Tetrahedral Pegs in Square Holes

Abstract

The first examples of diboron complexes of the tetrapyrroles octaethylporphyrazine (OEPz) and 2,9,16,23-tetra-t-butyl-phthalocyanine (Pc) are reported, counterpoints to the better known monoboron tripyrroles, subporphyrazine and subphthalocyanine. Two stereochemical possibilities are observed, with cisoid-B 2 OF 2 (OEPz), both cisoid-B 2 OPh 2 (OEPz) and transoid-B 2 OPh 2 (OEPz), transoid-B 2 OF 2 (Pc) and cisoid-B 2 OPh 2 (Pc) having been isolated and characterised, including structure determinations for the OEPz complexes. This variation in stereochemistry, which can be extended to include the previously reported transoid-B 2 OF 2 (porphyrin), cisoid-[B 2 OF 2 (corrole)] − , and both transoid- and cisoid-B 2 OF 2 (calixphyrin), prompted a wider DFT study to elucidate the factors influencing the stereochemical preferences. This shows that the cisoid/transoid preference is correlated to the ease with which the macrocycle accommodates a rectangularly distorted N 4 cavity. Show more