Quantifying electronic similarities between NHC–gold(<scp>i</scp>) complexes and their isolobal imidazolium precursors

Azofra, Luis Miguel; Veenboer, Richard M. P.; Falivene, Laura; Vummaleti, Sai V. C.; Poater, Albert; Nolan, Steven P.; Cavallo, Luigi

doi:10.1039/c9cp02844g

Cited by 12 publications

(6 citation statements)

References 66 publications

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“…In this sense, Belpassi and Zuccaccia examined the σ donation and the π back-donation in Au(NHC)-based complexes, taking into account the trans ligand to the NHC, continuing the work of Ciancaleoni and Belpassi in the same sense, although the latter only considered the use of phosphine ligands . More recently, the π back-donation has been analyzed to distinguish between cationic Au-NHC complexes and their isolobal NHC-proton compounds . However, for the case of Grubbs olefin metathesis catalysts, in order to properly define the NHC ligand, its description should be in combination with, at least, the trans Ru–P bond.…”

Section: Introductionmentioning

confidence: 99%

σ/π Plasticity of NHCs on the Ruthenium–Phosphine and Ruthenium═Ylidene Bonds in Olefin Metathesis Catalysts

et al. 2020

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The nature of the Ru bonding environment in a set of Grubbs catalysts has been studied by means of density functional theory (DFT). On the one hand, for a set of 20 [Ru( CH 2)(NHC)(PCy 3)][Cl] 2 second-generation adducts, the results show that calculated 31 P NMR shieldings exhibit a good correlation with the calculated R(Ru−P) bond lengths, which are in turn strongly correlated with the calculated PCy 3 ligand dissociation energies. Bond energy decomposition analysis (EDA) also indicates that there is a strong correlation between the σ and π orbital interaction energies for the Ru−PCy 3 bond, while no correlation was found for the case of the bond between the Ru moiety and the N-heterocyclic carbene (NHC) ligands, Ru−NHC. Furthermore, π orbital interaction energies of the Ru−PCy 3 bond were found to be strongly correlated with the calculated PCy 3 ligand dissociation energies, as well as with the R(Ru−P) bond lengths, confirming the significance of the π back-donation component from Ru to PCy 3 in determining the lability of the PCy 3 ligand in the studied adducts. On the other, for a set of 17 [Ru(CHR)(NHC) x (PCy 3) 2−x ]-[Cl] 2 first (x = 0)-and second-generation (x = 1) complexes, DFT results show that changes occurring in the 13 C NMR shielding of the Ruylidene bond are mainly due to σ(RuC) → π*(RuC) molecular orbital (MO) transitions. Good correlations are observed between σ(13 C) and the energy gaps of the MOs involved in such transitions, between the binding energies of the ylidene moiety and the rest of the Ru fragment, as well as with the R(RuC) bond lengths. Finally, our novel preliminary results suggest that, once the metallacycle intermediate is formed by reaction with ethylene, 13 C′(β) NMR shielding retains the NMR information from σ(13 C) in the 16e species, in contrast to what happens with the 13 C(α) NMR shielding.

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Section: Introductionmentioning

confidence: 99%

σ/π Plasticity of NHCs on the Ruthenium–Phosphine and Ruthenium═Ylidene Bonds in Olefin Metathesis Catalysts

et al. 2020

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“…However, differences are scarcer than expected. In particular, IMes and SIMes ligands are thermodynamically more stable than IMe by 0.73 kcal mol –1 and 1.10 kcal mol –1 , respectively, which, at the same time would be more stable than the larger IPr and IPr* ligands, but by less than 1 kcal mol –1 . Kinetically, the energy barriers range from 9.55 kcal mol –1 for IMe to 12.91 kcal mol –1 , not for IPr*, but for IPr.…”

