A cyanide of this element is used to convert aryl halides to aryl nitriles, while two aryl halides can be coupled using this element in the Ullman reaction.  
A cyanide of this element is used to convert aryl halides to aryl nitriles, while two aryl halides can be coupled using this element in the Ullman reaction.  An acetylide of this element couples with an aryl halide in the Castro Stephens reaction.  The use of this element is replaced by tetraflouroborate in the Schliemann reaction, a modification of another reaction in which halides of this element reacts with aryl diazonium salts; that reaction is named for Sandmeyer.  A negative ion of this element bonds ionically to lithium in a halide-replacing reagent named for Gilman, and this element causes the change in color in both Fehling's and Benedict's reagents.  For 10 points, name this metallic element with atomic number 29 and symbol Cu.
A cyanide of this element is used to convert aryl halides to aryl nitriles, while two aryl halides can be coupled using this element in the Ullman reaction.  
Copper [accept Cu before mention]