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Tuning the Electronic Properties of Main-Group Species by N-Heterocyclic Vinyl (NHV) Scaffolds. | LitMetric

Tuning the Electronic Properties of Main-Group Species by N-Heterocyclic Vinyl (NHV) Scaffolds.

Acc Chem Res

Molecular Inorganic Chemistry and Catalysis, Inorganic and Structural Chemistry, Center for Molecular Materials, Faculty of Chemistry, Universität Bielefeld, Universitätsstrasse 25, D-33615 Bielefeld, Germany.

Published: February 2022

AI Article Synopsis

  • The text discusses the significance of π-conjugation in organic chemistry, highlighting N-heterocyclic vinyl (NHV) substituents derived from N-heterocyclic carbenes (NHCs) which are useful in tuning the structure and properties of molecular materials.
  • NHVs and their derivatives, such as N-heterocyclic vinylidenes (NHVDs), have unique electronic characteristics due to their highly polarizable C═C bonds, influenced by adjacent π-donor nitrogen atoms.
  • The electronic properties of compounds like diphosphenes and divinyldiphosphenes can be controlled by the choice of the carbene unit, which affects their HOMO and

Article Abstract

ConspectusMolecules and materials with easily tunable electronic structures and properties are at the forefront of contemporary research. π-Conjugation is fundamental in organic chemistry and plays a key role in the design of molecular materials. In this Account, we showcase the applicability of N-heterocyclic vinyl (NHV) substituents based on classical N-heterocyclic carbenes (NHCs) for tuning the structure, properties, and stability of main-group species (E) via π-conjugation and/or π-donation.NHVs such as [(NHC)═CR] (R = H or aryl) are monoanionic ligands formally derived by the deprotonation of N-heterocyclic olefins (NHOs), (NHC)═CHR. Further deprotonation of [(NHC)═CR] (R = H) is viable, giving rise to N-heterocyclic vinylidene (NHVD) species such as (NHC)═C. NHVs and NHVDs feature a highly polarizable exocyclic C═C bond because of the presence of adjacent π-donor nitrogen atoms. The nature of the NHC, in particular the π-acceptor property, has a direct consequence on the polarity of the C═C bond and hence on the magnitude of π-conjugation in the derived molecules. Thus, the electronic structure, especially the energy and shape of frontier molecular orbitals, HOMO and LUMO, of derived species can be fine-tuned by a judicious choice of the carbene unit. For instance, the HOMO of classical diphosphenes (RP═PR) (R = alkyl or aryl) is invariably the phosphorus lone-pair orbital, while the P═P π-bond is HOMO - 1 or HOMO - 2. In strong contrast, the HOMO of divinyldiphosphenes (R = NHV) is mainly the P═P π-bond. This is owing to the π-conjugation, resulting in the lowering of the LUMO and raising of the HOMO energy. They have a remarkably small HOMO-LUMO energy gap (4.15-4.50 eV) and readily undergo 1e-oxidations, giving rise to stable radical cations and dications.By employing a similar approach, one can access divinyldiarsenes and the corresponding radical cations and dications as crystalline solids. The use of divinyldiphosphenes and divinyldiarsenes as promising ligands in the stabilization of metalloradicals has been shown. By a logical selection of singlet carbenes, stable 2-phosha-1,3-butadiene and 2-arsa-1,3-butadiene compounds, as well as related radical cations and dications, can be prepared as crystalline solids.The relevance of NHV ligands as potent π-donors has been demonstrated for the stabilization of elusive electrophilic phosphinidene and arsinidene complexes {(NHV)E}Fe(CO) (E = P or As). Moreover, stable singlet diradicaloid [(NHC)CP] and -quinodimethane derivatives [(NHC)CP] based on an NHVD framework are accessible as stable solids.In this Account, a special emphasis is given to the contributions from this laboratory. The author hopes that this Account will serve as a useful reference guide for researchers interested in studying and applying NHV and NHVD scaffolds in modern molecular chemistry and materials sciences.

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Source
http://dx.doi.org/10.1021/acs.accounts.1c00701DOI Listing

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