N,N′-dialkylimidazolium chloroplatinate(II), chloroplatinate(IV), and chloroiridate(IV) salts and an N-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 PtC4 with ethylene in the basic [EMIM]Cl/AlCl3 (1.3:1) ionic liquid (where [EMIM](+) = 1-ethyl-3-methylimidazolium) at 200 degreesC and structurally characterized (monoclinic P2(1)/c space group, a = 10.416(2) Angstrom, b = 7.3421(9) Angstrom, c = 15.613(2) Angstrom, beta = 101.53(2)degrees, Z = 4). This complex can be regarded as a stable analogue of the pi -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 (degreesC) 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 P2(1)/n space group (1, a = 7.6433(9) Angstrom, b = 16.353(2) Angstrom, c 9.213(1) Angstrom, beta = 113.56(1)degrees, Z = 2; 2, a = 8.601(1) Angstrom, b = 8.095(2) Angstrom, c = 13.977(2) Angstrom, beta = 19.75(2)degrees, Z = 2; 5, a = 10.353(2) Angstrom, b = 9.759(2) Angstrom, c = 10.371(2) Angstrom, beta = 92.98(3)degrees, Z = 2).