We report measurements on through-bond electronic transport properties of 1,4-phenylene diisocyanide-metal junctions. Nanoscale metal-molecule-metal junctions with self-assembled 1,4-phenylene diisocyanide layers were analyzed with variable temperature conductance measurements to reveal the dominant electronic transport mechanisms. Non-Ohmic thermionic emission is the dominant process, with isocyanide-Pd showing the lowest thermionic barrier of 0.22 eV.