In a food processor, grind the wafers semi-fine; transfer to a large bowl. Repeat with the pecans. Stir in the confectioners' sugar and cocoa.
In a small bowl, mix together the rum, brewed espresso, corn syrup and salt. Pour the liquid mixture into the dry and mix with your hands until combined.
Roll 2 tbsp. of the dough into a ball; repeat with the remaining dough. Roll the balls in the espresso powder. Transfer to a sealed container and refrigerate for 1 to 5 days.