Is delocalization a prerequisite for stability of ring systems? A case study of some inorganic rings

The chemistry of organoboron compounds has been primarily dominated by their use as powerful reagents in synthetic organic chemistry. Recently, the incorporation of boron as part of a functional target structure has emerged as a useful way to generate diversity in organic compounds. A commonly applied strategy is the replacement of a CC unit with its isoelectronic BN unit. In particular, the BN/CC isosterism of the ubiquitous arene motif has undergone a renaissance in the past decade. The parent molecule of the 1,2-dihydro-1,2-azaborine family has now been isolated. New mono- and polycyclic BN heterocycles have been synthesized for potential use in biomedical and materials science applications. This review is a tribute to Dewar's first synthesis of a monocyclic 1,2-dihydro-1,2-azaborine 50 years ago and discusses recent advances in the synthesis and characterization of carbon(C)-boron(B)-nitrogen(N)-containing heterocycles.

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“…[18–23] Although commonly referred to as the “inorganic benzene”, borazine's aromatic character remains controversial to date. [24–27] …”

Section: Introductionmentioning

confidence: 99%

Recent Advances in Azaborine Chemistry

2012

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“…Since BN and CC are considered to be isosteres, the explanation for the sharply different properties of BN/CC analogues most likely lies in differences in the bonding and electronegativity. The energies and sizes of the atomic orbitals formally combining to form the molecular orbitals of a CC bond are self‐evidently matched whereas the mismatched energies and sizes of the atomic orbitals combining in the BN bond make the σ‐bonding dipolar and the π‐bonding weaker due to less efficient overlap . The result is that BN compounds are generally kinetically and thermodynamically more reactive than their CC analogues.…”

Section: Figurementioning

confidence: 99%

Inorganic Triphenylphosphine

et al. 2018

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Ac ompletely inorganic version of one of the most famous organophosphorus compounds,t riphenylphosphine, has been prepared. Ac omparison of the crystal structures of inorganic triphenylphosphine,P Baz 3 (where Baz = B 3 H 2 N 3 H 3 )a nd PPh 3 shows that they have superficial similarities and furthermore,t he Lewis basicities of the two compounds are remarkably similar.H owever,t heir oxygenation and hydrolysis reactions are starkly different. PBaz 3 reacts quantitatively with water to give PH 3 and with the oxidizing agent ONMe 3 to give the triply-O-inserted product P(OBaz) 3 ,a ni norganic version of triphenyl phosphite; ac orresponding transformation with PPh 3 is inconceivable. Thermodynamically,w hat drives these striking differences in the chemistry of PBaz 3 and PPh 3 is the great strength of the B À Ob ond.

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“…In the world of inorganic chemistry a molecule of a comparable status is borazine (B 3 N 3 H 6 ) known also as “inorganic benzene” since BN is isoelectronic to CC. Although both species share similar physical properties borazine is classified as a nonaromatic compound deficient of any ring current based on the diamagnetic susceptibility exaltation method, nucleus independent chemical shift calculations, and 1 H chemical shifts of both H(B) and H(N) hydrogen atoms . And this is indeed strange since borazine features a regular plane hexagonal ring structure while it is possible to write down Kekulé‐type structures with N→B π bonding superimposed on the σ frame…”

Section: Introductionmentioning

confidence: 99%

The nature of the chemical bond in borazine (B₃N₃H₆), boroxine (B₃O₃H₃), carborazine (B₂N₂C₂H₆), and related species

Καλέμος

2018

Int J of Quantum Chemistry

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The bonding problem in borazine (B 3 N 3 H 6 ), boroxine (B 3 O 3 H 3 ), and carborazine (B 2 N 2 C 2 H 6 ) is successfully addressed through the consideration of the excited states of the constituent fragments, namely BH(a 3 P), NH(A 3 P), and CH(a 4 R 2 ). We propose the participation of resonant structures for all three species that help to explain the experimental findings. A discussion on the chemical pattern of the parental molecule benzene (C 6 H 6 ) helps to make coherent the whole bonding analysis on the titled species.ab initio, borazine, boroxine, carborazine, chemical bonding 1 | I N TR ODU C TI ON Chemistry is traditionally subdivided into several branches, two of which are inorganic and organic chemistry. Although the border lines between different subfields are nowadays blurry organic chemistry is mainly concerned with only one element of the periodic table, carbon, and the species it can form, while inorganic chemistry with all the rest. The richness of carbon chemistry is phenomenal and due to its third excited 5 S(2s 1 2p 3 ) state just 4.18 eV [1] above its ground 3 P(2s 2 2p 2 ) one. It suffices to mention that the ground state of simple organic species like, for example, CH 2 (X 3 B 1 ) [2] and consequently CH 4 (X 1 A 1 )[ CH 2 (X 3 B 1 )12H( 2 S)] are due to this C( 5 S) state. [3] The above point of view or way of interpreting the chemical bond is founded on our belief that molecules are made of atoms that may participate in a variety of quantum states beyond their ground ones.This was already known to the "old" masters (see e.g., Ref.[3] and references therein) of quantum chemistry but unfortunately it is largely forgotten nowadays. We strongly believe that the atoms in molecules [4] "hypothesis" provides the shortest path to reach a deep understanding of how molecules are formed.The most archetypal species of all of organic chemistry is benzene (C 6 H 6 ), a planar arrangement of six CH units in a D 6h structure. Since 1865, when Kekul e [5] first conjectured a ring shaped structure with alternating single (r) and double (p) bonds, benzene has been extensively studied from any imaginable point of view and perspective. Its most characteristic property, although not so clearly defined, is aromaticity, a rather strange [6,7] enhanced stability of ring shaped flat molecules with resonant bonds as compared to any other geometrical arrangement of the same collection of atoms. The above stability is largely attributed to the delocalization of the p electrons (e -) theoretically delineated by H€ uckel [8] in 1930.In the world of inorganic chemistry a molecule of a comparable status is borazine (B 3 N 3 H 6 ) known also as "inorganic benzene" since BAN is isoelectronic to CAC. Although both species share similar physical properties [9,10] borazine is classified as a nonaromatic compound deficient of any ring current based on the diamagnetic susceptibility exaltation method, nucleus independent chemical shift calculations, and 1 H chemical shifts of both H(B) and H(N) hydrogen atoms. [11][12][13][...

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Is delocalization a prerequisite for stability of ring systems? A case study of some inorganic rings

Cited by 33 publications

References 67 publications

Recent Advances in Azaborine Chemistry

Recent Advances in Azaborine Chemistry

Inorganic Triphenylphosphine

The nature of the chemical bond in borazine (B₃N₃H₆), boroxine (B₃O₃H₃), carborazine (B₂N₂C₂H₆), and related species

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Is delocalization a prerequisite for stability of ring systems? A case study of some inorganic rings

Cited by 33 publications

References 67 publications

Recent Advances in Azaborine Chemistry

Recent Advances in Azaborine Chemistry

Inorganic Triphenylphosphine

The nature of the chemical bond in borazine (B3N3H6), boroxine (B3O3H3), carborazine (B2N2C2H6), and related species

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The nature of the chemical bond in borazine (B₃N₃H₆), boroxine (B₃O₃H₃), carborazine (B₂N₂C₂H₆), and related species