Remarkably variable reaction modes of frustrated Lewis pairs with non-conjugated terminal diacetylenes

The frustrated Lewis pair P(o-tolyl)(3)/B(C6F5)(3) reacts with 1,7-octadiyne by acetylene C-C coupling to yield the zwitterionic product 2a. In contrast, the P(o-tolyl)(3)/B(C6F5)(3) Lewis pair reacts with 1,6-heptadiyne by a sequence involving 1,1-carboboration of a terminal acetylene to eventually yield the heterocyclic product 4.