Editing Palladium (section)

==Compounds==
{{Main|Palladium compounds}}
Palladium compounds exist primarily in the 0 and +2 oxidation state. Other less common states are also recognized. Generally the compounds of palladium are more similar to those of platinum than those of any other element.
<gallery mode="packed">
File:Alpha-palladium(II)-chloride-xtal-3D-balls.png|Structure of ''α''-PdCl<sub>2</sub>
File:Pd6Cl12-from-xtal-1996-CM-3D-ellipsoids.png|{{center|Structure of ''β''-PdCl<sub>2</sub>}}
</gallery>

===Palladium(II)===
[[Palladium(II) chloride]] is the principal starting material for other palladium compounds. It arises by the reaction of palladium with chlorine. It is used to prepare heterogeneous palladium catalysts such as palladium on barium sulfate, palladium on carbon, and palladium chloride on carbon.<ref>{{OrgSynth|title = Palladium Catalysts|author = Mozingo, Ralph |collvol = 3|collvolpages = 685|year = 1955|prep = cv3p0685}}</ref> Solutions of PdCl<sub>2</sub> in nitric acid react with [[acetic acid]] to give [[palladium(II) acetate]], also a versatile reagent. PdCl<sub>2</sub> reacts with [[ligands]] (L) to give square planar complexes of the type PdCl<sub>2</sub>L<sub>2</sub>. One example of such complexes is the [[benzonitrile]] derivative [[Bis(benzonitrile)palladium dichloride|PdCl<sub>2</sub>(PhCN)<sub>2</sub>]].<ref>{{cite book |pages=60–63 |volume=28 |doi=10.1002/9780470132593.ch13 |date=1990 |first1=Gordon K. |last1=Anderson |first2=Minren |last2=Lin |last3=Sen |first3=Ayusman |last4=Gretz |first4=Efi |title=Inorganic Syntheses |chapter=Bis(Benzonitrile)Dichloro Complexes of Palladium and Platinum |isbn=978-0-470-13259-3}}</ref><ref>{{cite journal |doi=10.1134/S1070328408110110 |title=Palladium complexes based on optically active terpene derivatives of ethylenediamine |journal=Russian Journal of Coordination Chemistry |volume=34 |issue=11 |pages=855–857 |year=2008 |last1=Zalevskaya |first1=O. A |last2=Vorob'eva |first2=E. G |last3=Dvornikova |first3=I. A |last4=Kuchin |first4=A. V |s2cid=95529734}}</ref>

{{block indent|1= PdCl<sub>2</sub> + 2 L → PdCl<sub>2</sub>L<sub>2</sub> (L = [[PhCN]], [[Triphenylphosphine|PPh<sub>3</sub>]], [[Ammonia|NH<sub>3</sub>]], etc.)}}

The complex [[bis(triphenylphosphine)palladium(II) dichloride]] is a useful catalyst.<ref>{{OrgSynth|title = Palladium-catalyzed reaction of 1-alkenylboronates with vinylic halides: (1Z,3E)-1-Phenyl-1,3-octadiene|collvol = 8|collvolpages = 532|author1-link=Norio Miyaura|author1= Miyaura, Norio|author2 = Suzuki, Akira|name-list-style=amp|year = 1993|prep = cv8p0532}}</ref>

[[File:Pd(OAc)2.jpg|thumb|left|[[Palladium(II) acetate]]]]
[[File:Platinum-palladium ore, Stillwater mine MT.JPG|thumb|Platinum-palladium ore from the Stillwater mine in the Beartooth Mountains, Montana, US]]
[[File:Sulfidic serpentintite (platinum-palladium ore) Johns-Manville Reef, Stillwater Complex.jpg|thumb|Sulfidic serpentintite (platinum-palladium ore) from the Stillwater mine in Montana]]

