Dihydridoboranes: Selective Reagents for Hydroboration and Hydrodefluorination.

The preparation of a new series of dihydridoboranes supported by N,N-chelating ligands, [R2NCH2CH2NAr]- (R = alkyl, Ar = aryl), is reported. These new boranes react selectively with carbonyls, imines, and a series of electron-deficient fluoroarenes. The reactivity is complementary to recognized reagents such as pinacolborane, catecholborane, NHC-BH3, and borane (BH3) itself. Selectivities are rationalized by invoking both open- and closed-chain forms of the reagents as part of equilibrium mixtures.