Palladium is a chemical element with the chemical symbol Pd (atomic number of 46) and is a soft silver-white metal that resembles platinum.
Palladium, platinum, rhodium, ruthenium, iridium and osmium form a group of elements referred to as the Platinum Group Metals. These have similar chemical properties, but palladium has the lowest melting point and is the least dense of them. The metal has the uncommon ability to absorb up to 900 times its own volume of hydrogen at room temperatures.
These unique properties of palladium and other platinum group metals account for their widespread use. Many of the drugs manufactured today either contain these metals or have a significant part in their manufacturing process played by them.
Palladium commonly exists in 0, +2, +4 (rare) oxidation states. Elemental palladium reacts with chlorine to give palladium(II) chloride. Palladium(II) chloride, also known as palladium dichloride is the chemical compound with the formula PdCl2. This is a common starting material in palladium chemistry. Palladium based catalysts are of particular value in organic synthesis. It is prepared bychlorination of palladium.
Preparation of PdCl2:
The anhydrous salt is prepared by heating loose palladium sponge to a dull red heat in a stream of Cl2. For a more in-depth literature refer the below link
Palladium(II) chloride is a common starting point in the synthesis of other palladium compounds. It is not particularly soluble in water or non-coordinating solvents, so the first step in its utilization is often the preparation of labile but soluble Lewis base adducts, such as those resulting from acetonitrile or benzonitrile. The acetonitrile complex is prepared by treating PdCl2in refluxing acetonitrile:
PdCl2 + 2 MeCN → PdCl2(MeCN)2
Although rarely suggested, inert-gas techniques are not necessary if the complex is to be used in situ. As an example,bis(triphenylphosphine)palladium(II) dichloride may be prepared from palladium(II) chloride by reacting it with triphenylphosphine in benzonitrile.
PdCl2 + 2 PPh3 → PdCl2(PPh3)2
Upon further reduction in the presence of more triphenylphosphine gives tetrakis(triphenylphosphine)palladium(0).
PdCl2(PPh3)2 + 2 PPh3 + 2.5 N2H4 → Pd(PPh3)4 + 0.5 N2 + 2 N2H5+Cl−
Palladium chloride may also be used to give heterogeneous palladium catalysts: palladium on barium sulfate, palladium on carbon, and palladium chloride on carbon.
Usage in synthetic organic chemistry:
Due to its ability to adsorb huge amounts of hydrogen (900 parts of Hydrogen per 1 part of Palladium) it has got a great prospective in fast developing Hydrogen Energy industry. Palladium is used in fuel cells to convert hydrogen and oxygen to electrical energy. But the most impressive part of Palladium is of course the chemical catalysis. It accomplishes a precise job as a powerful role in Palladium catalyzed coupling reactions.
Palladium compounds are used as a catalyst in many coupling reactions (given below), usually as homogeneous catalysts.
Suzuki reaction
Stille reaction
Hiyama coupling
Sonogashira coupling
Negishi coupling
Buchwald-Hartwig amination
Heck-Matsuda Reaction
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