Modification and Unexpected Reactivity of 2‑Borylbenzaldimines: Acylated and Silylated Derivatives as Well as Dimeric Compounds

Various
novel N-alkyl and N-benzyl
2-borylbenzaldimines 3 were prepared by condensation
of 2-(dimesitylboryl)­benzaldehyde (1) with amines. Further
functionalization of compound 3e was possible by deprotonation
and subsequent regioselective reaction with electrophiles to give
compounds 4. Applying similar conditions to 3a led to the unexpected formation of hitherto unknown dimeric compounds
(5 and 6). All structural types were fully
characterized, including by X-ray diffraction (XRD). Furthermore,
quantum chemical calculations on the SCS-MP2 and DFT levels gave insights
into the reaction mechanisms and the stereoselectivity. The B/N bonding
situation in these molecules was analyzed using Wiberg bond indices.
Preliminary UV–vis and fluorescence measurements indicate that
the substitution reaction leading to compounds 4 can
be utilized to tune the photophysical properties of these compounds.