A Porphyrin as a Binucleating Ligand: Preparation and Crystal Structure of a Porphyrin Complex Containing a Coordinated B2O2 Ring

A new coordination mode for the porphyrin ligand is found in B₂O₂(BCl₃)₂(tpClpp)] (tpClpp=dianion of 5,10,15,20-tetra-p-chlorophenylporphyrin; the p-chlorophenyl groups are omitted for clarity in the picture shown on the right). This complex contains a four-membered B₂O₂ ring in the cavity of the ligand. The two boron atoms are coplanar with the porphyrin molecule, which undergoes an elongation along the B???B axis to accomodate the unusual guest.