Step Forward to Stronger Neutral Organic Superbases: Fused Troponimines

Saadat, Kayvan; Shiri, Ali; Kovačević, Borislav

doi:10.1021/acs.joc.0c01466

Cited by 13 publications

(5 citation statements)

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“…These conjugated systems continue to arouse interest as a canonical structure for strong bases design. In this regard, a few significant papers published after 2016 can be cited [ 70 , 72 , 73 , 74 , 75 , 82 , 83 , 116 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 ]. Note that theoretical investigations have no such difficulties as those connected with experiments.…”

Section: Overview and Prospectsmentioning

confidence: 99%

Strong Bases and beyond: The Prominent Contribution of Neutral Push–Pull Organic Molecules towards Superbases in the Gas Phase

Raczyńska,

Gal,

Maria

2024

IJMS

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In this review, the principles of gas-phase proton basicity measurements and theoretical calculations are recalled as a reminder of how the basicity PA/GB scale, based on Brønsted–Lowry theory, was constructed in the gas-phase (PA—proton affinity and/or GB—gas-phase basicity in the enthalpy and Gibbs energy scale, respectively). The origins of exceptionally strong gas-phase basicity of some organic nitrogen bases containing N-sp3 (amines), N-sp2 (imines, amidines, guanidines, polyguanides, phosphazenes), and N-sp (nitriles) are rationalized. In particular, the role of push–pull nitrogen bases in the development of the gas-phase basicity in the superbasicity region is emphasized. Some reasons for the difficulties in measurements for poly-functional nitrogen bases are highlighted. Various structural phenomena being in relation with gas-phase acid–base equilibria that should be considered in quantum-chemical calculations of PA/GB parameters are discussed. The preparation methods for strong organic push–pull bases containing a N-sp2 site of protonation are briefly reviewed. Finally, recent trends in research on neutral organic superbases, leaning toward catalytic and other remarkable applications, are underlined.

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Section: Overview and Prospectsmentioning

confidence: 99%

Strong Bases and beyond: The Prominent Contribution of Neutral Push–Pull Organic Molecules towards Superbases in the Gas Phase

Raczyńska,

Gal,

Maria

2024

IJMS

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“…NICS has allowed tracking aromaticity variation during protonating a base. [20][21][43][44] For example, Maksić et al [20] utilized some approaches, including NICS, and have inferred more aromatic stabilization promotes higher basicity. They have also deduced that the protonation induces spreading aromatization over the protonated bases.…”

Section: Organic Bases Have Received Considerable Attention Due To Theirmentioning

confidence: 99%

“…The impacts of the protonation on the magnetic profiles and aromaticity of proton sponges and superbases have been a subject of interest. NICS has allowed tracking aromaticity variation during protonating a base [20–21,43–44] . For example, Maksić et al [20] .…”

Section: Introductionmentioning

confidence: 99%

Predicting a New Δ‐Proton Sponge‐Base of 4,12‐Dihydrogen‐4,8,12‐triazatriangulene through Proton Affinity, Aromatic Stabilization Energy, and Aromatic Magnetism

Al-Yassiri

Puchta

2023

ChemPhysChem

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Herein, we report designing a new Δ (delta‐shaped) proton sponge base of 4,12‐dihydrogen‐4,8,12‐triazatriangulene (compound 1) and calculating its proton affinity (PA), aromatic stabilization, natural bond orbital (NBO), electron density ρ(r), Laplacian of electron density ∇2ρ(r), (2D‐3D) multidimensional off‐nucleus magnetic shielding (σzz(r) and σiso(r)), and scanning nucleus‐independent chemical shift (NICSzz and NICS). Density functional theory (DFT) at B3LYP/6‐311+G(d,p), ωB97XD/6‐311+G(d,p), and PW91/def2TZVP were used to compute the magnetic shielding variables. In addition, relevant bases like pyridine, quinoline, and acridine were also studied and compared. The protonation of compound 1 yields a highly symmetric carbocation of three Hückel benzenic rings. Comparing our findings of the studied molecules showed that compound 1 precedes others in PA, aromatic isomerization stabilization energy, and basicity. Therefore, the basicity may be enhanced when a conjugate acid gains higher aromatic features than its unprotonated base. Both multidimensional σzz(r) and σiso(r) off‐nucleus magnetic shieldings outperformed electron‐based techniques and can visually monitor changes in aromaticity that occur by protonation. The B3LYP/6‐311+G(d,p), ωB97XD/6‐311+G(d,p), and PW91/def2TZVP levels showed no significant differences in detailing isochemical shielding surfaces.

