Remote Stereochemistry of a Frustrated Lewis Pair Provides Thermal and Photochemical Control of Reactivity

Hydroboration of tBuCCSR with (C6F5)2BH generate the B/S FLPs, (C6F5)2B­(RS)­CCH­(tBu) (R = ptol, Me). For R = ptol the product Z-1 exhibits Z stereochemistry, is monomeric in solution and is capable of both classical Lewis acid–base and FLP reactivity. Photoisomerization of Z-1 affords E-1, which features an intramolecular S–B interaction promoted by the remote steric influence of the tert-butyl group. E-1 is not active as an FLP under ambient conditions but reacts with phenylacetylene when activated with either heat or light. The stereochemical outcome of the product is dependent on the stimulus employed.