The compound HF2P is a strong base toward B4H8, forming a 1:1 adduct. The adduct is significantly more stable than COB4H8 or F3PB4H8. The 11B nmr spectrum can be explained in terms of a boron cage structure similar to that found in (CH3)2NPF2B4H8. Investigation of the 19F nmr of the previously reported compound (CH3)2NPF2B4H8 suggests the existence of isomers for this compound, but no isomers were found for F2PHB4H8. © 1969, American Chemical Society. All rights reserved.