Addition of RNC (R = p -CH 3 C 6 H 4 , C 6 H 5 CH 2 , or CH 3 ) to Mn 2 (CO) 5 (dpm) 2 (dpm = Ph 2 PCH 2 PPh 2 ) produces Mn 2 (CO) 5 (CNR)(dpm) 2 with a terminal isocyanide. Heating of this complex produces Mn 2 (CO) 5 (dpm) 2 (R = CH 3 or C 6 H 5 CH 2 ) or Mn 2 (CO) 4 (CNR)(dpm) 2 (R = p -CH 3 C 6 H 4 ). The latter probably contains a four-electron doubly-bridging isocyanide ligand.