Ethylene‐Bridged Tetradentate Bis(amidines): Supramolecular Assemblies through Hydrogen Bonding and Photoluminescence upon Deprotonation

Sterically crowded tetradentate bis(amidines) encapsulate their N–H functionalities or unveil them to undergo inter‐ and intramolecular hydrogen bonding both in solid state and solution, depending on a subtle interplay between the amidine backbone substituents. X‐ray crystallography reveals for four...

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Bibliographic Details
Published in:European journal of organic chemistry 2020-06, Vol.2020 (22), p.3243-3250
Main Authors: Calderón‐Díaz, Alvaro, Arras, Janet, Miller, Ethan T., Bhuvanesh, Nattamai, McMillen, Colin D., Stollenz, Michael
Format: Article
Language:English
Subjects:
Amidines
Chemical bonds
Crystallography
Density functional calculations
Dimerization
Dimers
Encapsulation
Ethanol
Hydrogen
Hydrogen bonding
Hydrogen bonds
Isomers
Luminescence
Photoluminescence
Solvents
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Summary:Sterically crowded tetradentate bis(amidines) encapsulate their N–H functionalities or unveil them to undergo inter‐ and intramolecular hydrogen bonding both in solid state and solution, depending on a subtle interplay between the amidine backbone substituents. X‐ray crystallography reveals for four distinct ZZ(syn/syn) and EE(syn/syn) bis(amidines) that bulky terminal N‐Mes groups in combination with N2C‐tBu or N2C‐Ph substituents result in steric protection of the N–H moieties, whereas less crowded terminal p‐tBu(C6H4) groups either show encapsulation (N2C‐tBu) or hydrogen bonding (N2C‐Ph), the latter resulting in a bis(amidine) dimer formed by inter‐ and intramolecular hydrogen bonds. Moreover, a supramolecular solvent adduct consisting of one bis(amidine) and four ethanol molecules is presented. DFT calculations show that both the dimerization and formation of the solvent adduct is associated with a significant energy gain (dimerization: ΔE = –27.7 kcal/mol; formation of ethanol adduct: ΔE = –64.3 kcal/mol). The corresponding four Li bis(amidinates) are weakly blue to green‐emissive in THF solution. Overall, a new series of highly flexible bis(amidines) has been examined. Flexible ethylene‐bridged tetradentate bis(amidines) either encapsulate their N–H moieties through steric protection or form versatile networks of hydrogen bonds both in the solid state and in solution. They also produce blue to green emissions upon deprotonation.
ISSN:1434-193X
1099-0690
DOI:10.1002/ejoc.202000207