A stable intramolecular Lewis adduct 1 was prepared by hydroboration of 2-diphenylphosphinobenzaldehyde with HB(C6F5)2. Despite its intramolecular Lewis pairing, 1 exhibits pronounced frustrated Lewis pair-type reactivity toward aldehydes, alkynes, azides, and isocyanides, enabling diverse transformations. Isolated products include aldehyde 1,2-addition derivatives (2-4), head-to-tail dimerized alkyne adducts (5 and 6), Staudinger-type phosphinimine (7), Lewis adducts of isocyanides (8 and 9), and the 4 + 2 cycloaddition product (10) from 2-isocyanonaphthalene. All compounds were fully characterized, and the reaction mechanism is also considered.
Li et al. (Mon,) studied this question.