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Controlling the Optoelectronic Properties of Pyrene by Regioselective Lewis Base‐Directed Electrophilic Aromatic Borylation
Author(s) -
Vanga Mukundam,
Lalancette Roger A.,
Jäkle Frieder
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201901231
Subject(s) - borylation , regioselectivity , chemistry , pyrene , electrophile , moiety , electrophilic substitution , alkyl , lewis acids and bases , combinatorial chemistry , medicinal chemistry , organic chemistry , aryl , catalysis
Given that pyrene represents one of the most versatile chromophores, the development of new selective routes for its functionalization and tuning of its emission properties is highly desirable. Pyrene‐based BN Lewis pair (LP)‐functionalized polycyclic aromatic hydrocarbons (PAHs) were prepared by regioselective Lewis base‐directed electrophilic aromatic substitution. The requisite 1,6‐dipyridylpyrene ligands were accessed by Suzuki–Miyaura cross‐coupling of 1,6‐bis(pinacolatoboryl)pyrenes with 2‐bromopyridine derivatives. Subsequent electrophilic borylation with BCl 3 in the presence of AlCl 3 and 2,6‐di‐ tert ‐butylpyridine as a hindered base produced the dichloroborane complexes, which were then in situ reacted with diphenyl or diethyl zinc. The presence or absence of alkyl chains in the 3,8‐positions of the pyrene moiety determined the position of the B−C bond formation (2,7 in the non‐K region versus 5,10 in the K region) and thereby also the size of the BN heterocycle (five‐ versus six‐membered). The impact of the regioisomeric borylation on the electrochemical, photophysical and structural properties was investigated and the conclusions supported by theoretical calculations. The rapid synthesis of derivatives that are borylated in the K region also suggests strong potential for the development of pyrene derivatives that are otherwise difficult to access.