The interactions of Cu(II) bishexafluoroacetylacetonate (Cu-II(hfac)(2)) with polycrystalline Ta surfaces under ultrahigh vacuum conditions are reported here for temperatures between 115 and 1000 K. Cu-II(hfac)(2) adsorbed at 115 K is reduced to Cu(O) by 450 K without the use of an external reducing agent. The reduction occurs without disproportionation of Cu(I) intermediates. This behavior is unique to Ta and differs sharply from reported results for TiN or other metallic substrates. The Cu overlayer is stable on the Ta surface to 750 K. Between 750 and 950 K a decrease in Cu intensity is observed which becomes more pronounced above 950 K. This decrease in Cu intensity is due to diffusion of Cu into the Ta substate.