Phosphinoboranes that combine bulky electron-rich phosphides and electron deficient B(C6F5)2 fragments produce monomeric phosphinoboranes that undergo facile addition of H2 to give the phosphine-borane adducts (R2PH)(HBR′2). This finding in combination with DFT calculations shed light on the uptake of H2 across a group 13−group 15 bond, a critical requirement for the development of recyclable H2 storage materials.