The complexes [Pd{?2-S,S'-H2B(mimMe)2}(?3-C3H4R)] (R = H, Me) have been obtained in high yield from the dichloromethane mediated reaction of the respective [Pd(Cl)(?3-C3H4R)] with K[H2B(mimMe)2]. Attempts to prepare analogous compounds of platinum have led instead to the observation of species consistent with incidences of B–H activation, including the unexpected and facile formation of [PtH(PPh3){?4-B(mimMe)3}]Cl.