The reactivity of the phosphanylphosphinidene complex [(DippN)(2)W(Cl)(eta(2)-P-PtBu2)](-) (1) toward chalcogens (Ch = Se, S) was studied. Reactions of stoichiometric amounts of 1 with chalcogens in DME yielded monomeric tungsten complexes with phosphanylphosphinidene chalcogenide ligands of the formula tBu(2)P-P-Ch (Ch = Se (in 2) and S (in 5)), which can be regarded as products of the addition of a chalcogen atom to a P=W bond in starting complex 1. The dissolution of selenophosphinidene complex 2 in nondonor solvents led to the formation of a dinuclear complex of tungsten (3) bearing a tBu(2)P(Se)-P ligand together with [tBuSe(2)Li(dme)(2)](2) and polyphosphorus species. Under the same reaction conditions, thiophosphinidene complex 5 dimerized via the formation of transient complex 7, possessing a thiotetraphosphane-diido moiety tBu(2)P(S)-P-P-PtBu2. The elimination of the tBu(2)PS group from 7 yielded stable dinuclear tungsten complex 8 with an unusual phosphinidene tBu(2)P-P-P ligand. The reaction of 1 with excess chalcogen led to the cleavage of the P-P bond in the tBu(2)P-P ligand and the formation of [(DippN)(2)W(PCh(4))](2)(2-) and [tBuCh(2)Li(dme)(2)](2). The isolated compounds were characterized by NMR spectroscopy and X-ray crystallography. Furthermore, the calculated geometries of the free selenophosphinidenes, tBu(2)P-P-Se and tBu(2)P(Se)-P, were compared with their geometries when serving as ligands in complexes 2 and 3.