Rates of Ionization of Pseudo Acids.<sup>1</sup> V. Steric Effects in the Base-catalyzed Ionization of Nitroethane

Pearson, Ralph G.; Williams, Forrest V.

doi:10.1021/ja01109a008

Cited by 32 publications

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“…Although tpy can only be protonated at the pyridine rings, which increases their acceptor strengths,[13c] the NR 3 moieties of ddpd should be more basic than the pyridine rings. For example, the p K a value of pyridinium ions [p K a (Hpy + ) = 5.3] is much lower than that of protonated 4‐dimethylaminopyridine [HDMAP + , p K a (HDMAP + ) = 9.6] . Hence, the opposite fluorescence behavior of tpy and ddpd is ascribed to different protonation sites.…”

Section: Resultsmentioning

confidence: 99%

Three‐in‐One Crystal: The Coordination Diversity of Zinc Polypyridine Complexes

et al. 2017

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The syntheses, structures, and photophysical properties of two new zinc(II) complexes bearing the tridentate N,N′‐dimethyl‐N,N′‐dipyridin‐2‐ylpyridine‐2,6‐diamine (ddpd) ligand are presented. Structural investigations through single‐crystal X‐ray diffractometry, NMR spectroscopy, and density functional theory calculations revealed a diverse coordination behavior that depends on the counterion. Spectroscopic (UV/Vis and emission spectroscopy) and theoretical techniques (DFT and time‐dependent DFT calculations) were employed to explore the photophysical properties of the complexes.

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Section: Resultsmentioning

confidence: 99%

Three‐in‐One Crystal: The Coordination Diversity of Zinc Polypyridine Complexes

et al. 2017

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“…Although the N-Me group of ddpd should be more basic [45,46], addition of acid protonates one terminal pyridine unit (N1) and both terminal pyridines rearrange to point inward allowing for one short and one medium long N1H1 … N2/N3 hydrogen bond with N … N distances in the cavity of 2.51, 2.81 and 3.24 Å (Figure 1b). This hydrogen bonding pattern favours the observed pyridine protonation site similar to pre-organized proton sponges with N … N distances between 2.3 and 2.6 Å [47].…”

Section: Properties Of the Ligand Ddpdmentioning

confidence: 99%

Ddpd as Expanded Terpyridine: Dramatic Effects of Symmetry and Electronic Properties in First Row Transition Metal Complexes

et al. 2018

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The 2,2′:6′:2″-terpyridine ligand has literally shaped the coordination chemistry of transition metal complexes in a plethora of fields. Expansion of the ligand bite by amine functionalities between the pyridine units in the tridentate N,N’-dimethyl-N,N’-dipyridine-2-yl-pyridine-2,6-diamine ligand (ddpd) modifies the properties of corresponding transition metal complexes, comprising redox chemistry, molecular dynamics, magnetism and luminescence. The origins of these differences between ddpd and tpy complexes will be elucidated and comprehensively summarized with respect to first row transition metal complexes with d2–d10 electron configurations. Emerging applications of these ddpd complexes complementary to those of the well-known terpyridine ligand will be highlighted.

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“…The stronger IP formation constants of DPP with Qu as compared to PhQu is in line with the higher basicity of Qu relative to PhQu, as estimated from their aqueous pKb values. 61 , 62 The similarity of the multimer formation constants for both bases may be somewhat unexpected. However, the similarity can be rationalized by the notion that multimer formation is primarily based on the interaction between the DPP – anion of an IP with DPP, and is thus little affected by the more distant bases within a multimeric aggregate.…”

Section: Resultsmentioning

confidence: 99%

Association Equilibria of Organo-Phosphoric Acids with Imines from a Combined Dielectric and Nuclear Magnetic Resonance Spectroscopy Approach

et al. 2021

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Aggregates formed between organo-phosphoric acids and imine bases in aprotic solvents are the reactive intermediates in Brønsted acid organo-catalysis. Due to the strong hydrogen-bonding interaction of the acids in solution, multiple homo- and heteroaggregates are formed with profound effects on catalytic activity. Yet, due to the similar binding motifs—hydrogen-bonds—it is challenging to experimentally quantify the abundance of these aggregates in solution. Here we demonstrate that a combination of nuclear magnetic resonance (NMR) and dielectric relaxation spectroscopy (DRS) allows for accurate speciation of these aggregates in solution. We show that only by using the observables of both experiments heteroaggregates can be discriminated with simultaneously taking homoaggregation into account. Comparison of the association of diphenyl phosphoric acid and quinaldine or phenylquinaline in chloroform, dichloromethane, or tetrahydrofuran suggests that the basicity of the base largely determines the association of one acid and one base molecule to form an ion-pair. We find the ion-pair formation constants to be highest in chloroform, slightly lower in dichloromethane and lowest in tetrahydrofuran, which indicates that the hydrogen-bonding ability of the solvent also alters ion-pairing equilibria. We find evidence for the formation of multimers, consisting of one imine base and multiple diphenyl phosphoric acid molecules for both bases in all three solvents. This subsequent association of an acid to an ion-pair is however little affected by the nature of the base or the solvent. As such our findings provide routes to enhance the overall fraction of these multimers in solution, which have been reported to open new catalytic pathways.

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Rates of Ionization of Pseudo Acids.¹ V. Steric Effects in the Base-catalyzed Ionization of Nitroethane

Cited by 32 publications

References 0 publications

Three‐in‐One Crystal: The Coordination Diversity of Zinc Polypyridine Complexes

Three‐in‐One Crystal: The Coordination Diversity of Zinc Polypyridine Complexes

Ddpd as Expanded Terpyridine: Dramatic Effects of Symmetry and Electronic Properties in First Row Transition Metal Complexes

Association Equilibria of Organo-Phosphoric Acids with Imines from a Combined Dielectric and Nuclear Magnetic Resonance Spectroscopy Approach

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Rates of Ionization of Pseudo Acids.1 V. Steric Effects in the Base-catalyzed Ionization of Nitroethane

Cited by 32 publications

References 0 publications

Three‐in‐One Crystal: The Coordination Diversity of Zinc Polypyridine Complexes

Three‐in‐One Crystal: The Coordination Diversity of Zinc Polypyridine Complexes

Ddpd as Expanded Terpyridine: Dramatic Effects of Symmetry and Electronic Properties in First Row Transition Metal Complexes

Association Equilibria of Organo-Phosphoric Acids with Imines from a Combined Dielectric and Nuclear Magnetic Resonance Spectroscopy Approach

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Rates of Ionization of Pseudo Acids.¹ V. Steric Effects in the Base-catalyzed Ionization of Nitroethane