen Multiple Bonds and Stabilized by Amido Imidazoline‐2‐imine Ligands

Martínez

Trzaskowski

2022

Chemistry A European J

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“…A downfield (lower field) chemical shift indicates a higher π-accepting nature of the carbene. DFT-NMR analyses also support this observation: the more downfield the chemical shift, the stronger the π acidity of the NHC . Compounds 5a ( 31 P −48.2 ppm) and 5b ( 31 P −48.3 ppm) as well as 6a ( 77 Se −3.0 ppm) and 6b ( 77 Se −15.1 ppm) each exhibit a very high field chemical shift in comparison to other singlet carbenes (Table ).…”

Section: Results and Discussionmentioning

confidence: 99%

Quantifying the Electronic and Steric Properties of 1,3-Imidazole-Based Mesoionic Carbenes (iMICs)

et al. 2020

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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 properties of iMICs is lacking. This is most likely due to the absence of rational synthetic routes to suitable iMIC compounds. Herein, we report the synthesis of the appropriate phosphinidene (iMIC Ar )PPh (iMIC Ar = :CCH(NDipp) 2 CAr; Ar = Ph (5a), DMP (5b); DMP = 4-Me 2 NC 6 H 4 ; Dipp = 2,6-iPr 2 C 6 H 3 ), selenium (iMIC Ar )Se (Ar = Ph (6a), DMP (6b)), and nickel carbonyl compounds (iMIC Ar )Ni(CO) 3 (Ar = Ph (7a), DMP (7b)). The π-accepting property of iMIC Ar (Ar = Ph (2a), DMP (2b)) has been evaluated by 31 P and 77 Se NMR spectroscopic analyses of 5 and 6, respectively. The overall donor property of 2 has been assessed by determining the Tolman electronic parameter (TEP) of 7. Studies suggest that iMIC Ar (2) are stronger σ donors and weaker π acceptors compared to classical N-heterocyclic carbenes (NHCs). The steric profile of iMIC Ar (2) has been obtained by calculating the percentage buried volume (%V bur ) for (iMIC Ar

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“…This is the case also for the complexes in the present work ( Figure S7 in the SI). In attempts at understanding the observed correlation between the d P A /s P A and the RuPA bond distance, a search was made for an electronic property that could correlate with these factors, and a remarkably good correlation (R 2 = 0.912, Figure 4) was found between the calculated shielding at PA, s [44][45][46][47][48] These studies have been extremely useful in getting deeper insight on the bonding properties around the studied atom, with possible extrapolation to other properties such as reactivity. [49][50][51][52][53][54][55] The flourish of recent studies for a high diversity of atoms is a clear indication that chemists wish to learn more NMR information.…”

Section: Computational Detailsmentioning

confidence: 99%

³¹P Chemical Shifts in Ru(II) Phosphine Complexes. A Computational Study of the Influence of the Coordination Sphere

et al. 2020

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NMR chemical shift has been the most versatile marker of chemical structures, by reflecting global and local electronic structures, and is very sensitive to any change within the chemical species. In this work, a set of Ru(II) complexes with the same five ligands and a variable 6 th ligand L (none, H2O, H2S, CH3SH, H2, N2, N2O, NO + , C=CHPh, and CO) is studied, using as the NMR reporter, the phosphorus PA of a coordinated bidentate PAN ligand (PAN = o-diphenylphosphino-N,N'dimethylaniline). The chemical shift of PA in RuCl2(PAN)(PR3)(L) (R = phenyl, p-tolyl or p-FC6H4) was shown to increase as the RuPA bond distance decreases, an observation that was not rationalized. This work, using density functional theory (DFT) calculations, reproduces reasonably well the observed 31 P chemical shifts for these complexes, and the correlation between the shifts and the RuPA bond distance as L varies. An interpretation of this correlation is proposed using a Natural Chemical Shift (NCS) analysis based on the Natural Bonding Orbital (NBO) method. This analysis of the principal components of the chemical shift tensors shows how the s-donating properties of L have a particularly high influence on the phosphine chemical shifts.

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Theoretical NMR spectroscopy of N-heterocyclic carbenes and their metal complexes

Cited by 30 publications

References 86 publications

Structural and Electronic Properties of Boranes Containing Boron‐Chalcogen Multiple Bonds and Stabilized by Amido Imidazoline‐2‐imine Ligands

Structural and Electronic Properties of Boranes Containing Boron‐Chalcogen Multiple Bonds and Stabilized by Amido Imidazoline‐2‐imine Ligands

Quantifying the Electronic and Steric Properties of 1,3-Imidazole-Based Mesoionic Carbenes (iMICs)

³¹P Chemical Shifts in Ru(II) Phosphine Complexes. A Computational Study of the Influence of the Coordination Sphere

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Theoretical NMR spectroscopy of N-heterocyclic carbenes and their metal complexes

Cited by 30 publications

References 86 publications

Structural and Electronic Properties of Boranes Containing Boron‐Chalcogen Multiple Bonds and Stabilized by Amido Imidazoline‐2‐imine Ligands

Structural and Electronic Properties of Boranes Containing Boron‐Chalcogen Multiple Bonds and Stabilized by Amido Imidazoline‐2‐imine Ligands

Quantifying the Electronic and Steric Properties of 1,3-Imidazole-Based Mesoionic Carbenes (iMICs)

31P Chemical Shifts in Ru(II) Phosphine Complexes. A Computational Study of the Influence of the Coordination Sphere

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³¹P Chemical Shifts in Ru(II) Phosphine Complexes. A Computational Study of the Influence of the Coordination Sphere