<i>N</i>,<i>N</i>‘-Dialkylimidazolium Chloroplatinate(II), Chloroplatinate(IV), and Chloroiridate(IV) Salts and an <i>N</i>-Heterocyclic Carbene Complex of Platinum(II): Synthesis in Ionic Liquids and Crystal Structures

The first imidazole-type carbene complex of platinum(II), cis-(C2H4)(1-ethyl-3-methylimidazol-2-ylidene)PtCl2, has been obtained by reacting PtCl2 and PtCl4 with ethylene in the basic [EMIM]Cl/AlCl3 (1.3:1) ionic liquid (where [EMIM]+ = 1-ethyl-3-methylimidazolium) at 200 °C and structurally characterized (monoclinic P21/c space group, a = 10.416(2) Å, b = 7.3421(9) Å, c = 15.613(2) Å, β = 101.53(2)o, Z = 4). This complex can be regarded as a stable analogue of the π-alkene−Pd(II)−carbene intermediate in the Heck reaction. In addition, a series of new N,N‘-dialkylimidazolium salts of platinum group metals of the type [RMIM]2[MCln], where [RMIM+] = 1-alkyl-3-methylimidazolium and M = Pt(II), Pt(IV), or Ir(IV), have been prepared and characterized. The salts [EMIM]2[PtCl6] (1) and [EMIM]2[PtCl4] (2) were prepared in the ionic liquid [EMIM]Cl/AlCl3 and the salts [BMIM]2[PtCl4] (3) and [BMIM]2[PtCl6] (4) (where [BMIM]+ = 1-n-butyl-3-methylimidazolium) and [EMIM]2[IrCl6] (5) in aqueous or acetonitrile media. From TGA measurements, salts 1−5 decompose in air in several steps eventually to form the corresponding metal, the onset of decomposition being observed at (°C) 260 (1), 220 (2), 200 (3), 215 (4), and 210 (5). The structures of 1, 2, and 5 were determined by single-crystal X-ray analysis. The three salts crystallize in the monoclinic P21/n space group (1, a = 7.6433(9) Å, b = 16.353(2) Å, c = 9.213(1) Å, β = 113.56(1)o, Z = 2; 2, a = 8.601(1) Å, b = 8.095(2) Å, c = 13.977(2) Å, β = 91.75(2)o, Z = 2; 5, a = 10.353(2) Å, b = 9.759(2) Å, c = 10.371(2) Å, β = 92.98(3)o, Z = 2).