The synthesis, structure, and reactivity of a base-free terminal actinide phosphinidene metallocene have been comprehensively studied. The salt metathesis reaction of the thorium methyl iodide complex Cp-2 '''Th(I)Me (2; Cp ''' = eta(5)-1,2,4-(Me3C)(3)C5H2) with Mes*PHK (Mes* = 2,4,6-(Me3C)(3)C6H2) in THE furnishes the first stable base-free terminal phosphinidene actinide metallocene, Cp-2 '''Th=PMes* (3). Density functional theory (DFT) shows that the bonds between the Cp-2 '''Th2+ and [PMes*](2-) fragments are more covalent than those in the related thorium imido complex. While the phosphinidene complex 3 shows no reactivity toward alkynes, it reacts with a variety of heterounsaturated molecules such as CS2, isothiocyanate, nitriles, isonitriles, and organic azides, forming carbodithioates, imido complexes, metallaaziridines, and azido compounds. These experimental observations are complemented by DFT computations.