A Lewis base supported terminal uranium phosphinidene, [eta(5)-1,3-(Me3C)(2)C5H3]2U(= P-2,4,6-(Bu3C6H2)-Bu-t)(OPMe3) (5), is isolated from the reaction of the uranium methyl chloride [eta(5)- 1,3-(Me3C)(2)C5H3](2)U(Cl) Me (4) with 2, 4, 6-(Me3C)(3)C6H2PHK in toluene in the presence of Me3PO. Moreover, the reactivity of uranium phospinidene 5 toward a series of small molecules was comprehensively explored. While no reactivity of 5 with internal alkynes is observed attributed to steric hindrance, it readily reacts in good yields with various small molecules including isothiocyanates, aldehydes, imines, diazenes, carbodiimides, nitriles, isonitriles, and organic azides, yielding uranium sulfidos, oxidos, metallaheterocycles, and imido complexes.