Boron calixphyrin complexes: exploring the coordination chemistry of a BODIPY/porphyrin hybrid

Boron complexes of calix[4]phyrins (1.1.1.1) were prepared by reacting the free-base ligands with BF ·Et O. The reaction conditions can be efficiently tailored to produce mono- or di-boron calixphyrins. Mono-BF calixphyrins with boron coordinating to either the dipyrrin, BF [H(Calix)], or dipyrromethane, BF [H(Calix)] and BF [H (Calix)] , bonding sites were isolated. The dipyrromethane isomer, BF [H(Calix)], isomerises into BF [H(Calix)] which kinetic studies and DFT calculations indicate is an intramolecular process. Two isomers of B OF (Calix) were isolated, one isomer bonding via the dipyrrin sites with the FBOBF moiety in cisoid geometry, and the second isomer bonding via the dipyrromethane sites with the FBOBF moiety in transoid geometry. Although the cisoid/dipyrrin isomer was calculated to be most energetically favourable for B OF (Calix), the isolation of the transoid/dipyrromethane isomer is postulated to occur via the presumed intermediate (BF ) (Calix), for which DFT indicated a preference for transoid/dipyrromethane geometry.