===Palladium(0)===
Palladium forms a range of zerovalent complexes with the formula PdL<sub>4</sub>, PdL<sub>3</sub> and PdL<sub>2</sub>. For example, reduction of a mixture of PdCl<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub> and PPh<sub>3</sub> gives [[tetrakis(triphenylphosphine)palladium(0)]]:<ref>{{cite book |volume=13 |pages=121–124 |first1=D. R. |last1=Coulson |doi=10.1002/9780470132449.ch23 |date=1972 |last2=Satek |first2=L. C. |last3=Grim |first3=S. O. |series=[[Inorganic Syntheses]] |title=Tetrakis(triphenylphosphine)palladium(0) |isbn=978-0-470-13244-9}}</ref>

{{block indent|2 PdCl<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub> + 4 PPh<sub>3</sub> + 5 [[Hydrazine|N<sub>2</sub>H<sub>4</sub>]] → 2 Pd(PPh<sub>3</sub>)<sub>4</sub> + N<sub>2</sub> + 4 N<sub>2</sub>H<sub>5</sub><sup>+</sup>Cl<sup>−</sup>}}

Another major palladium(0) complex, [[tris(dibenzylideneacetone)dipalladium(0)]] (Pd<sub>2</sub>(dba)<sub>3</sub>), is prepared by reducing [[sodium tetrachloropalladate]] in the presence of [[dibenzylideneacetone]].<ref>{{cite journal |doi=10.1039/C29700001065 |title=A novel palladium(0) complex; bis(dibenzylideneacetone)palladium(0) |journal=Journal of the Chemical Society D: Chemical Communications |issue=17 |pages=1065 |year=1970 |last1=Takahashi |first1=Y |last2=Ito |first2=Ts |last3=Sakai |first3=S |last4=Ishii |first4=Y}}</ref>

Palladium(0), as well as palladium(II), are catalysts in [[palladium-catalyzed coupling reactions|coupling reactions]], as has been recognized by the 2010 [[Nobel Prize in Chemistry]] to [[Richard F. Heck]], [[Ei-ichi Negishi]], and [[Akira Suzuki]]. Such reactions are widely practiced for the synthesis of fine chemicals. Prominent coupling reactions include the [[Heck reaction|Heck]], [[Suzuki reaction|Suzuki]], [[Sonogashira coupling]], [[Stille reaction]]s, and the [[Kumada coupling]]. [[Palladium(II) acetate]], [[tetrakis(triphenylphosphine)palladium(0)]] (Pd(PPh<sub>3</sub>)<sub>4</sub>), and [[tris(dibenzylideneacetone)dipalladium(0)]] (Pd<sub>2</sub>(dba)<sub>3</sub>) serve either as catalysts or precatalysts.<ref>{{cite book |chapter-url=https://books.google.com/books?id=WLb962AKlSEC&pg=PA392 |chapter=Application to Organic Synthesis |page=392 |title=The Organometallic Chemistry of the Transition Metals |first=Robert H. |last=Crabtree |publisher=John Wiley and Sons |date=2009 |isbn=978-0-470-25762-3}}</ref>

