Lewis Acid Effects on Calculated Ligand Electronic Parameters

Shanahan, James P.; Szymczak, Nathaniel K.

doi:10.1021/acs.organomet.0c00407

Cited by 17 publications

(12 citation statements)

References 92 publications

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“…Finally, the FLA output must be viewed under a pragmatic lens as the nature of what constitutes Lewis acidity is complex and continues to evolve. Bond strength alone is not the singular factor influencing the response; others such as charge density, orbital energies, and electronegativity, to name a few, are known to impact Lewis acidic behavior, and the reported results generate relative values for these specific conditions. − We continue to address these important topics so that the FLA approach can become a more robust method. These results will be reported in due course.…”

Section: Discussionmentioning

confidence: 99%

Fluorescent Lewis Adducts: A Practical Guide to Relative Lewis Acidity

et al. 2020

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Experimentally determining the strength of a Lewis acid is a highly desirable and important task that has implications across the chemical sciences. Recently, we developed a new fluorescence-based method for evaluating the relative acidity of a small series of Lewis acids across the p- and d-blocks of the periodic table with great precision against a series of Lewis basic fluorescent dithienophosphole oxide probes. In this report, we considerably expand the scope of the fluorescent Lewis adduct method by systematically investigating the apparent acidities of more than 50 Lewis acids in toluene. Notably, a number of the investigated Lewis acids have never been experimentally measured before. Our refined guide, which now also alleviates the uncertainties that we identified with our original method, is simple and reliable. It shows extreme sensitivity to small structural or electronic perturbations and can account for coordinative flexibility or aggregation events that occur in solution, providing an alternative method for Lewis acidity determination that is complementary to the established nuclear magnetic resonance-based methods.

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Section: Discussionmentioning

confidence: 99%

Fluorescent Lewis Adducts: A Practical Guide to Relative Lewis Acidity

et al. 2020

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“…Recent exploration of dynamic secondary coordination sphere Lewis acid and H-bonding interactions include metal-N 2 (Figure a) − and metal-N 2 H 4 (Figure c) complexes that accent studies by Sellmann and co-workers which outline secondary coordination sphere H-bonding with N 2 H 2 ligands (Figure b). − Guided by a developing understanding of the nitrogenase FeMo-cofactor, Sellmann’s complexes modeled possible cluster sulfur–N 2 H 2 H-bonding interactions . These complexes, typically hosting Ru or Fe centers, possess “bifurcated” H-bonding whereby the N 2 H 2 ligand simultaneously engages in a short and long H-bonding interaction with proximal S-donors (Figure b).…”

Section: Introductionmentioning

confidence: 99%

“…22−27 Since the lifetime of free diazene is so short in solution (aqueous N 2 H 2 decay: k = 2.2 × 10 4 M −1 s −1 at 25 °C), 28 isolable metal-diazene complexes enable the study of N 2 H 2 and the effects of coordination at metal centers by a wide variety of spectroscopic and other direct methods. 22−54 Recent exploration of dynamic secondary coordination sphere Lewis acid and H-bonding interactions include metal-N 2 (Figure 3a) 55−57 and metal-N 2 H 4 (Figure 3c) 58 complexes that accent studies by Sellmann and co-workers which outline secondary coordination sphere H-bonding with N 2 H 2 ligands (Figure 3b). 31−42 Guided by a developing understanding of the nitrogenase FeMo-cofactor, Sellmann's complexes modeled possible cluster sulfur−N 2 H 2 H-bonding interactions.…”

Section: ■ Introductionmentioning

confidence: 99%

Uncovering Redox Non-innocent Hydrogen-Bonding in Cu(I)-Diazene Complexes

et al. 2021

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The life-sustaining reduction of N2 to NH3 is thermoneutral yet kinetically challenged by high-energy intermediates such as N2H2. Exploring intramolecular H-bonding as a potential strategy to stabilize diazene intermediates, we employ a series of [ xHetTpCu]2(μ-N2H2) complexes that exhibit H-bonding between pendant aromatic N-heterocycles (xHet) such as pyridine and a bridging trans-N2H2 ligand at copper(I) centers. X-ray crystallography and IR spectroscopy clearly reveal H-bonding in [pyMeTpCu]2(μ-N2H2) while low-temperature 1H NMR studies coupled with DFT analysis reveals a dynamic equilibrium between two closely related, symmetric H-bonded structural motifs. Importantly, the xHet pendant negligibly influences the electronic structure of xHetTpCuI centers in xHetTpCu(CNAr2,6‑Me2 ) complexes that lack H-bonding as judged by nearly indistinguishable ν(CN) frequencies (2113–2117 cm–1). Nonetheless, H-bonding in the corresponding [ xHetTpCu]2(μ-N2H2) complexes results in marked changes in ν(NN) (1398–1419 cm–1) revealed through resonance Raman studies. Due to the closely matched N–H BDEs of N2H2 and the pyH0 cation radical, the aromatic N-heterocyclic pendants may encourage partial H-atom transfer (HAT) from N2H2 to xHet through redox-non-innocent H-bonding in [ xHetTpCu]2(μ-N2H2). DFT studies reveal modest thermodynamic barriers for concerted transfer of both H-atoms of coordinated N2H2 to the xHet pendants to generate tautomeric [ xHetHTpCu]2(μ-N2) complexes, identifying metal-assisted concerted dual HAT as a thermodynamically favorable pathway for N2/N2H2 interconversion.

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“…Thus, we anticipate that the actual catalyst in the H/D exchange could be different with and without the presence of Cu(OAc) 2 . This is perhaps expected since Lewis acids are known to bind to ligands and alter the electron density of the metal center . For the ( R PNP)Rh catalysts, Lewis acids could potentially bond to carboxylate ligands.…”

Section: Resultsmentioning

confidence: 99%

Effects of Additives on Catalytic Arene C–H Activation: Study of Rh Catalysts Supported by Bis-phosphine Pincer Ligands

Kong

Liu

et al. 2020

Organometallics

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Hydrogen−deuterium exchange (H/D exchange) is a method commonly used for studying catalytic activation of C−H(D) bonds by transition metal complexes. In this study, a series of additives were studied for H/D exchange of toluene-d 8 with acetic acid (HOAc) using ( R PNP)Rh(X) complexes (R = phosphine substituents including cyclohexyl, isopropyl, and tert-butyl; X = trifluoroacetate or acetate) as the precatalysts. Cu(OAc) 2 and AgOAc additives were found to benefit Rh-mediated C−H(D) activation of toluene with meta−para selectivity by facilitating the conversion to active ( R PNP)Rh species and stabilizing the Rh catalysts from decomposition to inactive Rh(s). In contrast, nonoxidizing Lewis acid additives, such as B(OMe) 3 or NaOAc, were not effective at facilitating Rh-catalyzed toluene C−H activation. The complexes ( R PNP)Rh III (H)(X) 2 and [( R PNP)Rh I (CO)][X] (X = TFA or OAc) were found to be intermediates of the catalytic the H/D exchange.

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Lewis Acid Effects on Calculated Ligand Electronic Parameters

Cited by 17 publications

References 92 publications

Fluorescent Lewis Adducts: A Practical Guide to Relative Lewis Acidity

Fluorescent Lewis Adducts: A Practical Guide to Relative Lewis Acidity

Uncovering Redox Non-innocent Hydrogen-Bonding in Cu(I)-Diazene Complexes

Effects of Additives on Catalytic Arene C–H Activation: Study of Rh Catalysts Supported by Bis-phosphine Pincer Ligands

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