In Search of the Perfect Triple BB Bond: Mechanical Tuning of the Host Molecular Trap for the Triple Bond B≡B Fragment

The coordination of the B<sub>2</sub> fragment by two σ-donor ligands L: could lead to a diboryne compound with a formal triple bond L:→B≡B←:L. σ-Type coordination L:→B leads to an excess of electrons around the B<sub>2</sub> central fragment, whereas π-back-donation from the...

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Autores principales:	Shmuel Zilberg, Michael Zinigrad
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	B≡B triple bond diboryne π-back-donation host molecule strain energy Organic chemistry QD241-441
Acceso en línea:	https://doaj.org/article/20b41470e4164bb9b4ce7ab1a3ad7c7b
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spelling	oai:doaj.org-article:20b41470e4164bb9b4ce7ab1a3ad7c7b2021-11-11T18:26:43ZIn Search of the Perfect Triple BB Bond: Mechanical Tuning of the Host Molecular Trap for the Triple Bond B≡B Fragment10.3390/molecules262164281420-3049https://doaj.org/article/20b41470e4164bb9b4ce7ab1a3ad7c7b2021-10-01T00:00:00Zhttps://www.mdpi.com/1420-3049/26/21/6428https://doaj.org/toc/1420-3049The coordination of the B<sub>2</sub> fragment by two σ-donor ligands L: could lead to a diboryne compound with a formal triple bond L:→B≡B←:L. σ-Type coordination L:→B leads to an excess of electrons around the B<sub>2</sub> central fragment, whereas π-back-donation from the B≡B moiety to ligand L has a compensation effect. Coordination of the σ-donor and π-acceptor ligand is accompanied by the lowering of the BB bond order. Here, we propose a new approach to obtain the perfect triple BB bond through the incorporation of the BB unit into a rigid molecular capsule. The idea is the replacement of π-back-donation, as the principal stabilization factor in the linear NBBN structure, with the mechanical stabilization of the BB fragment in the inert molecular capsule, thus preserving the perfect B≡B triple bond. Quantum-chemical calculations show that the rigid molecular capsule provided a linear NBBN structure and an unusually short BB bond of 1.36 Å. Quantum-chemical calculations of the proposed diboryne adducts show a perfect triple bond B≡B without π-back-donation from the B<sub>2</sub> unit to the host molecule. Two mechanisms were tested for the molecular design of a diboryne adduct with a perfect B≡B triple bond: the elimination of π-back-donation and the construction of a suitable molecular trap for the encapsulation of the B<sub>2</sub> unit. The second factor that could lead to the strengthening or stretching of a selected chemical bond is molecular strain produced by the rigid molecular host capsule, as was shown for B≡B and for C≡C triple bonds. Different derivatives of icosane host molecules exhibited variation in BB bond length and the corresponding frequency of the BB stretch. On the other hand, this group of molecules shows a perfect triple BB bond character and they all possess a similar level of HOMO.Shmuel ZilbergMichael ZinigradMDPI AGarticleB≡B triple bonddiboryneπ-back-donationhost moleculestrain energyOrganic chemistryQD241-441ENMolecules, Vol 26, Iss 6428, p 6428 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	B≡B triple bond diboryne π-back-donation host molecule strain energy Organic chemistry QD241-441
spellingShingle	B≡B triple bond diboryne π-back-donation host molecule strain energy Organic chemistry QD241-441 Shmuel Zilberg Michael Zinigrad In Search of the Perfect Triple BB Bond: Mechanical Tuning of the Host Molecular Trap for the Triple Bond B≡B Fragment
description	The coordination of the B<sub>2</sub> fragment by two σ-donor ligands L: could lead to a diboryne compound with a formal triple bond L:→B≡B←:L. σ-Type coordination L:→B leads to an excess of electrons around the B<sub>2</sub> central fragment, whereas π-back-donation from the B≡B moiety to ligand L has a compensation effect. Coordination of the σ-donor and π-acceptor ligand is accompanied by the lowering of the BB bond order. Here, we propose a new approach to obtain the perfect triple BB bond through the incorporation of the BB unit into a rigid molecular capsule. The idea is the replacement of π-back-donation, as the principal stabilization factor in the linear NBBN structure, with the mechanical stabilization of the BB fragment in the inert molecular capsule, thus preserving the perfect B≡B triple bond. Quantum-chemical calculations show that the rigid molecular capsule provided a linear NBBN structure and an unusually short BB bond of 1.36 Å. Quantum-chemical calculations of the proposed diboryne adducts show a perfect triple bond B≡B without π-back-donation from the B<sub>2</sub> unit to the host molecule. Two mechanisms were tested for the molecular design of a diboryne adduct with a perfect B≡B triple bond: the elimination of π-back-donation and the construction of a suitable molecular trap for the encapsulation of the B<sub>2</sub> unit. The second factor that could lead to the strengthening or stretching of a selected chemical bond is molecular strain produced by the rigid molecular host capsule, as was shown for B≡B and for C≡C triple bonds. Different derivatives of icosane host molecules exhibited variation in BB bond length and the corresponding frequency of the BB stretch. On the other hand, this group of molecules shows a perfect triple BB bond character and they all possess a similar level of HOMO.
format	article
author	Shmuel Zilberg Michael Zinigrad
author_facet	Shmuel Zilberg Michael Zinigrad
author_sort	Shmuel Zilberg
title	In Search of the Perfect Triple BB Bond: Mechanical Tuning of the Host Molecular Trap for the Triple Bond B≡B Fragment
title_short	In Search of the Perfect Triple BB Bond: Mechanical Tuning of the Host Molecular Trap for the Triple Bond B≡B Fragment
title_full	In Search of the Perfect Triple BB Bond: Mechanical Tuning of the Host Molecular Trap for the Triple Bond B≡B Fragment
title_fullStr	In Search of the Perfect Triple BB Bond: Mechanical Tuning of the Host Molecular Trap for the Triple Bond B≡B Fragment
title_full_unstemmed	In Search of the Perfect Triple BB Bond: Mechanical Tuning of the Host Molecular Trap for the Triple Bond B≡B Fragment
title_sort	in search of the perfect triple bb bond: mechanical tuning of the host molecular trap for the triple bond b≡b fragment
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/20b41470e4164bb9b4ce7ab1a3ad7c7b
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In Search of the Perfect Triple BB Bond: Mechanical Tuning of the Host Molecular Trap for the Triple Bond B≡B Fragment

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