The platinum diboran(4)yl complexes 1-3 have been prepared by the selective oxidative addition of one B-Hal bond in aryl-substituted diboranes(4) Hal(2)B(2)Ar(2) (Hal = Cl, Ar = mes, dur; Hal = I, Ar = mes). Because of the electron deficiency of the remote B2 atom, all species show a rare dative Pt-B bonding interaction, whose magnitude is strongly dependent on the nature of the halide substituent.