The dimeric platinum phosphinidene complex [Pt(dppe)(mu-PMes)](2) (1; dppe = Ph2PCH2CH2PPh2, Mes = 2,4,6-Me3C6H2) was prepared by double deprotonation of [Pt(dppe)(mu-PHMes)](2)[BF4](2) (3); use of 1 equiv of base gives the monocationic complex [{Pt(dppe)}(2)(mu-PHMes)(mu-PMes)][BF4] (2), which can also be made from 1 and 1 equiv of HBF4. NMR data suggest that complex 1 contains pyramidal mu-phosphinidene ligands, and it undergoes nucleophilic reactions typical of a tertiary phosphine. Alkylation with MeI affords [Pt(dppe){mu-P(Me)Mes}](2)[BF4](2) (4), BH3.THF gives the borane adduct [Pt(dppe){mu-P(BH3)Mes}](2) (5), and air oxidation yields [Pt(dppe){mu-P(O)Mes}](2) (6). However, reaction with sulfur gives the monomeric trithioxophosphorane complex Pt(dppe)(S(3)PMes) (7), which was prepared independently from Pt(dppe)(trans-stilbene) and [MesPS(2)](2).