Conformational Flexibility and Size of Large trans-Vinylene-Bridged Thiaporphyrinoids Influence Boron Coordination Modes.

Two π-extended core-modified porphyrinoids were synthesized and structurally characterized to probe boron-induced geometry switching and modulation of electron delocalization. trans-Vinylene-bridged hexathiadodecaphyrin forms the largest fully characterized porphyrinoid BODIPY-type complex while retaining the parent open-form geometry, whereas octathiahexadecaphyrin does not support boron coordination. Notably, a smaller figure-of-eight tetrathiaoctaphyrin analogue exhibits unusual direct C-B bond formation, highlighting the pronounced structural sensitivity of expanded porphyrinoids and their utility in accessing unconventional bonding and coordination modes.