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Divergent and Multi‐Stage Photoisomerization of Four‐Coordinated Boron Compounds with a Naphthyl‐Pyridyl/Thiazolyl Backbone
Author(s) -
He Zhechang,
Liu Lijie,
Zhao Zhenhui,
Mellerup Soren. K.,
Ge Yuxin,
Wang Xiang,
Wang Nan,
Wang Suning
Publication year - 2020
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.202000775
Subject(s) - photoisomerization , isomerization , chemistry , boron , regioselectivity , diastereomer , substituent , photochemistry , molecule , medicinal chemistry , stereochemistry , organic chemistry , catalysis
Examination of the photoreactivity of a new class of N,C‐chelate organoboron compounds, including a series of unsymmetrically substituted boron molecules, B(naph‐pyridyl)(Ar 1 )(Ar 2 ) and B(naph‐thiazolyl)(Ar 1 )(Ar 2 ), led to the discovery of new and divergent photothermal isomerization phenomena. These include the clean and regioselective photoisomerization by unsymmetrical boron, forming borepin isomers, some of which further isomerize to the corresponding boratanorcaradiene diastereomer pairs as a result of the generation of two chiral centers. Significantly, the boratanorcaradienes involving a 3‐thienyl substituent on boron were found to thermally convert to BN‐fluoranthene annulated borapentalene via an unprecedented reversible boratacyclopropane–boratacyclopentene rearrangement. Changing the pyridyl donor to a thiazolyl donor on the boron was found to provide the B(naph‐thiazolyl)(Mes) 2 compounds with a distinct new photoisomerization pathway—instead of borepin, forming new blue fluorescent polycyclic azaborinine species. This work illustrates the richness and complexity of boron photochemistry.