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Ethylene‐Bridged Tetradentate Bis(amidines): Supramolecular Assemblies through Hydrogen Bonding and Photoluminescence upon Deprotonation
Author(s) -
CalderónDíaz Alvaro,
Arras Janet,
Miller Ethan T.,
Bhuvanesh Nattamai,
McMillen Colin D.,
Stollenz Michael
Publication year - 2020
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.202000207
Subject(s) - chemistry , amidine , adduct , steric effects , intramolecular force , hydrogen bond , supramolecular chemistry , deprotonation , dimer , medicinal chemistry , molecule , photochemistry , solvent , stereochemistry , organic chemistry , ion
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 N 2 C‐ t Bu or N 2 C‐Ph substituents result in steric protection of the N–H moieties, whereas less crowded terminal p ‐ t Bu(C 6 H 4 ) groups either show encapsulation ( N 2 C‐ t Bu) or hydrogen bonding ( N 2 C‐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.