Organoplatinum

Organoplatinum chemistry is the chemistry of organometallic compounds containing a carbon to platinum chemical bond, and the study of platinum as a catalyst in organic reactions. Organoplatinum compounds exist in oxidation state 0 to IV, with oxidation state II most abundant. The general order in bond strength is Pt-C (sp) > Pt-O > Pt-N > Pt-C (sp3). Organoplatinum and organopalladium chemistry are similar, but organoplatinum compounds are more stable and therefore less useful as catalysts. Organoplatinum chemistry is the chemistry of organometallic compounds containing a carbon to platinum chemical bond, and the study of platinum as a catalyst in organic reactions. Organoplatinum compounds exist in oxidation state 0 to IV, with oxidation state II most abundant. The general order in bond strength is Pt-C (sp) > Pt-O > Pt-N > Pt-C (sp3). Organoplatinum and organopalladium chemistry are similar, but organoplatinum compounds are more stable and therefore less useful as catalysts. Most organoplatinum(0) compounds contain alkene and alkyne ligands. Carbonyl complexes are rare, and the analogue of Ni(CO)4 is elusive. The alkene and alkyne ligands serve as two-electron donors, for example in the complexes (PPh3)2Pt(C2H4) and (PPh3)2Pt(C2Ph2). The ethylene ligand in (PPh3)2Pt(C2H4) is labile and exchanges with alkynes and electrophilic alkenes, even C60 a fullerene. A general synthetic route to (PPh3)2Pt(un) (un = alkene, alkyne) is reduction of potassium tetrachloroplatinate with ethanolic potassium hydroxide or hydrazine in presence of a phosphine ligand such as triphenylphosphine and the alkene or alkyne. Such reactions proceed via the intermediacy of cis-dichlorobis(triphenylphosphine)platinum(II). Nitrogen-based ligands do not often support the formation of platinum complexes of alkenes and alkynes. Zerovalent organoplatinum complexes lacking phosphine ligands are often prepared via PtCl2(COD). where C7H10 is norbornene. Platinum(I) compounds are uncommon but generally are diamagnetic because they have Pt-Pt bonds. An example is the dication 2+. A historically significant organoplatinum(II) compound is Zeise's salt, which is obtained from ethylene and potassium tetrachloroplatinate: The colourless diolefin complex dichloro(cycloocta-1,5-diene)platinum(II) is a more modern relative, and is more widely used. The stability and diversity of platinum(II) alkene complexes contrasts with the rarity of alkene complexes of nickel(II). Platinum allyl complexes are also common. In contrast to nickel chemistry, where compounds such as CpNi(L)X are common, cyclopentadienyl derivatives of Pt(II) are rare, consistent with the reluctance of Pt(II) to become pentacoordinate.