When this element is exposed to air for a long time, it forms a green surface layer called verdigris.
Evans et al.Â developed bisoxazoline complexes of this element to catalyze enantioselective DielsÂ–Alder reactions. Penicillamine is a chelating agent used to isolate and remove excess levels of this element in the body. A combination of this element and palladium can catalyze the coupling of terminal alkynes to aryl halides. It's not silver, but a solution composed of potassium tartrate dissolved in this element's sulfate is used as a test for reducing sugars. This element is used in the (*) Sonogashira coupling and in Fehling's solution. Two alkyl groups and a lithium ion bond to this element in a class of reagents useful for carbonÂ–carbon bond formation named for Henry Gilman. When this element is exposed to air for a long time, it forms a green surface layer called verdigris. For 10 points, what element combines with tin to form the alloy bronze?
Evans et al.Â developed bisoxazoline complexes of this element to catalyze enantioselective DielsÂ–Alder reactions.
copper [or Cu]