Linear annulation of two 2,3-biphenylenediyl
moieties to a 1,4-dibora-2,5-cyclohexadiene
core via its carbon atoms leads to the boron-doped phenylene-containing
oligoacene (B-POA) DBI. The optoelectronic properties
of DBI are unlike those of related boron-doped polycyclic
aromatic hydrocarbons (B-PAHs), such as 6,13-dihydro-6,13-diborapentacene
(DBP). Herein we disclose two new B-POAs, which provide
insight into fundamental structure–property relationships.
The first is a π-extended DBI congener (e-DBI), in which two 2,3-benzo[b]biphenylenediyl
moieties are linearly annulated to the central B2C4 ring and behaves partly similar to DBI: it is
a strong electron acceptor and has a deep red color. In contrast to
the nonluminescent DBI, it shows red fluorescence (quantum
yield: 12%), which changes to blue-green upon addition of excess F–-ions. In the presence of 0.4 equiv of F–, nearly white emission is observed (CIE1931: (0.3320|0.4056)). If
biphenylenediyl moieties are angularly attached to the B2C4 ring via their 1,2-positions, the resulting mixture
of “v”- and “z”-shaped B-POA isomers (v/z-DBI) behaves distinctly different from linear DBI: the electrode potentials required for the reversible two-electron
reductions of v/z-DBI are significantly more cathodic,
and v/z-DBI is an orange rather than red solid and emits
green light (quantum yields 65%) upon irradiation.
A convenient and straightforward approach to performing oxidative coupling reactions in flow is presented. A collection of electron-rich benzene derivatives was subjected to this protocol, and the distinct utility of molybdenum pentachloride (MoCl) is established. Using this unexplored protocol, biphenyls could be obtained in 21-91% isolated yield. This simple protocol opens a new chapter in reagent-mediated dehydrogenative coupling reactions, and yields are compared to classical approaches.
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