cis-3,4-Dicyano-3-hexene undergoes cyclotrimerization with BCl3 to form the new subtriazaporphyrin chloro[ hexaethylsubtriazaporphyrinato] boron( III). The hydroxo derivative of this macrocycle has also been made, and the X-ray crystal structure of the hydroxy form was determined. Electronic absorption and magnetic circular dichroism spectra of the hydroxo monomer species were interpreted using time-dependent density functional theory calculations.