C-C Activation to BNB-Embedded Indenophenanthrenes. Electronic Structure and Reactivity

The BNB-embedded indenophenanthrenes 3 have been synthesized by reduction of LBX2 (2; L represents a BN phenanthrene ligand and X = Br, Cl) with 2 equiv of potassium graphite under ambient conditions. The formation of 3 very likely goes through an aminoborylene intermediate, which underwent an intramolecular insertion into a C-C bond to close the polycyclic structure. DFT calculations disclosed the delocalized BNB 3c-2e interaction in the BNBC2 five-membered ring of 3. Treatment of 3a with IPr (1,3-diisopropyl-4,5-dimethylimi-dazol-2-ylidene) selectively led to the coordination of IPr to one of two boron atoms, the structure of which has been confirmed by an X-ray single-crystal analysis.