Synthesis and Properties of 2-(Dimesitylboryl)benzylideneamines

Lithiation of 2-(2-bromophenyl)-dioxolane (1) followed by reaction with dimesitylboron fluoride afforded 2-(2-dimesitylborylphenyl)-dioxolane (2) which was deprotected to afford 2-dimesitylboryl-benzaldehyde (3). Compound 3 reacts with aliphatic amines such as n-butylamine and ethanolamine to afford the corresponding imines 2-(dimesitylboryl)benzylidenebutylamine (4) and 2-(dimesitylboryl)benzylideneethanolamine (5), respectively. Structural studies indicate coordination of the imine-nitrogen atom to the boron center. Imines 4 and 5 emit a green fluorescence near 510 nm with quantum yields approaching 10 %. TD-DFT calculations suggest that this emission arises from an intramolecular charge-transfer excited state.