Tetrameric thienylcopper and pentanuclear thienylcuprate

The reaction between 2-bromothiophene and magnesium with subsequent addition of copper(I) chloride in tetrahydrofuran followed by dioxane yields thienylcopper, [Cu4(C4H3S)4] (1). Without the addition of dioxane, magnesium thienylcuprate(I), [Mg(THF)6][Cu5(C4H3S)6]2 (2) is formed. Both copper(I) complexes are oligomeric and are bridged by the thienyl ligands solely through carbon donors, thus lacking CuS bonds. The former compound, 1, is tetranuclear with a square-planar copper core and CuCu distances of 2.453(3) and 2.507(3) Å, and 2.464(2) and 2.489(2) Å within the two crystallographically independent molecules, respectively; there is a weak Cu⋯S interaction of 3.118(5) Å between these two molecules. The anion of 2 is a closo trigonal bipyramidal cluster of copper atoms in which the (ax)–(eq) edges are bridged by the thienyl ligands. Thus the Cu(ax)Cu(eq) distances bridged by carbon are short, 2.497(5) and 2.503(5) Å, indicative of three-centre CuCCu two-electron bonds, whereas the Cu(eq)⋯Cu(eq) and Cu(ax)⋯Cu(ax) distances are considerably longer at 3.135(7) and 3.423(8) Å, respectively. The lack of participation of sulfur in bonding within the [Cu5(C4H3S)6]− cluster is discussed.