===Other oxidation states===
Although Pd(IV) compounds are comparatively rare, one example is [[sodium hexachloropalladate(IV)]], Na<sub>2</sub>[PdCl<sub>6</sub>]. A few [[compounds of palladium(III)]] are also known.<ref>{{Cite book |doi=10.1007/978-3-642-17429-2_6 |pmid=21461129 |pmc=3066514 |chapter=Palladium(III) in Synthesis and Catalysis |title=Higher Oxidation State Organopalladium and Platinum Chemistry |volume=35 |pages=129–156 |series=Topics in Organometallic Chemistry |year=2011 |last1=Powers |first1=David C |last2=Ritter |first2=Tobias |isbn=978-3-642-17428-5}}</ref> Palladium(VI) was claimed in 2002,<ref name="pmid11786638">{{cite journal |doi=10.1126/science.1067027 |pmid=11786638 |title=Synthesis and Structure of Formally Hexavalent Palladium Complexes |journal=Science |volume=295 |issue=5553 |pages=308–310 |year=2002 |last1=Chen |first1=W |last2=Shimada |first2=S |last3=Tanaka |first3=M |bibcode=2002Sci...295..308C |s2cid=45249108}}</ref><ref name="pmid11786632">{{cite journal |doi=10.1126/science.1067921 |pmid=11786632 |title=CHEMISTRY: A New Oxidation State for Pd? |journal=Science |volume=295 |issue=5553 |pages=288–289 |year=2002 |last1=Crabtree |first1=R. H |s2cid=94579227}}</ref> but subsequently disproven.<ref>{{cite journal |pmid=19750645 |year=2002 |last1=Aullón |first1=G |title=Hexakis(silyl)palladium(VI) or palladium(II with eta2-disilane ligands? |journal=Angewandte Chemie International Edition in English |volume=41 |issue=11 |pages=1956–9 |last2=Lledós |first2=A |last3=Alvarez |first3=S |doi=10.1002/1521-3773(20020603)41:11<1956::AID-ANIE1956>3.0.CO;2-#}}</ref><ref>{{cite journal |pmid=19750644 |year=2002 |last1=Sherer |first1=E. C |title=Electronic structure and bonding in hexacoordinate silyl-palladium complexes |journal=Angewandte Chemie International Edition in English |volume=41 |issue=11 |pages=1953–6 |last2=Kinsinger |first2=C. R |last3=Kormos |first3=B. L |last4=Thompson |first4=J. D |last5=Cramer |first5=C. J |doi=10.1002/1521-3773(20020603)41:11<1953::AID-ANIE1953>3.0.CO;2-H |doi-access=}}</ref>

Mixed valence palladium complexes exist, e.g. Pd<sub>4</sub>(CO)<sub>4</sub>(OAc)<sub>4</sub>Pd(acac)<sub>2</sub> forms an infinite Pd chain structure, with alternatively interconnected Pd<sub>4</sub>(CO)<sub>4</sub>(OAc)<sub>4</sub> and [[Palladium(II) bis(acetylacetonate)|Pd(acac)<sub>2</sub>]] units.<ref name="pmid25319757">{{cite journal |doi=10.1002/anie.201408461 |pmid=25319757 |title=A Motif for Infinite Metal Atom Wires |journal=Angewandte Chemie International Edition |volume=53 |issue=51 |pages=14087–14091 |year=2014 |last1=Yin |first1=Xi |last2=Warren |first2=Steven A |last3=Pan |first3=Yung-Tin |last4=Tsao |first4=Kai-Chieh |last5=Gray |first5=Danielle L |last6=Bertke |first6=Jeffery |last7=Yang |first7=Hong}}</ref>

When alloyed with a more [[Electronegativity|electropositive]] element, palladium can acquire a negative charge. Such compounds are known as palladides, such as [[gallium palladide]].<ref>{{cite journal |last=Armbrüster |first=Marc |title=Intermetallic compounds in catalysis – a versatile class of materials meets interesting challenges |journal=Science and Technology of Advanced Materials |publisher=Informa UK Limited |volume=21 |issue=1 |date=2020-01-31 |issn=1468-6996 |doi=10.1080/14686996.2020.1758544 |pages=303–322 |pmid=33628119 |pmc=7889166 |bibcode=2020STAdM..21..303A}}</ref> Palladides with the [[stoichiometry]] RPd<sub>3</sub> exist where R is [[scandium]], [[yttrium]], or any of the [[lanthanides]].<ref>{{cite journal |last1=Wang |first1=Qiaoming |last2=Collins |first2=Gary S. |title=Nuclear quadrupole interactions of 111In/Cd solute atoms in a series of rare-earth palladium alloys |journal=Hyperfine Interactions |volume=221 |issue=1–3 |year=2013 |issn=0304-3843 |doi=10.1007/s10751-012-0686-4 |pages=85–98 |arxiv=1209.3822 |bibcode=2013HyInt.221...85W |s2cid=98580013}}</ref>