Dihydridoboranes: Selective Reagents for Hydroboration and Hydrodefluorination.

The preparation of a new series of dihydridoboranes supported by -chelating ligands, [RNCHCHNAr] (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-BH, and borane (BH) itself. Selectivities are rationalized by invoking both open- and closed-chain forms of the reagents as part of equilibrium mixtures.