Clue: Carbon, hydrogen and metals: I turn them into gold (9)
Answer: ALCHEMIST
Explanation: Definition: metals: I turn them into gold
An anagram ('turn') of C ('carbon') plus H ('hydrogen') plus 'metals I', with a definition that invades the wordplay (although I doubt even an alchemist would have tried to start with either hydrogen or carbon) – and, of course, alchemists did not succeed in turning anything into gold.