Section: Resultsmentioning

confidence: 98%

Phenoxylation of Alkynes through Mono‐ and Dual Activation Using Group 11 (Cu, Ag, Au) Catalysts

et al. 2020

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NHC‐gold(I) based catalysts have displayed outstanding results toward hydroalkoxylation of terminal and internal alkynes in solvent‐free conditions and using low catalyst loadings. It has been demonstrated that, in the hydrophenoxylation reaction the gold complex is composed by two moieties that determine the rate of the reaction by activating both substrates synergistically, i.e. [Au(OR)(NHC)] and [Au(η2‐alkyne)(NHC)]+. Then, these bimetallic systems act cooperatively toward the hydroalkoxylation reaction. Herein, density functional theory studies were carried out to get insights on the mechanism of hydrophenoxylation. The rate‐determining step, which corresponds to the formation of the C(alkyne)–O(alcohol) bond between [Au(OR)(NHC)] and [Au(η2‐alkyne)(NHC)]+, was studied using energy decomposition analyses (EDA). It was found that the C–O bond shows strong electrostatic and orbital interactions between both fragments in the homobimetallic, heterobimetallic and monogold mechanisms. Moreover, the analyses were expanded to copper and argentum, and the steric sensibility was also studied through the use of different NHC ligands, including IMes, IMe, SIMes, IPr, and IPr*, that differ on their steric demand.

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“…This study was extended with [(NHC)PPh] adducts and it was shown that the 31 P NMR chemical shift only qualitatively correlates with the π acceptor properties of the NHCs . A recent computational study of various [(NHC)AuCl] complexes focused on Au NMR found a correlation between the π‐accepting ability of these complexes and the 197 Au chemical shift . Furthermore, they also found that the paramagnetic shielding tensor of the carbene‐C atom is the main shielding term which shows variation by changes in the (NHC) moiety.…”

Section: Introductionmentioning

confidence: 94%

Orbital Decomposition of the Carbon Chemical Shielding Tensor in Gold(I) N‐Heterocyclic Carbene Complexes

et al. 2020

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The good performance of N‐heterocyclic carbenes (NHCs), in terms of versatility and selectivity, has called the attention of experimentalists and theoreticians attempting to understand their electronic properties. Analyses of the Au(I)–C bond in [(NHC)AuL]+/0 (L stands for a neutral or negatively charged ligand), through the Dewar–Chatt–Duncanson model and the charge displacement function, have revealed that NHC is not purely a σ‐donor but may have a significant π‐acceptor character. It turns out, however, that only the σ‐donation bonding component strongly correlates with one specific component of the chemical shielding tensor. Here, in extension to earlier works, a current density analysis, based on the continuous transformation of the current density diamagnetic zero approach, along a series of [(NHC)AuL]+/0 complexes is presented. The shielding tensor is decomposed into orbital contributions using symmetry considerations together with a spectral analysis in terms of occupied to virtual orbital transitions. Analysis of the orbital transitions shows that the induced current density is largely influenced by rotational transitions. The orbital decomposition of the shielding tensor leads to a deeper understanding of the ligand effect on the magnetic response properties and the electronic structure of (NHC)‐Au fragments. Such an orbital decomposition scheme may be extended to other magnetic properties and/or substrate‐metal complexes.

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Quantifying electronic similarities between NHC–gold(i) complexes and their isolobal imidazolium precursors

Abstract: The σ and π donor/acceptor properties of the carbon–gold bond are manifested by changes in 197Au spectroscopic data.

Cited by 12 publications

References 66 publications

σ/π Plasticity of NHCs on the Ruthenium–Phosphine and Ruthenium═Ylidene Bonds in Olefin Metathesis Catalysts

σ/π Plasticity of NHCs on the Ruthenium–Phosphine and Ruthenium═Ylidene Bonds in Olefin Metathesis Catalysts

Phenoxylation of Alkynes through Mono‐ and Dual Activation Using Group 11 (Cu, Ag, Au) Catalysts

Orbital Decomposition of the Carbon Chemical Shielding Tensor in Gold(I) N‐Heterocyclic Carbene Complexes

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