Reaction of [Pt(kappa(2)-C,N-ppy)(dmso)Cl], 1 (Hppy = 2-phenylpyridine), with Na[H2B(mb)(2)] (Hmb = 2-mercapto-benzimidazole) smoothly afforded the complex {[(kappa(3)-S,B,S-HB(mb)(2)]Pt(kappa(2)-C,N-ppy)H}, 2, featuring a strong reverse-dative Pt -> B sigma interaction in the solid state. When dissolved in thf (or acetone) solution, 2 undergoes a reversible Pt H bond activation, establishing an equilibrium between the hexacoordinated 2 and the tetracoordinate complex {[(kappa(2)-S,S-H2B(mb)Pt(kappa(2)-C,N-ppy)}, 3, as ascertained by multinuclear NMR Hydrolysis of the B-N bond in 2/3 resulted ultimately in the formation of a dimeric half-lantern platinum(II,II) complex [{Pt(kappa(2)-C,N-ppy)(mu(2)-kappa(2)-N,S-mb)}(2)], 4. The SC-XRD structures of 2 and 4 are reported.