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“…An effective strategy for enhancing the π-donor strength or +M character of an sp 2 -nitrogen substituent is to incorporate the imine carbon atom as a carbenium atom into a cyclic aromatic ring system, intrinsically required to achieve 2π or 6π Hückel aromaticity. , This polarizes the exocyclic imine CN functional group into a zwitterionic C (+) –N (−) bonding situation, thus enhancing the N-donor character. Typical examples following this idea are higher-order tris(cyclopropeneimino)guanidine, cyclopropeneimino proton sponge DACN, , and the bis- N , N ′-(1,3-dialkyl-4,5-dimethyl-1 H -imidazol-2(3 H )-yli-dene)guanidine bases (BIG bases) (Scheme ).…”

Section: General Strategies For the Molecular Design Of Superbasesmentioning

confidence: 99%

Design of Novel Uncharged Organic Superbases: Merging Basicity and Functionality

et al. 2021

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Conspectus One of the constant challenges of synthetic chemistry is the molecular design and synthesis of nonionic, metal-free superbases as chemically stable neutral organic compounds of moderate molecular weight, intrinsically high thermodynamic basicity, adaptable kinetic basicity, and weak or tunable nucleophilicity at their nitrogen, phosphorus, or carbon basicity centers. Such superbases can catalyze numerous reactions, ranging from C–C bond formation to cycloadditions and polymerization, to name just a few. Additional benefits of organic superbases, as opposed to their inorganic counterparts, are their solubility in organic reaction media, mild reaction conditions, and higher selectivity. Approaching such superbasic compounds remains a continuous challenge. However, recent advances in synthetic methodology and theoretical understanding have resulted in new design principles and synthetic strategies toward superbases. Our computational contributions have demonstrated that the gas-phase basicity region of 350 kcal mol–1 and even beyond is easily reachable by organosuperbases. However, despite record-high basicities, the physical limitations of many of these compounds become quickly evident. The typically large molecular weight of these molecules and their sensitivity to ordinary reaction conditions prevent them from being practical, even though their preparation is often not too difficult. Thus, obviously structural limitations with respect to molecular weight and structural complexity must be imposed on the design of new synthetically useful organic superbases, but strategies for increasing their basicity remain important. The contemporary design of novel organic superbases is illustrated by phosphazenyl phosphanes displaying gas-phase basicities (GB) above 300 kcal mol–1 but having molecular weights well below 1000 g·mol–1. This approach is based on a reconsideration of phosphorus(III) compounds, which goes along with increasing their stability in solution. Another example is the preparation of carbodiphosphoranes incorporating pyrrolidine, tetramethylguanidine, or hexamethylphosphazene as a substituent. With gas-phase proton affinities of up to 300 kcal mol–1, they are among the top nonionic carbon bases on the basicity scale. Remarkably, the high basicity of these compounds is achieved at molecular weights of around 600 g·mol–1. Another approach to achieving high basicity through the cooperative effect of multiple intramolecular hydrogen bonding, which increases the stabilization of conjugate acids, has recently been confirmed. This Account focuses on our efforts to produce superbasic molecules that embody many desirable traits, but other groups’ approaches will also be discussed. We reveal the crucial structural features of superbases and place them on known basicity scales. We discuss the emerging potential and current limits of their application and give a general outlook into the future.

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Step Forward to Stronger Neutral Organic Superbases: Fused Troponimines

Cited by 13 publications

References 68 publications

Strong Bases and beyond: The Prominent Contribution of Neutral Push–Pull Organic Molecules towards Superbases in the Gas Phase

Strong Bases and beyond: The Prominent Contribution of Neutral Push–Pull Organic Molecules towards Superbases in the Gas Phase

Predicting a New Δ‐Proton Sponge‐Base of 4,12‐Dihydrogen‐4,8,12‐triazatriangulene through Proton Affinity, Aromatic Stabilization Energy, and Aromatic Magnetism

Design of Novel Uncharged Organic Superbases: Merging Basicity and Functionality

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